Analysis of risperidone and its metabolite in plasma and saliva by LC with coulometric detection and a novel MEPS procedure

A new analytical method, based on the use of liquid chromatography with coulometric detection, has been developed and applied to quantify risperidone and its main active metabolite 9-hydroxyrisperidone in human plasma and saliva. The analytes were separated on a reversed phase C18 column, using a mobile phase composed of acetonitrile (26%) and a pH 6.5 phosphate buffer (74%). Pipamperone was used as the internal standard. A high sensitivity coulometric detection analytical cell containing two flow-through working electrodes was used: electrode 1 was set at +0.500 V and electrode 2 at +0.700 V. The detector response was linear over a plasma and saliva concentration range of 0.5–50.0 ng mL−1 for risperidone and 0.5–100.0 ng mL−1 for 9-hydroxyrisperidone. The limit of quantitation and the limit of detection for risperidone and 9-hydroxyrisperidone were 0.5 ng mL−1 and 0.17 ng mL−1, respectively. A novel clean-up procedure of biological samples was developed using the microextraction by packed sorbent technique, which gave good extraction yield for both the analytes, with absolute recovery values higher than 90.1%. The intra-day and the inter-day precision results, expressed by relative standard deviation values, were lower than 5.8%. Accuracy and selectivity assays were also satisfactory. The validated method has been successfully applied to the analysis of risperidone and 9-hydroxyrisperidone in plasma and saliva of psychiatric patients undergoing therapy with risperidone.