Nitrogen-selective Detection Research Articles

Potential of GC-Combustion-MS as a Powerful and Versatile Nitrogen-Selective Detector in Gas Chromatography.

Here, we show the potential and applicability of the novel GC-combustion-MS approach as a nitrogen-selective GC detector. Operating requirements to achieve reproducible and compound-independent formation of volatile NO species as a selective N-signal during the combustion step are described. Specifically, high temperatures (≥1000 °C) and post-column O2 flows (0.4 mL min-1 of 0.3% O2 in He) turned out to be necessary when using a vertical oven without makeup flow (prototype #1). In contrast, the use of a horizontal oven with 1.7 mL min-1 He as an additional makeup flow (prototype #2) required milder conditions (850 °C and 0.2 mL min-1). A detection limit of 0.02 pg of N injected was achieved, which is by far the lowest ever reported for any GC detector. Equimolarity, linearity, and peak shape were also adequate. Validation of the approach was performed by the analysis of a certified reference material obtaining accurate (2% error) and precise (2% RSD) results. Robustness was tested with the analysis of two complex samples with different matrices (diesel and biomass pyrolysis oil) and N concentration levels. Total N determined after the integration of the whole chromatograms (524 ± 22 and 11,140 ± 330 μg N g-1, respectively) was in good agreement with the reference values (497 ± 10 and 11,000 ± 1200 μg N g-1, respectively). In contrast, GC-NCD results were lower for the diesel sample (394 ± 42 μg N g-1). Quantitative values for the individual and families of N species identified in the real samples by parallel GC-MS and additional GC × GC-MS analyses were also obtained using a single generic internal standard.

The determination of pyrovaleron in the urine by gas chromatography in the combination with the method of extractive chilling-out and centrifugation

The express-method for the determination of pyrovaleron in the urine based on the combination with the method of extractive freezing-out and centrifugation of the samples as the preliminary stage of the preparation of a biological object for the analysis. The identification and quantitative determination of the substance of interest were performed using gas chromatography with nitrogen-selective detection. The preparation of the samples was carried out as a single-step procedure no longer than 30 min in duration. The limit of alpha-pyrovaleron detection in the urine was estimated at 1 mcg/ml. Its concentration after extraction from the urine increased by a factor of more than nine.

Application of comprehensive two-dimensional gas chromatography with nitrogen-selective detection for the analysis of fungicide residues in vegetable samples

Comprehensive two-dimensional gas chromatography (GCxGC) with nitrogen-phosphorus detection (NPD) has been investigated for the separation and quantitation of fungicides in vegetable samples. The detector gas flows (H 2, N 2 and air) were adjusted to achieve maximum response of signal whilst minimizing peak width. The comparison of different column sets and selection of the temperature program were carried out with a mixture of nine N-containing standard fungicides, eight of which were chlorinated. The results from GCxGC-NPD and GCxGC with micro electron-capture detection (μECD) were compared. External calibrations of fungicides were performed over a concentration range from 1 to 1000 μg L −1. The peak area calibration curves generally had regression coefficients of R 2 > 0.9980, however for iprodione which was observed to undergo on-column degradation, an R 2 of 0.990 was found. The limit of detection (LOD) and limit of quantitation (LOQ) were less than about 74 and 246 ng L −1, respectively. The intra-day and inter-day RSD values were measured for solutions of concentration 0.100, 0.500 and 1.50 mg L −1. For the 0.500 mg L −1 solution, intra- and inter-day precision of peak area and peak height for most of the pesticides were about 2% and 8%, respectively. Excellent linearity was observed for these standards, from 0.001 to 25.00 mg L −1. The standard mixture peak positions were identified by using GCxGC with quadrupole mass spectrometry (qMS). To illustrate the potential and the versatility of both GCxGC-NPD and GCxGC-μECD, the method was applied to determination of fungicides in a vegetable extract. Decomposition of one fungicide standard (iprodione) during chromatography elution was readily observed in the two-dimensional (2D) GCxGC plot as a diagonal ridge response in the 2D chromatogram between the degrading compound and the decomposition product.

Identification of Ammonia in Gas Emanated from Human Skin and Its Correlation with That in Blood

Identifying and measuring the ammonia gas that emanates from human skin, which we called skin gas, has been achieved using a modified gas chromatographic system with a nitrogen-selective detector (flame-thermoionic detector: FTD). The skin gas is collected with a home-made sampling probe or bag, which is used to cover the skin surface of a subject's wrist, or a finger, for 5 min. It was proved that ammonia was present in skin gas for healthy persons and patients with hepatic disease. The average amounts of ammonia were 1.7 +/- 0.4 and 2.7 +/- 0.8 ng/cm2; furthermore, there was a significant difference between them (p < 0.05). In addition, the ammonia levels present in skin gas were correlated with that in blood (r = 0.64, p < 0.05).

Simultaneous determination of nicotine and eight nicotine metabolites in urine of smokers using liquid chromatography–tandem mass spectrometry

A method based on liquid chromatography tandem mass spectrometry (LC–MSMS) applying atmospheric pressure chemical ionisation (APCI) in the positive ion mode was developed for the direct determination of nicotine, cotinine, trans-3′-hydroxycotinine, their corresponding glucuronide conjugates as well as cotinine- N-oxide, norcotinine, and nicotine- N′-oxide in the urine of smokers. The assay involves filtration of crude urine, fast liquid chromatography on a reversed-phase column and mass-specific detection using MSMS transitions. Deuterium-labeled nicotine, cotinine, and trans-3′-hydroxycotinine were used as internal standards. Glucuronides used as reference material were either chemically (cotinine- N-glucuronide) or enzymatically synthesized (nicotine- N-glucuronide and trans-3′-hydroxycotinine- O-glucuronide). Precision for the major nicotine analytes at levels observable in urine of smokers was better than 10%. Accuracy expressed in recovery rates in urine matrix for nicotine, cotinine, trans-3′-hydroxycotinine, and cotinine- N-glucuronide ranged from 87 to 113%. Quantitative results for the three glucuronides in urine samples of 15 smokers were compared to an indirect method in which the aglycons were determined with gas chromatography and nitrogen-selective detection (GC–NPD) before and after enzymatic splitting of the conjugates. Good agreement was found for cotinine- N-glucuronide (coefficient of variation, CV: 9%) and trans-3′-hydroxycotinine- O-glucuronide (CV: 20%), whereas the accordance between both methods was moderate for nicotine- N-glucuronide (CV: 33%). The described LC–MSMS method allows the simultaneous determination of nicotine and eight of its major metabolites in urine of smokers with good precision and accuracy. Since the method requires a minimum of sample clean-up and a very short time for chromatography (3 min), it is suitable for determining the nicotine dose in large-scale human biomonitoring studies.

Determination of remifentanil in human blood by capillary gas chromatography with nitrogen-selective detection

A validated method for the determination of remifentanil in human blood, applicable to all therapeutic concentrations, using capillary GC with nitrogen-specific detection and fentanyl as the internal standard has been developed. Citrated whole blood samples were extracted into 1-chlorobutane following precipitation of proteins with methanol. The drugs were back extracted into 10 m M HCl and re-extracted into methanol–1-chlorobutane. The extracts were reconstituted in methanol and injected onto a 25-m BPX-5 column. The lower limit of quantitation was 0.2 ng/ml with within- and between-day coefficients of variation of less than 15%.

High-performance liquid chromatography coupled with chemiluminescence nitrogen detection for the study of ethoxyquin antioxidant and related organic bases.

The Chemiluminescent Nitrogen Detector (CLND) for use with high-performance liquid chromatography (HPLC) allows for the low-level detection of nitrogen-containing compounds with simple quantitation. The nitrogen selective detector's equimolar response (i.e., equal response for nitrogen independent of its chemical environment) allows for any nitrogen-containing compound to be quantitated as long as the number of nitrogens are known. The HPLC-CLND provides a new detection method for analytes that are not available in large quantities or have unknown chemical or physical characteristics such as oxidation products, metabolites, or impurities. Ethoxyquin is a primary antioxidant that is used to preserve many food products and animal feeds. HPLC-CLND is used in the study of the oxidation products of ethoxyquin because limited quantities of these compounds are available and subsequent calibration curves are difficult to maintain. HPLC-CLND as a new method of detection has been evaluated for its equimolarity of response, linear range, limit of detection, and limit of quantitation.

Determination of chloro- and methylthiotriazine compounds in human urine: extraction with diethyl ether and C18 solid-phase extraction for gas chromatographic analysis with nitrogen-selective and electron capture detection

This paper describes an evaluation of extraction methods of triazine herbicides atrazine, simazine, prometryn, and ametryn and of three chlorodealkylated atrazine metabolites from human urine using diethyl ether and C18 solid-phase extraction (Sep-Pak C18 cartridges). The extracts were analysed by capillary gas chromatography using nitrogen selective and electron capture detectors. At ngml−1 concentrations the diethyl ether extraction recoveries of atrazine and simazine were almost quantitative (R.S.D. 10%), while the recoveries of other triazines ranged from 58% for deisopropylatrazine to 85% for deethylatrazine (R.S.D. 19–34%). The sensitivity of the method using a nitrogen selective detector ranged from 5ngml−1 for atrazine to 30ngml−1 for didealkylated atrazine. C18 solid-phase extraction with acetone as eluting solvent resulted in about 100% recoveries of all parent herbicides (R.S.D. 15–21%) with detection limits of 5ngml−1 for atrazine and 10ngml−1 for other herbicides. Comparably high recoveries of three dealkylated atrazine metabolites (R.S.D. 10–12%) were achieved from acidified urine samples (pH 2–3) only at concentrations lower than 100ngml−1. The diethyl ether extraction procedure served to identify occupational exposure to atrazine and simazine. Deethyldeisopropylatrazine was confirmed as the predominant urinary dealkylated metabolite followed by monodealkylated metabolites and unchanged atrazine.

Pharmacokinetics of tramadol in children after i.v. or caudal epidural administration

We have studied the pharmacokinetics of a single bolus dose of tramadol 2 mg kg-1 injected either i.v. or into the caudal epidural space in 14 healthy children, aged 1-12 yr, undergoing elective limb, urogenital or thoracic surgery. Serum concentrations of tramadol and its metabolite O-demethyl tramadol (MI) were measured in venous blood samples at various intervals up to 20 h by non-stereoselective gas chromatography with nitrogen-selective detection. All pharmacokinetic variables were evaluated using a non-compartmental model. After a single i.v. injection (n = 9), the mean elimination half-life of tramadol was 6.4 (SD 2.7) h, with a volume of distribution of 3.1 (1.1) litre kg-1 and total plasma clearance of 6.1 (2.5) ml kg-1 min-1. All of these pharmacokinetic variables were similar to those reported previously in adults. After caudal epidural administration (n = 5), mean elimination half-life was 3.7 (0.9) h, volume of distribution was 2.0 (0.4) litre kg-1 and total clearance was 6.6 (1.9) ml kg-1 min-1. The caudal/i.v. quotient of the AUC was 0.83, which confirms that there is extensive systemic absorption of tramadol after caudal administration. Serum concentrations of MI showed a time course typical of a metabolite after both modes of administration. Serum concentrations of MI after caudal administration were lower than those after i.v. injection.

Coupled LC-GC-NPD for Determination of Carbazole-Type PANH and Its Application to Personal Exposure Measurement

A coupled LC-GC method for the analysis of carbazole-type PANH has been developed and evaluated. Group separation and isolation of carbazoles from interfering acridines in a complex sample matrix was accomplished by using a back-flush technique and an in situ end-capped dimethylaminopropyl silica column in the HPLC part of the system. On-line injection of the carbazole fraction into the GC column was performed with a loop-type interface utilizing concurrent solvent evaporation technique. An LOD of 1–3 pg of individual carbazole compounds was achieved by nitrogen selective detection using an NPD. The method is shown to be robust and is demonstrated by application to personal exposure measurement in an aluminum reduction plant.

Olanzapine-Related Fatality

A 43-year-old male psychiatric outpatient died within hours of ingesting as much as 600 mg of olanzapine, a newer antipsychotic agent related to clozapine. Analysis of postmortem blood and urine by gas chromatography with nitrogen-selective detection yielded olanzapine concentrations of 1238 and 6987 micrograms/L, respectively, greatly in excess of levels expected following therapeutic administration of the drug. Based on the toxicology findings, the decedent's known history of suicide attempts, and the circumstances surrounding the death, this case was ruled a suicide by olanzapine overdosage.

Determination of nanogram amounts of dicyclomine with gas chromatography and nitrogen-selective detection.

Determination of nanogram amounts of dicyclomine with gas chromatography and nitrogen-selective detection.

Enantioselective determination of isradipine in human serum using chiral stationary phase liquid chromatography and gas chromatography with nitrogen selective detection.

rac-Isradipine is a dihydropyridine type calcium antagonist. Its calcium entry blocking effect is due primarily to the (+)-(S)-enantiomer. This study describes a sensitive enantioselective method for the determination of isradipine in human serum. Following alkaline extraction into hexane, the enantiomers of isradipine are separated quantitatively by high-performance liquid chromatography on a Chiralcel OJ column at 39 degrees C. The collected fractions were evaporated and assayed using capillary gas chromatography on a HP 50+ column with nitrogen selective detection. Using 2.0 ml of serum, 0.7 nmol/1 (0.26 ng/ml) of each enantiomer could be determined with acceptable precision. The method has successfully been used to measure (+)-(S)- and (-)-(R)-isradipine concentrations in samples from volunteers after intravenous and oral administration of isradipine.

Enantioselective determination of isradipine in human serum using chiral stationary phase liquid chromatography and gas chromatography with nitrogen selective detection

Enantioselective determination of isradipine in human serum using chiral stationary phase liquid chromatography and gas chromatography with nitrogen selective detection

Pyrolysis gas chromatography of some coals by nitrogen and phosphorus, flame ionisation and mass spectrometer detectors.

Pyroprobe pyrolysis technique was applied to some coals with very different geographic origins. The pyroprobe was coupled to a gas chromatograph and the products were detected using different systems: mass spectrometry (MS), nitrogen and phosphorus selective detector (NPD) or flame ionisation detector (FID). The MS data permitted the identification of most of the pyrolysis products. The production of nitrogen bearing compounds was studied with NPD data, and the amount of all pyrolysis products with FID data. This data was also used for principal component analysis and the results for a hierarchic cluster analysis which suggests a classification of coals.

A Sensitive, Validated Gas‐chromatographic Bioanalytical Method by Nitrogen Selective Detection of Deramciclane in Dog Plasma

A validated bioanalytical method has been developed for the determination of a new anxiolytic compound of deramciclane in dog plasma, using Lichrolut RP-18 solid-phase extraction and gas chromatography with nitrogen-phosphorous selective detector (GC-NPD). Gas-chromatographic separation was carried out by SPB-5 fused silica capillary column (30 m × 0·25 mm × 0·25 μm) after split injection, when the split liner was packed (3% silicone SE 30). An optimized two-level oven temperature program was used for the separation. The assay was validated with respect to selectivity, specificity, linearity, sensitivity, accuracy, precision, system suitability and plasma stability. All validation parameters were found to be within the internationally required limits. The limit of quantification of deramciclane in dog plasma was found to be 0·5 ng mL−1. The calibration curve showed good linearity (r=0·999) over the 0·5 and 100 ng mL−1 deramciclane plasma concentration range. The assay is sufficiently sensitive and relatively fast (12·5 min chromatographic run) to be used for routine monitoring and pharmacokinetic studies of deramciclane.

Contribution to the determination of the chemotherapeutic drug G1 in biological fluids

A sensitive gas chromatographic method for the quantitative determination of the new antibacterial and antifungal drug G1, 1-(5-bromofuran-2-yl)-2-bromo-2-nitroethene, has been optimized. The method involves a fast and single extraction step from spiked serum and urine samples. The G1 drug was quantified using an internal standard method and by means of a nitrogen-selective detector. The results are statistically significant and show that mean levels of G1 as low as 1 μg ml −1 can be measured accurately.

Structure of "unknown" soil nitrogen investigated by analytical pyrolysis

Curie-point pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and in-source pyrolysis-field ionization mass spectrometry (Py-FIMS) were applied for the first time to the structural characterization of organic nitrogen in hydrolyzates and hydrolysis residues resulting from the classical 6M HCl hydrolysis of mineral soils. Two well-described soils of widely different origin (i.e., a Gleysol Ah and a Podzol Bh) were investigated. Py-GC/MS was performed using a nitrogen-selective detector to detect and identify N-containing pyrolysis in the hydrolyzate (e.g., pyrazole and/or imidazole, N,N-dimethylmethanamine, benzenacetonitrile, propane- and propenenitriles) and the hydrolysis residue (e.g., pyrroles, pyridines, indoles, N-derivatives of benzene, benzothiazol, and long-chain aliphatic nitriles). Moreover, temperature-resolved Py-FIMS allowed us to record the thermal evolution of the N-containing compounds during pyrolysis. These were characterized by a particularly high thermostability compared to their thermal release from whole soils. The combination of pyrolysis with mass spectrometric methods permitted analyses of the identities and thermal stabilities of complex nitrogen compounds in hydrolysis residues of whole soils, which cannot be done by wet-chemical methods. Pyrolysis-methylation GC/MS with tetramethyl-ammonium hydroxide (TMAH) as methylating agent enabled the identification of N,N-dimethylbenzenamine and so confirmed the identification of benzeneamine by Py-GC/MS in nonmethylated hydrolysis residues. The described N-derivatives of benzene and long-chain nitriles are usually not detectable by pyrolysis-mass spectrometry of plants and microorganisms. These compounds are characteristic of soils, terrestrial humic substances and hydrolysis residues and seem to be specific, stable transformation products of soil nitrogen.

Pyrolysis-gas chromatography applied to the study of organic matter evolution in sewage sludge-amended soils using nitrogen-phosphorus, flame ionization and mass spectrometric detection

Pyrolysis in combination with gas chromatographic separation and simultaneous nitrogen-phosphorus and flame ionization detection is proposed for the determination of nitrogen compounds in soils. Peak identification was performed by mass spectrometry. The technique is considered as a complementary tool for use with other techniques for soil organic matter studies. The pyrolysis probe was placed directly in the horizontal injection port of a Perkin-Elmer Model 8700 chromatograph coupled with a nitrogen-selective detector and a flame ionization detector and into the vertical injection port of an HP-5890A chromatograph coupled with an HP-5989 mass spectrometer. This technique was applied to study the evolution of the organic matter in soils amended with sewage sludge samples.

Capillary gas chromatographic method for the determination of n-butyl- p-aminobenzoate and lidocaine in plasma samples

A fast capillary gas chromatographic method with nitrogen-selective detection is described that allows selective and reproducible quantification of n-butyl- p-aminobenzoate (BAB) and lidocaine in plasma. The sampling and sample storage conditions are critical for the quantification of BAB. Diisopropyl fluorophosphate, an organophosphorus pesticide, has to be added during sampling to prevent the rapid decomposition of BAB by cholinesterases.