Interferences in Atomic MS

Mass spectral interferences are observed in atomic MS. These interferences are of two types direct m/z overlap between two ions and matrix interferences that cause enhancement or suppression of analyte signals. 

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There are now five primary instrumental approaches to eliminating or reducing interferences in atomic MS (1) use of high mass resolution ICP-MS (HR-ICP-MS) (2) use of a collision ceU to break apart polyatomic interferences (3) use of gas-phase chemical reactions in a reaction cell to eliminate polyatomic interferences (4) changing the instrument operating conditions to form a cool or cold plasma as discussed earlier and (5) use of tandem quadrupoles in MS-MS mode to exclude all nontarget analyte masses. 

For additional discussion of interferences in ICP-MS. see K. E. Jarvis, A. L. Gray, and R. S. Houk, Handbook of Inductively Coupled Plasma Mass Spectrometry, Ch. 5. New York Blackie. 1992 G. Horlick and Y. Shao. in Inductively Coupled Plasmas in Analytical Atomic Spectrometry, 2nd ed., A Montaser and D. W. Golightly, Eds., pp. 571 -596 New York VCH-Wiley. 1992. 

Note that the interfacing of LC techniques with MS puts significant constraints on the solvents that can be used i.e., they must be volatile, with a low salt concentration, for MS compatibility. Narrow-bore columns, which use much smaller amounts of salt and organic modifier, appear to have potential for facilitating IEC-MS applications.40 Despite the excellent sensitivity of MS detection for most elements, however, there are cases where matrix effects can interfere. In this situation, combination of IEC with atomic emission spectrometry (AES) or atomic absorption spectrometry (AAS) may be preferable, and can also provide better precision.21 32 4142 Other types of... 

ICP-AES and ICP-MS analyses are hampered in almost all cases by the occurrence of sample matrix effects. The origins of these effects are manifold, and have been traced partly to physical and chemical aerosol modifications inside sample introduction components (nebulisation effects). Matrix effects in ICP-AES may also be attributed to effects in the plasma, resulting from easily ionised elements and spectral background interferences (most important source of systematic errors). Atomic lines are usually more sensitive to matrix effects than are ionic lines. There exist several options to overcome matrix interferences in multi-element analysis by means of ICP-AES/MS, namely ... 

An overview of commercial ICP mass spectrometers from different companies (quadrupole based ICP-MS with and without collision/reaction cell, double-focusing sector field instrumentation with single and multiple ion collectors, time-of-flight (ToF), ICP-ion trap-MS and non-commercial ICP-Fourier transform ion cyclotron resonance (FTICR) mass spectrometers is given in Figure 5.2. By using ion traps and FTICR mass spectrometers in ICP-MS isobaric interferences of atomic ions... 

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