Available online at www.sciencedirect.com Journal of Chromatography B, 858 (2007) 269–275 Determination of duloxetine in human plasma by liquid chromatography with atmospheric pressure ionization–tandem mass spectrometry and its application to pharmacokinetic study P. Senthamil Selvan, K. Veeran Gowda, U. Mandal, W.D. Sam Solomon, T.K. Pal ∗ Bioequivalence Study Centre, Department of Pharmaceutical Technology, Jadavpur University, Kolkata 700032, India Received 20 February 2007; accepted 2 September 2007 Available online 14 September 2007 Abstract A rapid, sensitive and accurate liquid chromatographic–tandem mass spectrometry (LC–MS–MS) method is described for the determination of duloxetine in human plasma. Duloxetine was extracted from plasma using methanol and separated on a C18 column. The mobile phase consisting of a mixture of acetonitrile and 5 mM ammonium acetate (45:55, v/v, pH 3.5) was delivered at a flow rate of 0.3 ml/min. Atmospheric pressure ionization (API) source was operated in positive ion mode. Multiple reaction monitoring (MRM) mode using the transitions of m/z 298.1 → m/z 44.0 and m/z 376.2 → m/z 123.2 were used to quantify duloxetine and internal standard (I.S.), respectively. The linearity was obtained over the concentration range of 0.1–50.0 ng/ml and the lower limit of quantitation (LLOQ) was 0.1 ng/ml. This method was successfully applied to pharmacokinetic study of a duloxetine formulation product after oral administration to healthy human subjects. © 2007 Elsevier B.V. All rights reserved. Keywords: Duloxetine; LC-API–MS–MS 1. Introduction Duloxetine hydrochloride is chemically known as (+)-N- methyl-3(1-naphthalenyloxy)-2-thiophenepropanamine hydrochloride (Fig. 1), it is a potent dual inhibitor of serotonin (5-hydroxytryptamine (5-HT)) and norepinephrine (NE) reuptake, possessing comparable affinities in binding to NE and 5-HT transport sites. It has been clinically used for the treatment of major depressive disorder, pain due to diabetic peripheral neuropathy and urinary incontinence [1–5]. For the pharmacokinetic study of a duloxetine formulation product in human subjects, an analytical method with sim- plicity and high sensitivity was required in our laboratory. A recent survey revealed that few methods were available for the determination of duloxetine in biological samples, which involved HPLC with UV detection, liquid chromatog- raphy with single-quadrupole mass spectrometric (LC–MS) ∗ Corresponding author. Tel.: +91 33 2414 6967; fax: +91 33 2414 6186. E-mail addresses: senthamil77@yahoo.com (P. Senthamil Selvan), tkpal 12@yahoo.com (T.K. Pal). method [6], liquid chromatographic–tandem mass spectrom- etry (LC–MS–MS) with solid phase extraction (SPE) [7,8], gas chromatography-nitrogen–phosphorus detection (GC-NPD) and gas chromatography–mass spectrometry (GC–MS) quanti- tation [9]. To our knowledge, atmospheric pressure ionization (API) source offers some advantages over atmospheric pressure chemical ionization (APCI), GC-NPD and GC–MS in terms of less background noises and suitability for small molecular com- pounds [7–9]. Ma et al. described a single-quadrupole mass spectrometry (LC–MS) with selected-ion monitoring (SRM) mode to detect the precursor ion [6]. But in our proposed method, a triple–quadrupole mass spectrometry (LC–MS–MS) with mul- tiple reaction monitoring (MRM) mode was used to detect both the precursor ion and fragment ion. It shows the high specificity of the proposed method. Taking into consideration the low lev- els of duloxetine in plasma, LC–MS–MS method with simple and economic sample preparation method is the first choice for our purpose. The extraction procedure described by Hoja et al. is cumbersome and involves multi step extraction; basic extrac- tion, acid back-extraction, acid wash and basic re-extraction [10] and the sample preparation procedure reported in Ma et al. also involves a multi step extraction wherein the entire extraction 1570-0232/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jchromb.2007.09.002