Matrix-effect observations in inductively coupled plasma mass spectrometry
Matrix effects in inductively Coupled plasma mass spectrometry (ICP-MS) may be divided into two basic categories: matrix induced spectral overlap problems and matrix induced signal intensity changes. In this work, matrix induced signal intensity changes are studied in some detail. In general, a high concentration of a matrix element results in the suppression of analyte signals. The degree of the matrix effect is strongly dependent on the nebuliser flow-rate and tends to be less severe at low nebuliser flow-rates than at high nebuliser flow-rates. While suppression effects seem most general, it is possible to observe enhancements, particularly at high nebuliser flow-rates. Plasma power and sampling depth do not appear to have a major influence on matrix effects. Definite mass trends are observed for the matrix effect. Heavy matrix elements cause the most severe matrix effects and light analytes are more seriously affected than heavier ones. Also, more severe matrix effects occur in the presence of matrix elements that have low ionisation potentials. Finally, the matrix effect depends more on the absolute concentration of the matrix element rather than on the relative concentration of matrix to analyte and thus matrix effects can be minimised by dilution. The main cause of the observed matrix effects appears to be a disturbance of the ion beam path through the ion optics and the mass spectrometer by the high concentration of the matrix element.