Speciation of arsenic in environmental and biological samples

Abstract

A novel arsine generator glass assembly is constructed and reported for the spectrophotometric determination and speciation of arsenic in real samples. In an arsine generator, sodium borohydride is added dropwise to the acidic sample solution and arsine thus formed is reacted with silver diethyldithiocarbamate (Ag-DDTC) - Tritron-X (TX-100) solution in pyridine to form a red coloured complex. The complex showed the absorption maximum at lambda(max) 540 nm. The molar absorptivity of the method was found to be (1.5.5) x 10(4) L mole(-1) cm(-1) at this wavelength. The presence of non-ionic surfactant, i.e. TX-100 in the Ag-DDTC solution, makes the method = 3 times more sensitive than the conventional Ag-DDTC method. Beer's law is obeyed in the concentration range of 0.05-2.80 mg L-1 of arsenic. The detection limit of the method was calculated to be 20 mug L-1 As. Speciation of arsenite from other forms of arsenic in sample solutions was carried out by extraction of arsenite with Pb-DDTC in chloroform, followed by spectrophotometric determination. After arsenite separation the sample is used for the arsenate determination. Total arsenic was determined by acid decomposition of the same sample. The speciation data were found to be comparable (2%) with ICP-MS, with better precision (< 1%). The method has been successfully applied for the speciation of arsenic in drinking water and dust samples of arsenic affecting the Rajnandgaon district of Chhattisgarh, India, and urine and blood samples of patients with arsenical diseases. Concentration of total arsenic in tube-well water of this area was 3-6 times more than the permissible limit. Dust samples contained less amounts of arsenic than the ground water.