Mechanism of Interference Effects by Matrix Element and Elimination of the Effect in ICP Mass Spectrometry

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The effects of concomitant elements in ICP-MS can be classified into non-spectroscopic (NS) and spectroscopic interferences. The degree of NS interference is affected by the difference in types of instrument. The mechanism of the interference is not necessarily clear. In order to elucidate the mechanism to reduce the interference effect, we investigated NS interference caused by various matrix elements and the variation of NS interference with changing operating conditions of plasma was measured.Mass dependency of signal suppression effect (SSE) was confirmed in this work. This may be caused by the collision of analyte ions with matrix ions in the supersonic expansions behind the sampler. The variation of SSE with varying voltage of ion lens element may be explained by the change in the space charge effect in the ion optics. The shift of ionization equilibria in the plasma cannot be neglected because the lower is the ionization potential of the matrix element, the larger the SSE. The S … More SE cannot be explained by a single mechanism but by a combination of several mechanisms. The extent of the contribution of each mechanism is considered to depend on the type of instrument employed and the operating conditions. It was also found that matrix effect can be decreased by using an appropriate operating condition, though the sensitivity decreases. The shift of ionization equilibria can be corrected with the internal standard method. Absolute quantity of matrix element introduced is concerned with the degree of matrix effect, therefore the dilution of the sample solution is useful for the reduction of the matrix effect.The overlap with doubly charged and oxide ions of a matrix element is also severe. The plasma potential was measured with a probe, because the intensity of these ions is affected by the potential. The doubly charged ions increased with the increase in the potential. The electrostatic shielding of the torch significantly reduces the potential and the intensity of doubly charged ions. Less