Non-aqueous capillary electrophoresis of biological samples after at-line solid-phase extraction

Solid-phase extraction (SPE) was coupled at-line to capillary electrophoresis (CE) for the determination of a series of basic test compounds (i. e. tricyclic antidepressants). The analysis was performed using a non-aqueous CE buffer, which resulted in baseline separation of all test compounds. This is in marked contrast with CE using aqueous buffers where hardly any separation was obtained either with or without micelles. The SPE procedure was used to remove simultaneously most of the water from the sample, because no direct analysis of aqueous samples is possible when a non-aqueous CE buffer is used. With the present method the antidepressants can be determined in both urine and serum. Analyte detectability is increased up to 10-fold due to trace enrichment during the extraction process; the limits of detection (LODs; UV 214 nm) are 30–300 ng mL−1 in urine and 300–1000 ng mL−1 in serum. TheRSD values (n=5) of the within-day and between-day precision are below 9% and 11% respectively. Therefore, the present procedure can be used for drug monitoring.