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DOI: 10.1039/C1RP90070F (Paper) Chem. Educ. Res. Pract., 2012, 13, 135-146

Exploring the potential for using inexpensive natural reagents extracted from plants to teach chemical analysis†

Supaporn Kradtap Hartwell
Chemistry Department, Xavier University, Cincinnati, Ohio, 45207-4221, USA. E-mail: kradtaps@xavier.edu; kradtas@yahoo.com; Tel: 513-745-3397

Received 29th September 2011 , Accepted 8th February 2012

First published on 28th February 2012

Abstract

A number of scientific articles report on the use of natural extracts from plants as chemical reagents, where the main objective is to present the scientific applications of those natural plant extracts. The author suggests that natural reagents extracted from plants can be used as alternative low cost tools in teaching chemical analysis, especially in school laboratories that have to operate within a tight budget. This article is presented in two parts, the first section being a review of the recent publications on using plant extracts as reagents for various chemical analyses, and the second section offers a perspective on the use of natural extract from plants in chemical education, especially focusing on teaching chemical analysis at the high school and undergraduate levels. A variety of topics are described that can be taught when using plant extracts in addition to the topics normally covered when using synthetic chemicals. Guidance on selection of an appropriate plant extract and sample is provided. By using plant extracts, the concept of green analytical chemistry can be introduced into the teaching/learning experience. This not only helps students to be aware of the natural availability of chemicals around them, but also leads to some useful and sustainable low cost analytical chemistry research.

Introduction, aims and scope

It has been universally accepted that teaching the concepts that lead to critical thinking and creativity in sciences can be done most effectively by providing the students with plenty of hands-on experiences (Russell et al., 2007; Iimoto and Frederick, 2011; Sneddon and Hill, 2011). One of the main objectives of chemistry teaching is instructing students how to conduct research using their knowledge in chemistry to find something new and valuable (Watts and West, 1992). Unfortunately, for most science students, their only experience working as a real scientist comes quite late, only when they enter graduate study programs where research is the main part of the curriculum (Samarapungavan and Westby, 2003). Some undergraduate schools have experienced a problem retaining science majors, as many students loose interest and drop out or change majors, and part of this problem has to do with the uninteresting activities that students feel is irrelevant to their lives and which leaves them feeling frustrated (Holbrook, 2005; Strobel and Strobel, 2007). Educational researchers have found that research activity helps to retain students and open opportunities for their future careers (Braun et al., 2001; Samarapungavan and Westby, 2003). Therefore, a short term project/research in which students have the chance to design and contribute intellectual ideas of their own is a critically important activity (Wenzel et al., 2012). Students who have such a chance, not only to do hands-on lab experimentation, but also to conduct short term research in high school and at the undergraduate level, are more inspired and prepared for higher education and the workforce (Braun et al., 2001; Samarapungavan and Westby, 2003).

In many small schools, especially those in developing countries, the cost involving laboratory and research is one big challenge to deal with (Sane 1994; Penker and Elston, 2003). Since laboratory equipment and supplies are very expensive, some schools including those with established laboratories and better funding, find they have to eliminate (Pienta, 2010) or modify some experiments to reduce costs (Parashar et al., 2006). Costs and other issues affecting the sustainability of chemistry education are of growing concern. Several basic models of approaching sustainability issues in chemistry education were recently described (Burmeister et al., 2012) and categorized into 4 approaches; namely Model 1: adopting green chemistry principles to the practice of science education lab work, Model 2: adding sustainability strategies as content in chemistry education, Model 3: using controversial sustainability issues for socio-scientific issues which drive chemistry education, and Model 4: chemistry education as a part of education for sustainable development (ESD) driven school development. Model 1 has been the focus of various academic institutions as can be seen from the growing numbers of articles and presentations proposing various ways of implementing the “green chemistry” concept into chemistry curriculums (Haack et al., 2005; Gron, 2008; Benedict, 2009; Gron, 2009; Haack, 2009).

“Green chemistry” or “Sustainable chemistry” is the design of chemical products or processes that reduce or eliminate the use or generation of hazardous substances (United States Environmental Protection Agency, 2012). The concept of green chemistry was introduced in the 1990s (Anastas and Warner, 1998; Anastas, 1999) and since then it has awakened awareness within the chemistry community to reduce chemical exposure and waste production in order to protect human health and the environment. There are many aspects of the green chemistry idea, as outlined in the 12 principles in green chemistry (Anastas and Warner, 1998). In chemical synthesis, application of these principles has mainly resulted in an emphasis on using less harmful alternative chemicals and/or alternate synthesis routes that consume lower amounts of chemicals with higher product yield as compared to conventional routes, and also an awareness and emphasis on the use of the recyclable chemicals (Barata-Vallejo et al., 2011; Mamada et al., 2011; Zhou et al., 2011). In analytical chemistry, green chemistry concepts have led to simpler analytical processes that are lower in operational cost and more rapid in order to reduce energy consumption (Wang, 2002; Armenta et al., 2008; Koel and Kaljurand, 2010). Several books, articles and presentations (Wang, 2002; He et al., 2007; Horoszewski et al., 2007; Armenta et al., 2008; Garcia-Reyes et al., 2009; Koel and Kaljurand, 2010) have been published that review the various ways of conducting green analytical chemistry, mostly with an emphasis on the development of automatic instrumentation, sensor technology, and methodologies that offer high sample throughput with micro-/nano-level sample and reagent consumption. The low cost aspects of analytical chemistry teaching are also covered in the area of adaptation of low cost materials for construction of analytical devices (Grudpan et al., 2009; Jacobson et al., 2011; Kradtap Hartwell et al., 2011). A few reports mentioned the use of natural reagents including plant, animal, and microbial sources in place of synthetic reagents for chemical analysis (Armenta et al., 2008; Grudpan et al., 2010; Jacobson et al., 2011).

This article focuses on using natural reagents extracted from plants as tools in teaching chemical analysis. Some easily available plants are low cost sources of highly priced commercial chemical/biochemical reagents such as enzymes. For example, crude extract of sweet potato root, which contains the enzyme polyphenol oxidase, was reported to be successfully used for determination of sulfite in wine (Fatibello-Filho and da Cruz Vieira, 1997). A common composition of many plant leaves, such as chlorophyll A, was also reported to be useful for determination of the amount of mercury ions (Hg2+) in water with less complicated water sample preparation as compared to the EPA standard method (Gao et al., 2006; United States Environmental Protection Agency, 2002). In this case, the “green chemistry” concept can be exploited in both environmental and economic aspects (Gron, 2008).

The first part of this article compiles and summarizes the publications relevant to the use of natural extracts from plants in chemical analyses. For this review part, published articles involving the use of natural extract from plants for various chemical analyses were searched from available electronic databases including SciFinder and ScienceDirect. These articles were reviewed for important points to show their usefulness and real applications. The usage of natural plant extracts are summarized and categorized for a clear understanding of how they have been applied in chemical analyses. Since this area of research normally makes use of locally available plants, many publications are in languages other than English, but the abstracts of some of those references are available. Supplemental data on plant species such as scientific names were researched from various books and websites. The applications are categorized based on the reaction and analytes involved. These published works place emphasis on the chemical analysis aspects without consideration of the chemistry educational (teaching-learning) aspects.

Educational aspects of using a green chemistry approach, and plant extract in particular, are discussed in the second part of this article, where the author offers a perspective based on teaching experiences. The author explains how the proposed method is relevant to the expected and educational outcome according to personal experiences as well as to the outcome expectation as outlined in many published articles in the area of education found in the available electronic database. This part of the article aims to express the practical concepts of chemical analysis teaching using plant extracts as alternative economic chemical reagents. Possible topics for teaching are suggested and the educational benefits of using natural extracts from plants in teaching and the student learning outcome are discussed. Suggestions are given on the appropriate selection of types of samples to be used for analysis. Limitations of using plant extracts are addressed as is how these limitations may lead to more useful topics for teaching and learning. Outcome assessment is given based on various articles on chemical analyses using plant extracts as reagents published in international peer reviewed journals and from the author’s own experience in co-supervising undergraduate projects using natural extracts from plants. The use of plant extracts as reagents in chemical analysis may help in creating effective and sustainable green analytical chemistry teaching in undergraduate and high schools with minimum budgets.

The state of the art in the literature

The documented cases of using plant extracts for chemical analyses seems to be limited in terms of accessibility to the readers/researchers due to the fact that they often only appear in non-English languages or in foreign journals and patents. Scientific databases, such as SciFinder, do include abstracts from some non-English language journals and patents. Even though the complete detailed article may not be available in the database, the English version abstracts normally contain keywords that enable the readers to gain some information about any plant extracts used and their purposes. A list of some plant extracts and their uses for chemical analyses as found in international journals that are easily accessible to researchers was accumulated and summarized by Grudpan and co-workers (Grudpan et al., 2010). Additional plant extracts that were not included in the previous work are mentioned here in Table 1. Scientific names, that can help aid in searching for local plants of the same family, are included.
Table 1 Summarization of some works that reported on applications of natural extracts from plants
Common name/part used Scientific name (family) Active substances Extraction medium/form used Reported applications/properties Suggested possible applications References
1. Plant extracts as acid–base indicator and for acidity assay
Globe Amaranth, Bachelor Button (flowers) Gomphrenaglobosa (Amaranthaceae) Betacyanin Water Acidity assay -as reported- Ueda et al., 2010
Beet root (roots) Beta vulgaris (Amaranthaceae) Betacyanin Water Acidity assay -as reported- Grudpan et al., 2010
Butterfly pea (flowers) Clitoriaternatea (Fabaceae (alt. Leguminosae)) Anthocyanin
Orchid (flowers) Dendrobium Sonia (Orchidaceae) Anthocyanin
Paper flower (flowers) Bougainvillea glabra (Nyctaginaceae) Betacyanin -not available- Indicator for strong acid–base titration and paper indicator -as reported- Heuer et al., 1994; Gaurav et al., 2010
Mulberry (fruits) Morusnigra Linn. (Moraceae) Anthocyanin 95% alcohol with 0.1% HCl Food coloring, medicine Self-indicator for acidity assay Qin et al., 2010
[thin space (1/6-em)]
2. Plant extracts as chromogenic/fluorogenic reagents for detection of metal ions
Tea (leaves) Camellia sinensis (Theaceae) Catechin Polyphenolic compounds Water, acetate buffer Quantitative analysis of iron and aluminum Quantitative analysis of other metal ions Tang et al., 2004; Grudpan et al., 2010; Pinyou et al., 2010
chlorophyll -not available- Study of complex of Zn and Cu with chlorophyll Immobilized on solid support for removal of metal ions from water Petrović et al., 2006
Spinach (leaves) Spinaciaoleracea (Amaranthaceae) chlorophyll -not available- —   Svec et al., 1991
[thin space (1/6-em)]
3. Plant extracts as sources of enzymes
Jack fruit (wood) Artocarpushetero Phyllus (moraceae) Tyrosinase inhibitor -not available- Antibrowning agent Quantitative analysis of tyrosinase, antioxidant activity studies Zheng et al., 2008
Pea Pisum Sativum L. (Fabaceae) NAD(P)+-dependent secondary alcohol dehydrogenase Water-soluble proteins from pea or soybean powders R-isomer selective for purifying racemic alcohol Quantitate alcohol Nagaoka, 2003
Soybean Glycine max (Fabaceae)
Wheat Triticumaestivum (Poaceae)
[thin space (1/6-em)]
4. Plant extracts for detection of substances other than metal ions and those involved in enzymatic reaction
Seaweed and Kelp (leaves) -Unspecified- (possible families: Akkesiphycaceae, Alariaceae, Chordaceae, Costariaceae, Laminariaceae, Lessoniaceae, Pseudochordaceae) Iodine Water Disinfectant for cooking utensil, Supplemental pills Screening for the presence of starch in certain food, determination of iodine number of oil Zou et al., 1990; Park, 2003
Cinnamomum plant cinnamomum (Lauraceae) 1,7,7-trimethyl bicycle [2.2.1] heptan-2-one, 3,3-dimethyl-2-methylene bicycle [2.2.1] haptane, etc. Essential oil/steam distillation Formaldehyde scavenging from furniture/paint Quantitative analysis of formaldehyde Peng, 2003
Mango (tree bark) Vimang Mangiferaindica L (Anacardiaceae) Polyphenols, triterpenes, phytosterols, fatty acids and microelements Supplement pill Against serum oxidative stress Quantitative analysis of H2O2 Pardo-Andreu, et al., 2006
Sesame (seed) Sesamumindicum (Pedaliaceae) Sesamol (3,4-methylenedioxyphenol Natural phenol obtained by the hydrolysis of sesamolin from sesame seeds Fluorogenic reagent for determining radicals Antioxidant Makino et al., 2010
[thin space (1/6-em)]
5. Plant extracts or plant tissues as part of analytical device
Coconut (fibers) Cocusnucifera L. (Arecaceae) Peroxidase Mix fibers with carbon paste electrode Quantitative analysis of benzoyl peroxide in facial cream and shampoo Determination of other substances related to peroxidase enzyme reaction Kozan et al., 2010
Raspberry (fruit) Rubusfruticosus (Rosaceae) Anthrocyanin Juice Dye for solar cell Acid–base indicator Smestad, 2008
[thin space (1/6-em)]
6. Others
green cestrum, green poison berry, or Chilean cestrum Cestrum parqui (Solanaceae) Saponins Ether of petrol to remove lipids, followed by extractions in methanol Spermicidal Study its effect on other cells Jellard et al., 2011
Horseweed, Canadian Horseweed, Canadian Fleabane, Coltstail, Marestail and Butterweed. Conyza Canadensis Or Erigeron canadensis L. (Asteraceae) Polysaccharide Water Antioxidant and antiaggregatory blood platelets Aids in blood studies involving blood platelets Olas et al., 2006
Cranberry Vaccinium macrocarpon (Ericaceae) benzoic acid (BA) Selectively remove (“chemically subtract”) a single compound from a complex mixture Anti-adhesive effects versus uropathogenic (uroepithelial T24 cells) Escherichia coli. Food preservative Chen et al., 2008
Upon BA removal, the anti-adherent activity of the fraction was fully retained
Rosemary (leaves) Rosmarinusofficinalis (Labietae) Carnosic acid and carnosol as antioxidants Methanol followed by solid-phase-extraction Additive for food packaging Antioxidant activity Bentayeb et al., 2007
Olive (fruit) Oleaeuropaea (Oleaceae) Antioxidant Centrifugation to separate the polyphenolic rich liquid layer from waste water from industrial olive oil process Additive for cooked and raw meat to improve lipid stability Apply to analysis of oxidation of vegetable oil Carpenter et al., 2007; O’Grady et al., 2008; DeJong and Lanari, 2009
Grape (seed) Vitisvinifera (Vitaceae) Commercial

The main applications of plant extracts from the reported works can be categorized into 6 areas as follows:

(1) Using plant extracts, especially ones that contain anthocyanins or betacyanins as acid–base self-indicators: Anthocyanins and betacyanins change color (maximum light absorption wavelength) or absorptivity (degree of light absorption at the same wavelength) in response to the pH change.

(2) Using plant extracts, especially ones that contain polyphenolic compounds, as chromogenic/fluorogenic reagents to form colored/fluorescent complexes with metal ions: Polyphenolic compounds, for example tannin, can form colored complexes with some metal ions.

(3) Using plant extracts as sources of enzymes for chemical/biochemical analysis based on enzyme-substrate reactions: Enzymes from plants can be used for quantitative analysis of substances that are involved in or inhibit the enzyme reaction.

(4) Using plant extracts as reagents for chemical analyses (other than quantitative analysis of metal and enzymatic reaction): Some examples are using extract of cinnamomum plant for formaldehyde scavenging, and using extract of sesame seed for quantitative analysis of radicals.

(5) Using plant parts or natural dyes from plants as part of device/sensor operation: The biosensor research area has reported the use of various plant tissues such as from seed and fruit peel to directly be incorporated into the sensor device.

(6) Using plant extracts for other purposes that may be useful in chemical/biochemical analysis: Some natural extracts can be used as sources of biochemical substances such as spermicide, or insecticide.

Educational perspectives on the use of natural reagents extracted from plants in teaching chemical analysis

Advantages of using plant extracts in chemical analysis

Among natural resources, plant extracts in particular provide several advantages. Key benefits include the fact that 1) there are usually many plants to choose from that are easily and locally available at low cost or no cost at all, 2) plants are a renewable source (green chemistry), 3) the extraction process can be performed in simple facilities, 4) there is less conflict on ethical issues as compared to using animals in scientific experiments, 5) working with plants is usually less hazardous as compared to working with microbial sources, and 6) extended teaching/learning topics can be covered as compared to using ready-to-use synthetic reagents.

Many topics that can be taught using reagents from plant extracts arise during the extraction process itself. These topics can broaden students’ experiences as compared to working with ready-to-use synthetic reagents. Using plant extract in a short term research project can create a problem-based learning environment as shown in examples of undergraduate student projects described in later section. The additional benefit in student awareness of environmental protection by reducing toxic chemical waste should also promote the sense of civic responsibility. When using plant extracts, issues such as stability, availability, and interferences arise that may seem like limitations as compared to using synthetic chemicals. However, these limitations can be exploited to keep students thinking and learning about how to deal with these issues.

Practical ideas on using plant extracts as reagents for teaching chemical analysis

Several important steps need to be developed in order to carry out any relevant scientific study. These include making observations, asking questions, setting the hypothesis, designing experiments to test the hypothesis, carrying out experiments, collecting data, analyzing data, and arriving at the conclusions. However, the short time period usually allotted for a normal laboratory course is rarely sufficient to experience all aspects of the scientific process. For example, many students never get a chance to be involved in designing an experiment. Due to time constraints, instructors normally have all the steps for the experiment already prepared. Therefore, it is important that the chemistry curriculum include the term project in which students can explore the whole scientific process. Even though that short-term project may not be a topic relevant to their future research work, learning how to conduct research from the beginning to the end is what gives them the capability to attack any research problem in the future. Therefore, the valuable experience of conducting research is truly a way to “gain education through science” (Holbrook, 2005; Burmeister et al., 2012) which should be the objective of teaching rather than to “learn science through education” which limits a student’s ability to adapt the learning process in order to learn something new.

In many countries around the world educators strive to provide a quality education to the next generation. Unfortunately though, the available budgets to achieve their aims often fall short of the amount needed. It has become more important for instructors to be able to adapt (make changes in teaching by creating alternative method), adopt (make use of successful existing alternative method) and adjust (accept that changes are needed) in order to keep at the standard level of teaching in their constrained economic situations. The expected learning outcome should never be sacrificed to meet the demands of reducing costs. Developing a “sustainable teaching pedagogy,” an art of teaching that does not depend so largely upon economic fluctuation, would allow one to always be effective, even with little funding. The use of low cost devices together with low cost reagents should enable us to maximize the use of available resources to conduct sustainable and effective teaching and learning experiences within a limited budget.

As summarized by Tyson (Tyson, 1989) and Woodget (Woodget, 2003), education in analytical chemistry expects a certain quality from the students. To become an analytical chemist, a student must have knowledge and skill not only in chemistry context, but also in relevant fields including chemometrics, computer, personal and business management. Students also have to continuously educate themselves through meetings and conferences. Can these expectations be met if students are educated through term projects that utilize plant extracts instead of synthetic chemicals? With the careful guidance and set up of the research direction, the answer is YES. In fact, using plant extracts can offer even more than the expectations listed above. More up to date teaching pedagogies always emphasize “multidisciplinary learning” in which students have an opportunity to learn and apply knowledge across the disciplines (Hixson et al., 1996). One question that students will simultaneously ask when dealing with plant extract is, “What kind of plants can we use for chemical analyses?” This question will lead to the exploration of plant species and relevant information. Students will learn that various seasons and geographic areas affect the availability of the plant and/or amount of interested chemicals in those plants. This is a clear example how chemistry will cross disciplines with botany, ecology, environmental and geographical subjects. Another learning aspect that recently seems to be in the focus is the relation of science with civic responsibility. In the past, science and social responsibility were thought of as two unrelated topics, and that resulted in a government policy that undervalued safety issues concerning chemical exposure and pollution (Wilson and Schwarzman, 2009). Now, teaching pedagogies that emphasize the relation between science and civic responsibility are promoted (Gurney and Statford, 2009; McClure and Lucius, 2010). In the USA, both governmental and private sectors support the increase in social responsibility of conducting science research, for example, via a long term project called Science Education for New Civic Engagements and Responsibilities (SENCER) (Shachter, 2005; Middlecamp et al., 2006). The goal is to promote research that solves real world problems that occur in society and those that do not create problems or degrade the living standards of mankind. Civic responsibility can be broadly defined as “active participation in the public life of a community in an informed, committed, and constructive manner, which focuses on the common good” (Gottlieb and Robinson, 2006). Literally, civic responsibility may be thought of as an obligation of a citizen to have social responsibility. In science, apart from ethical and copyright issues, the responsibility in conducting research using environmentally benign methods e.g. green chemistry approaches (including the use of plant extracts) should be considered as another aspect of civic responsibility. With the main aim of reduction of harmful chemicals usage, environmental problems could be reduced (Mooney, 2004). Keeping the environment healthy is one important point scientists should always keep in mind as part of their citizen responsibility when conducting research.

Possible areas of student research using plant extracts

Based on the applications of natural plant extracts in chemical analysis as summarized in Table 1, some areas can still be explored further. In several of the published works, the intention was not to use plants as sources of reagent for chemical analysis but rather for some other purposes such as medicinal and food additives (Zheng et al., 2008; Qin et al., 2010). However, if considering the relevant chemical reaction between active substances in those plant extracts with certain analytes that may be useful to quantify or identify, then it is possible to utilize those plant extracts for chemical analyses. For those references, possible uses of plant extracts in chemical analysis are suggested as also shown in Table 1. For example, pea and soybean proteins have been reported to contain alcohol dehydrogenase enzyme with selectivity toward the R-isomer of racemic alcohols (Nagaoka, 2003). Apart from using pea and soybean protein extracts for purifying a certain isomer of racemic alcohol as reported, they could potentially be used in the quantitative analysis of alcohol content in various samples.

According to the six categories of applications of the reviewed articles mentioned earlier, additional investigations can be carried out that extend applications in those areas. For example, many plants with colorful flowers that contain anthocyanins and betacyanins can be used for acidity assay and can be used to introduce various titration techniques for comparison of results. For the application of plant extract as a complexing agent, there is potentially more room to grow because so far only a few metal ion species have been reported in the studies. Using plants as sources of enzymes can also be very useful. With their high specificities, it might be worthwhile to try using enzymes from plant extracts to conduct quantitative analysis in samples of complicated matrices (such as biological fluids). Enzyme studies (various enzyme kinetic variables and relevant plots) can be another useful topic in teaching. The chemicals in plants are various and complex. Only a few reports have identified chemicals in plant extracts, other than enzymes, that can be used to selectively react with an analyte of interest. Even though this area of research in identifying chemical components in the plant extracts may be complicated and requires advanced technologies, it is possible to adapt information from the published works for development of some simple chemical analyses that may be more suitable for high school or undergraduate levels. Some articles showed the direct applications of plant parts as parts of analytical devices. Information from these types of articles can give ideas about parts of plants that should be used as sources for extraction of active substances. Other direct uses of extracts from plants such as active ingredients in substances like pesticides may draw in more applications of life science related studies.

One of the fastest growing topics of study involves antioxidants. These substances are capable of protecting other molecules from being oxidized. Therefore, they are of major interest to be used as food and dietary supplements for preventing diseases which relate to oxidative stress. Numerous plants have been reported to have antioxidant activities. Familiar plant materials such as rosemary, sesame seed, sorghum bran, and daisy flower are just some examples (Xu et al., 2005; Bentayeb et al., 2007; Sikwese and Duodu, 2007; Nalewajko-Sieliwoniuk et al., 2008). However, it can be concluded that the use of plants with antioxidant activities in terms of chemical analysis, are mainly in the area of development of alternative method for measuring antioxidant activities (Makino et al., 2010). Comparison of antioxidant activities of various plants using standard analysis method is also another possible research topic. A few examples of using plant extracts that offer antioxidant activities in applications such as food or product additives are included in Table 1. This should be useful and would introduce students to highly up-to-date topics that are interesting to explore.

Additional topics that can be taught with plant extracts

The hands-on steps involved in doing extraction can be used to introduce many new and interesting concepts to students. Fig. 1 illustrates the common steps involved in chemical analysis and shows the comparison between using the plant extract and the synthetic chemical reagents. Using plant extract involves more steps, but those steps provide more opportunities for gaining knowledge from interdisciplinary areas such as biology, ecology, and environmental science, for instance in the initial steps of plant selection. Table 2 summarizes a variety of possible topics that can be taught during preparation of the plant extracts which otherwise would be overlooked if only synthetic reagents are used. Some of the items included in Table 2 are discussed in more detail in the following sections.
Diagram showing the additional possible teaching/learning topics when using plant extracts as compared to synthetic ready-to-use chemicals as reagents in chemical analysis.
Fig. 1 Diagram showing the additional possible teaching/learning topics when using plant extracts as compared to synthetic ready-to-use chemicals as reagents in chemical analysis.
Table 2 Various topics that can be taught during the plant extraction process
Step Variable /method involved Focus of teaching/learning
Plant selection • Publication data base • Scientific name
• Books about plants • Plant ecology
• Chemicals of interest in different parts of plants
Selection of extraction method • Various extraction methods • Differences among methods
• Data analysis for comparison of methods
• Criteria for practical selection of methods
Preparation of solvent for extraction • Common glassware handling • Green chemistry concept
• Balance • Aqueous vs. non aqueous based solvent
• pH meter • Dry vs. wet weight
• Solution preparation/concentration calculation
• Buffer solution/ionic strength/buffer capacity/pH
• Solubility/precipitation
Extraction • Blender/mortar/pistol • Filter /dialysis
• Filter • Filtering materials/pore size selection
• Centrifuge machine • Centrifugation force
• Liquid transfer
• Precipitate drying
Storage • Freeze drying machine or equivalent equipment • Comparison of percent signal decrease
• Oven

Extraction. Extraction is the process of separating active ingredients out of raw materials. In plant extraction, the extract is usually considered a crude extract, meaning that the active reagents may be extracted along with other substances. In many cases the crude extracts are sufficient for chemical analysis (Fatibello-Filho and da Cruz Vieira, 1997; Lupetti et al., 2002; Settheeworrarit et al., 2005; Gao et al., 2006; Monji et al., 2009; Pinyou et al., 2010; Grudpan et al., 2011). Apart from teaching about various types of extraction methods (e.g. mechanical pressing, steeping, maceration, distillation, ultrasonic), a comparison of these methods can be introduced along with the necessary statistical data processing. Students will need to consider the type of results or variables to be used in order to justify and evaluate the different extraction methods. This would be a good place to bring up the concept of efficiency in method, not just in terms of the results, but also to consider the simplicity, cost, and time requirements of each method. Further teaching of extended topics such as liquid–liquid extraction, distillation, or more advanced techniques such as solid phase extraction can also be covered.

The extraction process for plant material normally involves a solvent. To stay with the green chemistry way of teaching, water or aqueous buffer should be the first choice to start with. The extraction process itself can provide various teaching/learning topics such as wet vs. dry weight, buffer/solvent concentration calculation, solubility, and precipitation. During and after the extraction, a dilution process may be required. Dilution of the solvent/buffer is usually carried out in serial dilution fashion. After the extraction is completed, the plant residues should be removed. At this point, various filtering materials and methods can be introduced, such as selection of pore sizes and concepts of centrifugation (e.g. the relationship between force and separation efficiency, supernatant vs. precipitate). If the extract is protein/enzyme, dialysis may be carried out. This can be followed by liquid transfer techniques, the separation of liquid from solid with minimal loss of extract solution, and/or techniques for drying the precipitate. It may also be necessary to make volume adjustments or reconstitute the extract. This will involve the quantitative concept of how to keep volume or concentration of replicated extractions constant for a valid comparison.

Purification. It has been reported that crude extracts can be used successfully for quantitative analysis of various analytes of interest in real samples, as mentioned in the previous section. This normally requires a careful selection of real samples with non-complicated matrices that do not require some special sample preparation. To extend the use of the plant extracts, a purification process may be carried out. Working through the steps of the purification process will deliver more knowledge to students in areas such as various protein precipitation techniques, solid phase extraction, and solvent-solvent extraction. Modern extraction methods, such as micro-volume liquid–liquid extraction, solid phase micro-extraction and microwave extraction for example (Cha et al., 2009; Liu et al., 2009; Flamini and Cioni, 2010; Zhai et al., 2011), should be addressed and discussed to promote the green chemistry way of conducting research.

Chemical analysis with plant extracts – important considerations

Analytical chemistry focuses on two main areas of analysis, quantitative which concentrates on finding the amount or concentration of substances of interest, and qualitative, which concentrates on finding what substances are in the sample or whether the substance of interest is present in the sample. Most of the reported works involving plant extracts have been in the area of quantitative analysis. On the other hand, qualitative analysis is normally done by using plant extracts as samples to find out the chemical compositions in them. Both areas are concerned with analytical parameters i.e. accuracy, precision, sample throughputs, and cost. When using crude plant extracts in teaching chemical analysis, these important analytical parameters should also be taught. Therefore, it is important to select appropriate plant extract and type of sample, and to apply data analysis that can reveal these analytical parameters.
Selection of an appropriate plant extract. To make use of a plant extract in teaching chemistry analysis, the easiest starting point may be to choose a plant that already has a certain amount of background information known about it, either locally or in publication. Normally plants in the same family have something in common, including the similar natural chemicals found in them. By looking at the scientific names of plants, local plants of the same family/genus as those reported in literature from other parts of the world can be selected. This can lead to interesting information and applications. For example, commercial peroxidase enzyme comes mainly from horseradish (Sigma-Aldrich, 2011). This indicates that plants in the same family as radish should also contain peroxidase enzyme. Commercial purified lectin from wheat germ has been proven to have specific recognition toward bone alkaline phosphatase with minimum cross reaction from liver alkaline phosphatase (Kradtap Hartwell et al., 2007). Therefore, even though it may not be as effective as the commercial product, it should be possible to apply crude extract from wheat germ for determination of bone specific alkaline phosphatase as well.
Teaching analysis and data treatment processes. In the analysis and data/statistic processes, all the topics that can be introduced using synthetic chemicals can also be taught the same way with plant extracts, as also illustrated in Fig. 1. Depending on analytical techniques used, different instrumentation-based concepts can be taught along with the application of the plant extracts. For instance, if plant extract is used to form a colored complex with an analyte of interest, spectrophotometry can be introduced to the students. Relationships of color and wavelength, color intensity, concentration (Beer’s Law), and molecular absorptivity dependence of substances are just some examples that can be covered. Some extracts may change the pH of solution. Concepts about acid–base, neutralization, pKa–pKb, acidic and basic forms of substances, indicators, the use of pH meter, and acidity assay (quantitation of acid level) can all be easily involved. Comparisons can be made between the use of natural extract as an acid–base indicator and the use of synthetic indicators or with titration techniques that do not require indicators, i.e. electrochemistry based techniques. In addition, data and results analysis may be carried out in more dimensions than when just running experiments with standard chemicals. This is because in order to use a newly developed reagent, it is important to compare the results with the standard method or other standard reagents. At this point, various aspects of statistics e.g. T-test with different confidence levels, correlation plot, recovery studies, and % difference can all be introduced and discussed for their suitable uses in different circumstances.
Selection of samples to be analyzed using crude plant extracts as regents. Several things need to be considered when selecting a sample to use to demonstrate the application of a plant extract with real samples. The criteria for selection depend on the degrees of interferences encountered by other substances in the sample matrices. When crude extract is used it is possible to have many unidentified substances in the extract as well as the main active substance that we plan to use. Even though this is a limitation, it is still possible to use crude extract for real applications as demonstrated by some published works mentioned earlier. Samples should be chosen so that the analyte of interest is a dominant component. For example, calcium or iron dietary supplement pills can be used as samples for quantitative analyses of Ca2+ or Fe2+, respectively, with very low interferences from other ions. Waste water from certain factories may be rich in certain metal ions, such as the effluent from a ceramic factory could potentially be used as a source of Al3+ sample. Certain geographical areas have Fe3+ enriched groundwater that could be used to demonstrate the use of plant extracts for iron determination. Alternatively, the use of rust (iron oxide) could be used for the same purpose. Sometimes it may be difficult to find a real sample that contains a detectable level of the analyte of interest. It such cases, spiking of the sample (adding in a known amount of analyte into the sample matrices) and carrying out a recovery study can be performed as an alternate way to complete the application.
Limitations and the use of limitations for teaching purposes. The main limitation to using natural extract from plants (e.g. leaves, bark, roots) to perform chemical analysis is the seasonal dependence of plant availability. In some climates some plants lose their leaves during certain parts of the year. The various ages of the plant materials e.g. age of individual leaves, may also affect the amount of active species in the extract contained in different batches. This limitation can be turned into a useful teaching/learning experience as one tries to determine the appropriate method to store raw plant materials. For example, oven drying (with effect of temperature), freeze drying, and air drying methods can be carried out for comparison. Discussion on how heat, oxidation by oxygen, or change in pressure may affect the stability of active chemicals in plants should be valuable. Critical thinking on how to make, test, and ensure that various batches of the extracts contain a similar amount of active substance is important.

Another limitation encountered when working with natural plant extracts is that the desired plant species may be locally rare or nonexistent. For rare sources, it would be best to adapt the project for use with methods that consume less of the reagents. Another limitation can be the loss of stability of the extract over time or presence of fungus in the sample, for example. Finding the proper means of storage of the extract for further use, to improve stability and shelf life, can be a way to draw in more topics to cover in the undergraduate research project. Different methods can be investigated such as adding preservatives, treating with UV, heat, storage under inert gas, or other new ideas can be tried and tested to determine which method works best.

Outcome assessments

The objective of doing research is to find “new and valuable” information or the answer to a certain question. In the scientific community, this outcome is evaluated by peer review. Therefore, presentation and publication of the research with peer review are the ultimate way of research outcome assessment (Wenzel et al., 2012). Although undergraduate institutions face more difficulty as compared to graduate institutions in producing publishable research work, one recent study showed that there are a growing number of publications of undergraduate research (Leber et al., 2009). From some surveys conducted on the opinion of students toward conference participation (Mabreuk, 2009) and from student views toward publication (Hollich, 2010), undergraduate students seem eager to promote themselves and cultivate experiences from conference participation and article writing. Therefore, research supervisors and institutions should put forth effort in supporting students to reach that ultimate goal.

Publications in the area of using natural reagents in chemical analyses as found in the electronic database were mostly conducted at academic institutions, presumably with either graduate or undergraduate students. These publications therefore provide clear evidence that using plant extracts in chemical analyses is not only useful in a low cost teaching strategy, but it also yielded valuable knowledge that was accepted by peers. The author’s own experience in using plant extract in teaching a research term project course for undergraduate students also led to outcome beyond expectations. Some examples of undergraduate research projects co-supervised by the author are described next. The author would like to point out that these research projects are collaborative works among faculty members and students. Apart from learning all the aspects of conducting research, students realized the value of teamwork.

Example 1: Guava leaves (Psidium guajava L.) extract as natural reagent for determination of iron. This project emphasized students-involvement pedagogy, where the student came up with his own research topic with some guidance from instructors. This is categorized as “problem based learning” (Lanigan, 2008). The student observed that in the rural area of Thailand, where his grandparents lived, villagers always tested well water before using it for drinking and washing clothes. They did this by smashing some leaves of the guava plant, a common fruit tree in that area, and dropping them into the water. If the water turned brown, they said that it was not fit to drink or wash clothes without some sort of prior treatment. Although this method of water testing had been carried on for many generations, no one could provide any explanation about why guava leaves were used or for what substance they were testing. The student reported this observation and expressed that he wanted to investigate. The instructors guided the student to the online database and taught him how to use proper “keywords” to find as much information as possible about guava leaves and well water. The student found that guava leaves contain a high amount of tannin, and that well water in the area where his grandparents live may contain a high amount of iron which matched his observation of red soil in the area. This step led the student to further observations concerning the geographical and soil composition differences in various parts of the country. The student learned that tannin is a natural chemical that can form complexes with some metal ions. The student did a preliminary test by smashing the guava leaves and placing them into iron (III) chloride solutions of different concentrations and found that the solution turned brown at various degrees depending on the concentrations of iron (III) chloride. At about this same time the student learned how to use a low cost analysis system called “flow injection analysis” which was available in the laboratory. The student’s research topic started taking shape, and after discussion with the instructors, he settled on using a combination of extract from guava leaves and flow injection analysis system to quantitate iron ions. The student designed his experiments to optimize the systems and to test various conditions for extraction of natural reagents from guava leaves. The student decided on the green method of using aqueous buffer solution rather than organic solvent for extraction since it yielded adequate results and was safer to the environment. This choice indicated his sense of civic responsibility to keep the environment safe when conducting research. Concluding his research, the student wrote up the report to submit to the faculty committee. In addition, the instructors and student proceeded further by writing an article and submitting it to an international peer reviewed chemistry journal. The article, which was accepted for publication (Settheeworrarit et al., 2005), is an extraordinary outcome for an undergraduate student research work, considering the low budget and minimum facility employed.
Example 2: Green tea (Camellia sinesis) extract as alternative natural reagent for determination of iron. This project was a follow-up project from the previous one. The new student was informed by the instructors that one drawback of the previous project was the seasonal dependence of the guava leaf availability and that this limitation should be overcome. This is slightly different from the previous project and may be categorized as “method development based learning” where more information was given to the student (Lanigan, 2008). The instructors left it up to the student to come up with the way to solve this problem. One way would be to study how to increase the shelf life of the guava leaves extract for long term use, but the student came up with an alternative reagent that does not have seasonal dependence. During the time of this study, TV commercials often advertised green tea drinks and several magazines had published the benefits of drinking green tea. The student applied her knowledge gained from reading to come up with the idea that the dry tea leaves, always available in convenient stores, may be a good choice as an alternative seasonally-independent natural reagent for chemical analysis. Because this student conducted experiments based on the process published by the former student who had studied guava leaves extract with iron, she missed the opportunity to design her own experimental steps. Therefore, the instructors saw the importance of adding more requirements for this project by asking the student to evaluate green tea extract with other reagents or methods. The student had to think about which chemical reagent/method should be used to make the comparison. The student did the book/literature search for some acceptable standard methods for quantitative analysis of iron, and selected the standard method that uses a chemical that was readily available in the stock room. Then the student designed the experiment using real samples (iron supplements) to compare the standard method with the flow injection-green tea method. Again, apart from defending the research project with the faculty committee, the student helped to draft the article that was successfully published in an international peer reviewed chemistry journal (Pinyou et al., 2010).
Example 3: Indian Almond (Terminalia Catappa L.) leaves extract for determination of Aluminum. Another student questioned the use for chemical analysis of leaves of the Indian Almond, a common tree found around campus. The student investigated the chemical composition of the leaves as reported by botanists and chemists. It was found that, similar to guava leaves and tea leaves, Indian Almond contains a high amount of polyphenolic compounds. Preliminary testing by the student revealed that Indian Almond extract can form color complex with aluminum ion as well as iron. Based on the first two published articles, this student already had many guidelines for the experimental setup. Therefore, the instructors required that the student study the method of increasing shelf life of the extract for future use, an aspect which had not been done by previous students. The student designed 2 sets of experiments; one dealt with keeping leaves for future extraction process, and the second dealt with keeping the extract solution for further use. The student made progress and gained successful results adequate for the undergraduate project. Part of the research was presented by the student at an international conference (Insain et al., 2011) and the testing for real applications is in progress.

Conclusions

There are many examples, including ones from the author’s own experience, of using simple plant crude extracts for chemical analyses. These processes are safe for undergraduate/high school students to conduct. Most students come out of a research project with better experience if the projects are not too difficult and are ones that the students can manage and relate to (Braun et al., 2001). The use of easily available materials in conducting research as well as taking into account the personal experiences of the students tends to maximize student involvement and enhance interest in taking up research. Using low cost plant extract in chemical analysis teaching is a green chemistry approach and this does not have to sacrifice the quality of chemistry education. With careful guidance and design of the research projects, valuable outcome to the scientific community, civic responsibility through environmental safety awareness, and favorable experiences for the students in conference participation and publications can all be achieved within a minimum budget. This is an effective way of creating a sustainable teaching/learning process.

Acknowledgements

Financial and facility support from the Chemistry Department, Xavier University, is acknowledged.

References

  1. Anastas P.T. and Warner J.C., (1998), Green Chemistry: Theory and Practice (pp. 29–56). New York: Oxford Univ. Press.
  2. Anastas P.T., (1999), Green chemistry and the role of analytical methodology development, Crit. Rev. Anal. Chem., 29, 167–175.
  3. Armenta S., Garrigues S. and de la Guardia M., (2008), TrAC, Trends Anal. Chem., 27, 497–511.
  4. Barata-Vallejo S., Nudelman N.S. and Postigo A., (2011), Curr. Org. Chem., 15, 1826–1842.
  5. Benedict L.A., (2009), Greening up analytical chemistry: Preparing students for a greener graduate school or industrial career, Abstracts of Papers, 237th ACS National Meeting, Salt Lake City, UT, USA, March 22–26, CHED-1219.
  6. Bentayeb K., Rubio C., Batlle R. and Nerín C., (2007), Direct determination of carnosic acid in a new active packaging based on natural extract of rosemary, Anal. Bioanal. Chem., 389, 1989–1996.
  7. Braun D., Vanasupa L., London B., Kingsbury K. and Smith H., (2001), Cultivating graduate students: Techniques to inspire effective research, Materials Research Society Symposium Proceedings, 684E (Impacting Society through Materials Science and Engineering Education), Paper No. GG 1.2.
  8. Burmeister M., Rauch F. and Eilks I., (2012), Education for sustainable development (ESD) and chemistry education, Chem. Educ. Res. Pract., 13(2) 10.1039/c1rp90060a.
  9. Carpenter R., O’Grady M.N., O’Callaghan Y.C., O’Brien N.M. and Kerry J.P., (2007), Evaluation of the antioxidant potential of grape seed and bearberry extracts in raw and cooked pork, Meat Sci., 76, 604–610.
  10. Cha E., Won M. and Lee D., (2009), Analysis of flavor composition of coriander seeds by headspace mulberry paper bag micro-solid phase extraction, Bull. Korean Chem. Soc., 30, 2675–2679.
  11. Chen S., Turner A., Jaki B.U., Nikolic D., van Breeman R.B., Friesen J.B. and Pauli G.F., (2008), An experimental implementation of chemical subtraction, J. Pharm. Biomed. Anal., 46, 692–698.
  12. DeJong S. and Lanari M.C., (2009), Extracts of olive polyphenols improve lipid stability in cooked beef and pork: contribution of individual phenolics to antioxidant activity of the extract, Food Chem., 116, 892–897.
  13. Fatibello-Filho O. and da Cruz Vieira I., (1997), Flow injection spectrophotometric determination of sulfite using a crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) as a source of polyphenol oxidase, Anal. Chim. Acta, 354, 51–57.
  14. Flamini G. and Cioni P.L., (2010), Odour gradients and patterns in volatile emission of different plant parts and developing fruits of grapefruit (Citrus paradise L.), Food Chem., 120, 984–992.
  15. Gao S., Tan G., Yuan H., Xiao D. and Choi M.M.F., (2006), A simple fluorometric method using chlorophyll a for determination of Hg2+ ion, Microchim. Acta, 153, 159–162.
  16. Garcia-Reyes J.F., Gilbert-Lopez B. and Molina-Diaz A., (2009), Flow-through solid-phase spectroscopy: A contribution to green analytical chemistry, Spectrosc. Lett., 42, 383–393.
  17. Gaurav P., Kumar J.N., Narendra N. and Chatap V.K., (2010), Bougainvillea glabra-A natural indicator, Pharmacognosy J., 2, 25–28.
  18. Gottlieb K. and Robinson G., (2006), A practical guide for integrating civic responsibility into the curriculum, (2nd ed.). Community College Press, A division of American Association of Community Colleges, Washington D.C.
  19. Gron L., (2008), Innovations, applications and education in green analytical chemistry, Abstracts, 60th Southwest Regional Meeting of the American Chemical Society, Nashville, TN, USA, November 12–15, SERM-247.
  20. Gron L., (2009), Green analytical chemistry: Application and education, ACS Symposium Series (pp. 103–116), 1011 (Green Chemistry Education).
  21. Grudpan K., Lapanantnoppakhun S., Kradtap Hartwell S., Watla-iad K., Wongwilai W., Siriangkhawut, W., Jangbai W., Kumutanat W., Nuntaboon, P. and Tontrong S., (2009), Simple lab-on-chip approach with time-based detection, Talanta, 79, 990–994.
  22. Grudpan K., Kradtap Hartwell S., Lapanantnoppakhun S. and McKelvie I., (2010), The case for the use of unrefined natural reagents in analytical chemistry - A green chemical perspective, Anal. Methods, 2, 1651–1661.
  23. Grudpan K., Kradtap Hartwell S., Wongwilai W., Grudpan S. and Lapanantnoppakhun S., (2011), Exploiting green analytical procedures for acidity and iron assays employing flow analysis with simple natural reagent extracts, Talanta, 84, 2011, 1396–1400.
  24. Gurney R.W. and Statford S.P., (2009), Integrating green chemistry throughout the undergraduate curriculum via civic engagement, ACS Symposium Series (pp. 55–77), 1011 (Green Chemistry Education).
  25. Haack J.A., Hutchinson J.E., Kirchoff M.M. and Levy I.J., (2005), Going green: Lecture assignments and lab experiences for the college curriculum, J. Chem. Educ., 82, 974–976.
  26. Haack J.A., (2009), New features of the greener education materials database, Abstracts of Papers, 237th ACS National Meeting, Salt Lake City, UT, USA, March 22–26, CHED-1174.
  27. He Y., Tang L., Wu X., Hou X. and Lee Y., (2007), Spectroscopy: The best way toward green analytical chemistry?, Appl. Spectros. Rev., 42,119–138.
  28. Heuer S., Richter S., Metzger J.W., Wray V., Nimtzt M. and Strack D., (1994), Betacyanins from bracts of Bougainvillea glabra, Phytochemistry, 37, 761–767.
  29. Hixson S.H., Richtol H.H. and Settle F.A., (1996), Systemic changes in the undergraduate chemistry curriculum: Emphasis on adaption and adoption, Chem. Educ., 1, 1–3.
  30. Holbrook J., (2005), Making chemistry teaching relevant, Chem. Educ. Int., 7, Retrieved from the World Wide Web, January 14, 2012, at http://old.iupac.org/publications/cei/vol6/index.html.
  31. Hollich D., (2010), Opportunities to publish undergraduate research, Am. Ceram. Soc. Bull., 89, 29.
  32. Horoszewski D.N., Crone W.C., Gentry K.L., Ng S.K.H., Johnson C., Lisensky G.C., Marmon J., Keefer D., Horger J., Nordell K.J. and Amankwah R., (2007), Low-cost laboratory experiments in nanoscience, Abstract of Papers, 233rd ACS National Meeting, Chicago, IL, March 25–29, CHED-252.
  33. Iimoto D.S. and Frederick K.A., (2011), Incorporating student-designed research project in the chemistry curriculum, J. Chem. Educ., 88, 1069–1073.
  34. Insain P., Pun-uam T., Khonyoung S., Lapanantnoppakhun S., Grudpan K., Kradtap Hartwell S., (2011), Determination of aluminum ion using Indian Almond Leaf (Terminalia Catappa L.) extract as a natural reagent, Abstract Book, 14th Asian Chemical Congress (p. 689), Bangkok, Thailand, September 5–8, 2011, PO-G2-02.
  35. Jacobson E.K., Pienta N.J., Slocum L.E., (2011), “Being naturally resourceful”: Ready-to-use resources from the Journal of Chemical Education, Abstract of Papers, 241st ACS National Meeting & Exposition, Anaheim, CA, March 27–31, CHED-32.
  36. Jellard S., Kamoun S., Mehdi M., Zakri S., Trabelsi M., Saad A. and Ajina M., (2011), Sperm immobilizing effect of leaves extracts of Cestrum parqui, J. Gynecol. Obstet. Biol. Reprod., 40, 211–215.
  37. Koel M. and Kaljurand M., (2010), Green Analytical Chemistry. Cambridge: RSC Publishing.
  38. Kozan J.V.B., Silva R.P., Serrano S.H.P., Lima A.W.O. and Angnes L., (2010), Amperometric detection of benzoyl peroxide in pharmaceutical preparations using carbon paste electrodes with peroxidases naturally immobilized on coconut fibers, Biosens. Bioelectron., 25, 1143–1148.
  39. Kradtap Hartwell S., Somprayoon D., Kongtawelert P., Ongchai S., Arppornchayanon O., Ganranoo L., Lapanantnoppakhun S. and Grudpan K., (2007), Online assay of bone specific alkaline phosphatase with a flow injection-bead injection system, Anal. Chim. Acta, 600, 188–193.
  40. Kradtap Hartwell S., Sripaoraya W. and Grudpan K., (2011), Assay of chondroitin sulfate using time-based detection in a simple lab-on-chip, J. Anal. Chem., 66, 135–138.
  41. Lanigan K.C., (2008), Teaching analytical method development in an undergraduate instrumental analysis course, J. Chem. Educ., 85, 138–140.
  42. Leber P.A., Williams B.R., Yoder C.H., (2009), The change in publication rates at undergraduate institutions during the last three decades, J. Chem. Educ., 86, 876–878.
  43. Liu X., Li J., Zhao Z., Zhang W., Lin K., Huang C. and Wang X., (2009), Solid-phase extraction combined with dispersive liquid–liquid microextraction for the determination for polybrominated diphenyl ethers in different environmental matrices, J. Chromatogr. A, 1216, 2220–2226.
  44. Lupetti K.O., Cruz Vieira I. and Fatibello-Filho O., (2002), Flow injection spectrophotometric determination of isoproterenol using an avocado (Persea Americana) crude extract immobilized on controlled-pore silica reactor, Talanta, 57, 135–143.
  45. Mabreuk P.A., (2009), Survey study investigating the significance of conference participation to undergraduate research students, J. Chem. Educ., 86, 1335–1340.
  46. Makino Y., Uchiyama S., Ohno K. and Arakawa H., (2010), Low-cost fluorometric determination of radicals based on fluorogenic dimerization of the natural phenol sesamol, Anal. Chem., 82, 1213–1220.
  47. Mamada M., Perez-Bolivar C. and Anzenbacher P., (2011), Green synthesis of polycyclic benzimidazole derivatives and organic semiconductors, Org. Lett., 13, 4882–4885.
  48. McClure C.P. and Lucius A.L., (2010), Implementing and evaluating a chemistry course in chemical ethics and civic responsibility, J. Chem. Educ., 87, 1171–1175.
  49. Middlecamp C.H., Jordan T., Shachter A.M., Lotttridge S. and Oates K.K., (2006), Chemistry, society, and civic engagement (part I): The SENCER project, J. Chem. Educ., 83, 1301–1307.
  50. Monji A.B., Zolfonoun E. and Ahmadi S.J., (2009), Application of water extract of slippery elm tree leaves as a natural reagent for selective spectrophotometric determination of trace amounts of molybdenum (VI) in environmental water samples, Toxicol. Environ. Chem., 91, 1229–1235.
  51. Mooney D., (2004), Effectively minimizing hazardous waste in academia: The green chemistry approach, Chem. Health Safety, 11, 24–28.
  52. Nagaoka H., (2003), Chiral resolution function with immobilized food proteins, Biotechnol. Prog., 19, 1149–1155.
  53. Nalewajko-Sieliwoniuk E., Nazaruk J., Antypiuk E. and Kojlo A., (2008), Determination of phenolic compounds and their antioxidant activity in Erigeron acris L. extracts and pharmaceutical formulation by flow injection analysis with inhibited chemiluminescent detection, J. Pharm. Biomed. Anal., 48, 579–586.
  54. O’Grady M.N., Carpenter R., Lynch P.B., O’Brien N.M. and Kerry J.P., (2008), Addition of grape seed extract and bearberry to porcine diets: Influence on quality attributes of raw and cooked pork, Meat Sci., 78, 438–446.
  55. Olas B., Saluk-Juszczak J., Pawlaczyk I., Nowak P., Kolodziejczyk J., Gancarz R. and Wachowicz B., (2006), Oxidant and antiaggregatory effects of an extract from Conyzacanadensis on blood platelets in vitro, Platelets, 17, 354–360.
  56. Parashar R., Parashar R.K. and Gupta V.P., (2006), Cost reduction of complexometric titrations by two burette method, J. Teach. Res. Chem., 13, 55–58.
  57. Pardo-Andreu G., Philip S.J., Riaño A., Sánchez C., Viada C., Núñez-Sellés A. and Delgado R., (2006), Mangiferaindica L. (Vimang) protection against serum oxidative stress in elderly humans, Arch. Med. Res., 37, 158–164.
  58. Park H., (2003) Disinfectant for cooking utensils which is harmless to human body and environmental by using iodine as natural extract of seaweed, Repub. Korean Konghaekongbo, Patent No. KR 2004101693.
  59. Peng C., (2003), Natural extract of cinnamomum plant as formaldehyde scavenging agent for indoor applications, Faming Zhuanli Shenqing Gongkai Shuomingshu, Patent No. CN 1431258.
  60. Penker W.C. and Elston H.J., (2003), Funding safety activities in secondary schools, J. Chem. Educ., 80, 1401–1402.
  61. Petrović J., Nikolić G. and Marković D., (2006), In vitro complexes of copper and zinc with chlorophyll, J. Serb. Chem. Soc., 71, 501–512.
  62. Pienta N.J., (2010), Cutting educational budgets (editorial), J. Chem. Educ., 87, 763.
  63. Pinyou P., Kradtap Hartwell S., Jakmunee J., Lapanantnoppakhun S. and Grudpan K., (2010), Flow injection determination of iron ions with green tea extracts as a natural chromogenic reagent, Anal. Sci., 26, 619–623.
  64. Qin C., Li Y., Niu W., Ding Y., Zhang R. and Shang X., (2010), Analysis and characterization of anthocyanins in mulberry fruit, Czech J. Food Sci., 28, 117–126.
  65. Russell S.H., Hancock M.P., McCullough J., (2007), Benefits of undergraduate research experiences, Education forum in Science, 316, 548–549.
  66. Samarapungavan A. and Westby E.L., (2003), Chemistry students developing understanding of the nature of science, Abstracts of Papers, 225th ACS National Meeting, New Orleans, LA, USA, March 23-27, CHED 1155.
  67. Sane K.V., (1994), Chemical education in the coming decades-challenges and opportunities, Chem. Sci., 106, 1389–1398.
  68. Settheeworrarit T., Kradtap Hartwell S., Lapanantnoppakhun S., Jakmunee J., Christian G.D. and Grudpan K., (2005), Exploiting guava leaf extract as an alternative natural reagent for flow injection determination of iron, Talanta, 68, 262–267.
  69. Shachter A.M., (2005), Sustainability, chemical education, and SENCER, Abstracts of Papers, 229th ACS National Meeting, San Diego, CA, USA, March 13-17, CHED-264.
  70. Sigma-Aldrich, (2011), Peroxidase enzymes, Enzyme explorer, Retrieved from the World Wide Web, September 20, 2011, at http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzymes/peroxidase-enzymes.html.
  71. Sikwese F.E. and Duodu K.G., (2007), Antioxidant effect of a crude phenolic extract from sorghum bran in sunflower oil in the presence of ferric ions, Food Chem., 104, 324–331.
  72. Smestad G., (2008), Titanium dioxide raspberry solar cell, Material research science and engineering center, University of Wisconsin-Madison, Retrieved from the World Wide Web, September 20, 2011, at http://mrsec.wisc.edu/Edetc/nanolab/TiO2/index.html.
  73. Sneddon P.H. and Hill R.A., (2011), Perceptions, views and opinions of university students about chemistry learning during practical work at school, Chem. Educ. Res. Pract., 12, 312–321.
  74. Strobel S.A. and Strobel G.A., (2007), Plant endophytes as a platform for discovery-based undergraduate science education, Nature Chem. Biol., 3, 356–359.
  75. Svec W.A., (1991), Chlorophylls, Boca Raton, FL: CRC Press.
  76. Tang D., Shen S., Chen X., Zhang Y. and Xu C., (2004), Interaction of catechins with aluminium in vitro, J. Zhejiang Univ. Sci., 5, 668–675.
  77. Tyson J.F., (1989), Modern analytical chemistry, Anal. Proc., 26, 251–254.
  78. Ueda M., Lapanantnoppakhun S., Wongwilai W., Teshima N., Sakai T. and Grudpan K., (2010), Exploiting a simple water extract of a flower as a natural reagent for acidity assay using a lab-on-chip, J. Flow Injection Anal., 27, 57–60.
  79. United States Environmental Protection Agency, Office of Water, (2002), Method 1631, Revision E: Mercury in water by oxidation, purge and trap, and cold vapor atomic fluorescence spectrometry, EPA-821-R-02-019.
  80. United States Environmental Protection Agency, (2012), Green chemistry, Retrieved from the World Wide Web, January 14, 2012, at http://www.epa.gov/greenchemistry/.
  81. Wang J., (2002), Real-time electrochemical monitoring: Toward green analytical chemistry, Acc. Chem. Res., 35, 811–816.
  82. Watts M. and West A., (1992), Progress through problems, not recipes for disaster, School Sci. Rev., 73, 57–63.
  83. Wenzel T.J., Larive C.K. and Frederick K.A., (2012), Role of undergraduate research in an excellent and rigorous undergraduate chemistry curriculum, J. Chem. Educ., 89, 7–9.
  84. Wilson M.P. and Schwarzman M.R., (2009), Toward a new U.S. chemicals policy: Rebuilding the foundation to advance new science, green chemistry, and environmental health, Environ. Health Perspectives, 117, 1202–1209.
  85. Woodget B.W., (2003), Teaching undergraduate analytical science with the process model, Anal. Chem., 307A–310A.
  86. Xu J., Chen S. and Hu Q., (2005), Antioxidant activity of brown pigment and extracts from black sesame seed (Sesamumindicum L.), Food Chem., 91, 79–83.
  87. Zhai Y., Sun S., Wang Z., Zhang Y., Liu H., Sun Y., Zhang H. and Yu A., (2011), Headspace single drop microextraction coupled with microwave extraction of essential oil from plant materials, J. Sep. Sci., 34, 1069–1075.
  88. Zheng Z., Cheng K., To J.T., Li H. and Wang M., (2008), Isolation of tyrosinase inhibitors from Artocarpusheterophyllus and use of its extract as antibrowning agent, Mol. Nutr. Food Res., 52, 1530–1538.
  89. Zhou B., Yang J., Li M. and Gu Y., (2011), Gluconic acid aqueous solution as a sustainable and recyclable promoting medium for organic reactions, Green Chem., 13, 2204–2211.
  90. Zou H.F., Li H.L., Zhang Y.K. and Lu P.C., (1990), Determination of iodine anion in dried kelp and iodized throat tablets by reversed-phase ion-pair liquid chromatography with direct UV detection, Chromatographia, 30, 228–230.

Footnote

† This article is part of a themed issue on sustainable development and green chemistry in chemistry education.
This journal is © The Royal Society of Chemistry 2012
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