Ionic liquid-assisted speciation studies of cobalt in nutritional supplements by temperature-controlled dispersive liquid phase microextraction prior to electrothermal atomic absorption spectrometry

BERTON, PAULA; ESCUDERO, LETICIA B.; WUILLOUD, RODOLFO G.

Campos Do Jordao

Congreso; 16th ANALYTICAL CHEMISTRY NATIONAL MEETING; 2011

University of Sao Paulo

Cobalt (Co), an essential trace element in nature, has an important role in many body functions, as a component of vitamin B12.1 However, unnecessary Co salts administration causes adverse side effects, since its accumulation promotes organ damage and dysfunction due to enhanced oxidative stress. Excessive Co in blood impairs thyroid activity and myocardial function, promoting carcinogenesis.2 Therefore, determination of Co species, such as vitamin B12 and inorganic Co (iCo), results critical to evaluate benefits and risks of Co occurring in nutritional supplements. However, the main difficulty in such samples lies in the high concentrations of potential interfering ions such as iron or zinc. Hence, preliminary preconcentration and sample clean-up steps are frequently required to achieve accurate, reliable and sensitive results. Microextractions techniques based on ionic liquids (ILs) combined with suitable complexing agents have been recently developed in analytical chemistry for metal precontentration.3 In the present work, a simple and rapid analytical method based on application of ionic liquids (IL) for iCo microextraction in a wide variety of nutrient supplement samples was developed. Inorganic Co was initially chelated with 1-nitroso-2-naphtol (1N2N) reagent followed by a modern technique named temperature-controlled ionic liquid dispersive liquid phase microextraction (TILDLME). The extraction was performed with 1-hexyl-3-methylimidazolium hexafluorophosphate [C6mim][PF6], with the aid of ultrasound to improve iCo recovery. Finally, the Co-enriched IL phase was solubilized in methanol and directly injected into the electrothermal atomic absorption spectrometer (ETAAS). Several parameters that could influence iCo chelation, microextraction and detection were carefully studied. Different approaches were evaluated to eliminate interferences. An enrichment factor of 60 was obtained with only 5 mL of sample solution. The limit of detection (LOD) was 5.4 ng L−1, while the relative standard deviation (RSD) was 4.7% (at 0.5 µg L−1 Co level and n = 10), calculated from the peak height of absorbance signals. The selective microextraction of this cobalt species was achieved only by controlling the pH value during the procedure. The method was thus successfully applied for the determination of inorganic Co species in nutritional supplements. 1) Lison, D. In Handbook on the Toxicology of Metals (Third Edition); Nordberg, G. F., Fowler, B. A., Nordberg, M., Friberg, L. T., Eds.; Academic Press: Burlington, 2007, pp 511. 2) Barceloux, D. G. J. Toxicol., Clin. Toxicol. 37, 1999, 201. 3) Martinis, E. M.; Berton, P.; Monasterio, R. P.; Wuilloud, R. G. TrAC-Tren. Anal. Chem. 29, 2010, 1184.