Journal of Chromatography B, 878 (2010) 1700–1706 Contents lists available at ScienceDirect Journal of Chromatography B journal homepage: www.elsevier.com/locate/chromb Solid-phase extraction of tramadol from plasma and urine samples using a novel water-compatible molecularly imprinted polymer Mehran Javanbakht a,∗ , Abdol Mohammad Attaran b , Mohammad Hadi Namjumanesh a , Mehdi Esfandyari-Manesh a , Behrouz Akbari-adergani c a Department of Chemistry, Amirkabir University of Technology, Tehran, Iran b Department of Chemistry, Payamenoor University, Delijan, Iran c Food & Drug Laboratory Research Center, Food & Drug Department, Ministry of Health and Medical Education, Tehran, Iran article info Article history: Received 23 December 2009 Accepted 8 April 2010 Available online 24 April 2010 Keywords: Molecularly imprinted polymer Solid-phase extraction Tramadol Plasma Urine abstract In this study, a novel method is described for the determination of tramadol in biological flu- ids using molecularly imprinted solid-phase extraction (MISPE) as the sample clean-up technique combined with high-performance liquid chromatography (HPLC). The water-compatible molecularly imprinted polymers (MIPs) were prepared using methacrylic acid as functional monomer, ethylene gly- col dimethacrylate as cross-linker, chloroform as porogen and tramadol as template molecule. The novel imprinted polymer was used as a solid-phase extraction (SPE) sorbent for the extraction of tramadol from human plasma and urine. Various parameters affecting the extraction efficiency of the polymer have been evaluated. The optimal conditions for the MIP cartridges were studied. The MIP selectivity was evaluated by checking several substances with similar molecular structures to that of tramadol. The limit of detection (LOD) and limit of quantification (LOQ) for tramadol in urine samples were 1.2 and 3.5 gL -1 , respectively. These limits for tramadol in plasma samples were 3.0 and 8.5 gL -1 , respectively. The recoveries for plasma and urine samples were higher than 91%. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Tramadol hydrochloride, trans-(±)-2-[(dimethylamino)meth- yl]-1-(3-methoxyphenyl)-cyclohexanol hydrochloride, is a syn- thetic analgesic (pain reliever). Like morphine, tramadol binds to receptors in the brain (opioid receptors) and inhibits reuptake of norepinephrine and serotonin, which appears to contribute to the drug’s analgesic effect. Tramadol, like other narcotics used for the treatment of pain, may be abused. Its therapeutic plasma concen- tration is in the range of 100–300 gL -1 [1]. Tramadol is rapidly and almost completely absorbed after oral administration but its absolute bioavailability is only 65–70% due to first-pass metabolism [2]. The drug has been quantified using different methods such as UV–vis spectrophotometry [3,4], voltammetry and amperometry [5], elecrophoresis with fluorescence [6] or electrochemilumines- cence [7] detection, gas chromatography with flame ionization [8], mass spectrometry [9–11] or nitrogen–phosphorus [12] detection. The methods described for the determination of tramadol in bio- logical samples involve high-performance liquid chromatographic ∗ Corresponding author. Tel.: +98 21 64543295; fax: +98 21 64543296. E-mail address: mehranjavanbakht@gmail.com (M. Javanbakht). (HPLC) methods with UV [13–15], fluorescence [16–18], electro- chemical [19] and mass spectrometry detection [20], but in most cases it combined with a liquid–liquid extraction (LLE) step using organic phases such as ethyl acetate [21–23], n-hexane [24] and tert-butyl methyl ether [17], that hindered the degree of automa- tion. Sample preparation is essential for the analysis of compounds in real samples. Due to unsatisfactory selectivity, the traditional sorbents usually cannot separate analytes efficiently in complex biological or environmental samples. Solid-phase extraction (SPE) is the most popular of clean-up techniques due to factors such as convenience, cost, time saving and simplicity. SPE is the most accepted sample pretreatment method today [25]. A relatively new development in the area of SPE is the use of molecularly imprinted polymers (MIPs) for the sample clean-up [26–29]. MIPs are syn- thetic polymers possessing specific cavities designed for a target molecule. MIPs are synthesized by the polymerization of different components. In the most common preparation process, monomers form a complex with a template through covalent or non-covalent interactions and are then joined by using a cross-linking agent. After removing of the template by chemical reaction or extraction, bind- ing sites are exposed which are complementary to the template in size, shape, and position of the functional groups, and consequently allow its selective uptake. MIPs are often referred to as ‘artificial 1570-0232/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jchromb.2010.04.006