Comparative studies of spectrochemical characteristics between axial and radial observations in inductively coupled plasma optical emission spectrometry.

By using an ICP optical emission spectrometer having two different observation modes, the authors compared the spectrochemical characteristics of various emission lines as viewed from the axial direction and the direction radial to the long axis of the plasma. The excitation temperature, the emission intensity, and the degree of ionization were investigated when iron and chromium were employed as the test sample and further potassium was added as an interfering element. These observations could lead to a similar conclusion that the emission intensities from the axial direction were more easily affected by the potassium addition. The reason for this effect is probably because the portion of the plasma observed from the axial direction includes the tail zone which is apart from the induction zone and thus has lower temperatures. On the other hand, in the radial observation, one can observe the emission intensities from a narrow portion of the plasma just above the load coil. The axial observation mode gave better analytical performance, including a lower detection limit as well as a better signal-to-background ratio, compared to the radial observation mode. However, interferences from co-existing elements should be noted if the axial observation is employed in practical applications.