Determination of thymol in human plasma by automated headspace solid-phase microextraction-gas chromatographic analysis

A reliable and sensitive method was developed for determination of thymol in human plasma by automated headspace solid-phase microextraction (SPME). After enzymatic cleavage of thymol sulfate thymol was extracted by a 65 microm polydimethylsiloxane-divinylbenzene crimped fiber (Supelco) after addition of sodium chloride and phosphoric acid (85%). Desorption of the fiber was performed in the injection port of a gas chromatograph at 220 degrees C (HP 5890; 50 m x 0.2 mm I.D., 0.2 microm HP Innowax capillary column; flame ionization detection). Fibers were used repeatedly up to 40 analysis. The recovery was 5% after 35 min of extraction. The calibration curve was linear in the range of 8.1-203.5 ng ml(-1) with a limit of quantitation (LOQ) of 8.1 ng ml(-1). The within-day and between-day precision and accuracy were < or = 20% at the LOQ and <15% at higher concentrations according to international guidelines for validation of bioanalytical methods. After administration of a thymol-containing herbal extract only thymol sulfate, no free thymol, could be detected in human plasma, thus analysis of thymol was after enzymatic cleavage of thymol sulfate. It is concluded that the newly developed automated method can be used in clinical trials on bioavailability and pharmacokinetics of thymol-containing herbal medicinal products.

A validated high-performance liquid chromatographic assay for the simultaneous determination of denaverine and its N-monodemethyl metabolite in human plasma

An isocratic reversed-phase high-performance liquid chromatographic method for the simultaneous determination of denaverine and its N-monodemethyl metabolite (MD 6) in human plasma is described. The assay involves the extraction with an n-heptane-2-propanol mixture (9:1, v/v) followed by back extraction into 12.5% (w/w) phosphoric acid. The analytes of interest and the internal standard were separated on a Superspher RP8 column using a mobile phase of acetonitrile-0.12 M NH4H2PO4-tetrahydrofuran (24:17.2:1, v/v), adjusted to pH 3 with 85% (w/w) phosphoric acid. Ultraviolet detection was used at an operational wavelength of 220 nm. The retention times of MD 6, denaverine and the internal standard were 5.1, 6.3 and 10.2 min, respectively. The assay was validated according to international requirements and was found to be specific, accurate and precise with a linear range of 2.5-150 ng/ml for denaverine and MD 6. Extraction recoveries for denaverine and MD 6 ranged from 44 to 49% and from 42 to 47%, respectively. The stability of denaverine and MD 6 in plasma was demonstrated after 24 h storage at room temperature, after three freeze-thaw cycles and after 7 months frozen storage below -20 degrees C. The stability of processed samples in the autosampler at room temperature was confirmed after 24 h storage. The analytical method has been applied to analyses of plasma samples from a pharmacokinetic study in man.

Determination of platinum complexes in clinical samples by a rapid flameless atomic absorption spectrometry assay

The frequent use of platinum (Pt) complexes in cancer chemotherapy and the application of new therapeutic options and dosing strategies have increased the need for rapid analytic procedures to determine Pt concentrations in the biologic fluids of patients. Therefore a flameless atomic absorption spectrometry method for the quantification of Pt in plasma and ultrafiltrate was developed and validated. A simple sample preparation of only one dilution step was established. Only 400 microL of whole blood was required for duplicate analysis of Pt in both matrices. The matrix-specific temperature programs took less than 75 seconds. The lower limit of quantification was 40 ng Pt/mL and 20 ng Pt/mL for plasma and ultrafiltrate, respectively. Suitable linearity could be reached using separate calibration curves for the high and low Pt concentration ranges. Recovery of Pt was complete, and there were no major stability problems. The accuracy and precision of the new method met the international criteria for the validation of bioanalytic methods. In addition, the use of different anticoagulants for clinical sampling, ultrafiltration systems, and ultrafiltration conditions were investigated. The assay has already been extensively applied to pharmacokinetic studies. In conclusion, the new Pt assay proved to be rapid, simple, sensitive, and suitable for clinical use.

On-line coupling of automated solid-phase extraction with high-performance liquid chromatography and electrochemical detection. Quantitation of oxidizable drugs of abuse and their metabolites in plasma and urine

The concentration effect of automated on-line solid-phase extraction (SPE) in combination with HPLC and very sensitive electrochemical detection was employed for the determination of N-ethyl-4-hydroxy-3-methoxy-amphetamine (HMEA, the main metabolite of the ecstasy analogue MDE), delta 9-tetrahydrocannabinol (THC) and 11-nor-delta 9-tetrahydrocannabinol-carboxylic acid (THC-COOH) in plasma and urine in comparison to a previously published psilocin assay. For the SPE either CBA (functional group: carboxypropyl)- or CH (functional group: cyclohexyl)-sorbent was used. The following separation was carried out on a reversed-phase column (LiChroCart, Superspher 60 RP select B from Merck). Depending on the hydrodynamic voltammogram of the analyzed substance the oxidation potential varied from 920 mV up to 1.2 V. In spite of using high potentials, precision and accuracy were always within the accepted statistical requirements. The limits of quantitation were between 5 ng/ml (THC, THC-COOH in plasma) and 20 ng/ml (HMEA in plasma). Advantages of on-line SPE in comparison with off-line methods were less manual effort, evidently smaller volumes (< or = 400 microliters) of plasma or urine and almost always higher recovery rates (> 93%). The assays have been successfully proven with real biological samples and found suitable for use in routine analysis.

Enantioselective bioanalysis of beta-blocking agents: focus on atenolol, betaxolol, carvedilol, metoprolol, pindolol, propranolol and sotalol

The recent developments in enantioselective HPLC-separation techniques are impressive and are driven by industrial and academic interests; thus there is for instance a high demand for developing stereoselective assays for chiral drugs in biological fluids. The beta-blocking agents, which possess an amino-propanol- or -ethanol side chain with at least one chiral centre, represent one of the most intensively investigated groups of more than 40 drugs introduced world wide. Seven of the most popular beta-blockers were chosen as representatives: atenolol; betaxolol; carvedilol; metoprolol; pindolol; propranolol; and sotalol, these span the whole range of lipophilicity to hydrophilicity (polarity). Enantioselective HPLC bioassays for these beta-blockers published so far, including techniques based on chiral derivatizing agents (CDAs), chiral stationary phases (CSPs) and chiral mobile phase additives (CMPAs) have been reviewed and documented in the light of general aspects together with pharmacokinetic and pharmacodynamic considerations.