Abstract
The determination of trace impurities in high purity cobalt is increasingly required because it is a raw material in the production of cobalt di-siliside, a useful material for very large scale integrated circuits owing to its very low electrical resistivity and high melting point. Therefore a highly precise, sensitive and rapid method for the determination of impurities in high purity cobalt by glow discharge MS (GDMS) is presented. For determination of the elements of interest, the optimum discharge voltage, current, electrode distance, and sample area were found to be 1 kV, 2.5 mA, 0.6 mm, and 12 mmφ, respectively. The mass spectrum of GDMS showed that the ion peaks of some impurities overlapped with, or were close to complexed molecular ion peaks. Such mass interference of the complexed molecular ion was reduced by cooling the sample with liquid nitrogen. In order to obtain precise quantitative values, the relative sensitivity factors for impurities in cobalt were determined by using laboratory reference samples, where the amounts of trace elements were determined by chemical analysis. For 8 elements examined here, the analytical results obtained by GDMS were in good agreement with those obtained by chemical analysis. Determination limits were 5 ppb for Li, Na, Cr and Fe, 50 ppb for K and Ni, and 0.1 ppb for Th and U, respectively.
