Determination of exifone in human plasma and urine by high-performance liquid chromatography with electrochemical detection

A high-performance liquid chromatographic method with electrochemical detection was developed for the determination of exifone in human plasma and urine. Exifone was extracted from acidified plasma or neutralized urine with diethyl ether and the evaporated extracts were analysed on a C18 reversed-phase column. The compound was eluted in about 8 min with acetonitrile-0.3 M orthophosphoric acid (15:85, v/v) at a flow-rate of 0.9 ml/min. This method gave accurate and reproducible results; the calibration graphs were linear (r greater than 0.99) over the range of 2.8-360 nmol/l for plasma and 0.18-36 mumol/l for urine, and concentrations as low as 1 nmol/l in plasma could be quantified. These results allowed this assay to be used for determinations in single-dose pharmacokinetic studies.     

Determination of phosphonoformic acid in human plasma and urine by high-performance liquid chromatography with electrochemical detection

Trisodium phosphonoformate (foscarnet) is used in the treatment of cytomegalovirus infections in immunocompromised patients, such as bone marrow and renal transplant recipients, as well as patients with the acquired immune deficiency syndrome. A simple high-performance liquid chromatographic assay is described using an electrochemical detector. The method is accurate, precise and reproducible. Hydrochlorothiazide is used as the internal standard. This assay allows measurement of foscarnet in biological fluids at concentrations as low as 33 microM. This method is being used for the analysis of samples in clinical trials and is important in the evaluation of the pharmacokinetic disposition of the drug.     

Analysis of vinca alkaloids in plasma and urine using high-performance liquid chromatography with electrochemical detection

The reversed-phase high-performance liquid chromatography with electrochemical detection was used to quantify plasma and urine levels of vinblastine, vincristine, vindesine and a metabolite of vinblastine, desacetylvinblastine. Sample clean-up consisted of solid-phase extraction with a Bond Elut CN column. The extracts were separated on a Hypersil ODS column. The mobile phase consisted of a mixture of methanol and 10 mM phosphate buffer (pH 7.0). The limit of sensitivity using electrochemical detection was 100 pg on-column for all compounds with a signal-to-noise ratio of 3. Quantification of the compounds in human plasma and urine was possible down to 1 ng/ml (ca. 1 pmol). Pharmacokinetic results show that the sensitivity of the method is adequate for drug monitoring in clinical research.     

Determination of vinclozolin metabolites in human urine by high-performance liquid chromatography and electrochemical detection

A sensitive and reliable method to assess occupational exposure to vinclozolin based on biomonitoring principles has been elaborated. The conditions for pretreating the human urinary samples were chosen in such a way that vinclozolin metabolites containing the intact 3,5-dichloroaniline (3,5-DCA) moiety are completely degraded into this amine by means of basic hydrolysis. After addition of 3,4-DCA as an internal standard, steam distillation and extraction, the analysis is carried out by high-performance liquid chromatography and electrochemical detection. The determination limit is 5 g 3,5-DCA/l urine. The method turned out to be sensitive enough to quantify not only occupational but also nutritional excretions of 3,5-DCA containing metabolites to some extent. Interpreting these results, which are verified by an independent method, it must be considered that in addition to vinclozolin some further crop protection agents are also based on the 3,5-DCA moiety.     

Determination of vinclozolin metabolites in human urine by high-performance liquid chromatography and electrochemical detection

A sensitive and reliable method to assess occupational exposure to vinclozolin based on biomonitoring principles has been elaborated. The conditions for pretreating the human urinary samples were chosen in such a way that vinclozolin metabolites containing the intact 3,5-dichloroaniline (3,5-DCA) moiety are completely degraded into this amine by means of basic hydrolysis. After addition of 3,4-DCA as an internal standard, steam distillation and extraction, the analysis is carried out by high-performance liquid chromatography and electrochemical detection. The determination limit is 5 microg 3,5-DCA/l urine. The method turned out to be sensitive enough to quantify not only occupational but also nutritional excretions of 3,5-DCA containing metabolites to some extent. Interpreting these results, which are verified by an independent method, it must be considered that in addition to vinclozolin some further crop protection agents are also based on the 3,5-DCA moiety.     

Measurement of plasma and urine amino acids by high-performance liquid chromatography with electrochemical detection using phenylisothiocyanate derivatization

The use of reversed-phase liquid chromatography (LC) with pre-column derivatization for the analysis of amino acid mixtures is becoming established as a possible cheaper alternative to commercial amino acid analysers. The available derivatization procedures all have disadvantages when applied to clinical samples, partly due to the interferences found with body fluids when ultraviolet or fluorescence detection is used. An LC method is described for the separation of amino acids in blood or urine, using pre-column derivatization with phenylisothiocyanate (PITC), gradient elution and electrochemical detection. The use of electrochemical detection of PITC derivatives virtually eliminates interferences and enables the secondary amino acids to be measured. Examples are shown of normal urine and plasma and samples from patients with cystinuria and maple syrup urine disease.     

Determination of cabergoline in plasma and urine by high-performance liquid chromatography with electrochemical detection.

A sensitive and selective high-performance liquid chromatographic method for the determination of cabergoline in plasma and urine has been developed. After buffering plasma and urine samples, cabergoline was extracted with a methylene chloride-isooctane mixture, back-extracted into 0.1 M phosphoric acid, then analysed by reversed-phase high-performance liquid chromatography. Quantitation was achieved by electrochemical detection of the eluate. The linearity, precision and accuracy of the method were evaluated. No interference from the biological matrices (human plasma and urine) was observed. The assay was still inadequate in terms of sensitivity for the quantitation of cabergoline plasma concentrations after a single oral dose of 1 mg of the drug to humans, but was successfully used in the determination of the urinary excretion of the drug.     

Sample preparation procedure for determination of dopamine sulfate isomers in human urine by high-performance liquid chromatography with dual-electrode electrochemical detection

We developed a procedure utilizing small columns of solid-phase extraction material for sample preparation for the determination of dopamine sulfate (DAS) isomers in human urine. Processed sample is then subjected to high-performance liquid chromatography (HPLC) with dual-series-electrode electrochemical detection. Dopamine 3-O-sulfate (DA-3-S) and dopamine 4-O-sulfate (DA-4-S) were determined using two different HPLC systems. The ratio of the urinary excretion rate of DA-3-S to DA-4-S was relatively constant, but the 24-h excretion rates of total DAS varied widely among individuals. This method should prove useful in future studies concerning the metabolic and physiologic roles of DAS isomers.     

Gunshot residue determination by high-performance liquid chromatography with electrochemical detection

A procedure for the detection of gunshot residue via the organic constituent diphenylamine is described. The method incorporates high-performance liquid chromatography with electrochemical detection.     

Simultaneous determination of clarithromycin and 14(R)-hydroxyclarithromycin in plasma and urine using high-performance liquid chromatography with electrochemical detection.

A sensitive method for the simultaneous high-performance liquid chromatographic determination of clarithromycin and its active metabolite in plasma and urine is described. Alkalinized samples were coextracted with an internal standard and analyzed on a C8 column using electrochemical detection. Recoveries were greater than or equal to 85% and consistent. Standard curves for plasma were linear in the range 0-2 micrograms/ml for both compounds (r greater than 0.99), with limits of quantification of approximately 10.03 micrograms/ml (0.5-ml sample). Within-day and day-to-day precision were good, with coefficients of variation mostly within +/- 5%; accuracy for both compounds were routinely within 90-110% of theoretical values. Standard curves for urine were linear in the range 0-100 micrograms/ml with limits of quantification of 0.5 micrograms/ml (0.2-ml sample). Urine assays also had similar within-day and day-to-day precisions and accuracy.