Speciation of chromium by dispersive liquid-liquid microextraction followed by laser-induced breakdown spectrometry detection (DLLME-LIBS)

In this study, an analytical methodology based on a combination of dispersive liquid-liquid microextraction with laser-induced breakdown spectrometry was evaluated for simultaneous pre-concentration, speciation and detection of Cr. The microextraction procedure was based on the injection of appropriated quantities of 1-undecanol and ethanol into a sample solution containing the complexes formed between Cr(VI) and diethyldithiocarbamate (DDTC). The main experimental factors affecting the complexation and the extraction of metal (pH, DDTC concentration, extractant and volume of disperser solvents) were optimized using a multivariate analysis consisting of two steps: a Plackett-Burman design followed by a Circumscribed Central Composite Design (CCCD). Under optimum microextraction conditions, the analytical figures of merit of the proposed methodology were assessed. The method was finally applied to the analysis of a certified reference material hard drinking water (ERM (R) CA011a), yielding results in good agreement with the certified value.