ICP-MS Measurement

Matrix Effects

In addition to the matrix effects encountered for ICP-OES that are discussed in Section 15, ICP-MS suffers from space charge effects and salt buildup on the orifice of the interface sampler cone.

Space Charge Effects

These effects are thought to occur at the MS interface, the region between the skimmer tip and ion optics and in the ion optics region. The net result is a suppression of the signal in high concentrations of a matrix element. The kinetic energy of the ion element matrix affects the degree of suppression with larger masses (higher kinetic energy) causing more depression than lower masses. Due to differences between instruments in interface and ion optic designs it is difficult to predict the conditions under which the effect is minimal. In my case, working at matrix element concentrations of 100 - 200 µg/g will cause only a slight reduction in the signal. Under 'cool plasma' conditions, I have found this suppression effect to be more pronounced. The approach taken in our laboratory is to attempt to keep the matrix element concentration at or below the 100 µg/g concentration level.

Salt Buildup

The buildup of salts/oxides in samples containing high levels of matrix elements (sea water is a common example) will result in partial or total clogging of the sampler cone. Techniques used to help control this effect include dilution to below 0.1% total solids, flow injection analysis, or ion exchange removal of the matrix component(s).

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