Mostly purchasers of laboratories buy a new ICP/MS. But not every laboratoria had the means for buying new chromatography equipment.
What is a ICP/MS?
An inductively coupled plasma mass spectrometer or ICP-MS is a coupling of an inductively coupled plasma (ICP) to a mass spectrometer. This enables the determination of metals and some non-metals with very high sensitivity. Recognition of concentrations of 10-12 grams per litre are possible.
ICP (Inductively Coupled Plasma) - A plasma is the fourth form that matter can take (in addition to solid, liquid and gas). It consists almost exclusively of free ions and electrons, making it electrically conductive.
The mass spectrometer consists successively of an
- interface, which must bring the ions supplied by the plasma from the extremely high temperature (> 5000 K) and atmospheric pressure to room temperature and high vacuum (< 0.001 Pa)
- ion optics, which must focus the free ions on the input lens of the actual
mass spectrometer. This is usually a quadrupole, an assembly of 4 metal (or metal evaporated ceramic) rods, which separate the different masses from each other with a kind of resonance principle (see quadrupole)
- an electron multiplier, a kind of detector, which amplifies one incident ion into a measurable electrical pulse by multiple collisions with active surfaces
- electronics that count these pulses and sort them into the masses selected by the quadrupole electronics. This mass selection can be done very quickly (within 1 millisecond), so that within one second a complete mass spectrum can be recorded and displayed on a computer.
The quadrupole consists of four parallel electrically conducting rods of circular cross-section, mounted at equal distances within a pair of insulating rings. They are electrically connected crosswise in pairs and are supplied with a positive or negative direct voltage, to which an alternating voltage is superimposed. When different ions pass through the quadrupole, ions of a certain m/z (mass-to-charge ratio) can be allowed to pass through and the others eliminated by varying the frequency of the alternating voltage. It is easier to change the magnitude of AC voltage and DC voltage together with the same result. The quadrupole acts as a mass filter.