Helium inductively coupled plasma-mass spectrometry: studies of matrix effects and the determination of arsenic and selenium in urine

This study on helium inductively coupled plasma-mass spectrometry (He ICP-MS) is concerned with three related issues. First, a boron nitride sampler was explored for reducing the extent of the secondary discharge prevalent in He ICP-MS. Second, an investigation of matrix effects was conducted by adding increasing concentrations of Na, U and SO42− to solutions containing As+ and Br+ as the analytes. Third, the practical utility of He ICP-MS was explored for the determination of As and Se in a urine standard reference material (NIST SRM 2670). The major observations were: (1) the most probable ion kinetic energy for 75As+ was 15 eV with a boron nitride sampler for an 800-W He ICP, similar to the results achieved when an aluminum sampler was used for He ICP-MS, but higher than the kinetic energies that are typically reported for Ar ICP-MS; (2) enhancement of As and Br signals by Na, U and SO42− were observed, but the enhancement effects could be corrected by the use of Se as an internal standard; and (3) analysis of the urine NIST SRM 2670, using standard addition and internal standardization, gave As and Se concentrations of 500 +- 130 ng/ml and 410 +- 80 ngml, respectively, as compared to certified values of 480 +- 100 ngml and 460 +- 30 ngml for As and Se, respectively. Finally, the current limitations of He ICP for practical spectrometric analysis of aqueous samples are briefly contrasted with spectrometric techniques involving microwave induced plasmas and Ar ICP.