The analysis of linear and monomethylalkanes in exhaled breath samples by GC×GC-FID and GC-MS/MS.

A new arrangement of the INCAT (inside needle capillary adsorption trap) device with Carbopack X and Carboxen 1000 as sorbent materials was applied for sampling, preconcentration and injection of C6C19n-alkanes and their monomethyl analogs in exhaled breath samples. For the analysis both GC-MS/MS and GC×GC-FID techniques were used. Identification of the analytes was based on standards, measured retention indices and selective SRM transitions of the individual isomers. The GC-MS/MS detection limits were in the range from 2.1 pg for n-tetradecane to 86 pg for 5-methyloctadecane. The GC×GC-FID detection limits ranged from 19 pg for n-dodecane to 110 pg for 3-methyloctane.

Determination of sevoflurane and its metabolite hexafluoroisopropanol by direct injection of human plasma into gas chromatography-tandem mass spectrometry.

The developed method for trace analysis of volatile components in plasma allows direct injection of up to 150 samples to the GC-MS/MS system without injector cleaning. This method requires no modification of plasma and the working environment does not interfere with the determination of these analytes. The method allows simultaneous quantification of non-polar sevoflurane and its polar metabolite hexafluoroisopropanol (free, unconjugated form). It is characterized by high repeatability and sensitivity with the detection limit of 0.009 mg L(-1) for sevoflurane and 0.018 mg L(-1) for hexafluoroisopropanol and the linear range 0.050-150 mg L(-1). The method was used to determine the concentration of sevoflurane and hexafluoroisopropanol in plasma samples of 7 patients undergoing general anesthesia with sevoflurane. The average concentration of sevoflurane and free hexafluoroisopropanol was 57.2 mg L(-1) and 0.39 mg L(-1), respectively. The method can be applied for clinical monitoring, as well as for analytical toxicology.

Equivalent chain lengths of all C4-C23 saturated monomethyl branched fatty acid methyl esters on methylsilicone OV-1 stationary phase.

Isomer mixtures of monomethyl branched saturated C7-C23 fatty acid methyl esters (FAME) were prepared by performing a methylene insertion reaction to the straight chain FAME and this study model was completed by using commercially available standards of C4-C7 FAME. The equivalent chain lengths (ECL) of all 220 C4-C23 monomethyl branched FAME on OV-1 stationary phase were measured, achieving an average repeatability of ±0.0004 ECL units. The monomethyl branched FAME was identified by GC on the basis of regularity of the fractional chain lengths (FCL) dependence on the number of carbon atoms (C(z)) of individual homologous series of methyl 2-, 3-, …, 21-FAME. The prediction of retention of the first homologues, having the new position of methyl group beginning at higher carbon atoms number, and analogously for the second, third, fourth, and other members of the homologous series, allowed the dependence FCL=f(C(z)) for the first and subsequent members of beginning homologous of monomethyl derivatives of FAME. The identification was confirmed by mass spectrometry. All of the methyl isomers of FAME, which could not be completely separated by gas chromatography due to having a methyl group in surroundings of the middle of the carbon chain, were resolved by mass spectrometry using deconvolution in a SIM-mode. Measured gas chromatographic and mass spectrometric data were applied for identification of the monomethyl branched saturated FAME in tongue coating.

Chemometric deconvolution of gas chromatographic unresolved conjugated linoleic acid isomers triplet in milk samples.

A generally known problem of GC separation of trans-7;cis-9; cis-9,trans-11; and trans-8,cis-10 CLA (conjugated linoleic acid) isomers was studied by GC-MS on 100m capillary column coated with cyanopropyl silicone phase at isothermal column temperatures in a range of 140-170 degrees C. The resolution of these CLA isomers obtained at given conditions was not high enough for direct quantitative analysis, but it was, however, sufficient for the determination of their peak areas by commercial deconvolution software. Resolution factors of overlapped CLA isomers determined by the separation of a model CLA mixture prepared by mixing of a commercial CLA mixture and CLA isomer fraction obtained by the HPLC semi-preparative separation of milk fatty acids methyl esters were used to validate the deconvolution procedure. Developed deconvolution procedure allowed the determination of the content of studied CLA isomers in ewes' and cows' milk samples, where dominant isomer cis-9,trans-11 is eluted between two small isomers trans-7,cis-9 and trans-8,cis-10 (in the ratio up to 1:100).

Gas chromatography analysis of benzene, toluene, ethylbenzene and xylenes using newly designed needle trap device in aqueous samples.

A newly designed needle trap device with Carbopack X as a sorbent material is used for sampling, preconcentration and injection of volatile analytes benzene, toluene, ethylbenzene and xylenes (BTEX) into gas chromatograph. The closed system of stripping the analytes from water samples was used. An injection port with a modified metal liner was used to desorb analytes trapped in needle trap device. The main advantage of needle trap device consists in the simple methodology and easiness and rapidity of the analysis. Needle trap device is suitable for sampling in field. The experimental parameters as breakthrough volume of stripping gas, linearity, repeatability and limit of detection (LOD) and quantification (LOQ) were investigated. LOD ranges from 0.05 to 0.07 microgL(-1) and relative standard deviation ranges from 0.5% to 11.6% at concentrations 5 and 0.1 microgL(-1), respectively.

Temperature-programmed gas chromatography linear retention indices of all C4-C30 monomethylalkanes on methylsilicone OV-1 stationary phase. Contribution towards a better understanding of volatile organic compounds in exhaled breath.

Monomethylated alkanes have been proposed to be contained in exhaled breath, their concentration pattern serving for identification of lung carcinoma, breast carcinoma and rejection of foreign tissue after heart transplant rejection. Improving the accuracy of identification for monomethylated alkanes will enhance work on their biochemical background which presently is unknown. The programmed temperature linear retention indices of all 196 C(4)-C(30) monomethylalkanes on OV-1 stationary phase were measured with an average repeatability of +/-0.07 index units (i.u.). The mixture of C(9)-C(30) monomethylalkanes was prepared by methylene insertion reaction to C(8)-C(29)n-alkanes mixture. The preliminary identification of monomethylalkanes was performed on the basis of the dependence of homomorphy factors on the number of carbon atoms of individual homologous series of monomethylalkanes (retention indices extrapolated with s=0.15 i.u.). The prediction of retention of isomers with new position of methyl group beginning at higher carbon atoms number, as well as for second, third, fourth, etc., member of homologous series allowed the dependence H(P)=f(C(n)) for first, second, third, etc., members of beginning homologous of monomethylalkane series (retention indices extrapolated with s=0.17 i.u.). The identification was confirmed by mass spectrometry. All gas chromatographic unseparated monomethylalkane isomers with methyl-group near the middle of molecule carbon chain were resoluted by mass spectrometric deconvolution. Obtained regular dependences H(P)=f(C(n)) allow precise retention prediction of monomethylalkanes C(30).

Capillary gas chromatography-mass spectrometry of all 93 acyclic octenes and their identification in fluid catalytic cracked gasoline.

The Kováts retention indices of all 93 acyclic octenes on polydimethylsiloxane and squalane as stationary phases as well as their mass spectra were measured. The means of gas chromatography-mass spectrometry (GC-MS) were used for confirmation of GC identification as well as for mass spectrometric deconvolution of the majority of gas chromatographic unseparated isomeric octene peaks. The distinction between corresponding E and Z acyclic octenes, that is either difficult or even impossible by means of GC-MS, was obtained on the basis of larger temperature coefficients of retention indices for Z isomeric octenes than for corresponding E isomers. The retention data expressed as homomorphy factors were correlated with the degree of branching, position of double bond, and position of alkyl group with respect to the double bond of acyclic octenes, and the structure-retention relationships were formulated. The 81 acyclic octenes were identified in FCC gasoline.

Needle concentrator for gas chromatographic determination of BTEX in aqueous samples.

A simple method of solventless extraction of volatile organic compounds (BTEX) from aqueous samples was developed and validated. A new arrangement of the full volume inside needle capillary adsorption trap (INCAT) device with Porapak Q as a sorbent material and wet alumina as a source of desorptive water vapour flow in a closed analytical system is presented. The analytical characteristics of developed device and of compared purge-and-trap (PTI) device for BTEX compounds are similar; the limits of detection as well as quantification are lower than 1 microg l(-1).

Theoretical and experimental study of recycle capillary gas chromatography with carrier gas propelled by a peristaltic pump.

A new technique of recycle capillary gas chromatography (RCGC) characterized by a very high separation efficiency of more than 10(6) theoretical plates has been developed to solve the problem of separation of isomers with similar physico-chemical properties. The technique replaces the recycle valve by a peristaltic pump that propels the carrier gas. A general model has been developed for description of RCGC characteristics and experimentally verified on the retention behaviour of methane and the separation of a test pair of 3-methyl-1-butene and 2-methylbutane.

Gas chromatographic-mass spectrometric characterization of all acyclic C5-C7 alkenes from fluid catalytic cracked gasoline using polydimethylsiloxane and squalane stationary phases.

Published retention indices of acyclic alkenes C5-C7 on squalane and polydimethylsiloxane as stationary phases were investigated, and reliable retention indices of alkenes from various sources were converted to separation systems used in a laboratory. Retention indices measured on available authentic commercial alkenes and on alkenic fraction of gasoline, published retention indices as well as means of GC-MS were used for verification of calculated retention indices. Retention of some gas chromatographic unseparated isomer pairs was obtained by mass spectrometric deconvolution using a specific single-ion monitoring. On the basis of these retention data, C5-C7 alkenes were identified and analyzed in the gasoline from fluid catalytic cracking. In the gasoline all 59 acyclic C5-C7 isomeric alkenes were determined at significantly different concentration levels.