A Rapid Determination of Taurine in Human Plasma by LC

Taurine is an amino acid which is not incorporated into proteins but found in the cytosol of many mammalian cells, in high concentrations (2–30 mM). Increase in plasma taurine concentration has already been reported after surgical trauma, X-radiation, muscle necrosis, carbon tetrachloride-induced liver damage, and paracetamol overdose. Plasma taurine concentration was measured using LC with fluorescence detection following derivatization by o-phtalaldehyde plus 3-mercapto-propionic acid and α-aminobutyric acid as internal standard. Under these conditions the retention time of taurine was 10 min. This method was sensitive enough, to quantify 150 pg mL⁻¹ and detect 50 pg mL⁻¹ of taurine ranging normally between 65 and 179 mmol L⁻¹ (8–22 μg mL⁻¹). The validated method allowed simple determination of human plasma taurine in pharmacokinetic and biomarker studies.

     

Mass spectral studies towards more reliable measurement of perfluorooctanesulfonic acid and other perfluorinated chemicals (PFCs) in food matrices using liquid chromatography/tandem mass spectrometry

Liquid chromatography/mass spectrometry (LC/MS) experiments are described, leading to a reliable method for the measurement of perfluorooctanesulfonic acid (PFOS) and other perfluorinated chemicals (PFCs) in foods. Separations were performed on new fluorinated stationary phases, RP Octyl (‐C₈F₁₇) or propyl‐perfluorobenzene (‐C₃H₆‐C₆F₅), to ensure resolution of PFOS and interfering taurohydroxycholate isomers. Aqueous ammonium formate (5 mM) and methanol were used as the mobile phases. The mass spectrometer was operated in negative electrospray ionisation mode, recording two transitions for each analyte and one for each internal standard. The purities of the analytical standards for the eleven target perfluoro analytes (C₇ to C₁₂ carboxylic acids, C₄, C₆ and C₈ sulfonic acids, and octanesulfonamide (PFOSA)) were found to be in close agreement with the supplied values; the lowest purity was 91%. Five candidate internal standards were investigated, ¹³C₄‐PFOS, ¹³C₄‐perfluorooctanoic acid, ¹³C₂‐perfluorodecanoic acid, D₉‐n‐ethylperfluorooctanesulfonamidoethanol (D₉‐n‐Et‐FOSE) and D₃‐n‐methylperfluorooctanesulfonamide (D₃‐n‐Me‐FOSA); the purities were all >98%. The use of tetrahydro‐PFOS generated backgrounds (>1 µg/kg) for perfluoroheptanoic acid and perfluorobutanesulfonic acid. Similarly D₉‐n‐Et‐FOSE was unacceptable and D₃‐n‐Me‐FOSA was volatile, leaving no clear candidate for normalisation of the measurement of PFOSA. Severe matrix‐induced suppression and enhancement effects influenced ionisation, making external calibration and quantification problematic. This was addressed by a parallel standard addition and matrix‐matching approach, comparing ionisation in methanol, in procedural blanks and in food‐based extracts. The limits of detection (LODs) of 0.001–0.01 µg/kg in solvent and 0.01–1 µg/kg in foods demonstrate that this method is suitable for the determination of PFCs in all food to the required 1 µg/kg reporting level. © Crown copyright 2009. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.     

Acid-catalysed acylations of bicyclo[3.3.1]nonan-2,6-diones: A novel preparation of the adamantane skeleton

The acid-catalysed acylations of bicyclo[3.3.1]nonan-2,6-dione 1 and its 9-thia-2 and 9-oxa-3 analogues with Ac₂O are described. At high acidity, C-acylation is favoured over O-acylation and for 1 and 2 intramolecular aldol condensation occurs with the formation of adamantanes 18 and 19 and 2-thiaadamantanes 15 and 16. These results are compared with alternative acylations of 2 using 2-acetoxypropene, (PhCO)₂O and acid halides.     

Analysis of glutamate in striatal microdialysates using capillary electrophoresis and laser-induced fluorescence detection

High-performance liquid chromatography (HPLC) with electrochemical detection has been used routinely to analyse the neurochemical constituents of brain microdialysates. However, conventional HPLC analysis requires large injection volumes and hence lengthy dialysis sampling times. Capillary electrophoresis (CE) is a rapid high-resolution separation technique with the ability to routinely handle very small sample volumes. If CE is coupled to a high-sensitivity detection system, such as laser-induced fluorescence (LIF), it becomes a powerful and rapid separation technique for the analysis of small-volume microdialysis samples.

These preliminary studies report reduced separation times for the excitatory amino acid glutamate, prederivatised with naphthalene 2,3-dialdehyde, and demonstrate its detection within small-volume brain microdialysis samples. The limit of detection for this system was 10⁻⁸ M.

Characterisation of striatal microdialysis samples comprised infusions of Ca²⁺-free artificial cerebrospinal fluid (aCSF) and Tetrodotoxin (TTx) (10 mM) to demonstrate that the detected transmitter is of neuronal origin and released in a calcium-dependent manner.

Removal of calcium from aCSF resulted in a decrease in glutamate in dialysis samples. Glutamate release significantly decreased (p<0.05) to ca. 40% of preinfusion control levels after 60 min and this level was maintained throughout the sampling period. These data suggest that glutamate release is, to some degree, a calcium-dependent process. TTx infusion (10 μM) produced a significant (p<0.05) reduction in glutamate release to ca. 10% of preinfusion levels. It would therefore appear that glutamate release is dependent on neuronal activity. In summary, we have demonstrated the establishment of CE-LIF and microdialysis for the measurement of glutamate.     

A Rapid Determination of Taurine in Human Plasma by LC

Taurine is an amino acid which is not incorporated into proteins but found in the cytosol of many mammalian cells, in high concentrations (2–30 mM). Increase in plasma taurine concentration has already been reported after surgical trauma, X-radiation, muscle necrosis, carbon tetrachloride-induced liver damage, and paracetamol overdose. Plasma taurine concentration was measured using LC with fluorescence detection following derivatization by o-phtalaldehyde plus 3-mercapto-propionic acid and α-aminobutyric acid as internal standard. Under these conditions the retention time of taurine was 10 min. This method was sensitive enough, to quantify 150 pg mL^?1 and detect 50 pg mL^?1 of taurine ranging normally between 65 and 179 mmol L^?1 (8–22 μg mL^?1). The validated method allowed simple determination of human plasma taurine in pharmacokinetic and biomarker studies.