Polyatomic Interference
Definition
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 arsenic-75 in HCl matrices, or argon dimer on selenium-80. The dominant accuracy problem in low-resolution ICP-MS, addressed by collision or reaction cells, mathematical correction, cool-plasma operation, or a sector analyser.
- Mechanism
- Plasma-formed ion at the analyte's nominal mass
- Example
- Argon-chloride on arsenic-75 in HCl matrices
- Main impact
- Accuracy loss in low-resolution ICP-MS
- Mitigation
- Collision/reaction cell, cool plasma, sector analyser
Common questions
How does a collision or reaction cell fix this?+
The cell uses a gas to break up or slow the larger, more collision-prone polyatomic ions before they reach the detector, so fewer of them survive to be miscounted as the target element.
Why does this matter for forensic trace-element work?+
Uncorrected polyatomic interference inflates or masks element concentrations in gunshot residue, glass or soil comparisons, which can shift a sample's elemental fingerprint enough to change a match conclusion.
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...
- Quadrupole ICP-MS
- Detection arm in which positive ions are extracted from the plasma through sampler and skimmer cones into a quadrupole mass filter that...