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Biomedical subjects

K E Rasmussen

Publications and source records attributed to K E Rasmussen.

At least 37 records · Page 2Linked to original sources
PubMed1995

Automated analysis of free and total concentrations of three antiepileptic drugs in plasma with on-line dialysis and high-performance liquid chromatography.

A fully automated method for determination of the free and total concentration of drugs with a varying degree of protein binding is described. The antiepileptic drugs phenytoin, carbamazepine and phenobarbitone were chosen to demonstrate the utility of this technique. The method was based on the ASTED system and combined on-line equilibrium dialysis at 37 degrees C with concentration of the dialysate on a trace enrichment column and HPLC determination with UV detection. The dialysis cell was a modification of the ASTED dialysis cell and 22% of the free concentration of the drugs were recovered in the recipient channel of the dialyser after 10 min of dialysis at 37 degrees C. The free concentration, the total concentration as well as the drugs protein binding could be determined. The method was shown to be well suited for routine monitoring of the free and the total concentrations of the drugs in plasma from epileptic patients.

Anticonvulsants↗
PubMed1993

Automated determination of free phenytoin in human plasma with on-line equilibrium dialysis and column-switching high-performance liquid chromatography.

Free phenytoin in human plasma was automatically determined by on-line equilibrium dialysis using the automated sequential trace enrichment of dialysate (ASTED) sample preparation system and HPLC. The dialysis cell was a modification of the cell supplied with the ASTED. Total phenytoin was analysed with the same analytical set-up and plasma protein binding was determined. Free phenytoin was determined in plasma from epileptic patients and the results were compared to those obtained by ultrafiltration. Automated determination of free and total phenytoin in plasma by the ASTED-HPLC combination was shown to be an accurate and reproducible method and the results in free phenytoin analyses were in agreement with those found with ultrafiltration. The sample throughput with the automated on-line combination of dialysis and column-switching HPLC was 75 samples in 24 h when the sample was dialysed at 37 degrees C.

Autoanalysis↗
PubMed1993

Automated sample preparation by on-line dialysis and trace enrichment. Analysis of morphine, 6-monoacetylmorphine, codeine, ethylmorphine and pholcodine in plasma and whole blood by capillary gas chromatography and capillary gas chromatography-mass spectrometry.

A fully automated sample preparation method for the determination of five opiates in human plasma and whole blood is described. The technique combines dialysis and trace enrichment prior to gas chromatography and gas chromatography-mass spectrometry. Dialysis and trace enrichment on a polymer column was shown to be a highly reliable method for sample preparation. The method can be used, after minor modification, to determine other basic drugs in plasma and whole blood. The method demonstrates the potential of the automated sequential trace enrichment of dialysate (ASTED) system for automated sample preparation.

Automation↗
PubMed1992

On-line dialysis and weak cation-exchange enrichment of dialysate. Automated high-performance liquid chromatography of pholcodine in human plasma and whole blood.

An automated method for the determination of pholcodine in plasma and whole blood is described. The technique combines dialysis and trace enrichment prior to high-performance liquid chromatography. Dialysis, trace enrichment on a weak cation-exchange column, separation on a cyano column and fluorescence detection was shown to be an extremely selective and sensitive method. The method has been used successfully in the analysis of real samples after administration of pholcodine. The automated method can be used, after minor modification, to determine other basic drugs in whole blood and plasma.

Analgesics↗
PubMed1992

Automated high-performance liquid chromatography of iopentol in human plasma and whole blood using on-line dialysis as sample preparation.

A fully automated high-performance liquid chromatographic method has been developed for the analysis of the radiographic contrast agent iopentol in human plasma and whole blood. This method is based on on-line sample preparation with dialysis followed by pre-column enrichment of the dialysate. The method was compared with a manual sample preparation method based on protein precipitation with tetrahydrofuran. The inter-assay and intra-assay variations and the limits of quantitation were the same for both methods. The on-line combination of dialysis and column-switching high-performance liquid chromatography was shown to be a reliable and time-saving technique for monitoring iopentol in human whole blood and plasma.

Chromatography, High Pressure Liquid↗
PubMed1992

Column-switching high-performance liquid chromatographic detection of pholcodine and its metabolites in urine with fluorescence and electrochemical detection.

A sensitive and selective method for the detection of pholcodine and its metabolite morphine in urine using high-performance liquid chromatography is described. It involves on-line clean-up of urine on a trace enrichment column packed with a polymeric strong cation-exchange material. Pholcodine and its metabolites were separated on two analytical columns with different selectivities. Pholcodine was detected by a fluorescence detector and morphine was detected electrochemically. One system, based on reversed-phase chromatography, applied a polystyrene-divinylbenzene column and gradient elution. The other system was based on normal-phase chromatography with a silica column and isocratic elution. Morphine was confirmed to be a metabolite of pholcodine by reversed-phase chromatography and electrochemical detection. Two unidentified metabolites of pholcodine were separated from pholcodine by normal-phase chromatography and detected by fluorescence detection.

Antitussive Agents↗
PubMed1992

On-line dialysis, liquid chromatography and post-column reaction detection of oxytetracycline in salmon muscle extracts.

The development of a sensitive automated method for residue control of oxytetracycline (OTC) in salmon muscle is described. Tissue homogenate is dialysed and the dialysate enriched on a small on-line polystyrene column. OTC and the internal standard (tetracycline) are separated by HPLC on a polystyrene column using an ion-pair eluent system. The column effluent is mixed with sodium hydroxide and irradiated at 366 nm and the resulting derivatives monitored by means of a fluorescence detector (excitation: 358 nm, emission: 460 nm). By the method OTC is detected down to 5 ng g-1. The standard curve was linear (r = 0.9999) over the range 50-1000 ng g-1. Within-day and between-day relative standard deviations (n = 6) at 50 and 200 ng g-1 ranged from 1.0 to 1.7%.

Animals↗
PubMed1991

Fully automated high-performance liquid chromatographic analysis of whole blood and plasma samples using on-line dialysis as sample preparation. Determination of oxytetracycline in bovine and salmon whole blood and plasma.

A fully automated technique for high-performance liquid chromatographic analysis of whole blood and plasma is described. Samples are automatically injected into a dialyser where proteins and blood cells are removed. The dialysates are concentrated on a small column prior to analysis. This technique is used for the determination of oxytetracycline in whole blood and plasma. After dialysis oxytetracycline and the internal standard, tetracycline, are retained on a polystyrene enrichment column and subsequently separated on a polystyrene analytical column by ion-pair chromatography. Using ultraviolet detection 50 ng/ml can be detected. Validation showed good within-day and between-day accuracy and precision. Different oxytetracycline concentrations were found in plasma and whole blood. This difference varied between the species.

Animals↗
PubMed1991

Automated analysis of oxolinic acid and flumequine in salmon whole blood and plasma using dialysis combined with trace enrichment as on-line sample preparation for high-performance liquid chromatography.

The use of dialysis as sample clean-up for high-performance liquid chromatography makes fully automated determination of drugs in whole blood and plasma possible. High recoveries of the analytes oxolinic acid and flumequine and the internal standard nalidixic acid are obtained after a short time of dialysis (7.3 min). The dilute dialysates are enriched on a small column packed with polystyrene. When dialysis is discontinued, the analytes are eluted by mobile phase to the analytical column. With UV detection the limit of detection was 50 ng/ml for both oxolinic acid and flumequine. Validation showed good precision and accuracy and good correlation between determinations in plasma and whole blood.

Animals↗
PubMed1991

Metabolic study of pholcodine in urine using enzyme multiplied immunoassay technique (EMIT) and capillary gas chromatography.

A study of pholcodine metabolism in man is reported. Three subjects received a single therapeutic oral dose of 50 mg pholcodine and urine samples were collected as long as a positive opiate response could be detected by EMIT (16-26 days). Pholcodine was found to conjugate with glucuronic acid and 15% (13-17%) of the pholcodine dose was excreted in urine as the glucuronide, and 29% (24-35%) as unconjugated pholcodine. Morphine was detected to be a metabolite of pholcodine and 0.5-1% of the pholcodine dose was excreted as morphine glucuronide. The identity of morphine was confirmed by capillary gas chromatography-mass spectroscopy (GC-MS).

Adult↗
PubMed1990

Determination of pholcodine and its metabolites in urine by capillary gas chromatography.

A sensitive and selective method for the determination of pholcodine and its metabolites in urine using capillary gas chromatography with nitrogen detection is described. The procedure includes enzymatic hydrolysis of urine by beta-glucuronidase and sample pretreatment on C2 solid-phase extraction columns. Validation of the method showed good sensitivity, precision and reproducibility. The method was useful for the study of pholcodine metabolism in man. Pholcodine was found to conjugate with glucuronic acid. Morphine was identified as a metabolite and another unidentified metabolite was also detected.

Chromatography, Gas↗
PubMed1990

Automated column-switching high-performance liquid chromatographic determination of flumequine and oxolinic acid in extracts from fish.

Two methods for automated analysis of extracts from edible muscle tissue of Atlantic salmon are described. Oxolinic acid and flumequine are extracted with phosphate buffer pH 9, and the extracts are analysed by high-performance liquid chromatography using a column-switching system. One method applies on-line concentration and clean-up of the extracts on a precolumn packed with polystyrene-divinylbenzene. This method was useful for the analysis of oxolinic acid and flumequine in the microgram/g range. The other method was based on on-line dialysis and concentration of the dialysate on the polymeric precolumn. This method was shown to be a reliable method for residue analysis, and the limit of detection was 2 ng/g for oxolinic acid and 3 ng/g for flumequine with fluorescence detection.

Animals↗
PubMed1989

Solid-phase extraction and high-performance liquid chromatographic determination of flumequine and oxolinic acid in salmon plasma.

Two methods for determination of oxolinic acid and flumequine in salmon plasma are described. The first method applies sample pretreatment on C2 disposable solid-phase extraction columns. The second method is based on direct plasma injection and on-line sample clean-up on a polystyrene-divinylbenzene precolumn. After column-switching, the analytes are separated on a polystyrene-divinylbenzene analytical column and detected with a fluorescence detector. Validation of the methods showed good sensitivity, precision and reproducibility. Both methods are well suited for determination of plasma levels of the drugs in pharmacokinetic studies in Atlantic salmon.

Animals↗
PubMed1989

High-performance liquid chromatographic determination of (R)-and (S)-proxyphylline in human plasma.

A reversed-phase high-performance liquid chromatographic assay has been developed for determination of (R)-(--)-and (S)-(+)-proxyphylline in human plasma. The procedure is based on liquid-solid extraction of proxyphylline from plasma followed by derivatization of extracted proxyphylline with (--)-camphanoyl chloride. The ratio between the enantiomers is calculated from the peak areas of the corresponding diastereoisomeric proxyphylline camphanates after injection into the liquid chromatograph. The recovery of proxyphylline from plasma was 88% (coefficient of variation = 4%) and proxyphylline was detectable from a plasma concentration of 0.2 micrograms/ml. Three different plasma extraction procedures for proxyphylline using Extrelut, Bond Elut, and Chem Elut columns have been developed and compared, and the rate of derivatization of the proxyphylline enantiomers with camphanoyl chloride has been studied.

Aminophylline↗
PubMed1989

Handling of psilocybin and psilocin by everted sacs of rat jejunum and colon.

Psilocybin and psilocin at luminal concentrations of about 20 nmol/ml were incubated aerobically with everted sacs from rat jejunum and colon. When incubation was terminated, samples of the lumen and blood side solutions and of the intestinal tissue were analyzed for parent drug and metabolites by HPLC using a multidetector system. Both sacs caused hydrolysis of psilocybin to psilocin, but the rate was much faster in the jejunum than in the colon. Tissue uptake of intact psilocybin was negligible or absent, and no transfer to the contraside of the parent drug could be demonstrated. In contrast, psilocin, whether formed by hydrolysis or added as a substrate, was well taken up by both intestinal segments and transferred to the blood side. In the colonic psilocybin experiments, this uptake and transfer was limited by a low hydrolytic rate. The results indicate that psilocybin under in vivo conditions is absorbed predominantly as psilocin. No further metabolism of either drug was observed, as opposed to the complex metabolism pattern that has been reported for serotonin, a close chemical relative to psilocin.

Animals↗
PubMed1986

Profiling of impurities in illicit amphetamine samples by high-performance liquid chromatography using column switching.

A simple high-performance liquid chromatographic method, suitable for routine profiling of impurities in illegally produced amphetamine, has been developed. Amphetamine is dissolved in acetonitrile-citrate buffer (pH 3) (2:8) and injected directly without further sample pre-treatment. The impurities are enriched on-line on a C8 extraction column, while amphetamine and polar diluents are washed out with water. After washing for 1.5 min, a six-port valve is switched and an acetonitrile-0.2 M butylamine in water (pH 8) gradient elutes the impurities from the extraction column on to a C18 analytical column where they are separated. The compounds are monitored by UV detection at 220 and 254 nm. The total extraction and analysis time is 30 min. The method allows automated extraction and analysis to be performed.

Adsorption↗