Automated method for volatile fatty acids determination in anaerobic processes using in-syringe magnetic stirring assisted dispersive liquid-liquid microextraction and gas chromatography with flame ionization detector.

Volatile fatty acids (VFAs) are key parameters to monitor anaerobic digestion processes. Thus, a fast, simple and precise determination of these analytes is necessary for a timely characterization of the biological processes present in municipal solid waste and wastewater treatment plants. In this work, an automated method for the extraction and preconcentration of VFAs, based on dispersive liquid-liquid microextraction with magnetic stirring in syringe, and gas chromatography with flame ionization detector for the separation and detection, is described. The effect of parameters such as the type and volume of extraction solvent, pH, salting out effect and stirring time, was studied using a multivariate and univariate experimental design. Extraction and preconcentration were performed simultaneously using tert-butyl methyl ether (TBME) as the extraction solvent, after stirring 100 s at a constant rate. The detection limits were in the range of 0.1 - 1.3 mg L-1 and a good linearity was observed up to 1000 mg L-1 of the studied VFAs, with a range of R2 between 0.9997 and 0.9999. The intra and interday precision expressed as relative standard deviation (n= 5) varied between 0.7 and 2.4% and between 1.7 and 7.0%, respectively. Subsequently, the developed method was successfully applied to evaluate the presence of VFAs in wastewater samples from anaerobic treatments and an average relative recovery of 102% was obtained.

Chemical composition, antioxidant, anti-inflammatory and antiproliferative activities of the essential oil of Cymbopogon nardus, a plant used in traditional medicine.

Objectives Natural products commonly used in traditional medicine, such as essential oils (EOs), are attractive sources for the development of molecules with anti-proliferative activities for future treatment of human cancers, e.g., prostate and cervical cancer. In this study, the chemical composition of the EO from Cymbopogon nardus was characterized, as well as its antioxidativeproperties and anti-inflammatory and antiproliferative activities on LNCaP cells derived from prostate cancer. Methods The chemical composition of the EO was determined by GC/FID and GC/MS analyses. The antioxidative properties were assessed using DPPH radical scavenging assay and ABTS+• radical cation decolorization assay, and the anti-inflammatory capacity was determined by the inhibition of the lipoxygenase activity. Antiproliferative activity was evaluated by MTT assay. Results Collectively, our data show that the major constituents of C. nardus EO are citronellal (33.06 %), geraniol (28.40 %), nerol (10.94 %), elemol (5.25 %) and delta-elemene (4.09 %). C. nardus EO shows modest antioxidant and anti-inflammatory activity compared to the standard galic acid. C. nardus EO exhibits the best antiproliferative activity on the prostate cancer cell line LNCaP with an IC50 of 58.0 ± 7.9 µg/mL, acting through the induction of the cell cycle arrest. Conclusions This study has determined that C. nardus EO efficiently triggers cytotoxicity and pens a new field of investigation regarding the putative use of this EO in vivo.

Post-column reaction with a 3D-printed two-stage microreactor and flame ionization detection for carbon compound independent response in fast gas chromatography.

Fast gas chromatography that leverages the high chromatographic efficiency of narrow bore capillary column technology and temperature programming was successfully integrated with a third-generation low void-volume, 3D-printed two-stage microreactor. Effective management of extra-column effect and the capability to perform post-column backflushing were achieved with the incorporation of a recently commercialized, electronically controlled pneumatic switching device and a deactivated metal three-way microdevice. With this configuration, narrow bore capillary columns having internal diameters between 0.10 and 0.15 mm can be employed to produce chromatographic peaks in the domain of fast gas chromatography, with peak widths at half-height ranging from 0.42 s to 0.92 s for probe compounds having k over a range from 1.7 for toluene to 60 with the last analyte (nC44) eluted in less than 12 min. The carbon independent response capability of the 3D-printed microreactor affords unique and advantaged differentiators, for instance, conducting measurement of the target analytes using one single carbon-containing compound for calibration with an acceptable accuracy of ±10%, achieving a higher degree of accuracy by eliminating the need for multi-level and multi-compound calibration, and improving sensitivity for compounds that are not efficiently ionized by flame ionization detection. Using this platform, repeatability of retention times for 14 probe compounds was less than 0.1% RSD (n = 10), and less than 1.0% RSD (n = 10) for area counts. The utility of the analytical approach was illustrated with relevant, challenging applications.

The EZ:Faast Family of Amino Acid Analysis Kits: Application of the GC-FID Kit for Rapid Determination of Plasma Tryptophan and Other Amino Acids.

Plasma tryptophan (Trp) and other amino acids (AA) can be determined rapidly by gas (GC) or liquid (LC) chromatography using the Phenomenex EZ:Faast™ family of kits. Three kits are available: (1) GC-FID or -NPD, (2) GC-MS, and (3) LC-MS. The two GC kits can determine 32 AA, whereas the LC-MS can determine 5 additional AA. All three kits, however, share the same experimental procedure up to and including the preparation of derivatized AA. The method is based on solid-phase extraction (SPE), thus saving time on prior removal of plasma or other proteins and interfering substances and can be applied to other body fluids and experimental media and to supernatants of extracts of solid material. Briefly, SPE is performed using a proprietary cation-exchange mechanism. The acid solution of the internal standard ensures that the free amino acids are in an anionic form suitable for cationic binding. The alkaline nature of the elution medium ensures that the AA cations are released prior to derivatization. The latter involves production of chloroformate derivatives of both the amino and carboxylic acid groups. With experience, six plasma samples can be so processed within 12 min. The shortest analytical run is <7 min per sample using the GC-FID/NPD kit. Despite its many steps, the procedure becomes second nature and an enjoyable task. I have now used the GC-FID kit with manual injection to process >1600 plasma and other samples. Limit of detection of AA is 1 µM or less. The procedure has been validated and optimized for Trp and its main five brain uptake competitors.

Quantitative Analysis of Metabolites at the Single-Cell Level by Hydrogen Flame Desorption Ionization Mass Spectrometry.

To date, direct quantitation of cellular metabolites at the picoliter level or in a single cell is still a challenge due to tiny sampling materials, the accuracy of the sampling volume, and the ubiquitous matrix effect. Herein, picoliter magnitude quantitative analysis was performed using a pressure-assisted microsampling probe coupled to the hydrogen flame desorption ionization mass spectrometer (HFDI-MS). The sampling was accurately controlled with a picoliter pump, and the analytes were rapidly vaporized and quantitatively transferred to the gas phase by adequate heat. The vapor-phase analytes reacted with protonated water cluster ions by the proton-transfer reaction (PTR). The accurate sampling, flash thermal desorption, and proton-transfer ionization processes were conducted spatiotemporally, which could greatly reduce matrix effects to facilitate the quantitation of analytes without the internal standard. Furthermore, this workflow enabled the quantitation of cellular metabolites at the picoliter/single-cell level.

Fatty acid profile of milk from Saanen and Swedish Landrace goats.

Recent years have had an increased demand for goat milk and its products. The quality of goat milk is determined, in part, by the fatty acid (FA) profile, but there is little information about breed influence on the FA profile of goat milk. The aim of this study was to describe and compare FA profiles of goat milk produced by Saanen and Swedish Landrace breeds. FA profiles were analysed by gas chromatography with a flame ionisation detector using 100 m capillary column coated with ionic liquids of extreme polarity (SLB-IL111). The amounts of 19 FAs were measured. Analyses indicated that FA profile in the milk of Saanen goats differs from that of Swedish Landrace goats with the first having higher proportions of most SFA-s and the second having lower proportions of C16:0, C16:1 and C18:1. This knowledge enables the improvement of the quality of goat milk and goat milk-derived products.

High-throughput quantification of sodium saccharin in foods by ambient flame ionization mass spectrometry.

Ambient flame ionization (AFI) coupled with triple quadrupole tandem mass spectrometry was developed for quantitative analysis of sodium saccharin (SAC) in various food samples. Typically, the micro-flame by the combustion of n-butane provided a heating zone for fast desorption and ionization of analytes in milliseconds. Then high ion abundance of analyte could be produced in a short time, which made AFI-MS possess a very high sensitivity for SAC detection and was particularly appropriate for the quantification in multiple reaction monitor (MRM) mode. Liquid samples were introduced into outer flame using dip-it tips in order to facilitate a rapid and high-throughput analysis. Saccharin-d4 was used as the internal standard to compensate for the variations of the ion intensities. With a minimal sample preparation, a linear range of 4-100 µg/mL was developed with all linear relationships of different matrices (including coke, juice, liquors, sunflower seeds and sweetmeats) greater than 0.992. Recoveries for coke and apple matrices were ranged from 88.4% to 108.9% at the concentration of 5, 20, 80 µg/mL and the limits of detection (LODs) were in the range of 0.12-0.21 µg/mL. Furthermore, the feasibility of this method was exhibited by the quantification analysis of SAC in seventeen real samples. These results indicated that AFI-MS was a valuable strategy for rapid screening detection and precise quantification analysis of SAC in food.

Increasing Signal-to-Noise Ratio in Gas Chromatography - Electroantennography Using a Deans Switch Effluent Chopper.

Gas-chromatography-electroantennographic detection (GC-EAD) is a technique used in the identification of volatile organic compounds (VOCs), such as pheromones and plant host odors, which are physiologically relevant to insects. Although pheromones often elicit large EAD responses, other behaviorally relevant odors may elicit responses that are difficult to discern from noise. Lock-in amplification has long been used to reduce noise in a wide range of applications. Its utility when incorporated with GC-EAD was demonstrated previosuly by chopping (or pulsing) effluent-laden air that flowed over an insect antenna. This method had the disadvantage that it stimulated noise-inducing mechanoreceptors and, in some cases, disturbed the electrochemical interfaces in a preparation, limiting its performance. Here, the chopping function necessary for lock-in amplification was implemented directly on the GC effluent using a simple Deans switch. The technique was applied to excised antennae from female Heliothis virescens responding to phenethyl alcohol, a common VOC emitted by plants. Phenethyl alcohol was always visible and quantifiable on the flame ionization detector (FID) chromatogram, allowing the timing and amount of stimulus delivered to the antennal preparation to be measured. In our new chopper EAG configuration, the antennal preparation was shielded from air currents in the room, further reducing noise. A dose-response model in combination with a Markov-chain monte-carlo (MCMC) method for Bayesian inference was used to estimate and compare performance in terms of error rates involved in the detection of insect responses to GC peaks visible on an FID detector. Our experiments showed that the predicted single-trial phenethyl alcohol detection limit on female H. virescens antennae (at a 5.0% expected error rate) was 140,330 pg using traditional EAG recording methods, compared to 2.6-6.3 pg (5th to the 95th percentile) using Deans switch-enabled lock-in amplification, corresponding to a 10.4-12.7 dB increase in signal-to-noise ratio.

A comparison study on a sulfonated graphene-polyaniline nanocomposite coated fiber for analysis of nicotine in solid samples through the traditional and vacuum-assisted HS-SPME.

A simple, rapid, and reliable headspace solid-phase microextraction (HS-SPME) procedure, reinforced by applying vacuum in the extraction vial, was developed. It was applied for the extraction of nicotine in solid samples prior to determination by gas chromatography-flame ionization detection (GC-FID). First, the surface of a narrow stainless steel wire was made porous and adhesive by platinization to obtain a durable, higher surface area, and resistant fiber. Then, a thin film of sulfonated graphene/polyaniline (Sulf-G/PANI) nanocomposite was synthesized and simultaneously coated on the platinized fiber using the electrophoretic deposition (EPD) method. It was demonstrated that the extraction efficiency remarkably increased by applying the reduced-pressure condition in the extraction vial. To evaluate the conventional HS-SPME and vacuum-assisted HS-SPME (VA-HS-SPME) platforms, all experimental parameters affecting the extraction efficiency including desorption time and temperature, extraction time and temperature and moisture content of sample matrix were optimized. The highest extraction efficiency was obtained at 60°C, 10min (extraction temperature and time) and 280°C, 2min (desorption condition), for VA-HS-SPME strategy, while for conventional HS-SPME the extraction and desorption conditions found to be 100°C, 30min and 280°C, 2min, respectively. The Sulf-G/PANI coated fiber showed high thermal stability, good chemical/mechanical resistance, and long lifetime. For analysis of nicotine in solid samples using VA-HS-SPME-GC-FID, linear dynamic range (LDR) was 0.01-30µgg-1 (R2=0.996), the relative standard deviation (RSD%, n=6), for analyses of 1µgg-1 nicotine was calculated 3.4% and limit of detection (LOD) found to be 0.002µgg-1. The VA-HS-SPME-GC-FID strategy was successfully carried out for quantitation of nicotine in hair and tobacco real samples.

Gas chromatography with diode array detection in series with flame ionisation detection.

We introduce a gas chromatography detection approach that uses diode array detection operated in series with flame ionisation detection and demonstrate the utility of the detection approach for determination of volatile organic compounds. Diode array detection brings ultraviolet - visible spectroscopy (over a range of 190-640nm) onto the capillary gas chromatography time-scale, where average peak widths of analytes are on the order of 3-5s. The non-destructive nature of the diode array detector affords serially-coupled flame ionisation detection. This arrangement delivers near-simultaneous selective and universal detection without incurring additional analytical time, and without recourse to column flow splitting. The hyphenated technique is shown to be effective for chromatographic applications spanning an equivalent volatility range from C1 to C7n-paraffin hydrocarbons. The approach introduced herein provides increased sensitivity and selectivity for classes of compounds amenable to electronic spectroscopy such as alkenes, dienes, sulfurs, and aromatic compounds. The approach is demonstrated for direct measurement of carbon disulfide in work place atmospheres with a detection limit of 93pg on column and for the direct measurement of 1,3-butadiene in hydrocarbon matrices and ambient air with a detection of 73pg on column, each in less than 5min.

Methods to determine response factors for infrared gas imagers used as quantitative measurement devices.

Response factors (RF) can be used to characterize relative sensitivity of one compound vs. another compound for the same measurement instrument. Use of RF allows the analysts/operators to calibrate the instrument with one compound and make measurement for a large number of compounds. This method is adopted for Flame Ionization Detector (FID) based survey instruments used in the Leak Detection and Repair (LDAR) practice for control of fugitive emissions of volatile organic compounds. Gas detecting Infrared (IR) cameras have been used for leak detection. However, the RF for IR cameras has not been well established despite some attempt to develop a method for IR camera RF. In addition to a method proposed earlier (Method 1), two new methods for IR camera RF are proposed in this paper: Method 2 based on theoretical approach and Method 3 based on experimental approach. All three methods are examined and compared. Both Methods 2 and 3 have shown the ability to characterize the behavior of RF for various compounds and substantially higher accuracy than Method 1. Method 2 provides a mechanism to generate RF for a large number of compounds without conducting experiments, and is recommended for implementation. The RF derived from this method can be used both in the emerging field of Quantitative Optical Gas Imaging (QOGI) and to answer the most common question that IR camera users ask-whether a particular compound can be imaged by a particular IR camera. IMPLICATIONS: Infrared imager is an efficient tool for detecting gas leaks from process equipment and has been used in leak detection and repair (LDAR) programs for control of fugitive emissions. However, the information regarding which chemical compounds can be imaged and how sensitive a given infrared imager is for various compounds is limited. A theoretical method is presented in this paper that can answer these questions without conducting resource-intensive experiment. The results of this theoretical method has good agreement with experimental data. The method has been used to predict relative sensitivity for 398 compounds.

Gas chromatography fractionation platform featuring parallel flame-ionization detection and continuous high-resolution analyte collection in 384-well plates.

Gas chromatography (GC) is a superior separation technique for many compounds. However, fractionation of a GC eluate for analyte isolation and/or post-column off-line analysis is not straightforward, and existing platforms are limited in the number of fractions that can be collected. Moreover, aerosol formation may cause serious analyte losses. Previously, our group has developed a platform that resolved these limitations of GC fractionation by post-column infusion of a trap solvent prior to continuous small-volume fraction collection in a 96-wells plate (Pieke et al., 2013 [17]). Still, this GC fractionation set-up lacked a chemical detector for the on-line recording of chromatograms, and the introduction of trap solvent resulted in extensive peak broadening for late-eluting compounds. This paper reports advancements to the fractionation platform allowing flame ionization detection (FID) parallel to high-resolution collection of a full GC chromatograms in up to 384 nanofractions of 7s each. To this end, a post-column split was incorporated which directs part of the eluate towards FID. Furthermore, a solvent heating device was developed for stable delivery of preheated/vaporized trap solvent, which significantly reduced band broadening by post-column infusion. In order to achieve optimal analyte trapping, several solvents were tested at different flow rates. The repeatability of the optimized GC fraction collection process was assessed demonstrating the possibility of up-concentration of isolated analytes by repetitive analyses of the same sample. The feasibility of the improved GC fractionation platform for bioactivity screening of toxic compounds was studied by the analysis of a mixture of test pesticides, which after fractionation were subjected to a post-column acetylcholinesterase (AChE) assay. Fractions showing AChE inhibition could be unambiguously correlated with peaks from the parallel-recorded FID chromatogram.

Development of continuous dispersive liquid-liquid microextraction performed in home-made device for extraction and preconcentration of aryloxyphenoxy-propionate herbicides from aqueous samples followed by gas chromatography-flame ionization detection.

In this study, a rapid, simple, and efficient sample preparation method based on continuous dispersive liquid-liquid microextraction has been developed for the extraction and preconcentration of aryloxyphenoxy-propionate herbicides from aqueous samples prior to their analysis by gas chromatography-flame ionization detection. In this method, two parallel glass tubes with different diameters are connected with a teflon stopcock and used as an extraction device. A mixture of disperser and extraction solvents is transferred into one side (narrow tube) of the extraction device and an aqueous phase containing the analytes is filled into the other side (wide tube). Then the stopcock is opened and the mixture of disperser and extraction solvents mixes with the aqueous phase. By this action, the extraction solvent is dispersed continuously as fine droplets into the aqueous sample and the target analytes are extracted into the fine droplets of the extraction solvent. The fine droplets move up through the aqueous phase due to its low density compared to aqueous phase and collect on the surface of the aqueous phase as an organic layer. Finally an aliquot of the organic phase is removed and injected into the separation system for analysis. Several parameters that can affect extraction efficiency including type and volume of extraction and disperser solvents, sample pH, and ionic strength were investigated and optimized. Under the optimum extraction conditions, the extraction recoveries and enrichment factors ranged from 49 to 74% and 1633 to 2466, respectively. Relative standard deviations were in the ranges of 3-6% (n = 6, C = 30 µg L(-1)) for intra-day and 4-7% (n = 4, C = 30 µg L(-1)) for inter-day precisions. The limits of detection were in the range of 0.20-0.86 µg L(-1). Finally the proposed method was successfully applied to determine the target herbicides in fruit juice and vegetable samples.

Comparison and validation of 2 analytical methods for the determination of free fatty acids in dairy products by gas chromatography with flame ionization detection.

Accurate quantification of free fatty acids (FFA) in dairy products is important for quality control, nutritional, antimicrobial, authenticity, legislative, and flavor purposes. In this study, the performance of 2 widely used gas chromatographic flame ionization detection methods for determination of FFA in dairy products differing in lipid content and degree of lipolysis were evaluated. We used a direct on-column approach where the isolated FFA extract was injected directly and a derivatization approach where the FFA were esterified in the injector to methyl esters using tetramethylammonium hydroxide as a catalyst. A comprehensive validation was undertaken to establish method linearity, limits of detection, limits of quantification, accuracy, and precision. Linear calibrations of 3 to 700mg/L (R(2)>0.999) and 20 to 700mg/L (R(2)>0.997), and limits of detection and limits of quantification of 0.7 and 3mg/L and 5 and 20mg/L were obtained for the direct injection on-column and the derivatization method, respectively. Intraday precision of 1.5 to 7.2% was obtained for both methods. The direct injection on-column method had the lower levels of limits of detection and quantification, because FFA are directly injected onto the GC as opposed to the split injection used in the derivatization method. However, the direct injection on-column method experienced accumulative column phase deterioration and irreversible FFA absorption because of the acidic nature of the injection extract, which adversely affected method robustness and the quantification of some longer chain FFA. The derivatization method experienced issues with quantification of butyric acid at low concentrations because of coelution with the injection solvent peak, loss of polyunsaturated FFA due to degradation by tetramethylammonium hydroxide, and the periodic emergence of by-product peaks of the tetramethylammonium hydroxide reaction that interfered with the quantification of some short-chain FFA. The derivatization method is more robust, and because the derivatization step can be automated, it is more suitable for routine analysis of FFA in dairy products. However, considerable scope exists to develop an alternative gas chromatography with flame ionization detection method to quantify FFA in dairy products without any limitations that is robust and accurate.

Green chromatography determination of fatty acid methyl esters in biodiesel.

This work proposes a green, simple and rapid chromatographic methodology for separation and determination of a group of 13 fatty acids methyl esters (FAMEs) by using a capillary gas chromatography with a flame ionization detector. The method was successfully applied for the determination of FAMEs in biodiesel samples from commercial and waste cooking oils, synthesized by homogeneous catalysis. Detection and quantification limits were in the µg L(-1) level. Direct injection of sample solution was compared with solid-phase extraction and solid-phase microextraction procedures, giving similar results. The lower analysis time represent considerable improvement compared with other papers. The described methodology is especially suitable for process control applications. The samples analysed showed total contents of FAMEs higher than 96.5%, which verifies the European regulations.

Development and validation of a gas chromatography-flame ionization detection method for the determination of epoxy fatty acids in food matrices.

A reliable and suitable method for the determination of epoxy fatty acids in various food matrices based on the Bligh and Dyer lipid extraction procedure was developed and validated. The method involves the use of a methylated epoxy fatty acid as internal standard (IS), extraction of the analytes from the matrices followed by room temperature methylation, a three-step solid phase extraction (SPE) separation of the fatty acid methyl esters (FAMEs), and detection with gas chromatography-flame ionization detection (GC-FID). The method was validated in four different food matrices chosen as model systems, namely, vegetable oils, unprocessed pork, fried potato crisps, and infant formula. The extraction technique allows the method to be applied for routine analysis of a large amount of samples. Intraday repeatability ranged from 1 to 19%, and interday reproducibility ranged from 2 to 9%. The limit of quantification (LOQ) ranged from 3.32 to 20.47 µg g(-1) of sample with recoveries ranging from 94 to 115%. The results verify the accuracy and reproducibility of the analytical technique and its ability to provide reliable quantification of epoxy fatty acids. Finally, levels of epoxy fatty acids in several food products on the Belgian market were screened and are presented.

Identification of volatiles by headspace gas chromatography with simultaneous flame ionization and mass spectrometric detection.

Volatiles are frequently abused as inhalants. The methods used for identification are generally nonspecific if analyzed concurrently with ethanol or require an additional analytical procedure that employs mass spectrometry. A previously published technique utilizing a capillary flow technology splitter to simultaneously quantitate and confirm ethyl alcohol by flame ionization and mass spectrometric detection after headspace sampling and gas chromatographic separation was evaluated for the detection of inhalants. Methanol, isopropanol, acetone, acetaldehyde, toluene, methyl ethyl ketone, isoamyl alcohol, isobutyl alcohol, n-butyl alcohol, 1,1-difluoroethane, 1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane (Norflurane, HFC-134a), chloroethane, trichlorofluoromethane (Freon®-11), dichlorodifluoromethane (Freon®-12), dichlorofluoromethane (Freon®-21), chlorodifluoromethane (Freon®-22) and 1,2-dichlorotetrafluoroethane (Freon®-114) were validated for qualitative identification by this method. The validation for qualitative identification included evaluation of matrix effects, sensitivity, carryover, specificity, repeatability and ruggedness/robustness.

Internally heated membrane interfaced to a gas chromatography flame ionization detector.

Volatile Organic Compounds (VOCs) mixtures in aqueous solutions have been investigated using a simple and efficient all-in-one on-line sampling, isolation, enrichment and pre-concentration internally heated membrane connected to a gas chromatography flame ionization detector (GC-FID). In our previous study with the internally heated membrane, no GC column was used in the instrument. In this new study, we introduce a GC column in the instrument design and this makes it possible for mixtures to be investigated. This new experimental design enabled high resolution separation of analyte mixtures capable of being adsorbed, diffused, and desorbed from the device for detection with an FID. With the new design we present data from investigation of competitive adsorption effects on the membrane. The data showed that analyte adsorption and diffusion onto the membrane can be affected when mixtures of analytes are introduced. The application of multiple linear regressions approach to the data enabled us to correct for the problem of competitive adsorption. Analyte adsorption and diffusion was affected by the diffusion coefficients of the analytes; the higher the diffusion coefficient the better the extraction from the membrane. Increasing the sampling time from 1 to 4 min increases the response by 77%. The sampling time responses were linear up to 4 min sampling time. Above 4 min sampling time, the data deviate from linearity. The effect of adding salt to standards has no effect on analyte absorption onto the membrane. The detection limits for key VOCs studied with an internal standard calibration ranged from 0.2 to 194 ng cm(-3).

Metabolic fingerprinting of hard and semi-hard natural cheeses using gas chromatography with flame ionization detector for practical sensory prediction modeling.

Metabolic fingerprinting using gas chromatography with flame ionization detector (GC/FID) was used to generate a practical metabolomics-based tool for quality evaluation of natural cheese. Hydrophilic low molecular weight components, relating to sensory characteristics, including amino acids, fatty acids, amines, organic acids, and saccharides, were extracted and derivatized prior to the analysis. Data on 12 cheeses, six Cheddar cheeses and six Gouda cheeses, were analyzed by multivariate analysis. Prediction models for two sensory attributes relating to maturation, "Rich flavor" and "Sour flavor", were constructed with 4199 data points from GC/FID, and excellent predictability was validated. Chromatograms from GC/FID and gas chromatography/time-of-flight-mass spectrometry (GC/TOF-MS) were comparable when the same column was used. Although GC/FID alone cannot identify peaks, the mutually complementary relationship between GC/FID and GC/MS does allow peak identification. Compounds contributing significantly to the sensory predictive models included lactose, succinic acid, L-lactic acid, and aspartic acid for "Rich flavor", and lactose, L-lactic acid, and succinic acid for "Sour flavor". Since similar model precision was obtained using GC/FID and GC/TOF-MS, metabolic fingerprinting using GC/FID, which is a relatively inexpensive instrument compared with GC/MS, is easy to maintain and operate, and is a valid alternative when metabolomics (especially using GC/MS) is to be used in a practical setting as a novel quality evaluation tool for manufacturing processes or final products.

Liquid chromatography-flame ionisation detection using a nebuliser/spray chamber interface. Part 2. Comparison of functional group responses.

The application of a LC-nebuliser/spray chamber interface-flame ionisation detection has been demonstrated for the superheated water liquid chromatography of a wide range of aliphatic and aromatic analytes. The linearity and sensitivity of the response of volatile and involatile analytes have been compared. The response of the detector toward different analytes is similar to that in GC-FID and for volatile analytes was comparable to UV detection. However, the responses from involatile analytes, such as amino acids and carbohydrates, were poor and often lower than for a refractive index detector.