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Biomedical subjects

W J Leung

Publications and source records attributed to W J Leung.

13 recordsLinked to original sources
PubMed1981

Mass screening and confirmation of phencyclidine (PCP) in urine by radioimmunoassay/TLC.

A sensitive, rapid, and specific procedure is described for the mass screening and confirmation of PCP (phencyclidine) in urine specimens at concentrations as low as 0.3 microgram of PCP per mL. Specimens that test positive by radioimmunoassay must be confirmed by TLC using methylene chloride:n-butanol:concentrated NH4OH (85:15:0.5) as the developing solvent system. This separates PCP from other drugs or endogenous urinary substances.

Chromatography, Thin Layer↗
PubMed1980

Mass screening and confirmation of methaqualone and its metabolites in urine by radioimmunoassay-thin-layer chromatography.

A sensitive, rapid, and specific procedure is described for the mass screening and confirmation of methaqualone (Quaalude) in urine specimens. The method is sensitive to 1.0 microgram/ml levels of total methaqualone excretion products (free methaqualone, free hydroxylated methaqualone metabolites, and conjugated hydroxylated methaqualone metabolites). The raw urine is screened directly by radioimmunoassay, which is reactive to all the methaqualone excretion products. Specimens that are screened positive are confirmed by thin-layer chromatography using a solvent system of ethyl acetate-1,2-dichloroethane-chloroform (75:15:10) which separates methaqualone and its four major metabolites without interference from other drugs or urinary substances. The distinctive spot pattern produced by the methaqualone metabolites makes false positive results nearly impossible.

Chromatography, Thin Layer↗
PubMed1980

Thin-layer chromatographic screening and confirmation of methadone and its primary metabolite in urine.

A thin-layer chromatographic method for the simultaneous screening and confirmation of methadone and its primary metabolite (2-ethylidene-1,5-diemthyl-3,3-diphenylpyrrolidine) in urine specimens is presented. Urine is made basic and extracted with organic solvent. After separation and concentration, the residue is spotted, half on each of two thin-layer chromatography plates. One plate is developed in an ethyl acetate:methanol:diethylamine (90:10:1.6) solvent system and the second in an ethyl acetate:methylene chloride:propylamine (85:17:1.0) solvent system. Methadone and its primary metabolite can be detected in concentration as low as 0.5 micrograms/mL without interference from other drugs and urinary substances.

Biotransformation↗
PubMed1980

Screening and confirmation of opiates by thin-layer chromatography.

A thin-layer chromatography (TLC) procedure for the screening and confirmation of urinary codeine and morphine has been developed. Urine samples are hydrolyzed to liberate free codeine and morphine, extracted into an organic solvent, and concentrated. For screening, the extraction residues are spotted on TLC plates which are developed in chloroform:ethyl acetate:methanol:propylamine (35:45:5:5). For confirmation, the extraction residues are acetylated and then spotted on TLC plates which are developed in hexane:chloroform:diethylamine (50:30:7). The spots for the two drugs are visualized with acidified iodoplatinate. Codeine and morphine are well separated from one another and from normal urinary substances on both plates and can be detected at a concentration of 0.4 micrograms/mL.

Acetylation↗
PubMed1980

RIA opiates: structure versus reactivity.

Twenty-six different opiates were analyzed by radioimmunoassay (RIA) at five different concentrations. At attempt is made to relate structural differences to the affinity of the compounds for the Roche RIA morphine antibody. The effects of substituent placement on the morphine molecule are studied. As expected, the basic 5-ring opiate structure is essential for reactivity. Addition of an alkyl group to the oxygen in the 3-position increased affinity, but alteration of other key functional groups had a reverse affect.

Narcotics↗
PubMed1978

A survey of drug use among probationers in the Los Angeles area in 1976.

The results are presented from the analysis of 10,000 urine specimens from Los Angeles County probationers in early 1976 for the following drugs: amphetamine, methamphetamine, allylbarbital, amobarbital, butabarbital, pentobarbital, phenobarbital, secobarbital, morphine, codeine, methadone, primary metabolite of methadone, cocaine, benzoylecgonine, propoxyphene, norpropoxyphene, methaqualone, and phencyclidine. Over 27% of the urine samples analyzed were positive for at least one drug. Opiates were found to be the most widely used drugs, but multiple drug use was also quite common.

California↗
PubMed1977

Mass screening and confirmation of codeine and morphine in urine by radioimmunoassay-GLC.

A rapid, sensitive, and specific procedure is described for the mass screening and confirmation of codeine and morphine in urine specimens. The method is sensitive to 0.5-mug/ml levels of both opiates in free and/or conjugate forms. The raw urine is screened directly by radiommunoassay, which is reactive to both free and glucuronide forms of codeine and morphine. Specimens that are screened positive are confirmed by GLC using a flame-ionization detector. The opiates are analyzed as their acetyl derivat-ves on two different columns, OV-25 and Poly-A 103. This multiple approach eliminates false positives caused by interfering substances or structurally similar compounds present in the urine.

Chromatography, Gas↗
PubMed1977

Simultaneous determination of cocaine and benzoyl ecgonine in urine by gas chromatography with on-column alkylation.

A gas chromatographic procedure has been developed for the simultaneous determination of cocaine and benzoyl ecgonine in urine specimens. The two drugs are extracted by isopropanol/chloroform from urine samples saturated with a bisalt buffer. The organic extract is evaporated to dryness, and an aliquot of the residue is injected onto the gas chromatograph to determine the presence of cocaine and the location of any extraneous peaks. Benzoyl ecgonine is then analyzed as its particular alkyl ester subject to the least interference from extraneous peaks as observed in an initial underivatized injection. The reconstituted residue is co-injected with the appropriate dimethylformamide dialkyl acetal for on-column alkylation. The use of two columns or more than one benzoyl ecgonine alkyl ester gives positive identification, and the use of isopropyl benzoyl ecgonine as an internal standard allows accurate quantification.

Alkylation↗
PubMed1976

Rapid screening and confirmation of amphetamine, methamphetamine, methadone, and methadone metabolite in urine by gas/thin layer chromatography.

A method suitable for large scale screening and confirmation of urine speciments for amphetamine, methamphetamine, methadone, and its primary metabolite (2-ethylidene-1,5-dimethyl-3,3-diphenlypyrrolidine) is described. The drugs are extracted from alkaline urine into an organic solvent. The amphetamine drugs are then back-extracted into a small volume of acid and identified by gas chromatography both as free bases on a 10% Apiezon L-10% KOH column and as their trifluoracetamide derivatives on a 3% OV-17 column. The organic layer, which still contains methadone and its primary metabolite, is analyzed by split-sample thin-layer chromatography using two solvent systems: ethyl acetate: methylene cloride: concentrated ammonium hydroxide (90:10:0.7) and methanol: chloroform: concentrated ammonium hydroxide (74:25:0.8). These solvent systems separate methadone from its primary metabolite without interference from other drugs or urinary substances.

Amphetamine↗
PubMed1975

Thin-layer chromatographic screening and confirmation of basic drugs of abuse in urine.

Thin-layer chromatographic procedures are presented for the positive identification of methodone, primary metabolite of methodone (2-ethylidine-1,5-dimethyl-3,3-diphenylpyrrolidine), propoxyphene, norpropoxyphene, cocaine, benzoylecgonine, methoqualone, and phencyclidine from urine specimens. Initial screening of specimens is done by developing plates in ethyl acetate-methanol-diethylamine (90:10:1.6). Samples screened positive are confirmed in methylene chloride-methyl ethyl ketone-concentrated ammonium hydroxide (74:25:0.8), depending on the drug(s) indicated by the screening procedure. The method is quite sensitive, detecting most of the listed drugs at levels of 1.0 mug/ml or less.

Chromatography, Thin Layer↗
PubMed1975

Gas chromatographic/thin-layer chromatographic analysis of acetylated codeine and morphine in urine.

This procedure positively identifies codeine and morphine in urine. Urine samples are hydrolyzed and extracted with organic solvent, and the extracts are evaporated and acetylated. The presence of codeine and morphine is ascertained by gas chromatography (3% OV-25 and 3% Poly-A 103 columns) and confirmed by thin-layer chromatography (system: ethyl acetate/acetone/concd ammonium hydroxide, 100/10/4.5 by vol; reagent: iodoplatinate). As little as 0.5 mg each of codeine and morphine per liter, in free and conjugated forms, is detectable by this method.

Acetylation↗
PubMed1975

Thin layer chromatographic identification of phenothiazines in urine specimens.

Two newly developed, thin layer chromatographic (TLC) solvent systems are presented to separate and identify commonly used phenothiazines in the presence of other drugs in urine specimens. These solvent systems are 1) ethyl acetate: n-butanol: concentrated ammonium hydroxide (89:10:1.5) and 2) ethyl acetate: O-dichlorobenzene: concentrated ammonium hydroxide (90:9:1.4). The phenothiazines are identified on the TLC plates both by Rf values and by colors produced with ethanolic sulfuric acid and palladium chloride sprays. With this method 0.025 mug/ml levels of unchanged phenothiazines can be detected in urine specimens.

Antipsychotic Agents↗