Question

Can anyone tell me about the Inductively Coupled Plasma-Mass spectrometer?

Both an introduction to what is it, and about how it works in details.

Answer 1

Inductively Coupled Plasma-Mass spectrometer-

Inductively coupled plasma mass spectrometry (ICP-MS) is a type of mass spectrometry which is capable of detecting metals and several non-metals at concentrations as low as one part in 10¹⁵ (part per quadrillion, ppq) on non-interfered low-background isotopes. This is achieved by ionizing the sample with inductively coupled plasma and then using a mass spectrometer to separate and quantify those ions.

how it works-

Argon gas flows inside the concentric channels of the ICP torch. The RF load coil is connected to a radio-frequency (RF) generator. As power is supplied to the load coil from the generator, oscillating electric and magnetic fields are established at the end of the torch. When a spark is applied to the argon flowing through the ICP torch, electrons are stripped off of the argon atoms, forming argon ions. These ions are caught in the oscillating fields and collide with other argon atoms, forming an argon discharge or plasma.

The sample is typically introduced into the ICP plasma as an aerosol, either by aspirating a liquid or dissolved solid sample into a nebulizer or using a laser to directly convert solid samples into an aerosol. Once the sample aerosol is introduced into the ICP torch, it is completely desolvated and the elements in the aerosol are converted first into gaseous atoms and then ionized towards the end of the plasma.

Once the elements in the sample are converted into ions, they are then brought into the mass spectrometer via the interface cones. The interface region in the ICP-MStransmits the ions traveling in the argon sample stream at atmospheric pressure (1-2 torr) into the low pressure region of the mass spectrometer (<1 x 10-5 torr). This is done through the intermediate vacuum region created by the two interface cones, the sampler and the skimmer (see Figure 2).
Figure 2. The interface region of an ICP-MS.
(Figure reproduced with permission from PerkinElmer, Inc.)The sampler and skimmer cones are metal disks with a small hole (∼1mm) in the center. The purpose of these cones is to sample the center portion of the ion beam coming from the ICP torch. A shadow stop (see Figure 2) or similar device blocks the photons coming from the ICP torch, which is also an intense light source. Due to the small diameters of the orifices in the sampler and skimmer cones, ICP-MS has some limitations as to the amount of total dissolved solids in the samples. Generally, it is recommended that samples have no more than 0.2% total dissolved solids (TDS) for best instrument performance and stability. If samples with very high TDS levels are run, the orifices in the cones will eventually become blocked, causing decreased sensitivity and detection capability and requiring the system to be shut down for maintenance. This is why many sample types, including digested soil and rock samples must be diluted before running on the ICP-MS.