Interferences in ICPMS 2.1Mass spectral interferences

Advanced Analytical Chemistry – CHM 6157 ® Y. CAI Florida International UniversityUpdated on 9/14/2006 Chapter 3 ICPMS-2

2. Interferences in ICPMS2.1 Mass spectral

interferences

Skoog et al., 1999, Instrumental Analysis

Advanced Analytical Chemistry – CHM 6157 ® Y. CAI Florida International UniversityUpdated on 9/13/2006 Chapter 3 ICPMS

2.1.1 Isobaric overlapIsobaric interferences are due to two elements that have isotopes having substantially the same mass.

Quadrupole instruments: differ in mass by less one unit.


Generally Most elements in the periodic table have one (e.g. 59Co),

two (e.g. Sm, Samarium), or even three (e.g. Sn) isotopes that are free from isobaric overlap.

An isobaric interference occurs with the most abundant (sad!) and thus the most sensitive isotope, e.g. the very large peak for 40Ar+ overlaps the peak for the most abundant calcium isotope 40Ca+ (97%) making it is necessary to use the second most abundant isotope 44Ca+ (2.1%).

Isotopes with odd masses are free from overlap, while with even masses are not.

No isobaric peak interferences below 36 m/z.

Isobaric overlaps are exactly predictable!


2.1.2 PolyatomicPolyatomic ion interferences result from interactions between species in the plasma and species in matrix or atmosphere.

Argon, hydrogen and oxygen are the dominant species present in the plasma and these may combine with each other or

With elements from the analyte matrix or The major elements present in the solvents or acid

used during sample preparation (e.g. N, S. and Cl)


Vandercasteele and Block1997

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Vandercasteele and Block1997

This type of interference is found largely at m/z values of below 82.


Jarvis et al., 1997

Polyatomic ion peaks in both H2O2 and HNO3 are identical to those identified in de-ionized water and these media are therefore considered ideal matrices. However, the spectra in an HCl or H2SO4 matrix are more complex.


Vandercasteele and Block, 1997


Corrected for using a blanks Estimate the response of the interference

relative to the analyte Reduce water entering Plasma


2.1.3 Refractory oxide ionsRefractory oxide ions occur either as a result of incomplete dissociation of the sample matrix or from recombination in the plasma tail.

16 (MO+), 32 (MO2+) or 48 (MO3+) mass units above the M+ peak

The relative level of oxides can be predicted from the monoxide bond strength of the element concerned. Those elements with the highest oxide bond strength usually give the greatest yield of MO+ ions.

Plasma operating conditions can dramatically influence the formation of oxide ions


Jarvis et al., 1997


2.1.4. Doubly charged ions

The formation of doubly charged ion in the plasma is controlled by the second ionization energy of the element and the condition of plasma equilibrium.

Only those elements with a second ionization energy lower than the first ionization energy of Ar will undergo any significant degree of 2+ formation.

The effect of 2+ ions is two-fold: Sensitivity for the singly charged species Spectrum interferences for others


Jarvis et al., 1997

Interferences in ICPMS 2.1Mass spectral interferences

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