Selenium and Arsenic

Arsenic is ubiquitous in the environment in the form of inorganic and organic compounds in the trivalent and pentavalent states. In general, methylated and other organo-arsenicals are less toxic than inorganic forms of arsenic. Furthermore, pentavalent arsenic is considerably less toxic than trivalent. Hence, speciation of arsenic compounds is important when monitoring for contamination in environmental waters. For similar reasons, selenium must also be speciated according to its IV or VI valency states to properly assess the level of hazard present in contaminated environmental samples.

Spectrophotometric techniques such as Atomic Absorption (AA) and Inductively Coupled Plasma (ICP) emission are typically used to measure arsenic and selenium. However, ion chromatography (IC) can separate these metal species according to their valence states. Detection is most powerful and advantageous when MS is coupled to IC separation (see figures), particularly if ppm levels of other matrix anions such as sulfate are present.