Improved method for the determination of Arsenic (III) in water by molecular absorption spectrophotometry

Abstract

Arsenic analysis is essential, as it is a carcinogenic compound according to the International Agency for Research on Cancer (IARC).  Currently, there are techniques based on powerful equipment that allow quantification with very low detection limits as Inductively  Coupled Plasma (ICP). However, groundwater pollution issues are not respectful of equipment’s availability or local financial resources.  Furthermore, standardised methods on the market are not sufficiently accessible to laboratories in developing countries that use them as  a reference, and only methods available in reference books are commonly used. We have therefore modified the available colorimetric  method, which has a quantification limit of 25 µg/L, to achieve a detection limit of 5 µg/L, which is lower than the WHO  standard, in order to further identify groundwater samples that would present a high health risk due to consumption. Colorimetric  method based on silver diethyldithiocarbamate has been used. The effects of various parameters such as arsenic initial concentration (up  to 800 µg/L), volume of solution (35-120 mL) were evaluated on arsine quantification. The results reveal that for concentrations  below 25 µg/L, a test volume of 100 mL is sufficient to measure arsenic concentrations in water up to 5 µg/L. However multiple extraction  is indicated in the less concentrated samples (<5 µg/L) for reliable quantification. Experiments performed with the previously used zinc  shots show that washing with appropriate mixture several times and drying allows arsenic quantification with 10% loss of zinc activity