Spherisorb silica column

EDTA plasma samples were processed by protein precipitation of 50 µL plasma with 200 µL ice-cold 0.4% citric acid in acetonitrile containing 15 ng/mL aripiprazole-d₈. The samples were mixed for 10 min in a shaking apparatus followed by centrifugation at 5000g for 10 min at 15 °C and 150 µL supernatant was transferred to a 2 mL deep well plate. Calibration standards and quality control (QCs) were prepared by adding standard solution to blank plasma and prepared similarly to the plasma samples. The analysis was performed by HPLC–MS/MS using a Waters Acquity-Xevo TQ system controlled by UNIFI. The separation was done on a Waters Spherisorb Silica column (3 µm, 100 × 2.1 mm²) with a mobile phase consisting of water/acetonitrile (25/75 v/v) containing 1% formic acid, at a flow rate of 0.8 mL/min and a column oven temperature of 45 °C. A 3 µL sample was injected in partial loop with needle overfill mode. The mass spectrometer was operated in the positive electrospray mode with a desolvation temperature of 650 °C. The analytes were detected by multiple-reaction-monitoring: aripiprazole lauroxil (660.39–460.16 m/z), N-hydroxymethyl aripiprazole (478.17–448.16 m/z) and aripiprazole (476.15–285.09 m/z). The run time of the assay was 3.5 min with the peaks eluting between 1.45 and 1.84 min. The assay showed linearity over the concentration range of 2.00–1000 ng/mL.