Headspace Liquid-Phase Microextraction of Short-Chain Fatty Acids in Plasma, and Gas Chromatography with Flame Ionization Detection

Green Approaches to Sample Preparation Based on Extraction Techniques

Preparing a sample for analysis is a crucial step of many analytical procedures. The goal of sample preparation is to provide a representative, homogenous sample that is free of interferences and compatible with the intended analytical method. Green approaches to sample preparation require that the consumption of hazardous organic solvents and energy be minimized or even eliminated in the analytical process. While no sample preparation is clearly the most environmentally friendly approach, complete elimination of this step is not always practical. In such cases, the extraction techniques which use low amounts of solvents or no solvents are considered ideal alternatives. This paper presents an overview of green extraction procedures and sample preparation methodologies, briefly introduces their theoretical principles, and describes the recent developments in food, pharmaceutical, environmental and bioanalytical chemistry applications.

Effect of xylitol on gut microbiota in an in vitro colonic simulation

Objective

Xylitol has been commonly used as a sweetener and dental caries protective agent. However, how xylitol influences the composition and metabolism of gut microbiota is not known yet. This study aimed to dissect the changes of microbiota and their metabolites under xylitol supplementation in an in vitro colonic simulation.

Materials and methods

A single-phase continuous fermentation model was used to culture human fecal flora and the 16s rDNA and short chain fatty acid were analyzed.

Results and discussion

It was found that gut microbiota composition differentiated after xylitol supplementation only for the beginning 3 days. Xylitol significantly enhanced the relative amount of butyrate synthesizing bacteria such asClostridiumandPhascolarctobacterium. Meanwhile, xylitol increased the production of propionic acid and butyrate. An increase ofEscherichiapopulation sizes after xylitol supplementation was beyond expectation. By Spearman analysis, a positive relationship betweenEscherichiaandBifidobacteriumwas found.

Conclusion

xylitol can rapidly enhance the total amount of short chain fatty acids, but its influence will disappear after 3 days of fermentation. Results of this investigation can be a guideline for the further investigations on xylitol in relation to gut microbiota and the daily intake determinations.

A sensitive GC/MS detection method for analyzing microbial metabolites short chain fatty acids in fecal and serum samples

Gut microbiota and their major metabolites, short-chain fatty acids (SCFAs), are recognized as important players in gut homeostasis and metabolic disease occurance. A convenient and sensitive detection method is needed to profile SCFAs in limited and complex biological samples. The gas chromatography/mass spectrometry (GC/MS) is the most common method for SCFAs profiling in biological samples. Trimethylsilyl (TMS) derivatization reagents such as N, O-bis(trimethyl-silyl)-trifluoroacetamide (BSTFA) are commonly used in GC/MS analysis to improve sensitivity and accuracy, but they were barely used in SCFA analysis due to their sensitivity to moisture and the volatility of SCFAs. Here, we developed a rapid, convenient and reliable method for SCFAs profiling in small amounts of fecal and serum samples by GC/MS using BSTFA in combination with sodium sulfate dehydration pretreatment. SCFAs were extracted with anhydrous ether from acidified fecal water extract or serum samples, followed by dehydration with sodium sulfate and BSTFA derivatization at a reduced temperature. Select ion monitoring mode was used for highly sensitive quantification of SCFAs by GC/MS. The derivation with BSTFA at 37 °C or 22 °C showed an excellent linearity (R² > 0.999), good recoveries (81.27-128.42%), high repeatability (RSD < 2%) and low limit of detections (LODs) of different SCFAs ranging from 0.064 to 0.067 µM. All major SCFAs including acetic acid, propionic acid, isobutyric acid, butyric acid, isovaleric acid and valeric acid were identified and quantified accurately in fecal and serum samples. In conclusions, a reliable, convenient and sensitive method wasdeveloped for the measurement of SCFA and other volatile compounds in small biological samples using sodium sulfate dehydration pretreatment and BSTFA derivatization-based GC/MS analyses.

Cobalamin (Vitamin B12) Induced a Shift in Microbial Composition and Metabolic Activity in an in vitro Colon Simulation

Cobalamin deficiency is believed to be related to disturbances in cell division, neuropathy, nervous system disease and pernicious anemia. Elderly people are usually advised to supplement their diets with cobalamin. As cobalamin has several forms, the effects of different forms of cobalamin on gut microbiota were investigated in this study. After 7 days of supplementation, methylcobalamin had reduced the diversity of gut microbiota compared to that in the control and cyanocobalamin groups. After supplementation with methylcobalamin, the percentage of Acinetobacter spp. had increased to 45.54%, while the percentages of Bacteroides spp., Enterobacteriaceae spp. and Ruminococcaceae spp. had declined to 11.15, 9.34, and 2.69%, respectively. However, cyanocobalamin had different influences on these bacteria. Both cobalamins increased the amount of short-chain fatty acids, particularly butyrate and propionic acid. The cyanocobalamin group showed increased activity of cellulase compared with that in the other two groups. According to CCA and PICRUSt analysis, methylcobalamin had a positive correlation with Pseudomonas bacteria, propionic acid, and butyrate. Methylcobalamin promoted lipid, terpenoid, and polyketide metabolism by gut bacteria, promoted the degradation of exogenous substances, and inhibited the synthesis of transcription factors and secondary metabolites. Our results indicate that the various forms of cobalamin in the food industry should be monitored and regulated, because the two types of cobalamin had different effects on the gut microbiome and on microbial metabolism, although they have equal bio-activity in humans. Given the effects of methylcobalamin on gut microbiota and microbial metabolism, methylcobalamin supplementation should be suggested as the first option.

Liquid-phase microextraction in bioanalytical sample preparation

Liquid-phase microextraction (LPME) emerged in the mid-to-late 1990s, facing up to the main shortcomings of the classical liquid-liquid extraction. Since its origin, this new technique has been in continuous development driven by its successful and widespread use in the analytical sciences. Its inherent properties, such as low sample volume requirement, high preconcentration factors achieved and excellent sample clean-up, make LPME a very useful technique for bioanalytical sample preparation. This review focuses on the main LPME-related techniques, predominantly single-drop microextraction and supported hollow-fiber LPME, paying particular attention to the bioanalytical applications. A general view of the essential trends, including the description of promising extraction modes and solvents, is also highlighted.

Single-drop microextraction in bioanalysis

Bioanalysis usually requires a preparation procedure for sample cleanup or preconcentration. Conventional sample preparation techniques are often time consuming and labor intensive. Among recent progress in sample preparation, single drop microextraction (SDME) is one of the most efficient techniques providing both sample cleanup and preconcentration capabilities. In SDME, analytes are extracted from a sample solution into an acceptor drop and the drop is introduced to subsequent analysis. Since the volume of the acceptor drop is 1–10 µl or less, the consumption of solvents can be minimized and the preconcentration effect is enhanced. In this review, the basic principles of two-phase and three-phase SDME are described briefly and then recently developed modes of SDME, coupling with analytical instruments, and methods to enhance the drop stability are discussed. Recent applications of SDME to biological samples, including urine, blood and saliva, for the analysis of drugs, metal ions and biomarkers are reviewed.

Hollow fiber liquid-phase microextraction coupled with gas chromatography-flame ionization detection for the profiling of fatty acids in vegetable oils

The development of a two phase hollow fiber liquid-phase microextraction technique, followed by gas-chromatography-flame ionization detection (GC-FID) for the profiling of the fatty acids (FAs) (lauric, myristic, palmitic, stearic, palmitoleic, oleic, linoleic, linolenic and arachidic) in vegetable oils is described. Heptadecanoic acid methyl ester was used as the internal standard. The FAs were transesterified to their corresponding methyl esters prior to the extraction. Extraction parameters such as type of extracting solvent, temperature, extraction time, stirring speed and salt addition were studied and optimized. Recommended conditions were extraction solvent, n-tridecane; extraction time, 35 min; extraction temperature, ambient; without addition of salt. Enrichment factors varying from 37 to 115 were achieved. Calibration curves for the nine FAs were well correlated (r(2)>0.994) within the range of 10-5000 μg L(-1). The limit of detection (signal:noise, 3) was 4.73-13.21 ng L(-1). The method was successfully applied to the profiling of the FAs in palm oils (crude, olein, kernel, and carotino cooking oil) and other vegetable oils (soybean, olive, coconut, rice bran and pumpkin). The encouraging enrichments achieved offer an interesting option for the profiling of the minor and major FAs in palm and other vegetable oils.

Single drop microextraction--development, applications and future trends

Single drop microextraction (SDME) has emerged over the last 10-15 years as one of the simplest and most easily implemented forms of micro-scale sample cleanup and preconcentration. In the most common arrangement, an ordinary chromatography syringe is used to suspend microliter quantities of extracting solvent either directly immersed in the sample, or in the headspace above the sample. The same syringe is then used to introduce the solvent and extracted analytes into the chromatography system for identification and/or quantitation. This review article summarizes the historical development and various modes of the technique, some theoretical and practical aspects, recent trends and selected applications.

Developments in single-drop microextraction

Single-drop microextraction (SDME) has become a very popular liquid-phase microextraction technique because it is inexpensive, easy to operate and nearly solvent-free. Essentially, SDME combines extraction (and conceivably, cleanup) and concentration in a minimum number of steps, and thereafter, direct extract introduction into an analytical system. In this review, in order to encourage further development of SDME, we focus on its recent developments in its various guises. Its applications when used in combination with different analytical techniques, such as gas chromatography, high-performance liquid chromatography, inductively-coupled plasma mass spectrometry, capillary electrophoresis, mass spectrometry and electrothermal atomic absorption spectrometry, are summarized. SDME does have some limitations, and these are also discussed as well. Finally, an outlook on the future of the technique is given.