Automated Analysis of Antipsychotic Drugs Using Liquid Chromatography with Column Switching

Rapid and valid analysis of psychoactive drugs is expensive, when only few samples are analysed within one series. Samples are therefore often stored for several days to obtain sufficiently large sample numbers. Using assays that enable the determination of different drugs by the same procedure and that are run daily are advantageous. For psychoactive drugs a most suitable method is liquid chromatography with direct injection of serum or plasma without or with deproteinization followed by sample clean-up on a pre-column, column switching and chromatographic separation. For quantification spectrophotometry or mass spectrometry are available. We developed methods with spectrophotometric detection (HPLC-UV) and mass spectrometry (LC-MS) for determination of antipsychotic drugs.

HPLC-UV: Using C8 silica material for clean-up (20µm, 10×4.0mm I.D.), ODS Hypersil C18 (5µm, 250×4.6mm) and isocratic elution, the HPLC-UV method enabled determination of olanzapine, clozapine, norclozapine, quetiapine and perazine within a 30min run. The lower limit of quantification ranged between 5 and 50 ng/ml. The method was cheap and robust. However, it was not able to determine risperidone and its active metabolite or typical antipsychotic drugs like haloperidol because of insufficient sensitivity.

LC-MS: Using LC-MS with automated on line extraction, it was able to quantify amisulpride, clozapine, norclozapine, clozapine-N-oxide, haloperidol, risperidone, 9-hydroxyrisperidone, olanzapine, perazine, quetiapine and ziprasidone. C8 silica material (20µm, 10×4.0mm I.D.) was used for clean-up of deproteinized blood. After activation of the switching valve, samples were separated on a C12 column (4µm, 150×3.0 I.D.). [M+H]⁺ ions were detected in the selected ion mode within 6min with sufficient intra- and inter-day precision (<10%).

HPLC-UV or LC-MS with on line column switching are both suitable for TDM of antipsychotic drugs. The HPLC-UV method is inexpensive, but its lower limit of detection may be too high. LC-MS is more flexible but expensive than HPLC-UV. It may be applied to multiple new and old antipsychotic drugs.