Extraction induced by emulsion breaking: a novel strategy for the trace metals determination in diesel oil samples by electrothermal atomic absorption spectrometry Ricardo J. Cassella, * a Daniel M. Brum, b Carlos Eduardo R. de Paula a and Claudio F. Lima b Received 30th May 2010, Accepted 3rd August 2010 DOI: 10.1039/c0ja00035c This present work reports a novel strategy for the extraction of metals (Cu, Fe, Ni and Pb) from diesel oil and their determination by Electrothermal Atomic Absorption Spectrometry (ETAAS). The method is based on the formation of water-in-oil emulsions by vigorous mixing of the samples with a Triton X-114 solution containing HNO 3 and posterior breaking of the emulsion by heating. After the emulsion breaking, three well separated phases were obtained: (i) the upper phase, which is an organic phase containing only the diesel oil, (ii) an acidic aqueous phase containing the extracted metals and (iii) the lower phase, which is a surfactant-rich phase. The metals were concentrated in the aqueous phase, as a result of their acidic extraction from diesel oil. Several parameters that could influence the extraction efficiency and the time required to break the emulsions were evaluated such as the concentration and nature of the surfactant (Triton X-100 and Triton X-114), the HNO 3 concentration and the temperature. At best conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 7% w/v Triton X-114 and 10% v/v HNO 3 . Afterwards, the emulsions were broken by heating at 80  C for 15 min and then, the aqueous phase was collected and the metals were determined by ETAAS using external calibration with aqueous standard solutions. The limits of detection for Cu, Fe, Ni and Pb were equal to 114, 183, 145 and 294 ng L 1 and the limits of quantification were 380, 609, 484 and 980 ng L 1 , respectively. These limits were estimated for the original sample taking into account the preconcentration factor obtained due to the Extraction Induced by Emulsion Breaking (EIEB) application. The novel strategy was applied in the analysis of five samples of diesel oil and the obtained results fitted well with those obtained by the reference method. Also, a recovery test was performed by spiking the samples with known amounts of the metals in the form of organometallic standards and thus applying the proposed procedure. The recoveries were in the range of 85.2–109%. 1. Introduction Nowadays, it is well known that several problems are observed due to the presence of metals in oil products, especially those derived from petroleum. Firstly, the presence of metals strongly affects the stability of the oil because they act as catalysts in the oxidation of certain heteroatomic compounds containing N, O or S and hydrocarbons like alkenes, indenes and cyclic hydro- carbons. 1 As a consequence, some solid particles, usually called gum, are formed and they can accumulate on the inner surface of the engines thus affecting their efficiency, performance and durability. 2,3 Also, the presence of metals in liquid fuels is asso- ciated with corrosion, metal deposition on engine parts and poor fuel performance. 4,5 In this scenario, it is clear that the devel- opment of analytical methods for metals determination is required for the quality control of oiled samples. Such methods must present suitable sensitivity and must be as simple as possible to allow their use in routine analysis laboratories. Diesel oil is a mixture of hydrocarbons with boiling points that vary between 170 and 370  C, which corresponds to the inter- mediary distillate fraction from petroleum. Hydrocarbons present in the diesel oil contain 9 to 20 carbon atoms, corre- sponding to a fraction lighter than fuel oil and heavier than kerosene. 6 In general, the determination of metals in liquid fuels is not a simple task because they are very refractory to oxidation. Even so, the digestion of diesel oil has been carried out to prepare this kind of sample for the determination of different analytes 7–10 by spectrometric techniques. Ulrich and Wichser 7 reported a procedure based on the microwave assisted heating for diesel oil decomposition in acid medium with H 2 O 2 aiming at the determination of metals by ICP OES and ICP-MS. Sant’Ana et al. 8 also studied the decomposition of diesel oil in acid medium using microwave radiation. However, they employed a focused microwave oven in order to obtain a faster heating of the system. Hearn et al. 9 and Heilmann et al. 10 proposed similar methodologies for sulfur determination in diesel oil by ICP-MS after digestion of the samples in a closed vessel microwave oven. a Departamento de Qu ımica Anal  ıtica, Universidade Federal Fluminense, Outeiro de S.J. Batista s/n, Centro, Niter  oi/RJ, 24020-141, Brazil. E-mail: cassella@vm.uff.br; Fax: +55 21 2629 2143; Tel: +55 21 2629 2222 b Departamento de Qu ımica, Universidade Federal de Vic ¸osa, Av. Peter Henry Rolfs s/n, Vic ¸osa/MG, 36570-000, Brazil 1704 | J. Anal. At. Spectrom., 2010, 25, 1704–1711 This journal is ª The Royal Society of Chemistry 2010 PAPER www.rsc.org/jaas | Journal of Analytical Atomic Spectrometry Downloaded by Universidade Federal de Vicosa on 11 August 2012 Published on 03 September 2010 on http://pubs.rsc.org | doi:10.1039/C0JA00035C View Online / Journal Homepage / Table of Contents for this issue