ICP-MS

Question 1

ICP-MS system can be considered as 4 distinct functional units. What are they ?

Answer 1

1. Sample Introduction - including the ICP source to produce elemental ions at
   atmospheric pressure.
2. Injection of the ions into the vacuum system and focusing of the ion beam by the electrostatic lenses. Vacuum steps from atmospheric pressure to <2mbar in theinterface region to <10-4mbar in the ion lens region.
3. The quadrupole mass filter that separates the ions by mass/charge. The vacuum in this region is <1 X 10-6mbar. Pump-down time from atmospheric pressure is ~15min
4. Ion detection of each mass occurs as they are separated by the quadrupole. When changing the detector it is best to pump-down overnight to de-gas the detector

Question 2

What are the main parts of sample introduction system ?

Answer 2

1. Sample delivery - A peristaltic pump passes the liquid sample to the nebulizer, where a high velocity argon stream is used to generate a very fine aerosol of the sample. This ensures a constant flow of solution.
2. Generation of an aerosol from the liquid sample - The aerosol is generated by the nebulizer, the most commonly used nebulizer being the concentric type. The aerosol is then filtered and homogenized in the spray chamber. This has a small internal volume, so has fast washout and reduced memory effects. Quartz or inert (polypropylene) types are available.
3. Introduction of the aerosol to the plasma - The sample is transported from the spray chamber to the torch by the flow of argon gas through the nebulizer. The nebulizer and spray chamber are attached directly to the ICP torch, minimizing the distance that separates them.