What is Inductively coupled plasma mass spectrometry?

ICP Mass Spectroscopy is an analytical technique that uses plasma to ionize the sample. The ionized sample is then separated based on their charge to the mass ratio in the mass spectrometer. Thus, the ICP-MS has a high-temperature ICP source (for plasma) and a mass spectrophotometer. The ICP source converts the atoms of the sample into ions.

ICP torch:

Most common ICP uses the Argon gas system to generate plasma. The instrument has ICP (or Plasma) torch where the argon gas flows. The ICP torch is surrounded by RF load coils. The RF load coils are connected to the Radio-frequency generator. As the power is generated from the generator, there would be a generation of the oscillating electric and magnetic fields at the end of the torch. It will be followed by the generation of a spark that would ionize the argon gas flowing through the torch to argon ions. These ions will get caught in the oscillating field and collide with the other argon ions which would generate the Plasma or discharge.

Sample Ionisation:

The sample used in ICP-MS is in aerosol form. This form can be achieved by aspirating the liquid sample or dissolved sample into the Nebulizer. This aerosol is transferred towards the plasma torch, it is desolvated, and then the solid sample will be converted to a gaseous state which would be ionized at the end of the torch. The plasma or the argon discharge has a temperature of around 6000-10000 K and acts as an excellent ion source. However, most of the ions generated by the plasma are positively charged and thus, negatively charged ions such as Cl, F, Br, I, etc. cannot be ionized and analyzed easily with the help of ICP-MS.

Once the elements in the sample are converted into ions, they are then brought into the mass spectrometer via the interface cones.

The purpose of these cones are to sample the center portion of the ion beam coming from the ICP torch. A shadow stop will block the extra photons coming from the ICP torch. Thought the ICP-MS are very accurate and beneficial for analyzing compounds, the small orifice (opening) of the Sampler cone and Skimmer cone limits the amount of the solid sample dissolved (0.2% TDS) and analyzed. If the total dissolved solids in the sample are high, then the orifice of the cone will be blocked. Now, the ions are focused towards the entrance of mass spectrometer. This is facilitated by the Electrostatic lens which is positively charged. As the ions ejected from the ICP are positively charged, they would get repelled by the parallel positively charged electrostatic plated and focused on entrance aperture or slit of the mass spectrometer. The most commonly used Mass Spectrometer is Quadrupole mass analyzer