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A new bioanalytical method for the determination of melatonin in plasma with high-performance liquid chromatography (HPLC) and fluorescence detection preceded by solid-phase extraction has been developed and validated. Melatonin was extracted from 3 mL plasma using a Waters Oasis HLB solid-phase extraction cartridge and the elute was evaporated to dryness and dissolved in 200 microl mobile phase; acetonitrile-phosphate buffer, 0.01 M pH 7.2 (25:75, v/v). 125 microL was injected into the HPLC system and separation was carried out on a Waters SymmetryShield RP18 column 5 microm (250 x 4.6 mm). Excitation and emission wavelengths were set to 285 nm and 345 nm, respectively. The HPLC system was able to separate melatonin and internal standard (5-fluorotryptamine) from other endogenous indole compounds such as serotonin and tryptophan. Determination down to 0.10 nmol/L was possible, with an intra-assay precision of about 13%. Melatonin was stable in plasma for at least 30 days at about 23 degrees C.

A sensitive bioanalytical method for the determination of melatonin in saliva by solid‐phase extraction (SPE), high‐performance liquid chromatography (HPLC) and fluorescence detection has been developed and validated. Saliva was collected with a Salivette^® sampling device (Sarstedt) and a mixed‐mode SPE column was used for the extraction of melatonin and internal standard (N‐acetyl‐6‐methoxytryptamine) from the saliva. Chromatographic separation was performed using a HyPurity C18 LC column (150×2.1mm) with mobile phase acetonitrile – ammonium hydrogen carbonate buffer, 0.015M, pH6.8 (23:77, v/v). Excitation and emission wavelengths were set to 285nm and 345nm, respectively. The within‐day precision for the method at 50pmol/L was 7.9 % and the between‐day precision was 10.5 %. The limit of quantification was 50pmol/L.

A bioanalytical method for indirect determination of eflornithine enantiomers in 75 mu L human plasma has been developed and validated. L- and D-eflornithine were derivatized with o-phthalaldehyde and N-acetyl-L-cysteine to generate diastereomers which were separated on two serially connected Chromolith Performance columns (RP-18e 100 x 4.6 mm i.d.) by a isocratic flow followed by a gradient flow for elution of endogenous compounds. The diastereomers were detected with UV (340 nm). The between-day precisions for L- and D-eflornithine in plasma were 8.4 and 2.3% at 3 mu m, 4.0 and 5.1% at 400 mu m, and 2.0 and 3.7% at 1000 mu m. The lower limit of quantification was determined to be 1.5 mu m, at which precision was 14.9 and 9.9% for 1- and D-eflornithine, respectively.

A bioanalytical method for the determination of lumefantrine in 100 μl blood applied onto sampling paper, by solid-phase extraction and liquid chromatography, has been developed and validated. Whatman 31 ET Chr sampling paper was pre-treated with 0.75 M tartaric acid before sampling capillary blood to enable a high recovery of lumefantrine. Lumefantrine was extracted from the sampling paper, then further purified using solid-phase extraction and finally quantified with HPLC. The between-day variation was below 10% over the range 0.4-25 μM. The lower limit of quantification was 0.25 μM in 100 μl capillary blood. No decrease in lumefantrine concentration in dried blood spot is seen after 4 months storage at 22 °C. The method was also evaluated in field samples from patients in Tanzania after treatment with lumefantrine/artemether. Lumefantrine could be estimated accurately enough to assess bioavailability and treatment compliance on day 7 (i.e. 4 days after the last dose) after a standard regimen with the lumefantrine/artemether combination.