Advanced Analytical Chemistry

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

• Interferences in ICPMS
• 2.1 Mass spectral interferences

Skoog et al., 1999, Instrumental Analysis
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS

• 2.1.1 Isobaric overlap
• Isobaric interferences are due to two elements
  that have isotopes having substantially the same
  mass.
• Quadrupole instruments differ in mass by less
  one unit.

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

• 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!

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

• 2.1.2 Polyatomic
• Polyatomic 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)

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
?? 3000000
Vandercasteele and Block 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Vandercasteele and Block 1997 This type of
interference is found largely at m/z values of
below 82.
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
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.
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Vandercasteele and Block, 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Vandercasteele and Block, 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Vandercasteele and Block, 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS

• Corrected for using a blanks
• Estimate the response of the interference
  relative to the analyte
• Reduce water entering Plasma

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

• 2.1.3 Refractory oxide ions
• Refractory 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

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Jarvis et al., 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Jarvis et al., 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS

• 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

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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS
Jarvis et al., 1997
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Advanced Analytical Chemistry CHM 6157 Y.
CAI Florida International UniversityUpdated on
9/13/2006 Chapter 3 ICPMS

• A note on Interferences
• Always consider and compare the relative plasma
  responses of the analytes of the interest and the
  interferences. Sometimes, a real experiments may
  be needed.