Arsenic Analysis Method in Water

Arsenic is an odorless and tasteless metal pollutant that can cause significant harm at low levels in water. The EPA has decided that .010 parts per million (10 parts per billion) is the acceptable limit for arsenic in water. It is very difficult to sample and analyze water to detect arsenic at these low levels. For this reason, the EPA has proscribed Method 1669 for sampling ambient water for trace metals at EPA water-quality criteria levels.

Water-Quality Sampling

• Water-quality sampling entails gathering the water, transporting it to the laboratory and conducting analysis. Sampling for metal pollutants is difficult because the sampled water should only show the constituents in ambient water; however, samples can be contaminated by metallic or metal-containing sampling equipment, containers, labware, reagents and deionized water, as well as dirt and dust from automobile exhaust and even cigarette smoke.
  It is important to prevent outside contamination to the sample at every step of the collection, transport and analysis process.

Sampling

• During sampling, extra effort is made to avoid outside contamination; all equipment and bottles are cleaned using detergents, mineral acids and reagent water in the laboratory. Field work is conducted in an area known to be free of contaminants of concern; metal-free equipment is employed; and field workers are trained to avoid sources of contamination.

Analysis

• In the lab, the water sample is isolated into components. The isolated arsenic is then broken down into three chemical bonds using a chloride that is then converted into a gas using zinc. The gas can then be measured to detect very low levels of arsenic. The numeric value is then extrapolated back to the original water sample volume, taking into account the level of other contaminants measured.