Progress in the accuracy enhancement for elemental analysis by quadrupole-based plasma-SNMS

Abstract

The elemental quantification in plasma-based SNMS is hampered by the matrix dependence of the detection efficiencies. The signals of elements of unknown compounds can only be converted to concentrations with mean detection factors resulting in concentrations with an uncertainty mainly given by the matrix effect. This situation can be considerably improved by energy measurements of the sputtered particles. The energy distribution (ED) can be used in two ways. First, the exact knowledge of the ED to each detected element allows an element specific integration of the directly sputtered atoms eliminating thermal species from resputtered wall deposition. For a set of copper compounds the spread of the Cu detection factors could be reduced from ± 63% for the conventional measurement to ± 35% using energy resolved data. Second, the shape of the ED of postionised atoms differs considerably from all interfering species, such as clusters as well as twice charged atoms which could superimpose on the atomic signals. A quantitative shape analysis of the measured ED was developed to correct for these interfering species. Examples are given for both superpositions with cluster intensities and interferences with twice charged intensities. To reduce the additional time necessary to obtain the ED, the number of energy resolved data points was reduced in steps down to 3 points only which still reduced a superposition error to half of the value without ED based correction.