This standard specifies the determination of trace amount of arsenic in surface water, underground water and drinking water by spectrophotometric method with new salt. 250ml specimen and 3.00ml absorption solution is taken and 10mm cuvette is used. The minimum detectable concentration of this method is 0.4μg/L and the upper limit of determination is 12μg/L.
2 Principle
Potassium borohydride (or sodium borohydride) generates nascent hydrogen in the acid solution and makes the arsenic in specimen transformed into arsenic-hydrogen; the nitric acid-silver nitrate-polyvinyl alcohol-ethanol solution is taken as the absorption solution and makes the silver ion reduced to elemental silver and solution act like yellow. The absorbance is measured at 400nm place.
The chemical equation is as follows:
+H++3H2O→8[H]+H3BO3
2As3++6[H]→2AsH3↑
6Ag+AsH3+3H2O→6Ag+H3AsO3+6H+
