ICP-MS as a Technique
ICP (Inductively Coupled Plasma) Spectroscopy is an analytical technique used to measure and identify elements within a sample matrix based on the ionization of the elements withing the sample. Mass Spectrometer (MS) separates the ions out by their mass-to-charge ratio after going through the ICP, and the detector counts the number of selected ions per second which allows the instrument to determine the concentration of each chosen element.
ICP analysis requires the use of liquified sample solutions, so solid samples and biological samples are often digested prior to analysis. Once the sample is liquid, the ICP uses argon (Ar) carrier gas to aerosolize the sample sending only the smallest droplets through the chamber and into the argon plasma torch.
The Ar plasma causes the sample to desolvate and ionize, these ions are then extracted from the plasma by skimmer and interference cones and extraction lenses. After going through the lenses, the ion particles are further refined by going through an off-axis ion lens removing photons and neutral ions, reducing background noise.
Polyatomic ions which act as interferences are removed using kinetic energy discrimination, where the larger polyatomic ions lose energy faster than the analyte ions and are easily removed from the sample beam. From there, the beam of ions travels into the hyperbolic quadrupole of the mass spectrometer and the ions are separated by their mass-to-charge ratio, allowing only the selected ions to travel on towards the detector to be measured and reported by the ICP-MS in terms of counts per second and concentration.
For more information on ICP-MS, please see the USGS introduction to ICP-MS.