High-resolution Capillary Gas Chromatography Research Articles

Fingerprinting and identification of isolated plastic polymers with pyrolysis comprehensive two-dimensional gas chromatography and flame ionization detection.

An approach using pyrolysis with comprehensive two-dimensional gas chromatography with flame ionization detection is introduced for identifying common isolated plastic polymers. A quadrupole mass spectrometer is employed as a parallel detector to aid method development and improve polymer identification in complex matrices. Common plastic polymers including polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyamide, poly(methyl methacrylate), styrene-butadiene rubber, and polyethylene terephthalate are accurately identified within a total analysis time of 45min. A strategy to enhance compatibility of high-resolution capillary gas chromatography using a 150-µm internal diameter column technology and a larger internal volume microfurnace-based pyrolyzer is discussed. This strategy resulted in minimizing the band broadening effect caused by the pyrolyzer's internal volume and overcoming the slow pressure buildup when the sample is inserted into the furnace. Prolonged pressure buildup to reach a final pressure setting can cause a safety shutdown to the pneumatic control system. The developed approach is complementary to spectroscopic techniques by offering mass based, chemical composition analysis of plastics.

N – alkanes in molluscs of Shatt Al-Arab river

This study comprises monitoring of the n-alkanes in the Shatt Al-Arab river by using the seven molluscs species as bioindicators. These species are: snails Lymnaea auricularia, Theodoxus jordani, Physa acuta, Melanopsis nodosa, and Melanoides tuberculata and bivalves Corbicula fluminea and Corbicula fluminalis. The species of molluscs are collected from different locations of the Shatt Al-Arab river (along the region extended from Abu Al-Khasib to Garmat-Ali) during 2004 and 2005. Each species consisted of at least 3500 adult of individuals of uniform sizes. The hydrocarbons from these species were extracted and analyzed both by spectroflurometer (total hydrocarbons) and high resolution capillary gas chromatography (n-alkanes). The concentrations of total hydrocarbons in mollusc’s species of the Shatt Al-Arab river ranged from 1.93 μg/g dry weight in T. jordani to 26.56 μg/g dry weight in C. fluminea. The range of carbon chain length of n-alkanes in these individuals was ranging from C13 - C32. The bimodal distribution with two maxima around C17 and C27 suggested two different sources of hydrocarbons both biogenic and anthropogenic. The dominance of the odd carbon numbers n-alkanes (C15, C17, C25 and C29) in the mollusc’s species indicated biogenic origin of hydrocarbons .The pristane values were more than those of phytane. Pristane and phytane in the mollusc’s species suggest biogenic origin. CPI values are more than one indicating a biogenic origin of hydrocarbons in these species. Squalane is also present in some these species intimately related to anthropogenic sources of hydrocarbons. The presence of Unresolved Complex Mixture (UCM) reflects the anthropogenic sources. The lower fat contents were found in T. jordani (0.33 mg/g) and the higher were in C. fluminea (0.98 mg/g). A significant relationship is found between the fat contents and hydrocarbons concentrations in the tissues of molluscs species (r = 0.8 - 0.9).

Evaluation of Fatty Acid Compositions of the Margarines, Fat Spreads and Butters Currently Consumed in Japan

Using high-resolution capillary gas chromatography with flame ionization detection, we determined the fatty acid compositions of each ten sample of the margarines, fat spreads and butters currently consumed in Japan, with special reference to trans fatty acids. The total trans fatty acid contents of the margarines, fat spreads and butters examined were 0.19–1.49 g 100 g−1 (av. 0.71 g 100 g−1), 0.16–0.88 g 100 g−1 (av. 0.51 g 100 g−1), and 2.49–3.37 g 100 g−1 (av. 2.74 g 100 g−1), respectively, clearly showing lower levels of trans fatty acids in all the samples of margarines and fat spreads than those of butters. In addition, the total saturated fatty acid contents of the margarines, fat spreads and butters were 17.3–45.6 g 100 g−1 (av. 29.7 g 100 g−1), 4.51–25.6 g 100 g−1 (av. 16.2 g 100 g−1), and 48.8–54.8 g 100 g−1 (av. 52.4 g 100 g−1), respectively, also showing lower levels of saturated fatty acids in all the samples of margarines and fat spreads than those of butters. The most predominant trans fatty acid of butters is vaccenic acid (11t-18 : 1), comprising av. 30.4 % of total trans fatty acids, while in margarines and fat spreads trans 18 : 2 (9c,12t- and 9t,12c-isomers) and trans 18 : 3 (9c,12c,15t- and 9t,12c,15c-isomers) were the major ones, suggesting that they were derived from refined vegetable oils as raw materials. The present study demonstrates that modern Japanese margarines and fat spreads have significantly lower levels of trans fatty acids and saturated fatty acids than butters.

Branched Chain Fatty Acid Distribution in Beef Lipids (P08-110-19)

ObjectivesBeef is a rich source of branched chain fatty acids (BCFA) in the American diet. Once consumed, utilization of fatty acids depends on their lipid class in foods.Our objective is to characterize the distribution of BCFA among lipid classes in commercial ribeye steaks, specifically sampled from grass-fed, angus, and prime beef. MethodsBeef was obtained from a supermarket in Austin, Texas. Samples were cut into pieces (1 mm3) and extracted by the method of Bligh and Dyer. Extracts were fractionated into triacylglycerol (TAG), phospholipids (PL), cholesterol esters (CE), and free fatty acids (FFA) by thin layer chromatography (TLC). PL were further fractionated into phosphatidylcholine (PC), lyso-PC, phosphatidylserine (PS), phosphatidylethanolamine (PE), phosphatidylinositol (PI), and sphingomyelin (SM). Fatty acid methyl esters (FAME) were prepared from each fraction by treatment with BF3/methanol and analyzed by high resolution capillary gas chromatography (GC) with positive structure identification by MS/MS of the molecular ion. ResultsTotal BCFA in PL of grass-fed beef is the highest (1.25 ± 0.05%, w/w; mean ± SD) compared with those in PL of other beef. Total BCFA in TAG (1.30 ± 0.37%, w/w) were not different between angus and prime beef. BCFA were detected in all lipid fractions. Anteiso-15:0, anteiso-17:0, iso-15:0, iso-16:0, iso17:0, iso-18:0 were detected in most fractions. ConclusionsTotal BCFA in PL of grass-fed beef is the highest (1.25 ± 0.05%, w/w; mean ± SD) compared with those in PL of other beef. Total BCFA in TAG (1.30 ± 0.37%, w/w) were not different between angus and prime beef. BCFA were detected in all lipid fractions. Anteiso-15:0, anteiso-17:0, iso-15:0, iso-16:0, iso17:0, iso-18:0 were detected in most fractions. Funding SourcesThis study was supported by the National Cattleman’s Beef Association and the North Dakota Beef Commission.

Evidence of Reduced Agmatine Concentrations in the Cerebral Cortex of Suicides.

BackgroundThe polyamines are a group of ubiquitous low-molecular–weight aliphatic molecules that play an essential role in various physiological functions of the mammalian CNS. Previous literature has indicated alterations in the expression of polyamine-related genes in the brains of individuals who died by suicide, including downregulation of spermidine/spermine N1-acetyltransferase, a key enzyme involved in polyamine catabolism. One such polyamine, agmatine, has been shown to act as an antidepressant in animal models of depressive-like behavior. However, agmatine concentrations have not been explored in postmortem human brain of individuals who died by suicide.MethodsTo measure agmatine in postmortem human brain tissue, we employed our previously published high-resolution capillary gas chromatography in combination with mass spectrometry method. Using this method, we analyzed agmatine levels in a total of 120 tissue samples from Brodmann areas 4, 11, and 44 of 40 male subjects comprising controls (n=13), individuals who died by suicide and met criteria for major depressive disorder (n=14), and subjects who died by suicide and did not meet criteria for major depressive disorder (n=13).ResultsAgmatine fell within the expected nanomolar range and was significantly reduced in the cortex of suicides, irrespective of meeting criteria for major depressive disorder compared with controls.ConclusionsThis is the first gas chromatography-mass spectrometry study to analyze agmatine concentrations in human postmortem brain of individuals who died by suicide. These results add to our mechanistic understanding of the role that the polyamine stress response pathway may play in the neurobiology of major depression and/or suicide.

Analysis of Dioxins Concentration in Domestic Waste and Burnt Tyre Residue at Gosa Dumpsite in Abuja, Nigeria

This study examined the presence of dioxins – a persistent organic pollutant in domestic and burnt tyre waste residues and it’s comparison with German safety limits at the Gosa dumpsite in Abuja, Nigeria. The period of sampling and analysis was between January and March, 2011. Burnt tyre ashes and burnt solid waste residues from the dump sites were chemically analyzed to determine the concentration of the seventeen 2,3,7,8-substituted dioxins and furan congeners in absolute quantities using high resolution capillary column gas chromatography and low resolution mass spectrometry. The result of the analysis performed using the International Toxic Equivalent Factor (NATO/CCMS) for the calculation of the individual Toxic Equivalent Quotients (TEQs) of the seventeen 2,3,7,8- substituted dioxins and furan congers and a summation of the individual I-TEQs per sample shows that there is significant quantity of about 44 ng/kg TM of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a contaminant in Agent Orange, in one out of the five (1/5) analyzed samples. The maximum Total Polychlorinated dibenzo-p-dioxins/furans (PCCD/F) concentration recorded in this study was 1,350 ng/kg TM from sample Point 3. This was greater than the German Federal Soil Protection and Contamination Sites Ordinance (GFSPCSO) for Total PCDD/F equivalents for target concentration, agricultural, playground and residential landuse (which dominate the area under study) but less than its industrial landuse equivalent. There was also the presence of dioxins in the burnt domestic waste analysed with the Total PCDD/F (TEQ) of 6.6 ng/kg TM. The land usage of the area under investigation is closely interwoven across the land mass. Therefore, the results indicate that the population and activities within the area of study are under threat of health hazards that may arise from the high concentration of dioxins recorded by this study.

Fatty acid analysis by high resolution gas chromatography and mass spectrometry for clinical and experimental applications

Quantitative fatty acid profiles analyzed via fatty acid methyl esters (FAME) are among the most common metabolite panels and fit into the category of omics techniques. Recently, preparation and analysis methods for high throughput clinical analysis have become routine, and novel methods for structure analysis enable rapid identification of unknowns and confounded peaks. Observation of one hundred FAME in a single mixture is common with high resolution capillary gas chromatography columns. Structural analysis of FAME requires high resolution gas chromatography with specialized tandem mass spectrometry to obtain fragments indicative of structure. Covalent adduct chemical ionization provides unambiguous double bond positions, whereas electron ionization with fragmentation of the molecular ion identifies branch points. Quantitative analysis requires response calibration using external standards and/or isotopically labeled internal standards with mass spectrometry detection. Modern high throughput methods enable routine analysis of well behaved clinical samples. Careful attention to structure analysis using recent methods avoids biases due to interfering or mischaracterized fatty acids.

Gas chromatographic-mass spectrometric investigation of the chemical composition of the aquatic plant Wolffia arrhiza (Lemnaceae)

Abstract The ether and methanol extracts of Wolffia arrhiza (Lemnaceae) were analyzed using high resolution capillary gas chromatography coupled with mass spectrometry (GC-MS). The ether extract contains 32 compounds, mostly lipids and sterols, among which β-sitosterol is most prevalent. This is the first evidence of β-sitosterol detection in W. arrhiza. The most representative group of polar compounds of the methanol fraction is formed by 18 free amino acids. In addition, in the methanol extract there are a number of other nitrogen containing compounds: nucleobase and nucleosides. The third significant group in the total ion current in the methanol extract is formed by glycerol and glycerides. At the same time, the content of free sugar is very low.

Rapid separation of beryllium and lanthanide derivatives by capillary gas chromatography

DOI: 10.1002/jssc.201200537 Europium(III) derivative formed by reaction of the europium ion with a fluorinated β-diketonate reagent and a neutral donor. The resulting non-polar, thermally stable, and luminescent derivative partitions into cyclohexane upon formation and can be subjected to high-resolution capillary gas chromatography. This approach is used to separate derivatives of lanthanides that are adjacent to one another in the periodic table. In addition, an on-fiber SPME derivatization/concentration GC/MS method that uses a fiber preloaded with the same β-diketonate reagent is described for the analysis of beryllium(II) ion.

Prediction of capillary gas chromatographic retention times of fatty acid methyl esters in human blood using MLR, PLS and back-propagation artificial neural networks

Quantitative structure–retention relationship (QSRR) models correlating the retention times of fatty acid methyl esters in high resolution capillary gas chromatography and their structures were developed based on non-linear and linear modeling methods. Genetic algorithm (GA) was used for the selection of the variables that resulted in the best-fitted models. Gravitational index (G2), number of cis double bond (N cDB) and number of trans double bond (N tDB) were selected among a large number of descriptors. The selected descriptors were considered as inputs for artificial neural networks (ANNs) with three different weights update functions including Levenberg–Marquardt backpropagation network (LM-ANN), BFGS (Broyden, Fletcher, Goldfarb, and Shanno) quasi-Newton backpropagation (BFG-ANN) and conjugate gradient backpropagation with Polak–Ribiére updates (CGP-ANN). Computational result indicates that the LM-ANN method has better predictive power than the other methods. The model was also tested successfully for external validation criteria. Standard error for the training set using LM-ANN was SE = 0.932 with correlation coefficient R = 0.996. For the prediction and validation sets, standard error was SE = 0.645 and SE = 0.445 and correlation coefficient was R = 0.999 and R = 0.999, respectively. The accuracy of 3–2–1 LM-ANN model was illustrated using leave multiple out-cross validations (LMO-CVs) and Y-randomization.

ChemInform Abstract: Silver-Complexation Liquid Chromatography for Fast, High-Resolution Separations of Triacylglycerols.

A high-speed, high-resolution approach to silvercomplexation chromatography of triacylglycerols in vegetable fats and cocoa butter equivalents is described. Trisaturated and major isomeric unsaturated species with up to five double bonds are eluted within 12 min. A simple change of solvent composition enables elution of species with up to nine double bonds within the same time-frame. Throughput is three samples/hr (70 samples/24 hr with an automatic system). Short-term reproducibility of analytical data for the system gives standard deviations similar to those obtained in practice for high-resolution capillary gas chromatography of triacylglycerols, and quantitative accuracy is good. Details of column preparation, solvent gradient and system operation are given.

Evidence of Altered Polyamine Concentrations in Cerebral Cortex of Suicide Completers

Recent studies have implicated alterations in the expression of polyamine-related genes in the brains of suicide completers including widespread downregulation of spermidine/spermine N1-acetyltransferase, the key enzyme in polyamine catabolism, suggesting compensatory mechanisms attempting to increase brain levels of polyamines. Given the complexity of the polyamine system, quantification of the levels of the polyamines is an essential step in understanding the downstream effects of dysregulated gene expression. We developed a method using high-resolution capillary gas chromatography (GC) in combination with mass spectrometry (MS) for quantitation of polyamines from post-mortem brain tissue, which allowed us to accurately measure spermidine and putrescine concentrations in post-mortem brain tissues. Using this method, we analyzed putrescine and spermidine levels in a total of 126 samples from Brodmann areas 4, 8/9, and 11, from 42 subjects, comprising 16 suicide completers with major depression, 13 non-depressed suicide completers, and 13 control subjects. Both putrescine and spermidine levels fell within the expected nanomolar ranges and were significantly elevated in the brain of suicide completers with a history of major depression as compared with controls. These results were not accounted by possible confounders. This is the first GC-MS study to analyze the expression of putrescine and spermidine from post-mortem brain tissue and confirms the hypothesis raised by previous studies indicating alterations in putrescine and spermidine levels in suicide/major depression.

Novel aryl polycyclic aromatic hydrocarbons: Phenylphenanthrene and phenylanthracene identification, occurrence and distribution in sedimentary rocks

Numerous reports have recognised the presence of compounds with molecular weight 254 a.m.u. in aromatic fractions. However, their unequivocal identification has not been achieved due to a lack of reference substances. In geological samples, such m/z 254 compounds could potentially be represented by a number of structural isomers of binaphthyl, phenylphenanthrene, phenylanthracene and indenofluorene with each compound type possessing several positional isomers. In this work, all these m/z 254 compounds, with the exception of the tentatively recognised indenofluorenes, have been unequivocally identified in sedimentary rocks for the first time. Comparison of the mass spectra and the gas chromatography (GC) retention times of synthesised standards with the natural compounds in rocks shows that the major components of aromatic fractions are phenylphenanthrene isomers and, to a lesser extent, binaphthyls and 9-phenylanthracene. The elution sequence expressed as standard retention indices of all these m/z 254 isomers were determined by using high resolution capillary GC with three stationary phases: 5%, 35% and 50% (mole fraction) phenyl substituted methylpolysiloxane on HP-5MS, DB-35MS and DB-17MS columns, respectively. A survey of more than 350 sedimentary rock samples of varying origins and maturity (Rr 0.3–1.4%) reveals that relative abundances of the m/z 254 isomers depend on the maturity of the organic matter. The isomers initially appear at the onset of oil generation (Rr>0.5%) exclusively in diagenetically/catagenetically oxidised samples containing varying proportions of Types II and III kerogen. Interestingly, all five possible positional phenylphenanthrene isomers (including the most sterically hindered isomer 4-phenylphenanthrene) are present from the beginning of the oil generation window. Such a distribution suggests that low-regioselectivity reactions are likely to be involved in the formation. Interaction, during maturation, of phenyl radicals from primary cracking with aromatic moieties of more resistant terrigenic components of kerogen in an oxidising diagenetic realm is postulated to be responsible for the neoformation of phenylated aromatics in geological samples. Up to the final stages of oil generation, the evolution of the phenyl PAH distributions presumably involve 1,2-phenyl shift reactions and cyclisation, if allowed by the molecular geometry. A near thermodynamically-controlled distribution, with only 3- and 2-phenylphenanthrene and minor 2,2′-binaphthyl remaining, is approached when vitrinite reflectance reaches 1.2% (Rr). The three compounds seem to be persistent beyond the oil window as is suggested by their presence in hydrothermal oil formed at T>300°C.

Solid-Phase Microextraction Coupled to Fast Gas Chromatography for the Determination of Migrants from Polystyrene-Packaging Materials into Yoghurt

In view of the importance of a rapid determination of migrants in food, a headspace solid-phase microextraction coupled with fast high-resolution capillary gas chromatography (HS-SPME/fast GC) method has been developed for the rapid determination of styrene and ethylbenzene in polystyrene-packaged yoghurt. The method accuracy is satisfactory with recoveries ranging from 97% to 105%. The developed method was applied to the study of the variation in migrant content during the shelf-life of commercial-packaged yoghurts. Compared with conventional SPME/GC, the employment of a SPME/fast GC method led to reduction of both the SPME equilibration and analyte separation time; the method allowed the determination of styrene and ethylbenzene in about 15 min (including sampling, extraction and analysis). At the same time, several volatile organic compounds belonging to the key aroma compounds of the fermented milks were identified. The coefficient of variation in terms of peak area and retention time was included between 3% and 4% for all the components identified. Styrene and ethylbenzene have been quantified using the standard addition method. Calibration curves were linear for both the compounds in the range from 1 to 10 ng g−1 for ethybenzene and from 2 to 25 ng g−1 for styrene. Detection limits ranged from 0.5 to 0.6 ng g−1 and quantification limits from 1.0 to 2.2 ng g−1.

Creating a fatty acid methyl ester database for lipid profiling in a single drop of human blood using high resolution capillary gas chromatography and mass spectrometry

Capillary gas chromatography (CGC) in combination with mass spectrometry (MS) was optimized for the separation and detection of the fatty acids occurring in the lipid fraction of blood. A fingertip blood sample (ca. 50 μL) was transesterified into the methyl esters and analyzed on a 100 m × 0.25 mm ID column coated with a biscyanopropyl polysiloxane (HP-88) stationary phase. The method was retention time locked. Programmed temperature vaporization injection (PTV) in the solvent venting mode was applied to minimize the sample size, while maintaining high sensitivity. The total analysis time was ca. 60 min. Retention times and both electron impact (EI) and positive chemical ionization (PCI) mass spectrometry were combined to elucidate the fatty acids according to alkyl chain, degree of unsaturation and position of the double bonds. Using extracted ion chromatograms about 100 fatty acids and related compounds were detected in blood samples and most of them were identified. This work resulted in a very large fatty acid methyl esters database, containing retention time and mass spectral information that will be applied to metabolomic studies.

Fatty acid composition of erythrocyte membrane lipids in healthy subjects from birth to young adulthood

The fatty acid composition of erythrocyte membrane lipids may better reflect the fatty acid status of the organism than the fatty acid composition of plasma lipids. The present study aimed to provide normal values for erythrocyte fatty acid composition in a sizeable group of healthy subjects throughout the paediatric age group. The fatty acid composition of erythrocyte membrane phosphatidylcholine (PC) and phosphatidylethanolamine (PE) lipids was determined by high-resolution capillary gas chromatography in 188 apparently healthy subjects from birth to young adulthood (newborns: n=17, infants: n=97, children: n=38, young adults: n=36). The values of linoleic acid (C18:2n-6) increased steadily between birth and young adulthood (newborns: 6.49 [2.45], infants: 14.51 [4.32], children: 18.10 [3.25], young adults: 19.87 [2.03], PC lipids, shown as median [interquartile range, IQR], p<0.001]. In contrast, the values of arachidonic acid (C20:4n-6) were significantly higher in children than in young adults (PC: 9.48 [6.64] versus 8.00 [1.85], PE: 26.38 [3.98] versus 24.46 [2.44], p<0.05). The values of alpha-linolenic acid (C18:3n-3) decreased significantly between children and young adults (0.14 [0.11] versus 0.08 [0.07], PE lipids, p<0.05). The values of docosahexaenoic acid (C22:6n-3) increased significantly from infancy through childhood up to young adulthood (PE: 4.20 [2.41] and 4.55 [0.97] and 6.66 [1.81], p<0.05 and 0.001, respectively). We found significantly higher total trans isomeric fatty acid values in newborns than in infants (PC: 0.60 [0.27] versus 0.43 [0.19], p<0.05; PE: 0.66 [0.76] versus 0.30 [0.26], p<0.001). From the results, we conclude that: (1) the data obtained in the present study may serve as reference values in the evaluation of the fatty acid status from birth to young adulthood; (2) the significantly higher values of trans fatty acids at birth than at later stages of life may be of concern, because previous studies suggested that trans fatty acids may interfere with essential fatty acid metabolism during the perinatal period.

Biologically Active Contaminants of Intravenous Saline in PVC Packaging: Australasian, European, and North American Samples

We have previously found evidence of contaminants in 0.9% saline packaged in polyvinyl chloride (PVC) for clinical use. For this current study we asked two questions: (1) what are the organic chemical contaminants in solutions packaged in PVC? and (2) do the contaminants vary in bags manufactured in different countries? We studied samples of 0.9% saline packaged in PVC from Australasia, Europe, and North America. We analysed the saline solutions with high-resolution capillary gas chromatography - mass spectrometry. Components of the Australasian and European bags were also analysed using thermodesorption followed by gas chromatography and mass spectrometry. In three pairs of samples we found twenty-four different organic contaminants of the saline solutions. Diethylhexyl phthalate (DEHP) was found in all solutions; the concentrations were greater than 10 microg/l in the Australasian and European samples. All samples contained 2-ethyl hexanol (>50 microg/l), a DEHP breakdown product. The Australasian and North American samples contained cyclohexanone at concentrations of about 1000 microg/l. The cyclohexanone probably originated in joints at the bases of the bags. Both the Australasian and European bags contained t-butyl cyclohexanol (>500 microg/l) and t-butyl cyclohexanone (>50 microg/l). Printing ink on the outside of the bags was the most likely source for both of these contaminants. Several of the contaminants are toxic to animals. Little is known about the toxicity of combinations of contaminants.

Method Validation for Detection and Quantification of Cocoa Butter Equivalents in Cocoa Butter and Plain Chocolate

A European interlaboratory study was conducted to validate an analytical procedure for the detection and quantification of cocoa butter equivalents in cocoa butter and plain chocolate. In principle, the fat obtained from plain chocolate according to the Soxhlet principle is separated by high-resolution capillary gas chromatography into triacylglycerol fractions according to their acyl-C-numbers, and within a given number, also according to unsaturation. The presence of cocoa butter equivalents is detected by linear regression analysis applied to the relative proportions of the 3 main triacylglycerol fractions of the fat analyzed. The amount of the cocoa butter equivalent admixture is estimated by partial least-squares regression analysis applied to the relative proportions of the 5 main triacylglycerols. Cocoa butter equivalent admixtures were detected down to a level of 2% related to the fat phase, corresponding to 0.6% in chocolate (assumed fat content of chocolate, 30%), without false-positive or -negative results. By using a quantification model based on partial least-squares regression analysis, the predicted cocoa butter equivalent amounts were in close agreement with the actual values. The applied model performed well at the level of the statutory limit of 5% cocoa butter equivalent addition to chocolate with a prediction error of 0.6%, assuming a chocolate fat content of 30%.

Approaches to identifying and quantifying polycyclic aromatic hydrocarbons of molecular weight 302 in diesel particulates.

Among the PAH class of compounds, high molecular weight PAH are now considered as relevant cancer inducers, but not all of them have the same biological activity. However, their analysis is difficult, mainly due to the presence of numerous isomers and due to their low volatility. Retention indices (Ri) for 13 dibenzopyrenes and homologues were determined by high-resolution capillary gas chromatography (GC) with four different stationary phases: a 5% phenyl-substituted methylpolysiloxane column (DB-5 ms), a 35% phenyl-substituted methylpolysiloxane column (BPX-35), a 50% phenyl-substituted methylpolysiloxane column (BPX-50), and a 35% trifluoropropylmethyl polysiloxane stationary phase (Rtx-200). Correlations for retention on each phase were investigated by using 8 independent molecular descriptors. Ri has been shown to be linearly correlated to PAH volume, polarisability alpha, Hückel-pi energy on the four examined columns. Ionisation potential Ip is a fourth variable which improves the regression model for DB-5ms, BPX-35, and BPX-50 column. Correlation coefficients ranging from r2 = 0.935 to r2 = 0.952 are then observed. Application of these indices to the identification and quantification of PAH with MW 302 in certified diesel particulate matter SRM 1650a is presented and discussed.

Sol-gel poly(ethylene glycol) stationary phase for high-resolution capillary gas chromatography.

A sol-gel chemistry-based method was developed for the preparation of highly stable capillary gas chromatography (GC) columns with surface-bonded poly(ethylene glycol) (PEG) stationary phase. Through a single-step procedure, it concurrently provided column deactivation, stationary-phase coating, and chemical immobilization of the coated film. Sol-gel reactions were carried out within fused-silica capillaries that were filled with properly designed sol solutions containing two sol-gel precursors, two different triethoxysilyl-derivatized poly(ethylene glycol)s, two sol-gel catalysts, and a deactivation reagent. Hydrolytic polycondensation reactions led to the formation of a sol-gel coating chemically bonded to the inner walls of the capillary. A number of sol-gel coated fused-silica capillary columns were prepared using sol-gel-active PEG derivatives. These columns demonstrated many inherent advantages, the main being the strong anchoring of the coating to the capillary wall resulting from chemical bonding with the silanol groups on the fused-silica capillary inner surface. This chemical bonding yielded strongly immobilized PEG coatings with outstanding thermal stability (up to 320 degrees C). To our knowledge, such a high thermal stability has not been achieved so far on conventionally prepared PEG GC columns. Sol-gel PEG columns provided excellent chromatographic performances: high number of theoretical plates, excellent run-to-run and column-to-column reproducibility, and pronounced selectivity for a wide range of test solutes. Using n-octadecane as a test solute (k = 7.14), an efficiency value of 3200 theoretical plates/m was obtained on a 10 m x 0.25 mm i.d. fused-silica capillary column. Five sol-gel PEG columns provided RSD values of 1.09% for column efficiency (solute, n-octadecane), 1.37% for retention factor (solute, n-octadecane), and 0.9% for separation factor (for solute pair o- and p-xylene). In five replicate measurements using the same column, RSD values of less than 0.50% for the retention time and 1.36% for retention factor (k) were obtained.