Figures 3-10 represent the calibration graphs for the standard solutions displayed in Table 2, with and without the addition of cesium. Standards 3, 4 and 5 contained varying levels of Ca, K and Na. Sodium was present in concentrations high enough for ionization interference to have considerable influence on the signals of the other elements in the standard solutions.
Figures 3-6 show the effect of the varying levels of ionization interference, because of the varying EIE concentration between solutions, on the atomic lines of K (766.490 nm and 769.896 nm), Na (589.592 nm and 330.237 nm) and Ca (422.673 nm) as signal enhancement has produced upward curvature of the calibration. The addition of Cs nullified the effect of the varying levels of ionization interference, producing a more linear calibration. Adding Cs instead of matrix matching allows all elements to be determined in a single analysis because sample solutions with varying dilution factors, and varying concentrations of EIE, can be analyzed.
An ionic line for Ca (317.933 nm) was also used and upward curvature of the calibration was not found. The calibration for Mg (285.213 nm) atomic line exhibited little, if any, upward curvature as did the remaining atomic and ionic analyte lines. This is consistent with other reports4, 5 that the atomic lines of group I and to a lesser extent, group II elements, exhibit signal enhancement with increasing levels of EIE. The atomic lines of other elements and all ionic lines tend to exhibit signal suppression by EIE but the effect is not as severe.
In the Plasma 96 software, the maximum % error of the slope of the calibration, which is set in the calibration page of the method editor, only sets the limit of downward curvature for each specific element. The maximum % error of