Biomedical subjects

H Irth

Publications and source records attributed to H Irth.

47 records · Page 3Linked to original sources

PubMed1994

Bioanalysis of digoxin and its metabolites using direct serum injection combined with liquid chromatography and on-line immunochemical detection.

An automated dual-column liquid chromatographic assay for digoxin is described. Serum samples are directly injected onto a restricted-access solid-phase extraction support. After liquid chromatographic (LC) separation on a C18 analytical column, antigenic analytes are detected by means of post-column immunochemical detection (ICD) using fluorescein-labelled antibodies against digoxigenin. The detection limit of this assay is 160 pg/ml (preconcentration of 1.0 ml serum). With the present method digoxin and three of its cross-reactive metabolites were determined in serum taken from patients which were orally administered a 1-mg dose of digoxin. The results obtained with LC-ICD were compared with data provided by a batch immunoassay.

Biomarkers↗

PubMed1993

Liquid chromatographic determination of beta-cyclodextrin derivatives based on fluorescence enhancement after inclusion complexation.

A liquid chromatographic method using fluorescence detection for the determination of beta-cyclodextrin (beta CD) and its derivatives is presented. The chromatographic system is based on size-exclusion chromatography with the addition of the fluorophoric compound 1-naphthol to the mobile phase. Detection is based on fluorescence enhancement caused by the formation of inclusion complexes. By incorporating 10(-4) M 1-naphthol in the mobile phase, detection limits of 90, 27, 370 and 37 pmol were obtained for beta CD, hydroxypropyl-beta CD, trimethyl-beta CD and dimethyl-beta CD, respectively. The method was applied to the determination of dimethyl-beta CD in urine: the minimum detectable concentration was 0.2 microgram/ml after preconcentration of 10 ml of urine.

Chromatography, Liquid↗

PubMed1992

Bioanalysis of some anthracyclines in human plasma by capillary electrophoresis with laser-induced fluorescence detection.

A rapid method for the determination of daunorubicin, doxorubicin and epirubicin in human plasma is described. Samples are pretreated and concentrated by liquid-liquid extraction with chloroform and back-extraction into phosphoric acid, respectively. This pretreatment results in a sample matrix of low ionic strength in comparison with the electrophoresis buffer, permitting a 20-30-fold increase in the injected amount by zone sharpening when electrokinetic injection is applied. Analyte interaction with the capillary wall is prevented by using high acetonitrile contents in the electrophoresis buffer, which results in reproducible migration times and highly efficient separations. Laser-induced fluorescence detection provides an extremely sensitive and selective method without detectable biological interferences. The limit of determination of daunorubicin, epirubicin and doxorubicin in plasma ranges from 125 to 250 pg/ml.

Daunorubicin↗

PubMed1992

Enantioselective determination of R- and S-(alpha-bromoisovaleryl)urea in plasma using high-performance liquid chromatography after solid-phase extraction.

A stereoselective method has been developed for the determination of R- and S-(alpha-bromoisovaleryl)urea in plasma and saliva after oral administration. The chiral separation was carried out on Chiralcel OJ or OD columns with hexane--2-propanol as the mobile phase. The poor detection properties of the analyte required the development of an effective sample pretreatment procedure to enable ultraviolet detection at 210 nm. Solid-phase extraction using hydrophobic Amberlite XAD-2 in combination with washing steps at alkaline and acidic pH completely removed interfering components of the biological matrix and allowed the detection of the optical isomers at concentrations down to 10 ng/ml (0.05 microM). The method was validated by determining the recovery, linearity, accuracy and within-day and between-day repeatability at 50, 200 and 2000 ng/ml. Application to the analysis of plasma and saliva samples is demonstrated.

Bromisovalum↗

PubMed1991

Isotachophoresis as an on-line concentration pretreatment technique in capillary electrophoresis.

One of the major disadvantages of capillary electrophoresis (CE) is its limited loadability. Therefore, the on-line coupling of isotachophoresis (ITP) and CE was studied with regard to its potential for the improvement of the minimum concentration that can be measured by CE. Based on the concentrating and separating power of ITP, detection limits could be lowered by at least two orders of magnitude. Especially for biological samples containing proteins, it appeared that in non-treated capillaries the electromigration characteristics are hardly influenced when isotachophoretic pretreatment is applied. The potential of ITP-CE coupling is illustrated by the analysis of o-phthaldialdehyde and fluorescein isothiocyanate derivatives of a number of amino acids.

Amino Acids↗

PubMed1991

Increasing the effective concentration of melphalan in experimental rat liver tumours: comparison of isolated liver perfusion and hepatic artery infusion.

Regional chemotherapy allows further exploitation of the steep dose response curve of most chemotherapeutic agents, while systemic toxicity remains tolerable. We investigated the difference in maximally tolerated dose, pharmacokinetics and antitumour effect comparing administration of melphalan as a bolus in isolated liver perfusion (ILP) or via hepatic artery infusion (HAI). For these in vivo studies an experimental model for liver metastases in male WAG/Ola rats is obtained by subcapsular inoculation of CC531 rat colon carcinoma cells. In this system, ILP allowed administration of a two times higher dose than HAI (12 mg kg-1 vs 6 mg kg-1). In both treatment modalities systemic toxicity (leukopenia) was dose limiting. No hepatic toxicity was observed. Bolus administration of the maximally tolerated doses of melphalan in HAI (6 mg kg-1) and ILP (12 mg kg-1) resulted in four times higher concentrations in both liver and tumour tissue of the ILP treated rats. However, the ratio of mean drug concentration in liver vs tumour tissue appeared to be 1.5 times that found for HAI. In the range of the in tumour tissue measured melphalan concentrations the CC531 cells showed a steep dose response relationship in vitro. Whereas HAI resulted in significant tumour growth delay, complete remissions were observed in 90% of the rats treated with ILP. This study shows that with 12 mg kg-1 melphalan in ILP highly effective drug concentrations are achieved in CC531 tumour tissue; although the melphalan concentration in liver tissue shows an even higher increase than in tumour tissue, hepatic toxicity is negligible in this dose range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Trace-level determination of 3'-azido-3'-deoxythymidine in human plasma by preconcentration on a silver (I)-thiol stationary phase with on-line reversed-phase high-performance liquid chromatography.

A method was developed for the determination of 3'-azido-3'-deoxythymidine (AZT) in plasma. The method is based on the trace enrichment of AZT on a pre-column packed with a silver-loaded thiol stationary phase at pH 11.6. On-line desorption to the reversed-phase liquid chromatographic system is performed by injecting a plug of 50 microliters of 1 M perchloric acid on the silver (I)-thiol pre-column. Two different sample pretreatment methods - protein precipitation with perchloric acid and on-line clean-up via a polymeric PRP-1 pre-column - were applied for the determination of AZT in human plasma. The latter method allows the direct injection of plasma samples into the analytical system and can therefore easily be automated. With both methods detection limits in the order of 10(-8) M AZT were obtained after preconcentration of 1.0 ml of plasma, using UV detection at 267 nm.

Autoanalysis↗

PubMed1989

Trace enrichment on a metal-loaded thiol stationary phase in liquid chromatography: effect of analyte structure and pH value on the (de)sorption behaviour.

In order to obtain more information on the (de)sorption processes on a metal-loaded thiol phase, various compounds containing heterocyclic nitrogen atoms have been studied. Adenine and adenosine, which contain no carbonyl groups in a position ortho to the ring nitrogen, were chosen to study the role of the binding donor atoms and, therefore, of the 'minimum' structure required for efficient pH-dependent (de)sorption. The results indicate that a single heterocyclic nitrogen atom, preferably with a high pKa value, is sufficient to provide pH-dependent (de)sorption of chelating phases loaded with soft metal ions, such as Ag(I) or Hg(II), which can profitably be used in an on-line combination with column liquid chromatography. Barbiturates were chosen on the basis of their structural similarity with the earlier studied (halogenated) uracil derivatives. The (de)sorption behaviour of the barbiturates was studied as a function of the pH, the metal ion [Cu(II), Ag(I), Hg(II), Pd(II)] bound to the stationary phase and the type of stationary phase. The combined data show that the pKa value of an analyte and the stability constant of the complex formed with the metal ion sorbed on the stationary phase give a reliable indication of the optimum (de)sorption pH. Application of this principle is demonstrated by the determination of four barbiturates in plasma.

Adsorption↗

PubMed1988

Determination of disulfiram and two of its metabolites in urine by reversed-phase liquid chromatography and spectrophotometric detection after post-column complexation.

A selective method was developed for the determination of disulfiram and two of its metabolites, diethyldithiocarbamate (DTC) and copper (II) diethyldithiocarbamate [Cu(DTC)2], in complex (biological) samples by reversed-phase liquid chromatography (RP-LC) with post-column derivatization. In the first step, DTC is converted into lead (II) diethyldithiocarbamate [Pb (DTC)2] by adding lead (II) acetate. Disulfiram, Pb (DTC)2 and Cu (DTC)2 can be easily pre-concentrated on C18-bonded silica. After separation by isocratic RP-LC, derivation takes place in two solid state post-column reactors packed with metallic copper and copper (II) phosphate. Disulfiram reacts with metallic copper to form Cu (DTC)2. The same product is obtained by the ligand-exchange reaction between Pb (DTC)2 and copper (II) phosphate. Cu (DTC)2 can be detected selectively at 435 nm with good sensitivity (molar absorptivity, epsilon = 13,000). The derivatization reactions proceed rapidly and quantitatively, which was confirmed by comparison of absorption spectra. The applicability of this method is demonstrated for undiluted urine samples which, apart from the addition of lead (II) acetate and pre-concentration of C18-bonded silica, require no clean-up procedure.

Biotransformation↗

PubMed1986

Metallic copper-containing post-column reactor for the detection of thiram and disulfiram in liquid chromatography.

A reaction detector has been developed for the selective detection of thiram and disulfiram. The detection is based on the post-column complexation of these analytes on a solid-state reactor packed with finely divided metallic copper to form a coloured copper complex, copper(II) N,N-dimethyldithiocarbamate, with an absorption maximum at 435 nm. The method is combined with a pre-concentration and clean-up step on a pre-column to permit the sub-ppb determination of, e.g., thiram in surface water samples or disulfiram in urine. Separation is achieved by reversed-phase liquid chromatography.

Chromatography, Liquid↗

PubMedDate not supplied

HPLC coupled on-line to ESI-MS and a DPPH-based assay for the rapid identification of anti-oxidants in Butea superba.

A reversed-phase HPLC coupled on-line to a radical scavenging detection system and MS/MS was developed in order to combine separation, activity determination and structural identification of anti-oxidants in complex mixtures in one run. The sample was separated by HPLC and the eluate split into two flows. The major portion was fed into an electrospray ionisation MS/MS system, while the minor part was mixed with a free radical, 2,2'-diphenyl-1-picrylhydrazyl (DPPH), and the reaction determined spectrophotometrically. The negative peaks, which indicated the presence of anti-oxidant activity, were monitored by measuring the decrease in absorbance at 517 nm. The developed method was successfully applied to the identification of anti-oxidant compounds in a fraction, obtained by solid-phase extraction, of an extract of a Thai medicinal plant, Butea superba Roxb. The anti-oxidant compounds were separated and identified as procyanidin B2, (-)-epicatechin and procyanidin B5.

Antioxidants↗