Talanta 76 (2008) 669–673 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Cloud point extraction for cobalt preconcentration with on-line phase separation in a knotted reactor followed by ETAAS determination in drinking waters Ra ´ ul A. Gil a,b , Jos ´ e A. G ´ asquez a , Roberto Olsina a,b , Luis D. Martinez a,b , Soledad Cerutti b,∗ a ´ Area de Qu´ımica Anal´ıtica, Facultad de Qu´ımica Bioqu´ımica y Farmacia, Universidad Nacional de San Luis, Chacabuco y Pedernera, San Luis, C.P. 5700, Argentina b Instituto de Qu´ımica San Luis, INQUISAL-CONICET, Chacabuco y Pedernera, San Luis, C.P. 5700, Argentina article info Article history: Received 13 February 2008 Received in revised form 3 April 2008 Accepted 7 April 2008 Available online 12 April 2008 Keywords: Cloud point extraction On-line phase separation Cobalt determination Knotted reactor STPF–ETAAS abstract A novel method for cobalt preconcentration by cloud point extraction with on-line phase separation in a PTFE knotted reactor and further determination by electrothermal atomic absorption spectrometry (ETAAS) is proposed. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono- p-nonylphenylether (PONPE 7.5) and it was retained on the inner walls of a knotted reactor (KR). The surfactant rich-phase was removed from the knotted reactor with 75 L of methanol acidified with 0.8 mol L −1 nitric acid, directly into the dosing hole of the L’Vov graphite tube. An enrichment factor of 15 was obtained with a preconcentration time of 60s, with respect to the direct determination of cobalt by ETAAS in aqueous solutions. The value of the detection limit for the preconcentration of 5mL of sample solution was 10 ng L −1 . The precision, expressed as the relative standard deviation (R.S.D.), for 10 replicate determinations at 0.5 gL −1 Co level was 4.5%. Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1640e “Trace elements in natural water”). The method was successfully applied to the determination of cobalt in drinking water samples. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The toxicity of cobalt is low and it is considered as an essential element, which is required in the normal human diet in the form of vitamin B 12 (cyanocobalamin). For this reason, Co has been used in the treatment of anemia [1]. However, the ingestion or inhalation of large doses of this analyte may lead toxic effects [2,3]. Since one of the routes of incorporation of cobalt into the human body is by ingestion [4], its determination in drinking water becomes impor- tant. Cobalt concentration levels are very low in water samples, and therefore sensitive analytical techniques are required to carry out its detection. Electrothermal atomic absorption spectrometry (ETAAS) is one of the most sensitive techniques with low volumes of sample required for a large number of elements with detection limits in the gL −1 to ng L −1 range, and therefore it is often chosen for the deter- mination of analytes at trace levels [5]. However, in real samples of complex composition, matrix effects can significantly impact on ∗ Corresponding author. E-mail address: ecerutti@gmail.com (S. Cerutti). the performance of ETAAS. While interferences may be overcomed to various degrees by applying the “stabilized-temperature plat- form furnace” (STPF) concept [6], separation of the analyte element from the matrix is undoubtedly even more effective in avoiding matrix effects. The on-line coupling of a flow injection (FI) precon- centration and separation technique with ETAAS has proved to be a powerful technique for ultratrace determination of a variety of elements [3–5]. During the past years, cloud point extraction (CPE) has become one of the most preferred preconcentration methodologies to enhancing the sensitivity in metal analysis thanks to its poten- tial, benefits and versatility offered by this particular technique [6–10]. The principles and relevant applications of this separation methodology have already been discussed [6–10]. CPE is based on surfactant aggregates which together with ionic liquids have been recognized as the solvents of a modern era [11]. Both bulk solvent- soluble and solvent-insoluble species can reversibly interact with and bind to the micellar assembly. Sparingly soluble or non-water- soluble materials can be solubilized in water due to their binding to the micelles in solution [3]. This explains the fact that many analytical and other applications of surfactant micellar media have been based upon their analyte solubilization proficiencies. It has 0039-9140/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2008.04.004