Spectral Interference: Types, Avoidance and Correction

Avoidance: ICP-MS

The following are possible avoidance pathways:

• The use of high resolution ICP-MS.
• Matrix alteration through elimination – for example, elimination of S, and halogen containing reagents such as Cl.
• The use of reaction and or collision cells to destroy molecular interfering ions.
• Cool plasma to reduce background interferences.
• Separation of analyte(s) – for example the use of chromatography or solvent extraction, etc.
• The use of alternate ICP discharges such as He, mixed gas (He-Ar, N2-Ar, etc.).
• Low-Pressure ICP discharges.

The above approaches are just examples of some of the approaches that have been taken to avoid interferences. For a given application, it is suggested that a literature search be performed in an attempt to benefit form the vast amount of research that has been conducted in this area. In addition, instrument manufacturers are constantly revising and updating their instrumentation and software in an attempt to take advantage of new technologies. Thus, consulting with the manufacturer may help when interferences are encountered.

The fact is that the mass spectra of elements are much less detailed than in optical emission spectroscopy. Most elements have fewer than seven isotopes and many have only one (monoisotopic). When interference is encountered, it may be possible to go to another isotope even if it is less abundant. The difficulty in obtaining low detection limits in ICP-MS with interference correction is a function of the relative signal intensities and measurement precision as illustrated above for ICP-OES. If a correction cannot be avoided, many analysts seek alternate techniques rather than run the risk of reporting unreliable data.

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