Trifluoropropylmethyl Polysiloxane Research Articles

GC-MS and GC-IR analysis of regioisomeric cannabinoids related to 1-(5-fluoropentyl)-3-(1-naphthoyl)-indole

The compounds in this study are the regioisomeric 2-, 3-, 4-, 5-, 6- and 7-(1-naphthoyl) substituted 1-(5-fluoropentyl)-indoles and the 3-(1-naphthoyl) substituted isomer in this series is also known as AM-2201. These compounds are structurally similar to JWH-018 except for the additional fluorine at the terminal end of the n-pentyl side-chain. These six regioisomeric compounds have the identical elemental composition (C24H22FNO) and differ in the position of attachment of the 1-napthoyl group on the indole ring. The electron ionization mass spectra showed similar major fragment ions with a molecular radical cation of significant abundance at m/z 359. The six compounds have similar fragment ions at m/z 127 and 155 for the naphthyl and naphthoyl cations. There is a prominent fragment ion at m/z 342 [M−17]+ in the EI-MS of 1-(5-fluoropentyl)-3-, 4-, 5- and 6-(1-naphthoyl)-indoles due to the loss of the hydroxyl group and this ion is most prominent in the 3-(1-naphthoyl) substituted isomer (AM-2201).The six compounds were separated using gas chromatography on a capillary column containing a trifluoropropylmethyl polysiloxane (Rtx-200) stationary phase. The elution order appears to be related to the steric crowding of the indole ring substituents. The 7- and 2-(1-naphthoyl) substituted isomers eluted first due to the possibility for maximum interactions between the naphthyol and alkyl side-chains.The vapor phase infrared spectra differentiate among these six compounds based on the position of the 1-naphthoyl group on the indole ring. The vapor phase spectra for these compounds are compared to the non-fluorinated analogues, JWH-018 and its regioisomeric equivalents.

GC-MS and GC-IR Analyses of the Methoxy-1-n-pentyl-3-(1-naphthoyl)-indoles: Regioisomeric Designer Cannabinoids.

The indole ring regioisomeric methoxy-1-n-pentyl-3-(1-naphthoyl)-indoles represent indole ring-substituted analogs of the synthetic cannabinoid JWH-018. The electron ionization mass spectra show equivalent regioisomeric major fragments resulting from cleavage of the groups attached to the central indole nucleus. The characteristic (M-17)+ fragment ion at m/z 354 resulting from the loss of OH group is significant in the mass spectra of all four compounds. Fragmentation of the naphthoyl and/or pentyl groups yields the cations at m/z 314, 300, 244 and 216. The vapor-phase infrared spectra provide a number of characteristic absorption bands to identify the individual isomers. Gas chromatographic separations on a capillary column containing a film of trifluoropropylmethyl polysiloxane (Rtx-200) provided excellent resolution of these compounds, their precursor indoles and intermediate pentylindoles. The elution order appears related to the degree of crowding of indole ring substituents.

Differentiation of methylated indole ring regioisomers of JWH-007: GC–MS and GC–IR studies

The five regioisomeric methylated indole ring analogues of JWH-018 can be prepared directly from a common set of precursor materials. These five isomers include 2-methyl-1-n-pentyl-3-(1-naphthoyl)-indole (JWH-007) and its four regioisomeric analogues, 4-, 5-, 6- and 7-methyl substituted indoles. The EI-MS spectra show equivalent regioisomeric major fragments resulting from cleavage of the groups attached to the central indole nucleus. The characteristic [M−17]+ fragment ion at m/z 338 resulting from the loss of OH group is significant in the mass spectra of all the studied compounds except Compound 2 (JWH-007) which has two significant fragment ions at m/z 340 and m/z 270. Cations at m/z 298, 284, 228 and 200 result from fragmentation of the naphthoyl and/or n-pentyl groups. GC separations on a trifluoropropylmethyl polysiloxane (Rtx-200) provided excellent resolution of these compounds. The elution order appears to be related to the degree of crowding of indole ring substituents. The vapor phase infrared spectra in the range of 1700–700 cm−1 showed unique and characteristic absorption patterns for each of the five regioisomeric compounds which allowed for discrimination among the isomers in this set of cannabinoid compounds.

Comparison of Two Stationary Phases for the Determination of Phytosterols and Tocopherols in Mango and Its By-Products by GC-QTOF-MS.

Two different gas chromatography coupled to quadrupole-time of flight mass spectrometry (GC-QTOF-MS) methodologies were carried out for the analysis of phytosterols and tocopherols in the flesh of three mango cultivars and their by-products (pulp, peel, and seed). To that end, a non-polar column ((5%-phenyl)-methylpolysiloxane (HP-5ms)) and a mid-polar column (crossbond trifluoropropylmethyl polysiloxane (RTX-200MS)) were used. The analysis time for RTX-200MS was much lower than the one obtained with HP-5ms. Furthermore, the optimized method for the RTX-200MS column had a higher sensibility and precision of peak area than the HP-5ms methodology. However, RTX-200MS produced an overlapping between β-sitosterol and Δ5-avenasterol. Four phytosterols and two tocopherols were identified in mango samples. As far as we are concerned, this is the first time that phytosterols have been studied in mango peel and that Δ5-avenasterol has been reported in mango pulp. α- and γ-tocopherol were determined in peel, and α-tocopherol was the major tocopherol in this fraction (up to 81.2%); however, only α-tocopherol was determined in the pulp and seed. The peel was the fraction with the highest total concentration of phytosterols followed by seed and pulp, and “Sensación” was the cultivar with the highest concentration of total phytosterols in most cases. There were no significant differences between quantification of tocopherols with both columns. However, in most cases, quantification of phytosterols was higher with RTX-200MS than with HP-5ms column.

GC–MS studies on the six naphthoyl-substituted 1-n-pentyl-indoles: JWH-018 and five regioisomeric equivalents

The GC–MS properties of the synthetic cannabinoid drug of abuse 3-(1-naphthoyl)-1-pentylindole (JWH-018) and all 5 of its’ regioisomeric 1-naphthoyl substituted 1-n-pentylindoles are compared in this report. These compounds have the 1-naphthoyl-group attached at each of the possible substituent positions of the indole ring. The six compounds have the same elemental composition C24H23NO and the same substituents attached to the indole ring. The electron ionization mass spectra showed equivalent regioisomeric major fragment ions resulting from cleavage of the groups attached to the central indole nucleus. The characteristic (M−17)+ fragment ion at m/z 324 resulting from the loss of an OH group was significant in the EI-MS of 3-, 4-, 5- and 6-(1-naphthoyl)-1-pentylindole. Fragment ions occurred at m/z 127 and 155 for the naphthyl and naphthoyl cations common to all six regioisomeric substances. Indole containing fragments produced the cations at m/z 284, 270, 214 and 186. The unique fragment at m/z 141 observed in the 1,2- and 1,7-isomers resulted from a rearrangement involving the two indole substituents to yield the C10H7CH2+ cation. The major points of EI-MS differentiation of the synthetic cannabinoid JWH-018 from the other five isomers are the high relative abundance of both the m/z 144 ion and the m/z 324 ion in the JWH-018 spectrum.GC separations on a capillary column containing a trifluoropropyl methyl polysiloxane (Rtx-200) stationary phase provided excellent resolution of these six compounds. The elution order appears related to the relative distance between the two indole substituents with the lowest retention associated with minimum distance between the groups attached to the indole nucleus.

On-line liquid chromatography–gas chromatography: A novel approach for the analysis of phytosterol oxidation products in enriched foods

A novel methodology for the automated qualitative and quantitative determination of phytosterol oxidation products in enriched foods via on-line liquid chromatography–gas chromatography (LC–GC) was established. The approach is based on the LC pre-separation of acetylated phytosterols and their corresponding oxides using silica as stationary phase and a mixture of n-hexane/methyl tert-butyl ether/isopropanol as eluent. Two LC-fractions containing (i) 5,6-epoxy- and 7-hydroxyphytosterols, and (ii) 7-ketophytosterols are transferred on-line to the GC for the analysis of their individual compositions on a medium polar trifluoropropylmethyl polysiloxane capillary column. Thus, conventionally employed laborious off-line purification and enrichment steps can be avoided. Validation data, including recovery, repeatability, and reproducibility of the method, were elaborated using an enriched margarine as example. The margarine was subjected to a heating procedure in order to exemplarily monitor the formation of phytosterol oxidation products. Quantification was performed using on-line LC–GC-FID, identification of the analytes was based on on-line LC–GC-MS. The developed approach offers a new possibility for the reliable and fast analysis of phytosterol oxidation products in enriched foods.

Selective determination of dimenhydrinate in presence of six of its related substances and potential impurities using a direct GC/MS method

A novel simple, direct and selective gas chromatography–mass spectrometry (GC/MS) procedure was developed for the determination of the antihistamine drug dimenhydrinate (DMH) in presence of six of its related substances and potential impurities, namely, diphenylmethane, diphenylmethanol, benzophenone, orphenadrine, caffeine and 8-chlorocaffeine. The method involved resolution of the underivatized compounds using a trifluoropropylmethyl polysiloxane (Rtx-200) capillary column and the mass spectrometric detection was carried out in the electron-impact (EI) mode. Excellent baseline separation of DMH and the cited related substances was achieved in less than 15min. Quantification of the parent drug DMH was based on measuring its peak area. The reliability and analytical performance of the proposed method were validated with respect to linearity, range, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curve of DMH was linear over the range 50–500μg/mL with determination coefficient (R2)=0.9982. The proposed method was successfully applied for the assay of DMH in tablets dosage form with recoveries>96.80%.

Mass Spectral and Chromatographic Studies on Some Halogenatedphenyl-2-Piperazinopropanones.

Gas chromatography-mass spectrometry (GC-MS) studies on the halogenatedphenyl-2-piperazinopropanones (XPPPOs): Twelve XPPPOs were subdivided into four groups of compounds and studied using GC-MS. The four studied groups include the three ring-substituted fluorophenylpiperazinopropanones, chlorophenylpiperazinopropanones, bromophenylpiperazinopropanones and trifluoromethylphenylpiperazinopropanones. The three compounds in each group have equal mass and many common mass spectral fragment ions. Perfluoroacylation of the secondary amine nitrogen of these isomeric piperazines gave mass spectra with differences in relative abundance of some fragment ions but acylation did not alter the fragmentation pathway and did not provide additional MS fragments of discrimination among these isomers. The perfluoroacyl derivatives of these piperazines were resolved on a stationary phase of 100% trifluoropropyl methyl polysiloxane (Rtx-200).

GC–MS and FTIR evaluation of the six benzoyl-substituted-1-pentylindoles: Isomeric synthetic cannabinoids

This report compares the GC–MS and FTIR properties of all 6 regioisomeric benzoyl substituted-1-n-pentylindoles. These compounds have the benzoyl-group attached at each of the possible ring substituent positions of the indole ring. The six compounds have the same elemental composition C20H21NO yielding identical nominal and exact masses. Additionally, the substituents attached to the indole ring, benzoyl- and 1-n-pentyl-groups, are identical for all six isomers. The electron ionization mass spectra show equivalent regioisomeric major fragments resulting from cleavage of the groups attached to the central indole nucleus. Fragment ions occur at m/z 77 and 105 for the phenyl and benzoyl cations common to all six regioisomeric substances. Fragmentation of the benzoyl and/or pentyl groups yields the cations at m/z 234, 220, 214, 186 and 144. While the relative abundance of the ions varies among the six regioisomeric substances the 1-n-pentyl-3-benzoylindole and 1-n-pentyl-5-benzoylindole share very similar relative abundances for the major fragment ions.Chromatographic separations on a capillary column containing a 0.5μm film of 100% trifluoropropyl methyl polysiloxane (Rtx-200) provided excellent resolution of these six compounds. The elution order appears related to the relative distance between the two indole substituted groups. The latest eluting compounds (highest retention time) have the two substituents on opposite sides of the indole nucleus. Infrared absorption spectral data show the carbonyl absorption band for each of the benzoylindoles and provide distinguishing and characteristic information to individualize each of the regioisomers in this set of compounds.

Regioisomeric bromodimethoxy benzyl piperazines related to the designer substance 4-bromo-2,5-dimethoxybenzylpiperazine: GC–MS and FTIR analysis

A series of seven regioisomeric bromodimethoxy benzyl piperazines including the designer benzylpiperazine (4-bromo-2,5-dimethoxybenzylpiperazine) were synthesized and their analytical profiles evaluated using GC–MS and FT-IR. The mass spectra for the seven regioisomeric bromodimethoxy benzyl piperazines are almost identical with only the two 2,3-dimethoxy isomers showing one unique major fragment ion at m/z 214/216. Thus, mass spectrometry alone does not provide for the confirmation of identity of any one of the seven compounds to the exclusion of the other isomers. Perfluoroacylation of the secondary amine nitrogen for each of the seven regioisomers gave mass spectra showing some differences in the relative abundance of fragment ions without the appearance of any unique fragments for specific confirmation of structure. Attenuated total reflection infrared spectroscopy provides direct confirmatory data for differentiation between the seven regioisomeric aromatic ring substituted bromodimethoxy benzyl piperazines. Mixtures of the seven piperazine PFP derivatives were successfully resolved via capillary gas chromatography using a relatively polar stationary phase composed of 100% trifluoropropyl methyl polysiloxane.

Capillary gas chromatographic analysis of complex phytosteryl/-stanyl ester mixtures in enriched skimmed milk-drinking yoghurts

The capillary gas chromatographic (GC) separation of complex mixtures of plant steryl and stanyl fatty acid esters was achieved using a medium polar trifluoropropylmethyl polysiloxane as stationary phase. An approach allowing the facile synthesis of steryl/stanyl fatty acid esters was developed, thus creating the basis for a calibration of the method for the different types of ester mixtures to be expected in enriched foods. The usefulness of the approach for the rapid authentication of enriched low-fat products via qualitative and quantitative analysis of intact steryl and stanyl fatty acid esters was demonstrated by analysis of two skimmed milk-drinking yoghurts commercially available on the European market. Combining the extraction of lipids under acidic conditions with the GC separation step showed that one of the products contained a steryl/stanyl ester mixture obtained from long-chain sunflower oil fatty acids and sterols/stanols from tall oil. The other product, however, was shown to contain the rather unusual steryl/stanyl esters of the medium-chain octanoic and decanoic acid as ingredients.

Differentiation of methylbenzylpiperazines (MBPs) and benzoylpiperazine (BNZP) using GC‐MS and GC‐IRD

Three-ring substituted methylbenzylpiperazines (MBPs) and their isobaric benzoylpiperazine (BNZP) have equal mass and many common mass spectral fragment ions. The mass spectrum of BNZP yields a unique benzoyl-group containing fragment at m/z 122 and an additional major fragment at m/z 69 that allows its discrimination from the three MBP regioisomers. Perfluoroacylation of the secondary amine nitrogen of these isomeric piperazines gave mass spectra with differences in relative abundance of some fragment ions but acylation does not alter the fragmentation pathway and did not provide additional MS fragments of discrimination among these isomers. Gas chromatography coupled with infrared detection (GC-IRD) provides direct confirmatory data for the structural differentiation between the four isomers. The mass spectra in combination with the vapour phase IR spectra provide for specific confirmation of each of the isomeric piperazines. The underivatized and perfluoroacyl derivatives of these four piperazines were resolved on a stationary phase of 100% trifluoropropyl methyl polysiloxane (Rtx-200). Gas chromatography coupled with time-of-flight mass spectrometry provides an additional means of differentiating between the isobaric MBP and BNZP which have equivalent nominal masses but are different in their elemental composition and exact masses.

Differentiation of methoxybenzoylpiperazines (OMeBzPs) and methylenedioxybenzylpiperazines (MDBPs) By GC‐IRD and GC‐MS

The designer drug 3,4-methylenedioxybenzylpiperazine (3,4-MDBP), its positional isomer 2,3-methylenedioxybenzylpiperazine (2,3-MDBP) and three regioisomeric ring-substituted methoxybenzoylpiperazines (OMeBzPs) have identical elemental composition and no marked differences in their mass spectra with only the three methoxybenzoylpiperazine regioisomers showing one unique major fragment ion at m/z 152. Perfluoroacylation of the secondary amine nitrogen of these isomeric piperazines gave mass spectra with differences in the relative abundance of some fragment ions but did not alter the fragmentation pathway to provide unique ions for discrimination among these isomers. Exact mass determination using gas chromatography coupled to time-of-flight mass spectrometry (GC-TOF-MS) did not provide any discrimination among these compounds since the main fragment ions are of identical elemental composition. Gas chromatography coupled to infrared detection (GC-IRD) provides direct confirmatory data for the identification of the carbonyl containing compounds and the differentiation of the psychoactive designer drug 3,4-MDBP from its direct (2,3-MDBP) and indirect (OMeBzPs) regioisomers. The mass spectra in combination with the vapour phase infrared spectra provide for specific confirmation of each of the isomeric piperazines. The underivatized and perfluoroacyl derivative forms of the five piperazines involved in this study were resolved on a stationary phase of 100% trifluoropropyl methyl polysiloxane (Rtx-200).

GC-Based Analysis of Plant Stanyl Fatty Acid Esters in Enriched Foods

Approaches for the capillary gas chromatographic (GC) based analysis of intact plant stanyl esters in enriched foods were developed. Reference compounds were synthesized by enzyme-catalyzed transesterifications. Their identities were confirmed by means of mass spectrometry. Using a medium polar trifluoropropylmethyl polysiloxane stationary phase, long-chain plant stanyl esters could be separated according to their stanol moieties and their fatty acid chains. Thermal degradation during GC analysis was compensated by determining response factors; calibrations were performed for ten individual plant stanyl esters. For the analysis of low-fat products (skimmed milk drinking yogurts), the GC separation was combined with a "fast extraction" under acidic conditions. For fat-based foods (margarines), online coupled LC-GC offered an elegant and efficient way to avoid time-consuming sample preparation steps. The robust and rapid methods allow conclusions on both, the stanol profiles and the fatty acid moieties, and thus provide a basis for the authentication of this type of functional food ingredients.

GC-MS Studies on the Regioisomeric 2,3- and 3,4-Methylenedioxyphenethylamines Related to MDEA, MDMMA, and MBDB

Three regioisomeric 3,4-methylenedioxyphenethylamines having the same molecular weight and major mass spectral fragments of equal mass have been reported as drugs of abuse in forensic studies in recent years. These compounds are 3,4-methylenedioxy-N-ethylamphetamine (MDEA), 3,4-methylenedioxy-N-N-dimethylamphetamine (MDMMA), and N-methyl-1-(3,4-methylenedioxyphenyl)-2-butanamine (MBDB). The mass spectra of the regioisomers (2,3-methylenedioxyphenethylamines) are essentially equal to the three compounds reported as drugs of abuse. This paper reports the synthesis, mass spectral characterization, and chromatographic analysis of these six regioisomeric amines. The six regioisomeric methylenedioxyphenethylamines are synthesized from commercially available starting materials. The electron impact mass spectra of these regioisomers show some variation in the relative intensity of the major ions with only a couple of minor ions that may indicate side chain specific fragments. Differentiation by mass spectrometry is only possible after the formation of the perfluoroacyl derivatives, pentafluoropropionylamides (PFPA) and heptafluorobutrylamides (HFBA). Gas chromatographic separation on non-polar stationary phases (Rtx-1 and Rtx-5) is not successful at resolving the three 3,4-methylenedioxyphenethylamines from the three 2,3-methylenedioxyphenethylamines as the underivatized amines. The six underivatized amines are resolved on the more polar trifluoropropylmethyl polysiloxane Rtx-200 stationary phase as well as a permethylated beta-cyclodextran Rtx-bDEX stationary phase. Gas chromatographic separation is successful at resolving the four PFPA and the four HFBA derivatives on the Rtx-200 stationary phase as well as the permethylated beta-cyclodextran stationary phase. The 2,3-methylenedioxyphenethylamine derivatives (compounds 4 and 6) eluted before the 3,4-methylenedioxyphenethylamine derivatives (compounds 1 and 3) as both the PFPA and HFBA derivatives.

Stop-Flow Programmable Selectivity with a Dual-Column Ensemble of Microfabricated Etched Silicon Columns and Air as Carrier Gas

A series-coupled ensemble of microfabricated GC columns made by dry reactive ion etching of silicon substrates is evaluated for use with pneumatic selectivity enhancement techniques for targeted pairs of volatile organic compounds. Each column is 3.0 m long with a 150 miceom wide by 240 microm deep cross section. Dynamic coating was used to prepare a nonpolar column with a dimethyl polysiloxane stationary phase and a moderately polar column with a trifluoropropylmethyl polysiloxane stationary phase. Each column generates 5000-6000 theoretical plates. The columns are operated in series with the nonpolar column connected to a split inlet, the polar column connected to a flame ionization detector, and a valve connected between the column junction point and the inlet to the first column. When the valve is closed, the effluent from the first column passes directly into the second column. When the valve is open, both ends of the first column are at the inlet pressure, and flow stops in this column while increased flow is obtained in the second column. For analyte pairs that are separated by the first column but coelute from the column ensemble, the valve is opened for a few seconds after the first component of the pair has passed into the second column but the second component is still in the first column. The result is enhanced separation of the pair in the ensemble chromatogram. Relatively thick cross-linked stationary-phase films are used to increase retention for volatile compounds. The combination of air carrier gas and stationary-phase film thickness in the range 1-2 microm requires the use of relatively low average carrier gas velocities (typically less than 10 cm/s) for adequate resolving power of the column ensemble. Selectivity enhancement under isothermal conditions for a 14-component mixture of volatile organic compounds is demonstrated where neither of the columns alone nor the column ensemble without selectivity enhancement could obtain a complete separation.

Design, fabrication, and evaluation of microfabricated columns for gas chromatography.

The design, fabrication, and performance of gas chromatography columns etched in silicon substrates are described. Deep reactive-ion etching formed the 3-m-long, 150-microm-wide, 240-microm-deep rectangular cross section channels. A glass cover plate was anodically bonded to the remaining surface of the substrate forming the gastight channel. For some of the columns, the silicon channels were oxidized before the channels were sealed with the glass plates. Fused-silica capillary connecting tubes were sealed into ports on the edge of the 3.2-cm x 3.2-cm substrate chips. Dynamic coating was used to deposit a film of nonpolar dimethyl polysiloxane or moderately polar trifluoropropylmethyl polysiloxane stationary phase. The columns were evaluated in a conventional benchtop GC instrument with split injection and flame ionization detection. Column efficiency was evaluated by the use of plots of height equivalent to a theoretical plate versus average carrier gas velocity using both hydrogen and air as carrier gases. The number of theoretical plates measured at the average carrier gas velocity giving the minimum plate height ranged from 4600 to 8200 plates for the dimethyl polysiloxane columns and from 3500 to 5500 plates for the trifluoropropylmethyl polysiloxane columns. Minimum plate height was significantly smaller with air as carrier gas. For the nonpolar phase, the nonoxidized surface gave approximately 1500 plates more than the oxidized surface for both carrier gases. For the polar phase, the oxidized surface gave approximately 200 plates more than the nonoxidized surface. Isothermal chromatograms of a 20-component multifunctional mixture and temperature-programmed chromatograms of a normal alkane mixture are presented.

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.

Programmable selectivity for GC with series-coupled columns using pulsed heating of the second column.

A series-coupled ensemble of a nonpolar dimethyl polysiloxane column and a polar trifluoropropylmethyl polysiloxane column with independent at-column heating is used to obtain pulsed heating of the second column. For mixture component bands that are separated by the first column but coelute from the column ensemble, a temperature pulse is initiated after the first of the two components has crossed the column junction point and is in the second column, while the other component is still in the first column. This accelerates the band for the first component. If the second column cools sufficiently prior to the second component band crossing the junction, the second band experiences less acceleration, and increased separation is observed for the corresponding peaks in the ensemble chromatogram. High-speed at-column heating is obtained by wrapping the fused-silica capillary column with resistance heater wire and sensor wire. Rapid heating for a temperature pulse is obtained with a short-duration linear heating ramp of 1000 degrees C/min. During a pulse, the second-column temperature increases by 20-100 degrees C in a few seconds. Using a cold gas environment, cooling to a quiescent temperature of 30 degrees C can be obtained in approximately 25 s. The effects of temperature pulse initiation time and amplitude on ensemble peak separation and resolution are described. A series of appropriately timed temperature pulses is used to separate three coeluting pairs of components in a 13-component mixture.

GC analysis of human breath with a series-coupled column ensemble and a multibed sorption trap.

The combination of a tandem column ensemble and an on-line microsorption trap is used for the analysis of organic compounds in human breath samples. The four-bed sorption trap uses a series of discreet sorption beds containing three grades of graphitized carbon and a carbon molecular sieve to quantitatively remove most organic compounds from 0.8-L breath samples. The trap is then heated to 300 degrees C in approximately 1.5 s and maintained at this temperature for 10 s. The resulting vapor plug width is in the range 0.7-1.3 s for the compounds found in the breath samples. The separation is performed with a 15-m-long, 0.25-mm-i.d. capillary using a 0.5-microm-thick film of nonpolar dimethyl polysiloxane coupled in series to a polar column, either trifluoropropylmethyl polysiloxane or poly(ethylene glycol). Both column combinations are successful in separating the early-eluting compounds acetone, isoprene, pentane, methyl alcohol, and ethyl alcohol, which are all common in breath samples. The poly(ethylene glycol) combination gave better separation but showed relatively fast deterioration for repeated analysis of wet samples. Breath samples were obtained under different conditions (smoker, nonsmoker, gum chewer), and 25 compounds were identified in the various samples. Many additional peaks are observed but not identified. Analytical curves (log-log) of peak area versus sample volume for test compounds are linear in the range 80-800 cm3. Detection limits (3sigma) for several volatile compounds in 800-cm3 samples are in the 1-5 ppb range.