ELIMINATION OF INTERFERENCES IN THE DETERMINATION OF ARSENIC AND SELENIUM IN BIOLOGICAL SAMPLES BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The determination of As and Se in biological samples by inductively coupled plasma mass spectrometry is well known to be degraded by spectral interferences. The resolution of quadrupole mass analysers is insufficient to resolve As+ and Se' ions from polyatomic species such as ArCl+, ArAr+ and SO3+. A study of this problem in human serum also revealed substantial non-spectral interferences on these elements occurring in the presence of organic compounds. It is shown that both problems can easily be overcome by a combination of chemical modification (addition of 4% ethanol) with nebulizer flow-rate gas adjustment. Under these conditions the use of standard additions for calibration allowed As and Se to be determined accurately in samples of biological origin. The method developed was applied to human serum and urine and for both As and Se excellent agreement with certified values was obtained.