Speciation and determination of trace inorganic tellurium in environmental samples by electrodeposition-electrothermal atomic absorption spectroscopy

Abstract

A simple speciation method using selective electrodeposition with a mercury coated electrode in hydrochloric acid medium was developed for the speciation and determination of trace amounts of Te (IV) and Te (VI) in water samples by electrothermal atomic absorption spectroscopy (ETAAS). Bottled drinking water, river water and sea water samples were spiked with trace amounts of Te (IV) and Te (VI) and the spiked solutions were subjected to an electrodeposition process prior to determination by ETAAS. The method is based on the selective reduction of the tellurium (IV) at an uncontrolled applied potential (2.0 V) on the mercury coated electrode. In acidic media (1.0 M HCl solution) only Te (IV) can be electrodeposited onto the mercury electrode surface and separated Te (VI) remained in solution. The electrode was withdrawn from the solution and the spent electrolyte containing Te (VI) was measured by ET-AAS. Te (IV) was calculated as the difference between the measured total tellurium and Te (VI) content. The spiked recovery value varied between 93 to 97%. The experimental parameters of ET-AAS such as ashing and atomization temperature, ashing and atomization time, type and amount of modifier were optimized using a central composite design after a 2ⁿ⁻¹ fractional factorial experimental design. The obtained detection limit and characteristic mass for Te (IV) were 2.0 µg L⁻¹ and 20 pg, respectively. The application of the proposed method was investigated on water samples analysis.