Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) Quiz

Electrospray Ionization (ESI) and Matrix Assisted Laser Desorption Ionization (MALDI)

• ESI and MALDI are two common ionization techniques used in CE/MS
• CE/MS provides high separation efficiency and molecular mass information in a single analysis
• Advantages of CE/MS include:
  • High resolving power and sensitivity
  • Requires minimal volume (nL)
  • Analyzes at high speed
  • Major application is biological studies for protein and peptide analysis
  • Often used for routine analysis of pharmaceutical drugs

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)

Principle

• ICP torch serves as an atomizer and ionizer to produce positive metal ions
• Metal ions are sampled through a differentially pumped interface linked to a mass analyzer
• Spectra produced by ICP-MS are simpler and easier to interpret compared to conventional ICP optical spectra
• Resultant spectra consist of a simple series of isotope peaks for each element present

Instrumentation

• Positive ions are separated from electrons and molecular species by a negative voltage
• Then accelerated and focused by a magnetic ion lens onto the entrance orifice of a quadrupole mass analyzer

Performance Specifications

• Mass range of 3 to 300
• Ability to resolve ions differing in m/z by 1
• Dynamic range of six orders of magnitude
• Over 90% of elements in the periodic table have been determined by ICP-MS
• Measurement times of 10 s/element
• Detection limits in the range of 0.1 to 10 ppb for most elements
• Relative standard deviations of 2% to 4% for concentrations to the calibration curves

Spectroscopic Interferences

• Occur when an ionic species in the plasma has the same m/z values as an analyte ion
• Categories: Isobaric ions
• Isobaric ions: two elements with isotopes of essentially the same mass
• Examples: 40Ar+ and 40Ca+, 62Ni+, 63Cu+, 64Zn+, and 66Zn+
• Corrections can be carried out with appropriate software
• Some spectroscopic interferences can be reduced or eliminated by using high-resolution mass spectrometers

Matrix Effects

• Become noticeable at concomitant concentrations of > 500 to 1000 mg/mL
• Usually cause a reduction in the analyte signal
• Can be minimized by:
  • Using more dilute solutions
  • Altering the sample introduction procedure
  • Separating out the offending species
  • Using an internal standard

Applications

• ICP-MS is well suited to the rapid characterization and semiquantitative analysis of various types of naturally occurring and manufactured complex materials
• Easily adapted to multielement analyses