Zeitschrift für Chromatographie und Trenntechniken
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An Improved HPLC Method for Quantification of Metanephrine with Coulometric Detection

Pedro AQ, Soares RF, Oppolzer D, Santos FM, Rocha LA, Goncalves AM, Bonifacio MJ, Queiroz JA, Gallardo E and Passarinha LA

A rapid and straightforward analytical method, based on the use of RP-HPLC with coulometric detection, was developed and validated for the quantification of metanephrine, an O-methylated product in catechol-Omethyltransferase enzymatic assays. The isocratic separation was achieved on a reverse column with a mobile phase consisting of 0.1 M sodium dihydrogen phosphate, 0.024 M citric acid monohydrate, 0.5 mM sodium octyl sulphate and 9% acetonitrile (%v/v). The method was found to be linear between 0.25 and 15 nmol/mL with a determination coefficient of 0.9997 for metanephrine. Intra-and interday precision and accuracy were in conformity with the criteria accepted in bioanalytical method validation and the LOD and LLOQ were 0.25 nmol/mL. The main focus of the developed method is the lower LLOQ achieved that can have important implications in laboratory research for COMT activity determinations, in particular for the methionine 108/158 variant obtained either from native or recombinant extracts. Another major advantage of the present method is the shorter run times on automated chromatographic systems that allow the analysis of several samples in a short time. In addition, metanephrine was stable in the samples for at least 24 h at room temperature, for at least 24 h in HPLC system injector and for at least three freeze/thaw cycles. The developed method demonstrated higher sensitivity, precision, accuracy, stability, and linearity when compared with the methods previously described. Finally, a catechol-O-methyltransferase