Nitrogen-selective Detection Research Articles

Gas chromatographic determination of acetonitrile in air using a thermionic detector

A gas chromatographic procedure for the determination of acetonitrile (CH{sub 3}CN) in air is described, based on a thermionic nitrogen-selective detector. The lower limit of detection is 15 pg of CH{sub 3}CN for a blank value of 5.0 {plus minus} 3.2 pg. The method involves the collection of air in 2-dm{sup 3} vessels (glass or stainless steel) and preconcentration of acetonitrile by cryogenic trapping. Preconcentration by sorption on modified Chromosorb 102 was found unsuitable due to undesirable memory effects. Air samples stored in containers for periods longer than 3 days generally show a rise in CH{sub 3}CN concentration, so that air samples must be processed within a few days. precautions against contamination in the gas handling system or by intrusion of laboratory air also are important. Calibration tests based on gaseous and liquid dilution series lead to comparable accuracies of about 4% in each case but a better reproducibility for liquid calibration mixtures.

Capillary Gas Chromatographic Method for Determination of Benzylpenicillin and Other Beta-Lactam Antibiotics in Milk

A capillary gas chromatographic method is described for determining residues of beta-lactam antibiotic residues in milk, with specificity for benzylpenicillin (penicillin G), phenoxymethylpenicillin, methicillin, oxacillin, cloxacillin, dicloxacillin, and nafcillin. Residues are extracted from milk with acetonitrile. Samples are cleaned up by partitioning between aqueous and organic phases at different pH values. The penicillin residues are methylated with diazomethane to render them amenable to determination by gas chromatography on a methyl silicone fused silica column. Samples are introduced by split/splitless injection using a programmed temperature vaporization injector and are detected by nitrogen-selective thermionic detection. Internal standardization is used for quantitation. The limits of detection for all penicillins are well below 1 microgram/kg. Recoveries of spiked samples at 3 and 10 micrograms/kg are in the range of 42-85% (coefficients of variation 2-5%) and 41-92% (coefficients of variation 3-7%), respectively.

Simultaneous detection and quantitation of O6‐monoacetylmorphine, morphine and codeine in urine by gas chromatography with nitrogen specific and/or flame ionization detection

It is of importance to differentiate heroin intake from the absorption of opiate-containing pharmaceuticals or opiates from other sources. A method for the routine determination of O6-monoacetylmorphine (6-MAM), the specific metabolite of heroin in human urine, by gas chromatography and classical detectors without having recourse to gas chromatography/mass spectrometry-selected ion mode (GC/MS-SIM) is described. With dual detection by nitrogen selective and flame ionization detectors, the limits of detection for 6-MAM were determined to be 2 ng/mL and 4 ng/mL urine for a 10 mL sample. When applied to urines preliminarily screened for opiates, the results appeared consistent in comparison with those obtained by GC/MS-SIM. The method was also developed for the simultaneous quantitative analysis of morphine and codeine. The linearity was tested up to 600 ng/mL for the three compounds of interest 6-MAM, morphine and codeine and their absolute recoveries were 76%, 78%, 75% respectively.

Determination of hydrazine in hydralazine by capillary gas chromatography with nitrogen-selective detection after benzaldehyde derivatization

A method for the determination of hydralazine substance is described. Hydrazine is derivatized in aqueous media with benzaldehyde to benzalazine. After extraction to an organic phase containing a homologue as marker, the sample is subjected to capillary column gas chromatography with nitrogen-selective detection. A prolonged reaction with 0.1 M benzaldehyde of 20 min or more led to an increased level of benzalazine when hydralazine was analysed. An increase was also observed if the aqueous hydralazine sample had been allowed to stand for some time before and analysis. The final method involved the use of a 5-min reaction time, fresh solutions and the standard addition principle. The levels of hydrazine found in hydralazine hydrochloride were below 1 ppm (as bases, 1 ng/mg).

Determination of low-molecular-weight carboxylic acids in aqueous samples by gas chromatography and nitrogen-selective detection of 2-nitrophenylhydrazides

A gas chromatographic method was developed for the determination of low-molecular-weight carboxylic acids in aqueous samples based on a derivatization procedure compatible with aqueous solutions. The technique uses nitrogen-selective detection with a thermionic-specific detector after derivatization of carboxylic acids as 2- nitrophenylhydrazides. The hydrazides were extracted with ethyl acetate prior to injection into the gas chromatograph. The derivatives appear to be stable in ethyl acetate at 0–5° C for long periods and, therefore, can be stored for analysis at a later date. The detection limits of different short-chain acids are in the range 0.8–1.4 pmol per injected sample. The relative standard deviation is less than 10% at the 1 μM level. Examples of the use of the method are given for the determination of carboxylic acids in anoxic marine sediment pore waters, coastal sea water and Black Sea water samples.

Determination of a cytostatic agent, bendamustine, in plasma using capillary gas chromatography with nitrogen-selective detection

Determination of a cytostatic agent, bendamustine, in plasma using capillary gas chromatography with nitrogen-selective detection

Gas Chromatographic Determination of Nicotine in Environmental Tobacco Smoke: Collaborative Study

A gas chromatographic method for determination of vapor phase nicotine in environmental tobacco smoke (ETS) was collaboratively studied by 6 laboratories. Nicotine is desorbed from XAD-4 sample tubes with ethyl acetate containing triethylamine and determined by gas chromatography with nitrogen-selective detection. Each collaborator received blind duplicate samples at each of 6 nicotine concentrations. Three concentrations were generated by spiking XAD-4 tubes with known amounts of nicotine; the remaining 3 concentrations were ETS samples obtained in a carefully controlled environmental chamber containing sidestream and exhaled mainstream smoke from 1R4F Kentucky reference cigarettes. Repeatability and reproducibility relative standard deviations ranged from 4.4 to 11.1% and from 7.0 to 11.1%, respectively, for nicotine concentrations evaluated (up to 6 micrograms/cu m). The method has been adopted official first action.

Simultaneous identification and quantification of several opiates and derivatives by capillary gas chromatography and nitrogen selective detection

A capillary column gas chromatographic method is described for the simultaneous determination of morphine, codeine, heroin, 3- and 6-monoacetylmorphine, nalorphine, naloxone, ethylmorphine, and naltrexone. The drugs were extracted from 2 ml plasma, urine, or other biological samples, including tissue under alkaline conditions in chloroform-isopropanol-n-heptane (50:17:33, v/v), with levallorphan as an internal standard. The drugs were extracted into acid and then reextracted into chloroform after the acid had been alkalinized. After derivatization with trifluoroacetic anhydride, an aliquot was injected into a 25m capillary column equipped with a nitrogen phosphorus detector. The lower limits of detectability, extraction recovery, and the within-run and day-to-day precision of results were determined for each drug. Our results indicate that the procedure is suitable for use in overdose screening and therapeutic drug monitoring.

Nitrogen compounds in light cycle oils: identification and consequences of ageing

Basic and non-basic nitrogen compounds were selectively extracted from different light cycle oils (LCOs). The isolated fractions were analysed by nitrogen selective detector gas chromatography and by gas chromatography/mass spectrometry. The basic compounds are aniline and alkyl derivatives from C 1- to C 4- anilines. The non-basic compounds are indole, C 1- to C 4- alkylindoles, carbazole and C 1- to C 3-alkylcarbazoles. In the four different LCOs that we have investigated, the distributions of the nitrogen compounds are very similar and no other nitrogen compounds were found. It has been shown that after ageing, the distribution of nitrogen compounds is different: the evolution of indoles is more important than the evolution of anilines and carbazoles.

Assay of fluconazole by megabore capillary gas-liquid chromatography with nitrogen-selective detection

A megabore column gas-liquid chromatographic method which uses nitrogen-phosphorus detection was developed for the analysis of fluconazole in plasma, serum, cerebrospinal fluid, or urine. The assay was linear from 0.2 to 200 micrograms/ml and had an average coefficient of variation of 7%. The suitability of the assay for pharmacokinetic studies was demonstrated.

Simultaneous Gas Chromatographic Determination of Carbofuran, Metalaxyl, and Simazine in Soils

A method for extraction, cleanup, and simultaneous gas chromatographic detection of carbofuran, metalaxyl, and simazine in soils has been developed. Pesticide residues were extracted from soil with acetone containing 10% 0.2M HCl-KCl buffer (pH 2.0), cleaned up with methylene chloride-carbonate buffer (pH 10.7) solvent partitioning and solid-phase extraction on disposable silica gel columns, and quantitated with gas chromatography using a Supelcowax 10 megabore capillary column and a nitrogen-selective detector. Method limits of detection were 0.02 microgram/g for the 3 pesticides in surface soils (0-30 cm depths) and 0.02, 0.02, and 0.005 microgram/g in soils below 30 cm (subsoils) for carbofuran, metalaxyl, and simazine, respectively. Recoveries for carbofuran, metalaxyl, and simazine were 92.6 +/- 5.5, 93.6 +/- 5.0, and 88.4 +/- 6.7%, respectively, when soil samples were spiked with pesticide concentrations ranging from 0.02 to 2.0 micrograms/g.

Simultaneous identification and quantification of several opiates and derivatives by capillary gas chromatography and nitrogen selective detection.

A capillary column gas chromatographic method is described for the simultaneous determination of morphine, codeine, heroin, 3- and 6-monoacetylmorphine, nalorphine, naloxone, ethylmorphine, and naltrexone. The drugs were extracted from 2 ml plasma, urine, or other biological samples, including tissue under alkaline conditions in chloroform-isopropanol-n-heptane (50:17:33, v/v), with levallorphan as an internal standard. The drugs were extracted into acid and then reextracted into chloroform after the acid had been alkalinized. After derivatization with trifluoroacetic anhydride, an aliquot was injected into a 25m capillary column equipped with a nitrogen phosphorus detector. The lower limits of detectability, extraction recovery, and the within-run and day-to-day precision of results were determined for each drug. Our results indicate that the procedure is suitable for use in overdose screening and therapeutic drug monitoring.

Determination of dabequin in biological fluids by gas chromatography with a nitrogen-selective detector.

Quantitative determination of [benzo(6)-2-diethylaminoethylaminoquinoline, DQ], an antimalarial in whole blood and urine samples from patients with plasmodium vivax. Three methods of extraction are proposed

Determination of the partial benzodiazepine receptor agonist Ro 16-6028 in plasma by capillary gas chromatography with nitrogen-selective detection after conversion into the ethyl ester derivative

A highly sensitive capillary gas chromatographic method was developed to determine plasma levels of a novel partial benzodiazepine receptor agonist in man following the very low therapeutic doses required for anxiolysis. The compound was isolated from plasma by liquid-liquid extraction at basic pH, converted into the ethyl ester analogue by a two-step procedure, separated from plasma constituents by capillary gas chromatography and quantified by means of nitrogen-selective detection. Because of the thermolabile tert.-butyl ester function, the agonist could not be gas chromatographed without degradation. Formation of the far more stable ethyl ester analogue was achieved by treatment with hydrogen chloride in ethanol, followed by an ethylation step with diazoethane. The high sensitivity of the new method (about 100 pg/ml, using 1-ml plasma specimens) allowed the monitoring of plasma levels of the agonist for up to 8 h (about three elimination half-lives) after a single 0.1-mg oral dose to human volunteers. The practicability of the procedure was demonstrated by the analysis of more than 600 plasma samples from clinical studies performed with human volunteers.

Determination of picogram levels of a novel α 2-adrenergic receptor antagonist in plasma using solid-phase extraction and capillary gas chromatography with nitrogen-selective detection

Determination of picogram levels of a novel α 2-adrenergic receptor antagonist in plasma using solid-phase extraction and capillary gas chromatography with nitrogen-selective detection

Gas chromatographic determination of gallopamil and norgallopamil in human plasma

A highly sensitive gas chromatographic assay is described for the simultaneous determination of gallopamil, a calcium channel blocking agent, and its major metabolite, norgallopamil. A multi-step extraction procedure is employed followed by on-column capillary gas chromatographic analysis using nitrogen-selective detection. Acetylation of norgallopamil is performed to enable accurate quantification of the metabolite. Linearity was achieved over the range 1–50 ng/ml for both analytes. Assay specificity, precision and accuracy were investigated.

Quantitative analysis of serum methohexital by GLC using capillary column and nitrogen-selective detection.

A gas chromatographic method for routine quantitation of methohexital in plasma samples is reported. One-step extraction in organic phase, the use of a fused silica capillary column, and nitrogen-selective detection permit simple, precise, and sensitive determination of methohexital in plasma. A linear relationship is described between peak height ratio and methohexital concentrations ranging from 0.125 to 50.0 micrograms/ml (r = 0.998). The sensitivity limit of the assay was 6 ng/ml in plasma. No interfering peak was observed with numerous other drugs. The procedure was successfully applied to the determination of pharmacokinetic parameters of methohexital after IV administration or continuous infusion in a child and an adult.

Autoinduction of Phenobarbital Elimination in the Dog

The literature provides no clear answer to the question of whether phenobarbital induces its own metabolism. To investigate this, the kinetics of phenobarbital in beagle dogs was examined using six phenobarbital doses (15, 30, 60, 100, 200, and 400 mg/d) for 3-week periods. Plasma concentrations of phenobarbital were measured by gas chromatography with a nitrogen–selective detector. The peak plasma concentrations ranged from 7.2 μg/mL with the 15-mg/d dose to 82 μg/mL with the 400-mg/d dose. A regression of phenobarbital clearance versus average plasma concentration gave an r2 value of 0.81. A 214% increase in the oral clearance of phenobarbital was obtained at the 400-mg/d dose level compared with the 15-mg/d level. The major determinant of this increased clearance was an increase in the elimination rate constant of phenobarbital from 0.18h−1 at the 15–mg/d dose to 0.36h−1 at the 400-mg/d dose. The apparent volume of distribution also tended to increase with dose. From these results it is suggested that one reason for the failure to observe autoinduction for phenobarbital in the past was the relatively low plasma concentrations attained in many experiments. In comparison, antipyrine clearance shows a much greater increase for the same phenobarbital concentrations, indicating that the subset of microsomal enzymes which affect phenobarbital are less sensitive to Phenobarbital induction than is the subset affecting antipyrine.

Determination of hydroxylamine traces in propionohydroxamic acid bulk drug and pharmaceutical preparations by capillary gas chromatography

A specific, sensitive, accurate, and precise capillary gas chromatographic assay for determining trace levels of hydroxylamine, a well-known mutagen, in propionohydroxamic acid bulk drug and oral preparations is described. The analytical procedure involves derivatization in a nonaqueous medium with cyclohexanone and use of an internal standard. The derivative is then determined by capillary GC with a cool on-column injector and a nitrogen-selective detector. Effects of different matrices on the measurement were also determined. The lower limit of quantitation was 7 ppm, and the response was linear from 10 to 260ppm. The procedure is simple and rapid enough for routine purposes.

Measurement of antidepressants using solid-phase extraction and wide-bore capillary gas chromatography with nitrogen-selective detection.

A comprehensive method is presented for the determination of nine antidepressant drugs and metabolites in serum: (1) amitriptyline, (2) nortriptyline, (3) imipramine, (4) desipramine, (5) maprotiline, (6) doxepin, (7) desmethyldoxepin, (8) protriptyline, and (9) trimipramine. Chlorimipramine is used as the internal standard. A simple solid-phase extraction procedure utilizing disposable reversed-phase C18 columns is described. Samples are analyzed by gas chromatography with nitrogen-selective detection using a wide-bore capillary column with a permanently bonded, non-polar stationary phase. The assay possesses linearity to 800 ng/mL for maprotiline and 500 ng/mL for the other antidepressants, sensitivity to at least 25 ng/mL, recovery ranging from 96 to 107%, and between-run precision reflected by CVs of 4.4 to 8.1%. Lack of interference is documented for over 27 commonly prescribed drugs. We conclude that the method reported here is ideally suited for monitoring therapeutic and toxic levels of antidepressant drugs.