Unexpected arsenic compound in routine determination of arsenic species in urine.

A validated method of anion exchange liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC-ICP-MS) was applied to determine arsenic species in human urine, particularly for occupational and environmental health investigations. In addition to the chromatographic peaks of arsenobetaine (As-B), dimethylarsinate (DMA), methylarsonate (MA), As(III) and As(V), which occur regularly, we have observed an additional As peak overlapping with that of As(V) in several routine analyses. Further investigations identified this unknown As compound as p-arsanilic acid, which had contaminated the urine samples due to application of a test strip for rapid determination of certain clinical parameters before shipment of the samples to the laboratory. It is essential that urine samples for trace element analysis do not come into contact with test strips, an important prerequisite that is not always considered in subsequent occupational biomonitoring.