Internal standardisation for arsenic and its species determination using inductively coupled plasma mass spectrometry

The signal of As measured by inductively coupled plasma mass spectrometry (ICP-MS) suffers from strong non-spectral interferences due to carbon and alkali metals. The accuracy of the determination of total As using ICP-MS and its species using anion-exchange chromatography coupled to ICP-MS was increased by using selenium as an internal standard. For chromatography, selenium was used in the form of a trimethylselenonium cation, which did not interact with the stationary phase and could be added directly to the mobile phase as the selenite was sufficient for total As determination. Selenium is able to correct non-spectral interferences caused by carbon or sodium up to concentrations of 3000 mg L^-1 C and 35 mg L^-1 Na, respectively, in the case of total As determination, and up to 3000 mg L^-1 C and 3450 mg L^-1 Na in the case of speciation analysis. Selenium as an internal standard was tested for the analysis of arsenobetaine in the DORM-2 standard reference material. The results were in good accordance with certified values regardless of NaCl spikes. Also, the results of total As determination in canned fish using a selenium internal standard were not affected by residual carbon in an imperfectly decomposed sample.