Preconcentration and speciation of arsenic in water specimens by the combination of solidification of floating drop microextraction and electrothermal atomic absorption spectrometry

A simple solidification of floating drop microextraction procedure for preconcentration and speciation of trace amounts of As(III) and As(V) in water samples has been proposed prior to electrothermal atomic absorption spectrometry (ETAAS). In this method, a free microdroplet of organic solvent is floated on the surface of aqueous solution while being agitated by a stirring bar placed on the bottom of the sample vial. The determination of As(III) was achieved by selective formation of the As(III)–pyrrolidine dithiocarbamate complex in the presence of 0.1 M HCl while As(V) forms a weak complex with the ligand in the same pH conditions. Total inorganic As(III, V) was extracted similarly after reduction of As(V) to As(III) with potassium iodide and sodium thiosulfate and As(V) concentration was calculated by difference. Pd(NO3)2 was used as a chemical modifier in ETAAS. Some important extraction parameters such as the type of organic solvent, solvent volume, sample stirring rate, sample solution temperature, salt addition and the exposure time on the extraction recovery were investigated and optimized. Under the optimized extraction conditions, the detection limit of 9.2 pg mL−1 and suitable precision (RSD < 8.6%), along with enhancement factor of 1000 for As were achieved. The developed method was applied successfully to speciation of As(III), As(V) and determination of the total amount of As in water samples.