Phenylic arsenic compounds are the main contaminants in groundwater at abandoned sites with a history of arsenic containing chemical warfare agents (CWA). A fast and sensitive HPLC-ICP-MS method was developed to determine inorganic arsenic compounds like arsenite and arsenate as well as the degradation products of the arsenic containing warfare agents (phenylarsonic acid, phenylarsine oxide, diphenylarsinic acid). Beside these arsenic species the groundwater samples contained also high iron contents (up to 23 mg/l as Fe(II)) which led to precipitates in the samples after coming into contact with the atmosphere. Preservation immediately after sampling by phosphoric acid has shown that a successful avoidance of any losses of any arsenic species between sampling and analysis was possible. The suggested analytical method was applied to groundwater samples taken from different depths at a polluted site. The main contaminant in the water samples was diphenylarsinic acid (up to 2.1 mg/l) identified by ESI-MS, but also elevated concentrations of inorganic arsenic (up to 240 microg/l) were found.