Results and discussion
Wavelength selection was based on the sensitivity of the line and the concentration of elements in each of the solutions. For most lines, spectral interference did not appear to be a major problem.
Ionic and atomic lines were selected for Ca and Mg so the effect of ionization interference on the two emission line types could be observed. Any variation in the results would also show the presence of spectral interference.
The K 766.490 nm line is known to be subject to spectral interference from Mg, so the K 769.896 nm line was also selected. The concentration of K in this sample was approximately 8.5 times that of Mg, and consequently the Mg spectral interference on the K 766.490 nm line was expected to be negligible. This expectation was confirmed when similar results were found for K at both lines.
For Cu, the 324.754 nm or 327.396 nm emission lines are generally used, although the 327.396 nm line is preferred. For both Cu lines, a small OH emission line from the aqueous matrix is observed and is more prominent with the axially-viewed plasma than with the radially-viewed plasma. The OH emission line is not resolved from the 324.754 nm line, which is used in the 2nd order (default or recommended setting), whereas the OH emission line is almost completely resolved from the 327.396 nm line, which is used in the 1st order.
Figures 1 and 2 show the wavelength scans for the Cu 327.396 nm and 324.754 nm emission lines