Ionisation corrections in the determination of impurities in solids by means of the M.S.7 mass spectrometer.
Determinations on the M.S.7 mass spectrometer of a number of trace elements have been made on standard samples, whose composition had previously been determined by independent techniques and which had been tested for homogeneity. From the ratios of the apparent contents, as determined on the M.S.7, to the true contents, a correction factor is obtained. This factor depends largely on ionisation phenomena at the source, but also includes other errors. It has been shown that for a number of elements such factors depart significantly from unity and that the value for a particular impurity depends on the matrix element. The variation of the factors showed no direct connection with the electrical parameter of the source. Cooling of the electrodes produced a significant reduction in the magnitude of the correction factor in the cases of only very few elements. In the absence of independent standards of similar composition to the sample, any figures obtained by mass spectrometry must be treated with caution unless the ionisation factor for the particular impurity in the particular matrix is known. This is especially the case for certain elements (e.g., S, Zn, Pb) known to be liable to give high factors.
Short
H G
HG
Metallurgy Division, National Physical Laboratory, Teddington, England.
Keene
B J
BJ