An Improved Validated Method for the Determination of Short-Chain Fatty Acids in Human Fecal Samples by Gas Chromatography with Flame Ionization Detection (GC-FID)

Short-chain fatty acids (SCFAs) are metabolites produced by the gut microbiota through the fermentation of non-digestible carbohydrates. Recent studies suggest that the gut microbiota composition, diet and metabolic status play an important role in the production of SCFAs. The primary objective of this study was to develop a simplified method for SCFA analysis in human fecal samples by gas chromatography with flame ionization detection (GC-FID). The secondary objective was to apply the method to fecal samples collected from a clinical trial. The developed GC-FID method showed excellent linearity (R2 > 0.99994), with a limit of detection (LOD) ranging from 0.02 to 0.23 µg/mL and a limit of quantification (LOQ) ranging from 0.08 to 0.78 µg/mL. Recovery for the method ranged between 54.24 ± 1.17% and 140.94 ± 2.10%. Intra- and inter-day repeatability ranged from 0.56 to 1.03 and from 0.10 to 4.76% RSD, respectively. Nine SCFAs were identified and quantified (acetic, propionic, iso-butyric, butyric, iso-valeric, valeric, 4-methyl valeric, hexanoic and heptanoic acids) in freeze-dried fecal samples. The clinical trial compared participants with prediabetes mellitus and insulin resistance (IR-group, n = 20) to metabolically healthy participants (reference group, R-group, n = 9) following a 4-week intervention of a daily red raspberry smoothie (RRB, 1 cup fresh-weight equivalent) with or without fructo-oligosaccharide (RRB + FOS, 1 cup RRB + 8 g FOS). The statistical analysis (Student's t-test, ANCOVA) was performed on PC-SAS 9.4 (SAS Institute). Acetic acid was higher in the R-group compared to the IR-group at baseline/week 0 (p = 0.14). No significant changes in fecal SCFA content were observed after 4 weeks of either RRB or RRB + FOS.

Improved magnetic solid-phase extraction based on magnetic sorbent obtained from sand for the extraction of pesticides from fruit juice

BACKGROUND

A combination of magnetic solid-phase extraction using an efficient and cheap magnetic sorbent obtained from sand and dispersive liquid-liquid microextraction has been developed for the extraction of nine multiclass pesticides (clodinafop-propargyl, haloxyfop-R-methyl, fenoxaprop-P-ethyl, oxadiazon, penconazole, diniconazole, chlorpyrifos, fenazaquin, and fenpropathrin) from commercial fruit juices (sour cherry, pomegranate, grape, watermelon, orange, apricot, and peach juices). The enriched pesticides were determined by gas chromatography-flame ionization detector and gas chromatography-mass spectrometry. The sorbent was natural iron oxide entrapped in silica along with some impurities. In this method, to extract the analytes from the samples, an appropriate amount of the magnetic sorbent (at mg level) is added. Then the sorbent particles are isolated from the solution using an external magnetic field and the adsorbed analytes are desorbed from the sorbent by acetone. In the following, a dispersive liquid-liquid microextraction procedure is carried out to concentrate the analytes more and to reach low limits of detection.

RESULTS

Under optimized extraction conditions, the method revealed satisfactory repeatability (relative standard deviation ≤8% for intra-day and inter-day precision), reasonable extraction recovery (43.3-55.9%), high enrichment factors (433-559), and low limits of detection (0.45-0.89 μg L^-1 ).

CONCLUSION

The method was applied in the analysis of pesticides in various fruit juices. Chlorpyrifos was found in peach juice at a concentration of 27 ± 2 μg L^-1 (n = 3) using a gas chromatography-flame ionization detector. To verify the results, the peach juice was also injected into gas chromatography-mass spectrometry after applying the proposed extraction method. © 2022 Society of Chemical Industry.

Baseline correction method for dynamic pressure gradient modulated comprehensive two-dimensional gas chromatography with flame ionization detection

A baseline correction method is developed for comprehensive two-dimensional (2D) chromatography (GC × GC) with flame-ionization detection (FID) using dynamic pressure gradient modulation (DPGM). The DPGM-GC × GC-FID utilized porous layer open tubular (PLOT) columns in both dimensions to focus on light hydrocarbon separations. Since DPGM is nominally a stop-flow modulation technique, a rhythmic baseline disturbance is observed in the FID signal that cycles with the modulation period (P_M). This baseline disturbance needs to be corrected to optimize trace analysis. The baseline correction method has three steps: collection of a background "blank" chromatogram and multiplying it by an optimized normalization factor, subtraction of the normalization-optimized background chromatogram from a sample chromatogram, and application of Savitzky-Golay smoothing. An alkane standard solution, containing pentane, hexane and heptane was used for method development, producing linear calibration curves (r² > 0.991) over a broad concentration range (7.8 ppm - 4000 ppm). Further, the limit-of-detection (LOD) and limit-of-quantification (LOQ) were determined for pentane (LOD = 2.5 ppm, LOQ = 8.2 ppm), hexane (LOD = 0.9 ppm, LOQ = 3.0 ppm), and heptane (LOD = 1.9 ppm, LOQ = 6.4 ppm). A natural gas sample separation illustrated method applicability, whereby the DPGM produced a signal enhancement (SE) of 30 for isopentane, where SE is defined as the height of the tallest ²D peak in the modulated chromatogram for the analyte divided by the height of the unmodulated ¹D peak. The 30-fold SE resulted in about a 10-fold improvement in the signal-to-noise ratio (S/N) for isopentane. Additional versatility of the baseline correction method for more complicated samples was demonstrated for an unleaded gasoline sample, which enabled the detection (and visual appearance) of trace components.

Analytical GC-FID Method for the Determination of Organic Solvents in Radiopharmaceuticals

BACKGROUND

Organic solvents play an indispensable role in most of the radiopharmaceutical production stages. It is almost impossible to remove them entirely in the final formulation of the product.

OBJECTIVE

In this presented work, an analytical method by gas chromatography coupled with flame ionization detection (GC-FID) has been developed to determine organic solvents in radiopharmaceutical samples. The effect of injection holding time, temperature variation in the injection port, and the column temperature on the analysis time and resolution (R ≥ 1.5) of ethanol and acetonitrile was studied extensively.

METHODS

The experimental conditions were optimized with the aid of further statistical analysis; thence, the proposed method was validated following the International Council for Harmonisation (ICH) Q2 (R1) guideline.

RESULTS

The proposed analytical method surpassed the acceptance criteria including the linearity > 0.990 (correlation coefficient of R²), precision < 2%, LOD, and LOQ, accuracy > 90% for all solvents. The separation between ethanol and acetonitrile was acceptable with a resolution R > 1.5. Further statistical analysis of Oneway ANOVA revealed that the increment in injection holding time and variation of temperature at the injection port did not significantly affect the analysis time. Nevertheless, the variation in injection port temperature substantially influenced the resolution of ethanol and acetonitrile peaks (p < 0.05).

CONCLUSION

The proposed analytical method has been successfully implemented to determine the organic solvent in the [¹⁸F]fluoro-ethyl-tyrosine ([¹⁸F]FET), [¹⁸F]fluoromisonidazole ([¹⁸F]FMISO), and [¹⁸F]fluorothymidine ([¹⁸F]FLT).

Metal 3D-printed catalytic jet and flame ionization detection for in situ trace carbon oxides analysis by gas chromatography

A gas chromatographic approach for the determination and quantification of trace levels of carbon oxides in gas phase matrices for in situ or near-line/at-line analysis has been successfully developed. Catalytic conversion of the target compounds to methane via the methanation process was conducted inside a metal 3D-printed jet that also acted as a hydrogen burner for the flame ionization detector. Modifications made to a field transportable gas chromatograph enabled the leveraging of advantaged microfluidic-enhanced chromatography capability for improved chromatographic performance and serviceability. The compatibility with adsorption chromatography technology was demonstrated with in-house constructed columns. Sustained reliable conversion efficiencies of greater than 99% with respectable peak symmetries were attained at 400°C. Quantification of carbon monoxide and carbon dioxide at a parts-per-million level over a range from 0.2 ppm to 5% v/v for both compounds with a respectable precision of less than 3% relative standard deviation for peak area (n = 10) and a detection limit of 0.1 ppm v/v was achieved. Linearity with correlation coefficients of R² greater than 0.9995 and measured recoveries of >99% for spike tests were achieved. The 3D-printed steel jet was found to be reliable and resilient against potential contamination from the matrices owing to the in situ backflushing capability.

by gas chromatography with flame ionization detection

Dihydroartemisinic acid (DHAA) is the direct precursor to artemisinin, an effective anti-malaria compound from Artemisia annua L. (A. annua), and it can be transformed to artemisinin without the catalysis of enzyme. A rapid and sensitive analysis of DHAA in A. annua is needed to screen excellent plant resources aimed to improve artemisinin production. In order to develop a rapid and sensitive determination method for DHAA in plant, the extraction and analysis conditions were extensively investigated in the present work. As a result, extraction of powdered A. annua leaves at 55°C for 50 min with chloroform resulted in the highest yield of DHAA, with a recovery of >98%. The precision of this gas chromatographic procedure ranged from 1.22 to 2.94% for intra-day and from 1.69 to 4.31% for inter-day, respectively. The accuracy was 99.55-103.02% for intra-day and 98.86-99.98% for inter-day, respectively. The measured LOQ and LOD values of the proposed method reached 5.00 and 2.00 μg/mL, respectively. Validation indicated the method was robust, quick, sensitive and adequate for DHAA analysis.

The Application of Chemical Derivatization in Forensic Drug Chemistry for Gas and High-Performance Liquid Chromatographic Methods of Analysis

The analyses of solid-dosage forensic drug samples can be enhanced by chemical derivatization followed by gas chromatography or high-performance liquid chromatography. Using these techniques permits improved detection and chromatography of some illicit drugs and their manufacturing by-products. This review focuses on the use of chemical derivatization in conjunction with gas chromatography-flame ionization detection, gas chromatography-electron capture detection, gas chromatography-mass spectrometry, high-performance liquid chromatography-ultraviolet detection and high-performance liquid chromatography-fluorescence detection in the analysis of illicit drug samples. These drugs include the amphetamines, barbiturates, cannabis, fentanyls, opium, and hallucinogens. Discussion on sensitivity enhancement and determination of enantiomeric composition using gas chromatography and high-performance liquid chromatography is included. An entire section is devoted to the chemical derivatization and chromatographic analyses of manufacturing by-products found in illicit amphetamine and methamphetamine, heroin, and cocaine samples. This review also includes a section that describes practical elements and experimental design associated with chemical derivatization-chromatographic analyses..