Talanta 78 (2009) 270–277 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Single-drop micro-extraction and diffuse reflectance Fourier transform infrared spectroscopic determination of chromium in biological fluids Devsharan Verma, Santosh Kumar Verma, Manas Kanti Deb ∗ School of Studies in Chemistry, Pt. Ravishankar Shukla University, Raipur, Chhattisgarh 492 010, India article info Article history: Received 25 July 2008 Received in revised form 8 November 2008 Accepted 10 November 2008 Available online 25 November 2008 Keywords: Single-drop micro-extraction DRS-Fourier transform infrared spectroscopy Quantitative determination of Cr(VI) Biological fluids abstract The present paper deals with a new micro-extraction procedure for selective separation of Cr(VI) in the form of a metaloxy anionic species namely dichromate (Cr 2 O 7 2- ) with N 1 -hydroxy-N 1 ,N 2 - diphenylbenzamidine (HOA) in to dichloromethane and its subsequent and rapid diffuse reflectance Fourier transform infrared spectroscopic (DRS-FTIR) determination employing potassium bromide matrix. The diffuse reflectance Fourier transform infrared spectroscopy gives both qualitative and quan- titative information about the dichromate. The determination of chromium is based on the analytical peak selection, among the various vibrational peaks, at 902 cm -1 . The micro-extraction was based on the liquid–liquid solvent extraction (LLSE) principle. The dichromate binds with the nitrogen and oxy- gen atoms of N 1 -hydroxy-N 1 ,N 2 -diphenylbenzamidine (HOA) and forms 1:2, Cr(VI):HOA complex in 0.1 mol L -1 HCl medium. The formation of above complex, in the acidic medium, is confirmed by the appearance of chocolate-brown color in the micro-extract. The speciation studies of Cr(III) and Cr(VI) is done by conversion of Cr(III) into Cr(VI) utilizing H 2 O 2 as an oxidizing agent. The chemistry of pure dichromate and that of its HOA complex is discussed. The limit of detection (LoD) and the limit of quan- tification (LoQ) of the method are found to be 0.01 gg -1 Cr 2 O 7 2- and 0.05 gg -1 Cr 2 O 7 2- , respectively. The standard deviation value and the relative standard value at a level of 10 g Cr 2 O 7 2- /0.1 g KBr for n = 10 is found to be 0.26 g Cr 2 O 7 2- and 2.6%, respectively. The relative standard deviation (n = 8 and 6) for the determination of dichromate (Cr 2 O 7 2- ) in real human biological fluid samples is observed to be in the range 3.1–7.8%. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The dubious behavior of chromium has fascinated chemists over the years. On one hand exposure to high-chromium concentration, especially hexavalent chromium leads to toxicity due to its ability to oxidize biomolecules, notably DNA [1,2] and exert its noxious influ- ence on the cell, causing carcinogenic effects; and on the contrary it has been recognized as an essential trace mineral required for nor- mal sugar and fat metabolism. Organic chromium potentiates the action of insulin and is the active component of a substance called GTF (glucose tolerance factor), along with vitamin B 3 and amino acids. Determination of very low-chromium concentrations in “unex- posed” biological material (animal and human tissues, blood, urine, food, as well as water and air) is extremely difficult and many problems still need to be solved [3]. An accurate assessment of human exposure and nutritional chromium requirements depends ∗ Corresponding author. Tel.: +91 771 2593367. E-mail address: debmanas@yahoo.com (M.K. Deb). on reliable analytical results. Thus, the need for new procedures on determination of chromium with low-detection limit, high-sample throughput, applicability to low-sample size, etc., particularly in biological samples wherein sample size is a real challenge to the chemist, is a perpetual demand for the purpose of clinical diagno- sis. Speciation of chromium often involves a separation steps, such as ion exchange [4,5], capillary electrophoresis [6,7], nano-material micro-column separation [8], and solid-phase extraction (SPE) [9]. Various methods have been used for subsequent determination of chromium, for instance, spectrophotometry [10], atomic absorp- tion spectrometry (AAS) [4,9], inductively coupled plasma-atomic emission spectrometry (ICP-AES) [8] and inductively coupled plasma-mass spectrometry (ICP-MS) [7]. However, these methods are only suitable for relatively large sample volumes. In many common analytical methods, the volume of the sample is very small. In GC, HPLC and graphite furnace atomic adsorp- tion spectrometry (GF-AAS), this volume is usually around 5–20 L, while in diffuse reflectance Fourier transform infrared spectroscopy (DRS-FTIR) it is around 3–10 L. The chromatographic techniques often suffer from disadvantages such as incomplete derivatization, being time-consuming and entailing complicated operating proce- dures. The determination of Cr(VI) using GF-AAS have also some 0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2008.11.020