Isotope-ratio Mass Spectrometry - Multiple Collector - Inductively Coupled Plasma - Mass Spectrometry (MC-ICP-MS)

Mass Spectrometry (MC-ICP-MS)

An MC-ICP-MS instrument is a multiple collector mass spectrometer with a plasma source. MC-ICP-MS was developed to improve the precision achievable by ICP-MS during isotope-ratio measurements. Conventional ICP-MS analysis uses a quadrupole analyser, which only allows single-collector analysis. Due to the inherent instability of the plasma, this limits the precision of ICP-MS with a quadrupole analyzer to around 1%, which is insufficient for most radiogenic isotope systems.

Isotope-ratio analysis for radiometric dating has normally been determined by TIMS. However, some systems (e.g. Hf-W and Lu-Hf) are difficult or impossible to analyse by TIMS, due to the high ionization potential of the elements involved. Therefore these methods can now be analysed using MC-ICP-MS.

Magnetic sector mass spectrometry requires a high acceleration potential in order to properly resolve species with different masses. Since the ion beam is normally positive, a multi-collector ICP-MS (unlike conventional ICP-MS) needs to have an ion source up to 8000 V positive, in order to keep the analyzer at electrical ground. This was one of the engineering challenges of developing MC-ICP-MS. Magnetic sector mass spectrometry also requires an ion beam with a relatively small range in ion energy. This is achieved in MC-ICP-MS by using an electrostatic and/or quadrupole pre-filter, which allows the ion energy of the beam to be homogenized before entering the magnetic sector.