Themed collection Analytical Methods Committee Technical Briefs

This article summarises the principles and assumptions underlying linear regression plots as used in method validation and in calibration experiments, and warns of problems that may arise when the assumptions are not valid.

Quoted values of measurement uncertainty (MU) are only ever estimates, being subject to their own uncertainties. This has implications for selecting a way to compare two values of MU.

This technical brief describes a tool in the form of a “periodic table” to assist in optimizing liquid chromatography separations selected by following the guidance provided in AMCTB No. 107.

A collaborative trial (an interlaboratory study) is reputed to be the most reliable way of validating an analytical procedure applied to a defined class of test material, however, the popularity of trials is declining while the need for information from them is escalating.

X-ray micro-computed tomography can provide information about the composition and internal structure of materials commonly found in heritage buildings such as natural stone, mortar, brick, concrete and wood.

This Technical Brief discusses the main advantages and limitations of hand-held X-ray fluorescence spectroscopy applied to archaeological artefacts, together with its potential to answer research questions for archaeologists and conservators.

This technical brief provides an overview of the decision making process for selecting LC techniques to separate known analyte(s) from a complex liquid matrix.

Fourier Transform Infrared (FTIR) spectroscopy is ideally suited to the cultural heritage sector due to the ability to apply it minimally or non-destructively with limited sample preparation, fast analysis times, relatively low cost, and relative ease of use.

This document aims to explain the existence of a confidence interval (CI) on every MU estimate, and how it can be evaluated, using a worked example that includes primary sampling within the measurement process.

This Technical Brief aims to illustrate the uses and applications of thermal desorption methods in analytical measurement.

Often wax-containing objects suffer degradation: analytical chemistry provides the key to designing appropriate conservation strategies and materials for such objects in heritage collections.

While the underlying principles of simplex optimisation are easy to understand and the small number of trial experiments involved make the approach very attractive, there are several important issues to be considered in the practical application of the method.

This Technical Brief outlines the principal analytical methods used in dye and mordant analysis, by explaining how to select the most appropriate experimental conditions and describing the types of instrumentation available.

Here we provide an introduction to multivariate statistics.

This Technical Brief outlines the SI units and quantities available for use in analytical chemistry and explains the care that must be taken if alternative approaches are followed.

This Technical Brief introduces the use of X-ray micro computed tomography in cultural heritage.

This Technical Brief informs both analysts and less technically aware users of the capabilities and limitations of thermal desorption equipment and measurement methods.

This Technical Brief outlines the basic principles of optimisation, and introduces some of the most commonly used approaches.

This Technical Brief aims to explain how the new second edition of the Eurachem guide, Measurement uncertainty arising from sampling, differs significantly from the first edition that was published in 2007.

This Technical Brief aims to inform both analysts and less-technically aware users of the applications, capabilities and limitations associated with the use of hand-held infra-red and Raman instrumentation.

This article explains what a p-value is and the pros and cons of using them. Concluding that they are a useful method of interpreting data.

This Technical Brief describes the principal internationally recognised approach to decision and detection limits.

This Technical Brief describes the basic concepts of laser-induced breakdown spectroscopy, presents relevant aspects of instrumentation and discusses how the technique is applied in the context of cultural heritage studies.

This Technical Brief explains how accreditation and certification of sampling is already in place in certain application sectors, and the potential benefits it can bring as it is applied to new sectors. Accreditations provides the framework within which both samplers and analytical chemists can demonstrate appropriate quality.

This Technical Brief provides an overview and describes the evolution of hand-held X-ray fluorescence instrumentation designed for inorganic elemental analysis and how it can be used for in situ analysis and on-site decision making.

This Technical Brief describes a new way to define and express measurement uncertainty in analytical methods using the uncertainty factor.

Analytical sciences regression methods are important for instrumental analysis and method comparison studies, this technical brief discusses the importance and correlation of coefficient values.

This technical brief explains why four of the International System of Units’ seven base units – the mole, the ampere, the kelvin, and the kilogram – have been re-defined.

Analytical pyrolysis (Py), especially when coupled with gas chromatography and mass spectrometry (Py-GC-MS), is a powerful technique for the characterisation and identification of organic materials used in artwork.

Beam sampling occurs in most micro-analytical measurements, such as those by Secondary Ion Mass Spectrometry. The uncertainty of such measurements must therefore include the uncertainty arising from this sampling process.

This Technical Brief focuses on the application of FTIR spectroscopy and outlines the different types of materials commonly found in museum collections. The different types of attachments and techniques are also described here.

The normal distribution is the expected outcome when a result stems from numerous stages of the measurement process, each of which introduces a small independent error. Sometimes we need to test whether a dataset complies with that expectation.

An overview of mass spectrometry instrumentation is combined with a novel presentation of the techniques and components which aids in decoding their acronyms.

Surface-enhanced Raman spectroscopy (SERS) has been increasingly used in the last decade for the identification of organic colourants in works of art. This technical brief focuses on the practical aspects of SERS in its application to the analysis of cultural heritage material.

The digital polymerase chain reaction provides an important step forwards in the quantitative study of DNA.

General guidelines for the proficiency testing of sampling are required to handle the special complications involved.

X-ray fluorescence is used for a wide variety of purposes in the examination of heritage objects made from porcelain.

This technical brief aims to dispel the mythology of metrology, explain important aspects and demonstrate the value of metrology to chemical measurements.

Diffuse reflectance spectrophotometry in the ultraviolet, visible and near-infrared spectral range is becoming a widely-used tool for the non-invasive analysis of cultural heritage objects.

ISO 13528 (2015) describes several types of score suitable for interlaboratory studies, but only the simple z-score based on fitness for purpose is recommended here for chemical proficiency tests.

The term ‘representative sample’ has been redefined many times and become ambiguous. The recommended alternative is ‘appropriate sample’, implying an uncertainty the is fit for purpose.

The datasets provide opportunities for the analyst to try out a variety of statistical procedures for investigating the outcome of chemical measurements.

The strengths and limitations of two approaches to the uncertainty derived from sampling (UfS) are compared. Quantitatively, the experimental approach for estimating UfS is more reliable.

Precision, quantified as its inverse, is strongly dependent on the conditions of measurement, and is importantly related to uncertainty.

The Grubbs test can be used to identify outliers in the results of replicated measurements. The Cochran test is used to identify groups of results with outlying variance in analysis of variance.

Scoring in proficiency testing of analytical laboratories should be based on a fitness-for-purpose criterion.

This Technical Brief outlines the advantages and limitations of Raman spectroscopy in cultural heritage research, what the technique can be used for and what type of information can be gathered. The different types of equipment, lasers and experimental set-ups are also discussed.

Heritage Science is the scientific study of cultural and historic artefacts to assist their conservation and preservation.

Ensuring the stability of the test material between sampling and analysis is an essential aspect of chemical measurement.

For the estimation of uncertainty from sampling, an unbalanced design combined with a robust analysis of variance provides an economic experiment that is not sensitive to a small proportion of outlying results. Software is provided.

The determination of nitrogen as a quantitative marker for meat fat-free protein and the calculation of meat content of compound foods is the established official chemical method to enforce labelling declarations of meat content in food products.

The determination of nitrogen as a quantitative marker for fat-free protein is the official chemical enforcement method for the calculation of seafood content of seafood products.

Many extraneous factors can affect an analytical result. Analysts preparing an uncertainty budget should use judgement in deciding whether to include uncertainty resulting from empirical tests of implausible influences.

A representative sample must be unbiased and with an associated between-sample standard deviation that is smaller than that regarded as fit for purpose in the application.

The polymerase chain reaction (PCR) has widespread analytical applications in the food, environmental, medical and forensic fields. This Technical Brief covers the basics of PCR and some of its variations.

Uncertainty from sampling can be estimated by using a hierarchical experiment, but the quality of the uncertainty estimates has to be balanced against the size (and cost) of the experiment.

Non-parametric statistical methods for significance testing make few assumptions about the distribution of results and are often simple to use.

Errors in chemical analysis are often discussed but seldom reliably attributed to specific causes. Feedback from participants in proficiency tests is an ideal source of information, however, and a recent study has shown that simple human error is by far the main culprit.

Good experimental design is important in many analytical and other chemical studies. The Plackett–Burman method is a popular and economical approach that gives information, in a manageable number of experiments, on the effects of many factors that might influence a chemical measurement.

Contracted-out analysis is normally conducted against a specification of the maximum uncertainty acceptable in the results. This Technical Brief outlines some methods by which customers can check whether the specification is being fulfilled.

Analysts following the GUM method for expressing the uncertainty of their results have a strong tendency to underestimate. This stems from the difficulty of expressing as a measurement model procedures as complex as chemical measurement. The discrepancy is referred to as ‘dark uncertainty’.

This Technical Brief outlines some examples of the importance of Bayesian statistical methods in a variety of areas of applied analytical science.

Samples from one target differ in composition from the target and from each other. Randomised duplication provides a basis for quality control of sampling and indicates when sampling uncertainty exceeds expectations.

The latest Technical Brief from the Analytical Methods Committee examines applications of regression methods for calibration and comparison.