Development of a low-cost gas chromatograph with a polyaniline-modified silica gel stationary phase for the isolation of hydrogen and carbon dioxide gases

Abstract

Gas chromatography (GC) is a widely used analytical technique in chemistry and various scientific fields for separating and analyzing volatile compounds within complex mixtures. Low-cost gas chromatography (GC) systems offer a fusion of affordability and analytical precision for scientific exploration and innovation. Such portable and cost-effective systems enable on-site testing, which is crucial in environmental monitoring, food safety, forensic analysis, and more. Here, we present a novel approach to enhance the performance of gas chromatography by developing a cost-effective and highly efficient stationary phase column material. For this, polyaniline (PANI)-modified silica gel was meticulously prepared through the in situ chemical polymerization method and characterized through various techniques such as field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy for the morphological, chemical bonding, and functional group analysis. The resultant material exhibited remarkable stability and selectivity, making it an ideal candidate for a stationary phase column. The column was connected through an Arduino-based detection system built by integrating commercially available low-cost H₂ and CO₂ detectors with Arduino and a LabVIEW-based program. The system enables a quantitative and qualitative analysis of H₂ and CO₂ gases. Through a series of chromatographic experiments, we have demonstrated the composite's efficacy in achieving superior separation properties, reduced analysis time, and enhanced resolution compared to conventional stationary phases. The use of PANI-modified silica gel in a GC stationary column for H₂ and CO₂ analysis has not yet been published or reported elsewhere.

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1. Introduction

Efficient separation of the two essential gases, hydrogen and carbon dioxide, with major industrial and environmental significance, is crucial in various domains.¹ Hydrogen serves as a significant energy carrier and is utilized extensively in chemical synthesis, fuel cells, and hydrogenation reactions in sectors including ammonia manufacture, petroleum refining, and many more.^2,3 As the role of hydrogen as a clean energy source garners increased attention, the demand for effective separation and purification methods continues to rise.^4,5 Conversely, carbon dioxide is a major greenhouse gas that has a significant impact on climate change, making its separation and capture indispensable in industrial gas purification, emission monitoring, and carbon sequestration technologies.⁶ Since hydrogen and carbon dioxide frequently coexist in different proportions during processes like syngas production, carbon capture and utilization (CCU), and biogas upgrading, the development of robust and selective separation technologies is paramount.^7,8

Gas chromatography (GC) is a powerful analytical technique that is commonly used for the separation, identification, and quantification of volatile components in a mixture.⁹ GC separates the analytes based on their distribution between the stationary phase of the column and a mobile phase gas stream.¹⁰ In general, various components in the mobile phase are differently attracted towards the stationary phase material, depending upon the interaction between the analytes, and thus move through the stationary phase at different rates. A conventional GC is a powerful, versatile, and expensive tool that requires high power (up to 2000–3000 V-ampere), making it non-field portable.¹¹ With the rising demands of rapid and on-site chemical analysis of complex mixtures, recently, there has been growing interest in the development of in-house built GC with minimal resources and novel stationary phase materials to enhance its working capabilities for specific analytes.¹² Such a do-it-yourself (DIY) system offers great advantages, including low cost, compact size, system portability, and rapid analysis for time-sensitive decisions.¹³ Further, they also help in minimizing any changes in sample composition that occur due to degradation, evaporation, oxidation, or adsorption.¹⁴ These DIY instruments use microcontrollers with commercially available sensors as the detection system.¹⁵ During the past few years, there have been a number of such portable GC instruments developed for both research and commercial laboratories.¹⁶ For instance, Hinterberger et al. reported the fabrication of an Arduino-based GC with a total cost of less than $100 for teaching purposes.¹⁵ Kaljurand et al. fabricated a low-cost, robust gas chromatograph for monitoring light hydrocarbon emissions into the environment.¹⁴

The primary point of improvement for these DIY-GC systems is the peak separation, which is directly dictated by the stationary phase and its separation capabilities for various analytes. Traditional GC systems for gas separation typically rely on molecular sieves, activated carbon, or specialized porous polymeric materials as stationary phases.¹⁷ While these materials provide good selectivity for certain gases, they often require precise control over temperature and pressure conditions to maintain performance.¹⁸ Furthermore, a lot of these stationary phases are expensive and might not be reusable, which limits their availability for applications where cost is a concern.¹⁹ Due to their high cost and complex infrastructure requirements, commercial GC systems with extensive separation capabilities are not often used in field applications, small-scale labs, or educational settings.²⁰

The advancement in materials science has led to the development of various stationary phase materials that offer improved separation of gas mixtures. One of the potential polymeric compounds for this application is polyaniline (PANI). PANI is one of the well-known conducting polymers with desirable physico-chemical properties, such as porous structure, stability, and affinity towards many types of analytes due to its ability to accommodate different types of interactions.²¹ In the context of gas chromatographic separations, PANI shows a high adsorption capacity.²² In a recent study, it was found that the saturation capacity (Q_sat) for PANI-based composites can be much higher than that of pure activated carbon and similar materials.²³ Therefore, PANI composites are good alternative materials for column packing in gas chromatographs. They have been used as sorbent materials in solid-phase extraction techniques, which are commonly used to isolate compounds from liquid matrices.²⁴ Mohammad et al. used PANI-modified silica gel for the efficient separation of organic dyes.²⁵ PANI, when combined with silica particles, forms a composite material that can exhibit higher physical and thermal stability and even maximize the surface area to increase the adsorption capacity.²⁶ Further, being inexpensive to synthesize and having excellent adsorption capacity and adjustable surface characteristics, it can be a viable substitute.²⁷ PANI's inclusion into silica gel adds functional groups that can interact with gas molecules selectively through hydrogen bonds, dipole interactions, or acid–base interactions.^28,29 Specifically, PANI contains amine groups in its structure, which interact with the CO₂ molecules by the partial formation of carbonates and bicarbonates, thereby increasing the solubility of CO₂ molecules.²¹ This increases the resolution and effectiveness of hydrogen and carbon dioxide separation. Despite these advantages, the use of polyaniline-modified silica gel as a stationary phase in gas chromatography is still largely unexplored, especially when it comes to the selective separation of hydrogen and carbon dioxide.

In this study, we present the development of a low-cost gas chromatograph incorporating a polyaniline-modified silica gel stationary phase for the efficient separation of hydrogen and carbon dioxide gases. In comparison to traditional silica-based stationary phases, we aim to increase peak resolution and separation efficiency by leveraging the unique adsorption properties of polyaniline and the large surface area of silica gel. The particle size and porosity of silica gel strongly influence the separation performance. For instance, larger particles facilitate a lower column backpressure, while small particles increase resolution due to a higher surface area (but increase volume backpressure). Thus, here we used silica particles of around 20–70 µm to obtain a balance between surface area and pressure drop, which is essential for our GC operation. This study also investigates the viability of creating an affordable GC system that can be assembled using readily accessible materials, making it a suitable alternative for laboratories with limited resources, educational institutions, and on-site monitoring field applications, where affordability and accessibility outweigh the pursuit of sensitivity (i.e. ppm level detection). The results of this study may help low-cost chromatographic methods become more widely used and create new opportunities for the use of polymer-based stationary phases in the separation of gas molecules.

2. Experimental section

2.1. Materials used

The chemicals used are of analytical grade and were used directly as purchased without further treatment. For instance, silica gel (60–120 mesh) and ammonium persulfate (APS, (NH₄)₂S₂O₈, 98%) were purchased from Loba Chemie Pvt. Ltd, aniline (ACS reagent, 99.5%) was purchased from Merck, and HCl (37%) was purchased from ACS Emparta.

For the detection of CO₂, an ACD10 infrared carbon dioxide sensor (ASAIR) was utilized, while for the detection of H₂ gas, an MQ-8 hydrogen gas sensor (Macfos India Pvt. Ltd) was used. An Arduino Uno was purchased from Macfos India Pvt. Ltd. A poly-tetrafluoroethylene (PTFE) pipe having a 6 mm outer diameter and 4 mm inner diameter was purchased from a local store and utilized for the preparation of the separation column. Nitrogen gas of high purity (99.999%) was used as a carrier gas.

2.2. Synthesis of PANI-modified silica gel

For the synthesis of a stationary phase column material, silica gel was modified using PANI functionalization through an in situ method. For this, silica gel was mixed during the in situ chemical oxidative polymerization reaction of aniline.²⁶ In brief, 4.566 g ammonium persulfate (APS) was dissolved in 200 ml of 2.5 M HCl solution under stirring at a temperature of less than 5 °C. To the prepared solution, 20 g silica gel was added and left for half an hour under vigorous stirring. After this, 4 ml of aniline was slowly added to the above solution. The solution was kept on stirring for 3 hours at room temperature for the complete polymerization of aniline. During this, the color of the solution turns green. The solution was then left for 24 hours and was centrifuged and washed with DI and 0.1 M HCl to remove the unreacted soluble components and aniline. It was further washed 2 times with acetone and finally dried in an oven at 90 °C to obtain the PANI-modified silica gel composite.

2.3. Development of a low-cost gas chromatographic setup

The practical application of the synthesized material was tested by developing a low-cost gas chromatographic setup. The schematic of the setup is shown in Fig. 1(a). For this purpose, the synthesized PANI-modified silica gel composite material was filled into a polymer pipe made up of poly-tetrafluoroethylene (PTFE) due to its low cost and flexibility. The material was filled in a way that made the column densely packed for the gas to get trapped. This densely packed column, by utilizing PANI-modified silica gel, was used as a stationary phase column. The length of the column was 2 m and its internal diameter was 4 mm. To further test the working of our dense column, a gas chromatographic set-up was assembled using an injection valve to inject the sample gas, a carrier gas inlet with a pressure controller, and a gas detection system. ACD10 and MQ-8 gas sensors were connected with an Arduino Uno microcontroller board, which was utilized to read the sensor values as well as to communicate with a LabVIEW-based computer program. The sensor values were plotted with respect to time and recorded into a text file for analysis. Nitrogen gas was used as a carrier gas. The gas separation mechanism is completely based on the solubility and interaction of gases with the densely packed column material. The photograph of the fabricated low-cost gas chromatograph with its components is presented in Fig. 1(b–d). All the experiments were performed at room temperature (25 ± 2 °C).

Fig. 1 (a) Schematic diagram and (b–d) photographs of the gas chromatographic set-up.

2.4. Characterization

The synthesized stationary phase column material was characterized morphologically through field emission scanning electron microscopy (FESEM) with a Nova Nano FESEM-450 instrument. Fourier transform infrared spectroscopy (FTIR) performed using a Spectrum 2 PerkinElmer instrument and Raman spectroscopy performed using an AIRIX STR 500 Raman spectrophotometer were utilized to elucidate the intricate molecular and structural changes underlying this novel composite material. For this purpose, the FTIR spectrum was recorded in the range from 400 to 4000 cm⁻¹, and the Raman spectrum was recorded in the range from 400 to 2000 cm⁻¹, respectively.

The limit of detection (LOD) is defined as the lowest amount of analyte gas that can be detected by the gas chromatograph, while being easily distinguished from the background noise, whereas the limit of quantification (LOQ) is the lowest amount that can be quantified with acceptable precision and accuracy. The calculations of LOD and LOQ values are based on the signal-to-noise ratio, and the formulas utilized are shown below:

LOD = 3.3 × (σ/S)

LOQ = 10 × (σ/S)

where σ is the standard deviation of the baseline noise determined by running multiple samples in the fabricated GC system and measuring the obtained peak areas and response, and S is the slope of the calibration curve obtained using various known concentrations. Linear regression was performed on the data to obtain the value of the slope of the calibration line.

The number of theoretical plates (N) represents a critical parameter in gas chromatography (GC) that quantifies column efficiency and influences the resolution of analyte separation. It is calculated through retention time (t_R) and peak width (W_1/2) using the following relationship:

The peak resolution (R_s) is calculated through peak intensities (t_R,CO2 and t_R,H2) and peak widths (W_H2 and W_CO2) for CO₂ and H₂ gases, respectively, using the formula

3. Results and discussion

3.1. FTIR analysis

Following the synthesis process, the material underwent certain characterization to investigate its chemical and morphological characteristics. For example, the presence of specific functional groups and chemical bonds was analyzed using the FTIR spectroscopy technique. Fig. 2 shows the FTIR spectra of pure PANI, pure silica, and PANI-modified silica gel. From the figure, we can see that all the characteristic peaks of pure silica are also present in the PANI-modified silica gel. However, the absorption peaks of stretching vibrations of alkyl groups become weak in the composite material as only traces of alkyl groups are formed due to the incomplete hydrolysis of tetraethylorthosilicate, which is suppressed by the incorporation of PANI in silica gel. The intense, sharp peak at 467 cm⁻¹ corresponding to the rocking vibrations of the Si–O–Si bond was influenced by the addition of PANI, and another broad band appears around 563 cm⁻¹ due to the formation of defects or the silica network's residual cyclic structure, as reported previously.³⁰Table 1 represents all the FTIR peaks obtained for pure silica as well as the PANI-modified silica gel material, with their corresponding bond assignments.³¹ All the fundamental peaks of pure silica are present in the spectrum, and in the case of PANI-modified silica gel, apart from the peaks of silica gel, some new peaks are formed at 573 cm⁻¹, 668 cm⁻¹, 706 cm⁻¹, 1228 cm⁻¹, 1295 cm⁻¹, 1486 cm⁻¹, 1564 cm⁻¹, and 3243 cm⁻¹ corresponding to the peaks of PANI,^32,33 whereas some peaks got slightly shifted, which are also explained in Table 1.

Fig. 2 FTIR spectra of pure PANI, pure silica, and PANI-modified silica gel.

Table 1 FTIR peaks and corresponding bond assignments

FTIR peaks (cm^−1)	Corresponding peak assignment (PANI-modified silica)
467	Deformation (rocking) vibration of Si–O–Si
573	Deformation vibration of Si–O–Si
668, 706	C–H bending out-of-plane from the 1,4-distributed benzene ring
799	Si–O–Si bending vibrations
1090	Asymmetric stretching vibration of the Si–O–Si bond in the SiO2 network
1228	Protonation of PANI (C–N group)
1295	C–N stretching vibrations (aromatic)
1486, 1564	C=C stretching vibrations of quinoid and benzoid rings
1640	Si–OH bending mode of vibration
2854	Symmetric –CH stretching
2925	Asymmetric –CH stretching
3243, 3443	Stretching of the –NH2 group due to protonation of PANI
3443	Si–OH stretching vibrations
Pure PANI peak assignments
588	Aromatic C–H out-of-plane bending vibrations
702, 878	C–H bending out-of-plane from the 1,4-disubstituted benzene ring
1123, 1236	Peaks due to the protonation of PANI (C–N group)
1293	C–N stretching aromatic
1478, 1563	C=C stretching vibrations of quinoid and benzenoid rings
503, 795, 1712	Vibrations from sulphonate groups attached to the aromatic rings
2921	C–H stretching vibrations
3209, 3441	Stretching of the –NH2 group due to the protonation of nitrogen

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3.2. Raman analysis

Raman characterization was utilized to unveil distinct vibrational bands corresponding to the molecular vibrations within the sample. Fig. 3 shows the Raman spectra of silica gel and PANI-modified silica gel. The fundamental peaks of silica gel are shown in Fig. 3 (inset). The peak at 495 cm⁻¹ is due to the ring breathing vibration of a 4-membered siloxane ring,³⁴ the peak at 800 cm⁻¹ is due to the bond bending vibrations parallel to the bisector of the Si–O–Si angle, and the peak at 985 cm⁻¹ is due to the symmetric stretch vibrations of silanols in SiO₂ (Si–OH groups).³⁵ After the functionalization,³⁶ the silica gel peaks were merged with the PANI peaks. Table 2 represents the corresponding peak assignment to the peaks formed as a result of functionalization with PANI. All the fundamental peaks of PANI are present in the spectrum, as also confirmed by the work reported earlier.^37–39

Fig. 3 Raman spectra of pure silica and PANI-modified silica gel.

Table 2 Raman peaks and corresponding bond assignments

Raman shift (cm^−1)	Corresponding peak assignment (PANI)
421	Out-of-plane vibrations of rings of the protonated emeraldine form of PANI
784	Quinine ring deformation vibrations
1170	C–H (in-plane) bending of quinoid rings
1220	C–N stretches of amine sites
1324	Stretching vibrations of an intermediate bond C⋯N^+
1341–1352	Carrier vibrations in PANI in C–N^+ polaronic structures
1491	C=N stretching of quinoid units
1558	C=C stretching of quinoid rings
1595	C–C stretching vibrations of quinoid ring

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3.3. FESEM analysis

The morphological characteristics of pure PANI and PANI-modified silica gel were investigated using field emission scanning electron microscopy (FESEM), revealing distinct structural features of both materials. The FESEM images of the pure PANI, as shown in Fig. 4(a), demonstrated a fibrous-like morphology, which is its inherent nature, forming elongated and intertwined nanofibers. These fibers create a network that could potentially enhance the binding of any specific gas molecules, contributing to the overall performance of the material in gas separation applications. The silica particles, within the size range of around 20 to 70 µm, were uniformly coated with PANI nanofibers, as shown in Fig. 4(b and c). The FESEM images showed that the silica particles served as a core material around which the PANI fibers were deposited and enveloped. Fig. 4(d) represents the magnified view of the PANI nanofibers coated on silica particles. Such integration can enhance the gas separation capabilities of the material due to the increased interaction sites for CO₂ gas molecules on the material's surface.

Fig. 4 FESEM images of (a) pure PANI, (b) 1% PANI-modified silica (magnified view showing the attached PANI on the silica material's surface), and (c and d) PANI-modified silica.

3.4. Performance with gas mixtures

The nitrogen adsorption isotherm investigations were carried out at 77 K, depicting the textural properties of the materials.⁴⁰Fig. 5(a–c) show the adsorption–desorption isotherms of pure PANI, pure silica, and the 1% PANI-modified silica material. From the graph in Fig. 5(a), it is evident that pure PANI has a microporous structure with type I characteristics (as defined by IUPAC)⁴¹ due to the overlapped adsorption and desorption cycles. The inset figure shows the micropore size distribution curve, confirming the dominant micropore size around 0.6 nm for pure PANI material. Unlike pure PANI, pure silica exhibits separate adsorption and desorption isotherms with a small and smooth hysteresis loop, confirming the mesoporous structure of the material, which is characterized by slit-like pores formed by loosely packed silica particles (see Fig. 5(b)). Furthermore, the PANI-silica composite also exhibits a similar textural behavior (i.e., type IV behavior with H3 hysteresis) as confirmed by the graph in Fig. 5(c). Similar results have already been reported elsewhere.⁴⁰ The BET surface area values of pure PANI, pure silica, and 1% PANI-modified silica are 239 m² g⁻¹, 229 m² g⁻¹, and 222 m² g⁻¹, respectively. The higher surface area value of pure PANI is mainly due to the microporous structure and nanofibrous morphology, as also evident from the FESEM images. The reduction in the surface area of pure silica after PANI modification can be due to the fact that PANI has covered the silica material, which reduced the effective pore volume and diffusion paths. The NLDFT/GCMC spectrum in Fig. 5(d) shows a sharp peak at around 30 nm, showcasing the size of most of the pores, while a slightly broad pore size distribution confirms the heterogeneous mesoporosity in the materials. Further, the overlapping of the two curves indicates that the composite's pore structure is largely inherited from the silica network, and the PANI coating modified the surface chemistry rather than affecting the textural properties or pore size.

Fig. 5 N₂ adsorption/desorption isotherm of (a) pure PANI (inset figure shows micropore volume distribution), (b) pure silica, and (c) the PANI-modified silica material, and (d) NLDFT/GCMC pore size distribution graph for mesoporous materials.

3.5. Performance with gas mixtures

The column was found to be effective at isolating H₂ and CO₂ gases. At first, the prepared GC was calibrated for CO₂ and H₂ gases by taking their different volume amounts from 0.4 ml to 7 ml for H₂ gas, and from 0.6 ml to 4 ml for CO₂ gas, respectively, with multiple injections. The detailed graphs are shown in Fig. 6 and 7, confirming the repeatability of each injection cycle.

Fig. 6 H₂ gas calibration curves for (a) 0.4 ml, (b) 0.6 ml, (c) 0.8 ml, (d) 1 ml, (e) 2 ml, (f) 3 ml, (g) 4 ml, (h) 5 ml, (i) 6 ml, and (j) 7 ml gas volume injections.

Fig. 7 CO₂ gas calibration curves for (a) 0.6 ml, (b) 0.8 ml, (c) 1 ml, (d) 2 ml, (e) 3 ml, and (f) 4 ml gas volume injections.

The above range was chosen as in this region our detectors can provide better peaks; beyond this, the peaks became saturated. From the theoretical calculations using a regression curve (formed using the graphs in Fig. 6 and 7), the limit of detection for CO₂ gas was obtained to be 0.54 ml, and the limit of quantification was 1.65 ml, whereas for H₂ gas, the limit of detection was 1.44 ml, and the limit of quantification was obtained to be 4.36 ml. However, we were able to detect good H₂ peaks of 0.4 ml volume concentration and CO₂ peaks of 0.6 ml volume concentration practically.

The gas chromatography experiments were performed using the gas mixtures of 50 : 30 : 20 (CO₂ : H₂ : CO). For this, a 3 ml mixture was taken in a syringe to perform the experiments to study the gas chromatography performance. The ratio taken for H₂ : CO₂ is 0.6 (50 : 30 for CO₂ : H₂) at the input side, and the data results obtained in output are 0.56, 0.61, and 0.64, respectively. The quantity of recovered gas is 3.64, 3.79, and 3.60, respectively, for three injection cycles with a resolution of 4.1 and a retention time of 1270 s and 343 s for CO₂ and H₂ gas, respectively. The recovery percentages of the results are 121%, 126%, and 120%, respectively, which fall within the acceptable range for such portable DIY systems, especially while analyzing lighter gases like H₂ and CO₂.^42–44 This higher recovery percentage can directly be attributed to the ionization enhancement effect.⁴⁵ Similar trends have already been reported in GC systems with a modified column and limited resolution.⁴⁵Fig. 8(a) represents the gas chromatogram taken for the three different injection cycles. A similar experiment was also carried out using paraffin-modified silica gel as a stationary phase column material; the results showed that the resolution was comparatively lower in comparison to the PANI-modified silica gel due to the higher interaction of PANI with polar CO₂ gas molecules (the comparison is shown in Fig. 8(b and c)). Furthermore, to evaluate the performance of our GC device theoretically, we have also compared our work with the recently available methods, and the list is represented in Table 3. Although the current state-of-the-art literature lacks low-cost DIY GC columns specifically for H₂ and CO₂ gas separation under similar experimental conditions, the table can still provide a performance efficiency benchmark through a broader contextual comparison over material composition and general column characteristics, which are independent of the analytes. Such a comparison is intended to situate our PANI-modified silica gel stationary phase within the spectrum of emerging low-cost chromatographic materials. The calculated number of theoretical plates, showcasing high value, and its comparison with that of other studies reported in the literature, as shown in the table, indicate better separation performance with sharper peaks and improved resolution.

Fig. 8 (a) Gas chromatogram of CO, CO₂, and H₂ gas taken for three different injection cycles using paraffin-modified silica gel, and (b and c) comparison of gas chromatograms of CO₂ and H₂ gas obtained using two different column materials, i.e., paraffin-modified silica gel and PANI-modified silica gel.

Table 3 Summary of various column characteristics and stationary phases

S. No.	Material	Column feature	Length × width × depth (cm × µm × µm)	Fabrication	Application	N max (plates/min)	Retention time (s)	Peak resolution	Ref.
1	SE-54	Semi-packed	100 × 160 × 250	Static	N-alkanes	55 366	30–8 s	—	46
2	HP-5 capillary column	Open rectangular	100 × 160 × 250	Static	(C5–C10, C12)	5490	120–360 s	—	46
3	OV-1	Serpentine	6 × 100 × 100	Static	Benzene, toluene	4850	Benzene (117.6 s), toluene (184.8 s)	6.33	47
4	Silicon	Semi-packed	100 × 150 × 180	Static	C9H20 and CH4	10 000	—	—	48
5	SWNTs	Serpentine	100 × 160 × 250	CVD	N-alkanes	1613	—	—	49
6	OV-1	Spiral	0.25 × 150 × 370	Static	C5–C6	68 696	—	—	50
7	rGO/ZnO	MCC	0.5 × 30 × 300	Sol–gel	C5–C12	11 363	4–121 s	1.28	51
8	Porapak Q	Rectangular	160 × 600 × 1200	Packing	CO and CH4	5800	CO (67 s) and CH4 (69 s)	1.5	52
9	CNT/graphene functionalized PDMS	Semi-packed	1.5–3 × NR × 300	Dynamic	C5–C11	—	5–90 s	0.8–5.2	53
10	SE-54	Wave post	200 × 40 × 300	Static	CWA simulant	1354	8–159 s	1.71–6.51	54
11	Microporous silica	Semi-packed	NA × 220 × 250	—	Alkane	—	24–130 s	Higher than 1.25 except for C1–C2 and C5–C6	55
12	Silicon nanowires	Rectangular	200 × 100 × 300	Etching	C6–C10	23 647	—	—	56
13	PANI-modified silica gel	Packed column	Length – 2 m	Chemical polymerization	H2, CO2	22 017.52	H2 (343 s) and CO2 (1270 s)	4.1	Present work
			Diameter – 4.8 mm

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4. Conclusion

The development of a low-cost Gas Chromatograph (GC) system, characterized by exceptional peak separation and retention time performance, represents a significant advancement in analytical chemistry. The cornerstone of this innovation rests upon the effectiveness of the GC column material in achieving precise and robust mixture separation and fabrication of the whole setup at low cost (typically around Rs. 5000 ($60)) while utilizing commonly available laboratory materials. The research created a platform that endows small-scale laboratories and researchers with the ability to resolve complex mixtures efficiently and provides a chance for graduate and undergraduate students in academic institutions to study and explore individual components of the system and implement further modifications with different functionalities for different gas separation requirements.

Coupling the favorable properties of PANI, such as good environmental stability, dense structure, and catalytic, antistatic, and anti-corrosion activities, and the favorable properties of silica gel, such as strength and high heat resistance, produced a new stationary phase material with improved structural properties as well as separation performance. Further, along with better stability and ease of synthesis, PANI offers good adsorption capabilities towards polar gases such as CO₂ due to the presence of amine moieties in the structure, which can interact with CO₂ to form complexes, which is the reason behind its excellent separation performance. The fabricated GC setup showed the limit of detection and limit of quantification values of 0.54 ml and 1.65 ml for H₂ gas and 1.44 ml and 4.36 ml for CO₂ gas, respectively. Thus, by developing a low-cost GC system utilizing polyaniline-modified silica gel as the stationary phase, this study aims to address the limitations of existing separation techniques and provide a more accessible solution for laboratories and industrial applications where cost, simplicity, and performance are critical factors. Furthermore, a patent has been published to highlight the novelty and potential application of this work.⁵⁷ The exceptional features of the GC column reported in this work are:

(1) It can provide both qualitative and quantitative measurements.

(2) It takes around 25 minutes for the complete analysis of the H₂ and CO₂ mixture.

(3) Data repeatability.

Author contributions

All authors have contributed to the study's conception and design. Nishel Saini: sample preparation, data collection and analysis, and writing – original draft. Rohith Krishna: sample preparation, investigation, and data analysis. Sanjay Kumar: investigation and data analysis. Kamlendra Awasthi: supervision, conceptualization, and writing – review & editing.

Conflicts of interest

There are no conflicts to declare.

Data availability

The data supporting this article have been included in the manuscript.

Acknowledgements

The author, Nishel Saini, is thankful to the Ministry of Education, India, for providing the fellowship. The authors also acknowledge the Materials Research Center, MNIT Jaipur, for providing all the characterization facilities.

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