Journal of Chromatography B, 931 (2013) 148–156 Contents lists available at SciVerse ScienceDirect Journal of Chromatography B j ourna l h o mepa ge: www.elsevier.com/locate/chromb Carrier mediated transport solvent bar microextraction for preconcentration and determination of dexamethasone sodium phosphate in biological fluids and bovine milk samples using response surface methodology Katayoun Mahdavi Ara, Zahra Akhoondpouramiri, Farhad Raofie ∗ Department of Chemistry, Faculty of Science, Shahid Beheshti University, G.C., P.O. Box 19839-4716, Tehran, Iran a r t i c l e i n f o Article history: Received 31 May 2012 Accepted 21 May 2013 Available online xxx Keywords: Dexamethasone sodium phosphate Solvent bar liquid phase microextraction Response surface methodology High performance liquid chromatography Human plasma and urine Bovine milk a b s t r a c t In the current study, a fast and simple preconcentration and sample clean up procedure was developed based on carrier mediated three phase solvent bar liquid phase microextraction (TPSB-LPME) method prior to high performance liquid chromatography (HPLC) equipped with an ultraviolet (UV) absorbance detector for simultaneous extraction and determination of trace amounts of dexamethasone sodium phosphate (DSP) in human plasma, human urine and bovine milk. According to this procedure, dexa- methasone sodium phosphate was extracted from an acidic aqueous sample (SP, 7.5 mL with pH = 6) into the organic solvent 1-octanol (containing 5%, w/v of Aliquat-336 as carrier) residing in the pores of a hol- low fiber and then back extracted into an alkali receiving phase (RP, 5 L of 0.65 M NaClO 4 with pH = 10) was located inside the lumen of the fiber. After the extraction period, the receiving phase was directly injected into HPLC. The effect of different extraction conditions (i.e., pH of source and receiving phases, ionic strength, stirring rate, counter-ion concentration and extraction time) on the extraction efficiency of DSP was investigated and optimized using central composite design (CCD) as a powerful tool. Under the optimal conditions, preconcentration factor of 320, extraction recovery of 23%, dynamic linear range of 1–1000 ng mL -1 (r 2 = 0.997) and limit of detection of 0.1 ng mL -1 were obtained. Eventually, applica- bility of the proposed method was successfully confirmed by extraction and determination of drug in plasma and urine samples and bovine milk with R.S.D.s < 8%. Comparing to the traditional methods, the proposed method exhibits high sensitivity and high preconcentration factors as well as good precision. The extraction setup is simple and due to active transport of analytes, high cleanup effect and good selectivity are obtained in the extraction process. This extraction technique is also the most economical sample preparation and preconcentration technique as compared to traditional extraction techniques. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Corticosteroids are naturally produced by the adrenal gland in the body and influence the functioning of most of the body’s systems. Dexamethasone sodium phosphate (DSP), 9-fluoro-11,17-dihydroxy-16-methyl-21-[phosphonooxy] pregna-1,4-diene-3,20-dione disodium (Fig. 1) is a long-acting synthetic glucocorticoid derived from hydroxycortisone that is a man-made version of a natural hormone produced by the adrenal glands. It is a slightly yellow crystalline powder with a pK a1 of 1.8 and a pK a2 of 6.4. DSP is a potent anti-inflammatory steroid widely used for treating inflammatory conditions, allergic reactions, shock, lymphomas and diseases related to adrenal ∗ Corresponding author. Tel.: +98 21 29902883; fax: +98 21 22431663. E-mail addresses: f raofie@sbu.ac.ir, fraofie@yahoo.com (F. Raofie). cortex insufficiency. It is also used in the short-term treatment of nausea caused by chemotherapy [1–3]. DSP is rapidly absorbed after oral administration and up to 65% of a dose is excreted in the urine in 24 h. The plasma concentration of DSP was found to be highest (3 g L -1 ) at 4 h, declining rapidly to about 0.5 g L -1 at 24 h [4]. It has been demonstrated that the pharmaceutical effects of DSP strongly depended on the distribution of DSP in tissues and body fluids. For a better understanding of these effects, a detailed investigation on the pharmacokinetics of DSP is very necessary. Additionally, determination of DSP in human plasma and urine is required because the use of dexamethasone and other corticosteroids is restricted by the International Olympic Committee due to the abuse of them as doping agents because of their supposed stimulating, analgesic, and anxiolytic effects [5]. Bearing in mind that, low concentrations of glucocorticosteroids are known to increase weight gain according to making muscles, dexamethasone has been illegally used to obtain an economical 1570-0232/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jchromb.2013.05.022