6. Analysis of arsenic

Arsenic in water can be detected in the laboratory or in the field. The TOP describes several commonly used field test kits, and outlines analytical methods approved by USEPA for laboratory testing.

Field test kits use a reducing agent such as zinc to transform arsenic compounds into arsenic trihydride (arsine gas). When exposed to a paper impregnated with mercuric bromide this produces a coloured compound that can be compared with a test strip.

Test kits are relatively inexpensive, portable and effective. However, field-test kits are generally inaccurate at lower concentrations of arsenic and some depend on subjective estimates by the tester. They often underestimate arsenic levels.

Laboratory analysis uses sophisticated techniques to measure arsenic in drinking water accurately, but this is not affordable in many parts of the world.

The method of choice is hydride generation-atomic absorption (AAS – HG), which converts arsenic compounds to their hydrides that are decomposed in an argon hydrogen flame. The TOP outlines several other methods including electrothermal atomic absorption AAS – GF), the use of silver diethyldithiocarbamate (SDDC), inductively coupled plasma (ICP) and anodic stripping voltammetry (ASV).