Quadrupole ICP-MS
Definition
Detection arm in which positive ions are extracted from the plasma through sampler and skimmer cones into a quadrupole mass filter that resolves them by mass-to-charge ratio. An electron multiplier counts the ions. Limits of detection sit between 1 and 100 parts per trillion; sector instruments push to sub-parts-per-trillion in clean matrices.
- Ion separation
- By mass-to-charge ratio via quadrupole filter
- Detector
- Electron multiplier, ion counting
- Typical LOD
- 1 to 100 parts per trillion
- Sector instrument LOD
- Sub-parts-per-trillion in clean matrices
- Sample introduction
- Sampler and skimmer cones from plasma
Common questions
Why does forensic trace evidence analysis favour quadrupole ICP-MS over sector-field instruments despite the higher detection limits?+
Quadrupole systems are considerably less expensive to purchase and operate, scan faster across multiple elements, and their detection limits are already low enough for most forensic elemental profiling tasks such as glass or gunshot residue comparison, making the sector instrument's extra sensitivity unnecessary for routine casework.
What limits a quadrupole mass filter's resolution compared to other mass analysers?+
A quadrupole separates ions using oscillating electric fields tuned to pass a narrow mass window, but this window is wider than a magnetic-sector or time-of-flight analyser can achieve, so quadrupole ICP-MS is more prone to isobaric and polyatomic interferences at the same nominal mass.
Related terms
- Collision and Reaction Cell (CRC)
- A pressurised cell between the skimmer and the quadrupole, charged with helium for kinetic-energy-discrimination collision mode or with hydrogen, ammonia or oxygen...
- Inductively Coupled Plasma (ICP)
- An argon discharge sustained at 6000 to 10000 K by an RF coil at 27.12 MHz wrapped around a quartz torch. Argon...
- Isotope Ratio Analysis
- Measurement of relative abundances of two or more isotopes of an element to 0.01 to 0.5 percent precision. Lead ratios fingerprint the...
- Optical Emission Spectrometry (OES)
- Detection arm in which excited atoms emit photons at characteristic wavelengths as they relax. A polychromator separates the light by wavelength and...
- Polyatomic Interference
- An ion formed in the plasma at the same nominal mass as a target analyte, for example argon-oxide on iron-56, argon-chloride on...