Available online at www.sciencedirect.com Journal of Chromatography A, 1185 (2008) 281–290 Micellar electrokinetic chromatographic method for the determination of letrozole, citalopram and their metabolites in human urine J. Rodr´ ıguez Flores ∗ , A.M. Contento Salcedo, M.J. Villase˜ nor Llerena, L. Mu ˜ noz Fern´ andez Department of Analytical Chemistry and Foods Technology, University of Castilla-La Mancha, 13071 Ciudad Real, Spain Received 3 December 2007; received in revised form 22 January 2008; accepted 24 January 2008 Available online 31 January 2008 Abstract 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 g/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 C 18 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. © 2008 Elsevier B.V. All rights reserved. Keywords: Micellar electrokinetic chromatography (MEKC); Letrozole (LE); Citalopram; Breast cancer; Antidepressant; Ruggedness and human urine 1. Introduction Aromatase (estrogen synthetase) is an enzyme that cataly- ses various steps in the conversion of androgens into estrogens. Letrozole (LE) is a potent and selective non-steroidal aromatase inhibitor that limits, for example, the conversion of adrenally generating androstenedione into estrone and testosterone into estradiol in peripheral tissues, as well as in tumours. It significantly also decreases estradiol concentration in serum for postmenopausal women. Besides, about estrogen dependent tumours cell death, it provides a powerful treat- ment for postmenopausal women with hormone-sensitive breast cancer [1]. The recommended therapeutic dose for letrozole is 2.5 mg per day. The major metabolic elimination route of letrozole allows to bis-4-cyanophenylmethanol (ME, its main metabolite) (Fig. 1). Letrozole and its metabolite are excreted ∗ Corresponding author. Tel.: +34 926 295300; fax: +34 926 295318. E-mail address: juana.rflores@uclm.es (J. Rodr´ ıguez Flores). unchanged and their apparent elimination half-life time in plasma has been reported within approximately 2 days [2]. Often, mental disorders such as depression and anxiety may arise secondary to the presence of breast cancer and, in many cases, it is therefore necessary to provide breast cancer patients with antidepressant treatment. Tricyclic antidepressants (TCAs) and selective serotonin re- uptake inhibitors (SSRIs) are frequently used in psychiatry for the treatment of major depression. The SSRIs are a recently introduced group of antidepressants that differ from the TCAs both in their chemical structure and in their mechanism of action, which explain the differences in their metabolism and pharma- cokinetics. The SSRIs are similar to the TCAs in terms of clinical efficacy but, because of their favourable pharmacological profile, they are regarded as safe and well-tolerated drugs [3,4]. Citalopram (CIT) is a commonly prescribed SSRI antidepres- sant; it is well absorbed from the gastrointestinal tract. Kinetic studies of CIT have shown a rapid and almost complete absorp- tion of the compound followed by slow elimination [5,6]. CIT is mainly metabolized in the liver, with the cytochrome sys- 0021-9673/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.chroma.2008.01.067