Because of the low resoln. of quadrupole mass filter, polyat. ions interfere with analyte ions in ICP-MS. To achieve accurate results it is urgently recommended to know the kind and the amt. of ions of the major concd. elements of the sample. The matrix elements of high purity Fe, low, and high alloy steels are Fe, Cr, Ni, Mn, Mo, and W. 175 Different polyat. ions of the matrix elements and those of HNO3, HCl, and HF are exptl. detd. in steel sample solns. Signal intensities higher than a threshold of 30 counts/s were considered as significant. 100 Isotopes of 25 elements show interference at 69 m/z-values.