Nano Research Facility School of Engineering & Applied Science



Inductively Coupled Plasma - Mass Spectrometer 


 The ICP-MS instrument employs a plasma as the ionization source and a mass spectrometer analyzer to detect the ions produced. It can simultaneously measure most elements in the periodic table and determine analyte concentration down to the sub nanogram-per-liter or part-per trillion level.



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ICP-MS Block Diagram


 ICP-MS block diagram

In general, liquid samples are introduced by a peristaltic pump, to the nebulizer where the sample aerosol is formed.

A double-pass spray chamber ensures that a consistent aerosol is introduced into the plasma.

Argon (Ar) gas is introduced through a series of concentric quartz tubes which form the ICP.

The torch is located in the center of an RF coil, through which RF energy is passed.

The intense RF field causes collisions between the Ar atoms, generating a high-energy plasma.

The sample aerosol is instantaneously decomposed in the plasma (plasma temperature is in the order of 6000 - 10000 K) to form analyte atoms which are simultaneously ionized.

The ions produced are extracted from the plasma into the mass spectrometer region which is held at high vacuum (typically 10-4 Pa).

The vacuum is maintained by differential pumping: the analyte ions are extracted through a pair of orifices,
known as the sampling and skimmer cones.

The analyte ions are then focused by a series of ion lenses into a quadrupole mass analyzer, which separates the ions based on
their mass/charge ratio.

Finally, the ions are measured using an electron multiplier, and are collected by a counter for each mass number.

The mass spectrum generated is extremely simple. Each elemental isotope appears at a different mass (e.g. 27Al would appear
at 27 amu) with a peak intensity directly proportional to the initial concentration of that isotope in the sample solution.

A large number of elements ranging from Lithium (Li) at low mass to Uranium (U) at high mass are

simultaneously analyzed typically within 1-3 minutes.

With ICP-MS, a wide range of elements in concentration levels from ppt to ppm level can be measured in a single analysis.



Mass spectrum of a coffee sample taken in helium collision mode