Long-term stability of five atypical antipsychotics (risperidone, olanzapine, paliperidone, clozapine, quetiapine) and the antidepressant mirtazapine in human serum assessed by a validated SPE LC-MS/MS method

Long-term sample stability of five atypical antipsychoticdrugs risperidone, paliperidone, clozapine, quetiapine and olanzapine and the antidepressant drug mirtazapine in serum was studied by use of a newly developed and validated analytical method based on solid-phase extraction and liquid chromatography-tandem mass spectrometry. Ascorbic acid was used as an antioxidative agent to stabilize olanzapine during storage and sample preparation.We assessed analyte stability on long-term storage in serum samples at 25 degrees C, 5 degrees C, -20 degrees C and -80 degrees C, and during five freeze-thaw cycles. Analytes were stable for 23 days at room temperature except for olanzapine and mirtazapine (17 days). All analytes were stable for at least 30 days at 5 degrees C. All analytes were stable for 270 days at -20 degrees C, except for paliperidone and mirtazapine with 60 days and 180 days, respectively. All analytes were stable for 270 days at -80 degrees C. Furthermore, all analytes were stable for five freeze-thaw cycles.We recommend storage at -80 degrees C when samples drawn for analysis of antipsychotic drugs are stored for more than 60 days, whereas a temperature of -20 degrees C is sufficient for storage less than 60 days.