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Biomedical subjects

J Wijsbeek

Publications and source records attributed to J Wijsbeek.

At least 37 records · Page 2Linked to original sources
PubMed1977

Variations in the bioavailability of thiazinamium methylsulfate.

Bioavailability after oral administration of the anticholinergic drug thiazinamium methylsulfate (Multergan), a phenothiazine derivative with a quaternary ammonium group in the molecule, has been studied in patients and volunteers by measuring the drug concentrations in plasma or the excretion of the parent drug in urine. The relative bioavailability as compared to intramuscular injection seems to be of the order of 10%. Much more of the drug is absorbed, however, but is metabolized during the first liver passage. Moreover, there seems to be a substantial interindividual variation in the bioavailability of the drug. Studies in a group of eight volunteers showed that there is also a substantial intraindividual variation, but its magnitude is smaller than that of the interindividual variation.

Administration, Oral↗
PubMed1975

Determination of low cencentrations of the quaternary ammonium compound thiazinamium methylsulphate in plasma and urine.

A sensitive and selective method for the quantitative determination of the quaternary ammonium antiacetylcholine-compound thiazinamium methylsulphate (Multergan) in plasma and urine is described. The procedure is based on ion pair extraction of the compound with iodide as the counter ion. This is followed by gas chromatography using an alkali flame ionization detector. The detection limit is 2 ng ml-1 with a recovery of 88-0 +/- 6-2% from plasma, 91-4 +/- 4-6% from urine. The described method can also be applied to other quaternary ammonium compounds.

Chromatography, Gas↗
PubMed1972

Cannabinoids with a propyl side chain in cannabis: occurrence and chromatographic behavior.

Neutral cannabinoids with a pentyl side chain-for example, cannabidiol, tetrahydrocannabinol, and cannabinol-are generally accompanied by homologs with a propyl side chain, of which at least one has psychotropic activity. Samples of hashish and marihuana from Asia especially sometimes have abundant amounts of propyl cannabinoids, the quantities being of the same order as that of the accompanying pentyl cannabinoids. Detection and identification of the propyl and pentyl cannabinoids in gas chromatography and thin-layer chromatography is discussed.

Alkanes↗
PubMedDate not supplied

Potentials of wide-bore fused silica capillary columns for substance identification by means of retention indices.

A wide-bore capillary column with a methylsilicone stationary phase has been evaluated with regard to its ability to identify substances by means of their retention indices. Column efficiency was compared with a normal packed column and a medium-bore capillary column, and the impact of carrier gas flow and load capacity were investigated. It was shown that under defined conditions retention indices on the wide-bore capillary column were comparable to those available in a data bank obtained on packed columns.

Chromatography, Gas↗
PubMedDate not supplied

Influence of biological matrix on retention behaviour and identification possibilities of selected neutral and acidic drugs in thin layer chromatography. An interlaboratory investigation.

Samples of autopsy blood and liver were spiked individually with aminophenazone, p-aminosalicylic acid, clordiazepoxide, clonazepam, cyclobarbital, furosemide, medazepam, phenacetin, phenazone, and phenobarbital and extracted with diethyl ether at pH 5. The extracts, as well as solutions of pure drugs, were developed in three thin layer chromatographic systems: chloroform:acetone (80:20), ethyl acetate:methanol:ammonia (85:10:5) and chloroform:methanol (90:10). The investigations performed in parallel in two laboratories showed that the intra- and inter-laboratory variability of RF values is larger for drugs extracted from liver. The biological matrix affected both precision and accuracy of results. The number of analysts involved in TLC procedures also affected the intra-laboratory precision.

Chromatography, Thin Layer↗
PubMedDate not supplied

Systematic analysis of solvents and other volatile substances by gas chromatography.

Four column packings for screening volatiles in biological material by gas chromatography are evaluated. Retention data are standardized by the calculation of retention indices, and packing materials are compared by discriminating power and identification power. A combination of 5% Carbowax 20M on Carbopack B and 0.3% Carbowax 20M on Carbopack C appears to be best suited for screening. Hydroxy-n-alkanes are used as reference substances for the calculation of retention indices.

Chromatography, Gas↗
PubMedDate not supplied

Isolation of acidic, neutral, and basic drugs from whole blood using a single mixed-mode solid-phase extraction column.

A solid-phase extraction procedure was developed for the isolation of acidic, neutral, and basic drugs from whole blood. A blood sample was sonicated, diluted with phosphate buffer, and the drugs were extracted on a mixed-mode bonded-phase silica column at pH 6.0. The extraction system was adjusted to pH 3.3 with acetic acid. After column drying, the drugs were selectively eluted from the column by two different eluates, which were collected separately. Acidic, neutral, and weakly basic drugs with lower pKa values (e.g., benzodiazepines) were present in the first acetone-chloroform (1:1) fraction. The other basic drugs were present in the second fraction (basic ethyl acetate). The drugs with pKa's close to the pH of the extraction system (pH 3.3) appeared in both fractions. The two fractions were evaporated until approximately 100 microL of solvent remained in the tube and were then analyzed on a gas chromatograph equipped with a wide-bore capillary column and flame ionization detector. The absolute recoveries of all tested drugs exceeded 81% at a concentration of 2 micrograms/mL.

Blood Chemical Analysis↗
PubMedDate not supplied

Pitfalls and solutions in the development of a fully automated solid-phase extraction method for drug screening purposes in plasma and whole blood.

A fully automated solid-phase extraction (SPE) method for drug screening is described. The extraction of 19 toxicologically relevant drugs from pretreated plasma and pretreated whole blood was accomplished automatically by a Gilson ASPEC system equipped with disposable 2.8-mL Bond Elut Certify columns. The automated extraction procedure includes 11 fundamental steps: column preconditioning; sample application; column washing; pH adjustment; elution of drugs by two eluents, which were collected into two separated tubes; addition of the chromatographic standard solution; and several SPE column rack movement steps. After evaporation, the drugs were quantitated by gas chromatography. Water was chosen as the transfer liquid in the ASPEC system because it was cheap and, more importantly, because it caused no protein precipitation problem. The effects of the sample and eluent flow rates were investigated, and it was found that low flow rates were necessary to recover the drugs maximally. In the study, the optimal flow rates of sample application, acetone-chloroform elution, and ammoniated ethyl acetate elution were 1.5, 0.72, and 0.33 mL/min, respectively. The absolute recoveries of 19 drugs from whole blood exceeded 82%, with relative standard deviations less than 5% at 2 micrograms/mL.

Blood Chemical Analysis↗
PubMedDate not supplied

Determination of basic drugs extracted from biological matrices by means of solid-phase extraction and wide-bore capillary gas chromatography with nitrogen-phosphorus detection.

Determination of basic drugs from biological matrices at concentration levels of 100-200 ng/mL was accomplished by using mixed-mode Bond Elut Certify columns and a gas chromatograph equipped with a nitrogen-phosphorus detector. The extraction procedure developed for general drug screening on a GC-FID system was found suitable for the extraction of basic drugs from plasma and whole blood for GC-NPD analysis. For urine samples, an extra wash step with 20% acetonitrile in water was required to obtain clean extracts. The recoveries of 18 basic drugs ranged from 77.7 to 104.5%, with relative standard deviations less than 7.0%.

Animals↗
PubMedDate not supplied

An enzymic digestion and solid-phase extraction procedure for the screening for acidic, neutral, and basic drugs in liver using gas chromatography for analysis.

Analysis of liver specimens is an important issue in forensic toxicology, but suitable workup and extraction methods for general screening purposes have been lacking until now. A workup and extraction scheme based on a recently developed procedure for the screening of biological fluids was developed that can be used for the screening of acidic, neutral, and basic drugs in liver. This method uses a single solid-phase extraction (SPE) column and gas chromatography-flame ionization detection (GC-FID) for the final analysis. First, the homogenized liver sample is sonicated and centrifuged; the resulting supernatant is applied to the SPE column. Elution of acidic, neutral, and some weakly basic drugs is then performed with acetone-chloroform and analyzed by GC-FID. Next, the pellet of tissue material obtained from the centrifugation is enzymically digested by subtilisin Carlsberg. This frees the drugs bound to the liver tissue. The resulting clear liquid is brought to the reconditioned SPE column. A wash step is introduced to remove acidic and neutral interferences and the basic drugs can then be eluted with ammoniated ethyl acetate. Using 100-mg wet liver samples spiked with 2 micrograms of amounts of various drugs, recoveries were 70-102% with relative standard deviations less than 9%. The resulting GC-FID chromatograms were virtually free of endogenous interferences. GC-nitrogen-phosphorous detection detected smaller amounts of nitrogen-containing drugs, again without endogenous interferences. With the SPE columns currently used, which contain a bed mass of 130 mg, the liver samples should be smaller than 200 mg because the endogenous compounds obtained after the digestion of the tissue will overload the column, which results in a lower recovery of the drugs of interest. Drugs that decompose under the digestion conditions (pH 10.5 at 60 degrees C for 1 h) may be lost in the present procedure. This phenomenon is being investigated further.

Flame Ionization↗