Question

Explain why ICP-MS is more sensitive than ICP-AES. Please explain why, do not just compare them, thanks!

Answer 1

ICP-OES

ICP-OES is regarded as suitable for the detection of most elements (73), with the exception of radioactive elements requiring analysis by gamma-ray spectroscopy, the halogen group, and trace contaminants found in the argon gas mixture that is used in the ICP-OES testing procedure. Common areas of application include food and beverage, environmental, toxicology, photonics, agricultural testing, petrochemicals, and other areas of application where rapid elemental analysis is of great interest. ICP-OES efficiently measures 1 to 60 elements per minute. Method development is relatively simple, and “analytical grade” solvents and reagents may be used for testing. Running ICP-OES samples does not require the attention of a specialist: a method can be calibrated by a specialist and run by average laboratory personnel. Medium sample volumes are best for ICP-OES. The biggest drawback is the high potential for spectral interference. Also, an ICP-OES system requires a high-volume gas installation in the laboratory.

ICP-MS
ICP-MS boasts excellent detection limits. By passing the positive ICP sample ions through a quadrupole mass filter and then the mass detector, the ICP-MS provides isotopic information and mass data. Of comparative elemental analysis techniques, including ICP-OES, FAAS, and GFAAS, ICP-MS is able to detect the largest number of elements (82). Very small volume samples can be used in ICP-MS. Run times for both ICP-OES and ICP-MS are relatively short, but ICP-MS is able to detect most elements in less than one minute, and even older systems can detect all the elements in less than five minutes. Some spectral and isotopic interference may be seen in ICP-MS, as can matrix effects and ionization effects. Some elements (S, K, Ca, Se, B, Br, etc.) have high detection limits via ICP-MS and appropriate configurations must be made to enable efficient testing.

An excellent ICP-MS set up may cost 2 to 3 times the cost of an ICP-OES system. The coating on ICP-MS detectors is light sensitive and wears off as ions hit the detector surface, so it must be replaced as needed. Operation can be left unattended, but should be monitored by a highly knowledgeable specialist, as method development is significantly more difficult than for ICP-OES. The operating costs for an ICP-MS system typically are and can be considerably greater than for an ICP-OES system, especially since cleanroom conditions must often be established to properly test in the parts per trillion (ppt) level. High purity grade reagents must be used with ICP-MS.

ICP-MS provides the added bonus of being able to detect the ions themselves rather than just the photons (-OES and -AES), as ICP-MS mates the plasma coupling technology with mass spectrometry. The markedly higher sensitivity of ICP-MS allows for detection limits in the parts per trillion (ppt) range.