Sensitive analysis of alkyl alcohols as decomposition products of alkyl nitrites in human whole blood and urine by headspace capillary GC with cryogenic oven trapping

The abuse of alkyl nitrites is becoming a serious social problem worldwide. In this report, a simple and sensitive method is presented for the determination of n-butyl alcohol, isobutyl alcohol, and isoamyl alcohol as decomposition products of alkyl nitrites in human whole blood and urine samples using capillary gas chromatography (GC) with cryogenic oven trapping. After heating a whole blood or urine sample containing each alkyl alcohol and t-butyl alcohol [the internal standard (IS)] in a 7-mL vial at 55 degrees C for 15 min, 5 mL of the headspace vapor is drawn into a gas-tight syringe and injected into a GC inlet port. The vapor is introduced into an Rtx-BAC2 medium-bore capillary column in the splitless mode at 0 degrees C oven temperature in order to trap the entire analytes, and then the oven temperature is programmed up to 240 degrees C for the GC measurements by flame ionization detection. These conditions give sharp peaks for each compound and the IS and low background noise for whole blood or urine samples. The detection limits of the analytes are 10 ng/mL for whole blood and 5 ng/mL for urine. Linearity and precision are also tested to confirm the reliability of this method. Isobutyl alcohol and methemoglobin could be determined from the whole blood samples of three male volunteers who had sniffed isobutyl nitrite.     

Sensitive determination of n-hexane and cyclohexane in human body fluids by capillary gas chromatography with cryogenic oven trapping

A sensitive method was developed for determination of n-hexane and cyclohexane in human body fluids by headspace capillary gas chromatography (GC) with cryogenic oven trapping. Whole blood and urine samples containing n-hexane and cyclohexane were heated in a 7.5 mL vial at 70 degrees C for 15 min, and 5 mL of the headspace vapor was drawn into a glass syringe. All vapor was introduced through an injection port of a GC instrument in the splitless mode into an Rtx-Volatiles middle-bore capillary column at an oven temperature of -40 degrees C for trapping volatile compounds. The oven temperature was programmed to 180 degrees C for GC with flame ionization detection. These conditions gave sharp peaks for both n-hexane and cyclohexane, a good separation of each peak, and low background impurities for whole blood and urine. The extraction efficiencies of n-hexane and cyclohexane were 13.2-30.3% for whole blood and 12.7-20.7% for urine. The coefficients of within-day variation in terms of extraction efficiency of both compounds were 5.0-9.5% for whole blood and 3.8-10.8% for urine; those of day-to-day variation for the compounds were not greater than 16.6%. The regression equations for n-hexane and cyclohexane showed good linearity in the range of 5-500 ng/0.5 mL for whole blood and urine. The detection limits (signal-to-noise ratio = 3) for both compounds were 1.2 and 0.5 ng/0.5 mL for whole blood and urine, respectively. The data on n-hexane or cyclohexane in rat blood after inhalation of each compound are also presented.     

Simple Analysis of Amphetamines in Human Whole Blood and Urine by Headspace Capillary Gas Chromatography with Large Volume Injection

Summary A very simple method for the analysis of methamphetamine and amphetamine in human whole blood and urine by headspace gas chromatography (GC) has been presented. It neither needs solid-phase microextraction nor cryogenic trapping devices, but only a conventional capillary GC instrument with flame ionization detection (FID). The two special points to be mentioned in this method are the in-matrix derivatization of amphetamines for vaporization and the capability of injection of as large as 5 mL of the headspace vapor into a GC instrument in the splitless mode for sensitive detection. After heating a whole blood or urine sample containing amphetamines, -methylbenzylamine (internal standard, IS) and heptafluoro-n-butyryl chloride under alkaline conditions in a 7.0-mL vial at 90 °C for 20 min, 5 mL of the headspace vapor was drawn with a glass syringe and injected into the gas chromatograph. During injection the column was at 40 °C to trap the analytes, and then the oven temperature was programmed up to 320 °C. Sharp peaks were obtained for each analyte and IS, and only a relatively small number of background impurity peaks for the whole blood and urine samples. The detection limits for each amphetamine were estimated to be 0.1 g mL^–1 for whole blood and 0.03 g mL^–1 for urine. Precision and linearity were also tested to confirm the reliability. Methamphetamine and amphetamine could be determined from whole blood and urine obtained at autopsy in three methamphetamine poisoning cases. The identity of each peak appearing in the gas chromatograms was confirmed by GC/mass spectrometry.     

Determination of curcumol in rat plasma by capillary gas chromatography with a hydrogen flame ionization detector

A simple and sensitive capillary gas chromatography with a hydrogen flame ionization detector (GC‐FID) method was developed for the determination of curcumol in rat plasma. From a variety of compounds and solvents tested, buagafuran was selected as the internal standard (IS) and acetonitrile was found to be the best protein precipitation agent and solvent for extracting curcumol from plasma and tissues samples. (Buagafuran was used as an internal standard. Curcumol was extracted by a protein precipitation with acetonitrile.) The samples were determined by GC on an HP‐5 column (30.0 m × 0.32 mm, 0.25 μm); inlet volume 2 μL; split ratio 10 : 1; inlet temperature 250°C; oven temperature 180°C; flow 1.0 mL/·min; FID 250°C; carrier gas N₂. The resulting retention times of curcumol and IS were 6.0 and 9.5 min. There was good linearity over the range 0.133–133.3 μg/mL (r = 0.9999) in plasma samples. The method recoveries were 97.7–102.0% in plasma, and the intra‐ and inter‐day variances (RSD) were less than 15% in all cases. The GC method was applied to develop a pharmacokinetics study in which experimental rats received a single administration of curcumol by intravenous injection. Copyright © 2009 John Wiley & Sons, Ltd.     

Liquid gas techniques for GC trace analysis

Liquid gases (LG), i.e. low boiling compounds with vapor pressures below 5 bar at room temperature, are introduced as solvents for trace analyses. A system for preparin, diluting and handling LG solutions safely and conveniently in 5 to 500 μl amounts was developed as well as a syringe for direct injection of μl-LG samples into capillary GC. Even technical grade LG are of high purity. GC/FID of LG solutions (starting at ?60°C) allows the separation of volatile traces from the solvent peak: e.g., dichloromethane can be measured in the picogram range.     

Quantitative determination of paraffin oil in blood by capillary gas chromatography

A capillary gas chromatographic method is described for the quantitative determination of liquid paraffin in blood. Paraffin is extracted from blood into n-heptane. After solvent evaporation and dissolution of the residue in 100–200 μl n-heptane one μl is injected into a gas chromatograph fitted with a fused silica capillary column (Permabond® OV-1-CB-0.1, 10 m × 0.32 mm i.d.) and flame ionization detector. Analysis is performed by using an oven program [50°C (3 min)?285°C (5 min), rise 10%min]. The sensitivity (1.5 ng hexadecane) and the reproducibility prove the applicability of the method for the determination of liquid paraffin in blood and for the study of the stability of the liquid paraffin hollow fiber membranes used in an extracorporeal liver support system.     

Fast Temperature Programming in Gas Chromatography using Resistive Heating

The features of a resistive-heated capillary column for fast temperature-programmed gas chromatography (GC) have been evaluated. Experiments were carried out using a commercial available EZ Flash GC, an assembly which can be used to upgrade existing gas chromatographs. The capillary column is placed inside a metal tube which can be heated, and cooled, much more rapidly than any conventional GC oven. The EZ Flash assembly can generate temperature ramps up to 1200°/min and can be cooled down from 300 to 50°C in 30 s. Samples were injected via a conventional split/splitless injector and transferred to the GC column. The combination of a short column (5 m×0.25 mm i. d.), a high gas flow rate (up to 10 mL/min), and fast temperature programmes typically decreased analysis times from 30 min to about 2.5 min. Both the split and splitless injection mode could be used. With n-alkanes as test analytes, the standard deviations of the retention times with respect to the peak width were less than 15% (n = 7). First results on RSDs of peak areas of less than 3% for all but one n-alkane indicate that the technique can also be used for quantification. The combined use of a short GC column and fast temperature gradients does cause some loss of separation efficiency, but the approach is ideally suited for fast screening as illustrated for polycyclic aromatic hydrocarbons, organophosphorus pesticides, and triazine herbicides as test compounds. Total analysis times – which included injection, separation, and equilibration to initial conditions – were typically less than 3 min.     

A new high temperature gas chromatograph incorporating a temperature programmable direct injector

A high temperature gas chromatograph has been developed which is capable of operating at column oven temperatures up to 500°C. In addition, the detector can operate at temperatures up to 500°C, and the injector up to 450°C. The injector on this instrument is a temperature programmable direct injector, designed specifically to introduce labile or high molecular weight samples into the GC without molecular weight discrimination. The design of this GC and injector will be described, and high temperature applications will be discussed.     

Gas chromatography with ballistic heating and ultrafast cooling of column

An overview of the existing methods for minimization of the analysis time in gas chromatography (GC) is presented and a new system for fast temperature programming and very fast cooling down is evaluated. In this study, a system of coaxial tubes, a heating/cooling module (HC-M), was developed and studied with a capillary column placed inside the HC-M. The module itself was heated by a GC oven and cooled down by an external cooling medium. The HC-M was heated at rates of up to 330 °C min⁻¹ and cooled at the rate of 6000 °C min⁻¹. The GC system was prepared for the next run within a few seconds. The HC-M permits good separation reproducibility, comparable with that of a conventional GC, expressed in terms of relative retention times and peak areas of analytes reproducibilities. The HC-M can be used within any commercial gas chromatograph.     

Co-solvent effects for preventing broadening or loss of early eluted peaks when using concurrent solvent evaporation in capillary GC. Part 2: n-Heptane in n-pentane as an example

Co-solvent effects are applied to allow use of concurrent solvent evaporation for applications requiring analysis of compounds eluted less than some 50° above the column temperature during sample introduction, i.e. at oven temperatures below some 100–120°C. Required conditions such as GC even temperature, concentration of the co-solvent and length of the uncoated pre-column (retention gap) are studied theoretically as well as experimentally for the case of n-heptane as co-solvent in n-pentane.     

Fast GC with a Small Volume Column Oven and Low Power Heater

A new apparatus for fast gas chromatography separations is described. It consists of a small volume oven containing a coiled fused silica capillary column that is heated by a flow of hot air. The oven can be heated at rates of 10 °C s^?1 with a 300 W heater. Benchmark studies at various temperature programming rates are described. Retention time relative standard deviations increase with increasing heating rate, but are at most about 1% when an 8 °C s^?1 heating rate is employed. The small size of the column oven makes it possible for it to be attached to a commercial GC instrument through an opening provided for installation of a second injector.     

Conformational behaviour and vibrational spectra of 3-methyl 2-butanethiol

The Raman spectra of 3-methyl 2-butanethiol in the temperature range-120° C to + 60° C have been recorded together with its liquid phase infrared spectrum at room temperature. The spectral analysis shows that the molecule of the compound exists in the liquid state, in three different rotameric configurationsA, B andC of which the formA is the stablest. Besides, a tentative assignment of the observed vibrational frequencies arising from the rotameric forms has been presented.     

Simultaneous Determination of Four Major Iridoid Glycosides in Scrophularia ningpoensis by CE

A simple, accurate and reproducible capillary electrophoresis method with UV detection has been developed for the simultaneous determination of four iridoid glycosides, 6-O-methyl-catalpol, aucubin, harpagide, and harpagoside, in Scrophularia ningpoensis (Xuan-shen). The running buffer was 100 mM borate (pH 9.3) containing 20% methanol. Applied voltage was 20 kV and temperature was 25 °C. Diphylloside A was used as an internal standard (IS) and detection was at 200 nm. The effects on separation of buffer pH, buffer concentration, and organic modifiers were investigated. The extracts of S. ningpoensis were well separated within 45 min.

     

Quantitative preparative gas chromatography of caffeine with nuclear magnetic resonance spectroscopy

Caffeine test solute was employed in combination with an internal standard (IS), 1,4‐dimethoxybenzene, in preparative‐gas chromatography (prep‐GC), with nuclear magnetic resonance (NMR) experiments. The IS served to: (i) quantify the trapping efficiency of an external trapping assembly, consisting of a capillary column cryotrap at the end of the analytical column; (ii) quantify the solute response in different NMR samples; and (iii) permit correlation of expected level of response of a compound in the NMR experiment, based on relative responses of the IS and solute in the GC result. The recovery rate of caffeine from multiple injections of sample (1×, 2×, 5× and 10×) was 69.6 ± 1.3%, which correlated well (R² = 0.999) with the number of injections of compound. The ¹H‐NMR spectrum was sufficient to enable structural characterisation of the reference caffeine compound, and was achieved with recovery of amounts of ≤10 μg from a single aliquot. Less than 400 μg of collected caffeine (40 replicate injections) was sufficient for structural characterisation by ¹³C‐NMR spectral analysis. The method allows development of approaches to separate unknown compounds in complex samples, and to separately use MS and NMR for their characterisation.     

Capillary electrophoresis separation of heterocyclic nitrosoamino acid-conformers at sub-ambient temperatures

The separation of a selected group of naturally occurring, heterocyclic nitrosoamino acids was achieved by capillary zone electrophoresis and the resolution of the syn and anti conformers improved as the temperature was lowered to 5 °C. The double peaks observed for each nitrosoamino acid are probably caused by the slow kinetics of conformational isomerism. The experimental setup consisted of a P/ACE 5510 electrophoresis system, a 57 cm polyacrylamidecoated capillary, and a 10 mM phosphate buffer, pH 7.2, containing 2 mM of 3-(N-N-dimethylmyristylammonio)propanesulfonate (DMMAPS) and 0.1% Tween 20. Our study shows that (a) the lower the temperature, the greater the resolution and the longer the migration times; and (b) different nitrosoamino acid conformers were resolved at different temperatures because of differences in the rate of isomerization. For example, the conformers of N-nitrosothiazolidine-4-carboxylic acid were partially resolved at 30 °C while those of N-nitrosoproline were well resolved at the same temperature.     

Fast Capillary Gas Chromatography: Comparison of Different Approaches

Savings in analysis time in capillary GC have always been an important issue for chromatographers since the introduction of capillary columns by Golay in 1958. In laboratories where gas chromatographic techniques are routinely applied as an analytical technique, every reduction of analysis time, without significant loss of resolution, can be translated into a higher sample throughput and hence reduce the laboratory operating costs. In this contribution, three different approaches for obtaining fast GC separations are investigated. First, a narrow-bore column is used under conventional GC operating conditions. Secondly, the same narrow-bore column is used under typical fast GC conditions. Here, a high oven temperature programming rate is used. The third approach uses a recent new development in GC instrumentation: Flash-2D-GC. Here the column is placed inside a metal tube, which is resistively heated. With this system, a temperature programming rate of 100°/s is possible. The results obtained with each of these three approaches are compared with results obtained on a column with conventional dimensions. This comparison takes retention times as well as plate numbers and resolution into consideration.     

A new type of two-dimensional packed+capillary column GC system. III. Instrumentation

Summary The constractional details of precolumns, its oven and connector have been given with two types of multiflow control modules. Two types of phases made in China, a silanized pellicular beads and a non silanized pellicular silica beads, with an optimum particle size of 20μm to 30μm were packed in the precolumn 20mm in length with the column efficiency of 4620 plates/meter at column temperature of 49°C. A 25m×0.22mm i.d. capillary column coated with bonded methylsilicone phase from Chrompack connected with the precolumn (250°C) has an efficiency of 5376 plates/meter for n-octane. But it decreased to 3149 plates/meter by decreasing the precolumn temperature to 130°C.     

Volatile phase profiling of mainstream smoke by glass capillary gas-chromatographic techniques

A heated injection system for a microprocessor-controlled GC has been developed for the (GC)² analysis of the volatile phase of whole smoke of a cigarette. Effects of injection port temperature and the presence of a Cambridge filter pad are demonstrated. Chromatograms are shown for smoke samples with and without a Cambridge Filter with the sample valve oven at 25°, 165° and 205°C. The use of a flame ionization and a nitrogen-phosphorous detector is illustrated.     

Influence of Gas Chromatographic Parameters on Determination of Decabromodiphenyl Ether

In this paper, we present a study on the influence of chromatographic parameters on determination of decabromodiphenyl ether in an attempt to arrive at optimum conditions that enhance its detection in environmental samples. Gas chromatography?Celectron capture detector (GC?CECD) equipped with digital pressure and gas flow control, ZB-5 capillary column of 15 and 30 m length (0.25 mm id, 0.25 ??m d _f) are used. 1 ??L of 20 ng ??L^?1 commercial decabromodiphenyl ether mixture dissolved in toluene is injected into the column in splitless mode and each parameter varied. Injection temperature of 290 °C, initial and final oven temperatures of 90 °C and 300?C310 °C, respectively, 1.0 min splitless time and 2.5 mL min^?1 flow rate found to be optimum on 15 m column. Under optimum condition, entrance of BDE209 into the column is improved; retention time reduced by a factor of three and high repeatability with almost no degradation observed. Finally, the developed method is validated using standard reference material and applied to indoor dust samples. The average concentrations of decabromodiphenyl ether found from dust analysis in ng g^?1 are 118 ± 6.6, 103 ± 11 and 26 ± 1.6 in hotel, office and computer room, respectively.     

Detection of ethanol in human body fluids by headspace solid-phase micro extraction (SPME)/capillary gas chromatography

Summary Ethanol has been found extractable from human whole blood and urine samples by headspace solid-phase micro extraction (SPME) with a Carbowax/divinylbenzene-coated fiber. After heating a vial containing the body fluid sample with ethanol, and isobutanol as internal standard (IS) at 70°C in the presence of (NH₄)₂SO₄, a Carbowax/divinylbenzene-coated SPME fiber was exposed in the headspace of the vial to allow adsorption of the compounds. The fiber needle was then injected into a middle-bore capillary gas chromatography (GC) port. The headspace SPME-GC gave intense peaks for both compounds; a small amount of background noises appeared, but did not interfere with the detection of the compounds. Recoveries of ethanol and IS were 0.049 and 0.026% for whole blood, respectively, and 0.054 and 0.085% for urine, respectively. The calibration curves for ethanol showed excellent linearity in the range of 80–5000 mg L^–1 for whole blood and 40–5000 mg L^–1 for urine; the detection limits for both samples were 20 and 10 mg L^–1, respectively. The data on actual determination of ethanol after the drinking of beer are also presented for two subjects.