Determination of arsenic by electrothermal atomic absorption spectrometry using headspace liquid phase microextraction after in situhydride generation

Abstract

A novel and extremely highly sensitive method for extraction and determination of arsenic in aqueous samples by headspace liquid phase microextraction combined with graphite furnace atomic absorption spectrometry is described. The arsenic species were converted to arsine in 3 mol dm⁻³ HCl sample solution by sodium tetrahydroborate (NaBH₄) in a closed headspace vial and during the 7 min extraction time at 35 °C it was reacted with AgDDC dissolved in a 4 µl microdrop mixture of 1∶3 pyridine∶benzyl alcohol suspended in the tip of a microsyringe. After the equilibrium between the arsine in the headspace and microdrop has been reached, the microdrop was retracted and directly transferred into a graphite furnace for determination of arsenic. Using 2 ml sample solution, an enrichment factor of 150 could be obtained with an overall efficiency of HG, transport and trapping of 30%. The detection limit was calculated to be 45 pg ml⁻¹ based on 3 s_b with an absolute value of 0.18 pg for a 4 µl injection into the graphite furnace. The relative standard deviation for five replicate analyses of 4 ng ml⁻¹ arsenic was 8.6%. The characteristic concentration was 30 pg ml⁻¹ equivalent to a characteristic mass of 0.12 pg with a calibration curve linear in the range of 45 pg ml⁻¹ to 4 ng ml⁻¹. The effects of interferences were also investigated. The results for determination of arsenic in reference materials, tap water, washing machine powder and spiked seawater demonstrated the accuracy, recovery and applicability of the presented method.