Micellar electrokinetic chromatographic method for the determination of letrozole, citalopram and their metabolites in human urine

A new micellar electrokinetic chromatographic method has been developed to analyse human urine samples containing a combination of a drug used for the treatment of breast cancer (letrozole), an antidepressant (citalopram) and their main metabolites. Best results were obtained by using 15 mM borate buffer (pH 9.2) containing 20 mM sodium dodecyl sulphate and 12% (v/v) 2-propanol as the background electrolyte. The separation was performed through a fused silica capillary at 40 °C with the application of 6 s (3.45 kPa) of hydrodynamic injection and 30 kV of separation voltage. Detection wavelength was 240 nm. Under these conditions, the migration times for all the studied compounds were ranged between 3.0 and 8.0 min. Linearity ranges were determined as 0.4-5.0 μg/mL for all the compounds. Detection limits between 12.5 and 25 ng/mL were determined in urine samples. According to the validation study, the developed method has been proven to be accurate, precise, sensitive, specific, rugged and robust. This method has been used to determine letrozole, citalopram and their metabolites in human urine at clinical levels. Prior to determination, the samples are purified and enriched by means of an extraction-preconcentration step with a preconditioned C18 cartridge and by eluting the compounds with methanol. The developed method was applied to the determination of these analytes in three urine samples from patients undergoing treatment with letrozole or citalopram.