Influence of the sample preparation method on the serotonin determination in plasma and platelets

Plasma or platelet serotonin concentration is commonly used to provide information about the serotonergic activity in various psychiatric or neurological diseases. Some difficulties have been described in the measurement of serotonin (5-HT) levels in plasma or platelets. We describe an isocratic liquid-chromatographic assay with amperometric detection for determination of 5-HT in the platelet pellet and in platelet-rich and platelet-poor plasma (PRP and PPP) in sample sizes of 100 microL of plasma. The method uses an RP(18) column and an amperometric detector with a thin-layer type electrochemical fl ow cell, with glassy carbon electrode maintained at a potential of +0.600 V vs an Ag/AgCl reference electrode. Determinations were performed in the presence or in the absence of plasma, since the biological matrix may affect the results. Different validation parameters were analysed: selectivity, accuracy, precision, linearity and stability. Reference values for 5-HT concentration in healthy adults (n = 12) were 6.6 nmol/10(9) platelets, for the platelet pellet, and 5.5 nmol/10(9) platelets, for PRP. The 100 microL sample volume used for the preparation of PPP did not make possible the determination of 5-HT levels with accuracy and precision.