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Biomedical subjects

W A Joern

Publications and source records attributed to W A Joern.

18 recordsLinked to original sources
PubMed1992

Marijuana testing in urine: use of a hexadeuterated internal standard for extended linearity, and ion trap vs mass selective detector gas chromatograph/mass spectrometer systems.

The use of a hexadeuterated internal standard for the assay of the marijuana carboxy metabolite in urine resulted in two significant improvements. First, the linearity of the procedure was increased considerably because of the minimal chromatographic peak overlap of the internal standard and carboxy metabolite derivatives. Second, again because of minimal peak overlap, the same extract could be analyzed with similar results by both the ion trap detector and mass selective detector gas chromatograph/mass spectrometer systems.

Deuterium↗
PubMed1981

Gas-chromatographic assay of free phenytoin in ultrafiltrates of plasma: test of a new filtration apparatus and specimen stability.

I describe a gas-chromatographic procedure involving a nitrogen detector for "free" (or "unbound") phenytoin in the concentration range 0.2-4.0 mg/L in ultrafiltrates of plasma. The CV (n = 10) for the assay was 2.9% for a 0.49 mg/L concentration, 1.5% for 2.02 mg/L. The sensitivity was 0.05 mg/L. The ultrafiltration process ("Ultra-Free" filters) used to separate the free phenytoin fraction from the bound fraction was tested. The mean of and CV for free phenytoin concentrations measured in eight replicate serum filtrates were 0.68 mg/L and 15%; for eight replicate plasma filtrates the values were 0.42 mg/L and 2.9%. Thus serum is not suitable for this procedure. Storage of plasma before filtration under a wide variety of times and temperatures has an insignificant effect upon the filtration process. Some evidence was found of occasional protein "leakage" through the filters.

Chromatography, Gas↗
PubMed1978

Micro-scale extractive alkylation procedure for the gas-chromatographic measurement of theophylline in serum and saliva, with use of a nitrogen detector.

In this 10-min gas-chromatographic assay for theophylline, a 25-microliter portion of serum or saliva sample, 100 microliter of extraction reagent, and 1.0 ml of solvent were mixed, the solvent separated and evaporated, and an aliquot of the reconstituted extract injected into the gas chromatograph. At a concentration of 11 mg/liter, within-run precision (CV) was 3.6% and run-to-run 2.9%. At 22 mg/liter, within-run precision was 2.8%. Concentration and instrument response are linearly related between 2 and 40 mg/liter. The limit of detection was 0.4 mg/liter. Results correlated well (r = 0.98) with those by another micro-scale gas-chromatographic procedure. Analytical recovery was estimated to exceed 90%, and no interferences from other xanthines or related drugs were observed.

Alkylation↗
PubMedDate not supplied

Detection of past and recurrent marijuana use by a modified GC/MS procedure.

A published gas chromatography/mass spectrometry method for detecting 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) in urine was modified. In the new procedure, five GC/MS ion peaks of a pentafluoropropylpentafluoropropionyl derivative of THC-COOH are monitored in the multiple-ion mode for improved reliability; two ion peaks of the trideuterated internal standard are used for greater quantitative precision; and methanolic KOH is employed instead of NaOH in the hydrolysis and extraction steps to produce a cleaner extract. Finally, the new procedure is designed to keep THC-COOH either in basic solution or in an organic solvent at all times to prevent adsorption onto glass or plastic, so that disposable, non-silanized glassware may be used. Patient urines were analyzed by both the new procedure and the EMIT method. For 32 specimens, the average and range of EMIT/GC/MS concentration ratios were 2.8 and 0.9-7.2, respectively. Concentrations of THC-COOH measured by the GC/MS procedure may be more indicative of recent marijuana use than the EMIT semi-quantitative concentration values.

Cannabis↗
PubMedDate not supplied

Routine detection of benzoylecgonine in urine at a sensitivity of 35 ng/mL by a combination of EMIT and gas chromatography/mass spectrometry.

The limit of detection of a published gas chromatographic/mass spectrometric (GC/MS) procedure for the detection of benzoylecgonine in urine was extended to 35 ng/mL. The GC/MS procedure then was used not only to confirm EMIT positives, but also to detect the presence of benzoylecgonine in urines that gave EMIT readouts below the low calibrator value, but higher than halfway between the negative and low calibrator values. Of 16 such patient urines, 12 were positive by the GC/MS procedure.

Cocaine↗
PubMedDate not supplied

Detection of alprazolam (Xanax) and its metabolites in urine using dual capillary column, dual nitrogen detector gas chromatography.

Alprazolam (Xanax) is a fairly new, yet very popular benzodiazepine tranquilizer. In 1985, it was 6th on a nationwide list of drugs mentioned in emergency room drug poisonings. A procedure was developed that allows alprazolam and its main urinary metabolites, alpha-hydroxyalprazolam and 3-hydroxymethyl-5-methyltriazolyl chlorobenzophenone, to be detected in urine specimens. A dual capillary column, dual nitrogen detector gas chromatographic system was used for reliable identification. Improved chromatographic performance was obtained by acetylating the metabolites. Method characteristics such as linearity, reproducibility, limit of detection, and recovery were determined. The method was tested by assaying urine specimens from hospitalized patients who had been ingesting alprazolam. In most cases, alpha-hydroxyalprazolam was found in the highest concentration and separated best from endogenous urine substances. A single dose concentration-time study was performed, and the time course of alprazolam and metabolite concentrations over 48 hours was determined.

Alprazolam↗
PubMedDate not supplied

Confirmation of low concentrations of urinary benzodiazepines, including alprazolam and triazolam, by GC/MS: an extractive alkylation procedure.

Urine samples containing diazolo- and triazolobenzodiazepines and metabolites were hydrolyzed with beta-glucuronidase and extracted with methylene chloride. The extracts were treated with methyl iodide, methylene chloride, and tetrahexylammonium hydrogen sulfate in basic solution to form the methyl derivatives of the drugs and metabolites. GC/MS analysis resulted in the following test characteristics: day-to-day precision at 360 ng/mL (120 ng/mL for the triazolobenzodiazepine metabolites) was 2.4 to 5.5% CV; calibration curves were linear to 6000 ng/mL (1000 ng/mL for the triazolobenzodiazepine metabolites), and operational limits of quantitation were in the range 13-25 ng/mL.

Alkylation↗