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ICPMS Reaction and Collision Cells

 

ICPMS Polyatomic Interferences

The argon plasma can contain polyatomic ions.  Two examples of these polyatomic ions are ions generated by argon itself, argon dimer (Ar2+) and argon oxide (ArO+) produced when water is present.  With a mass of 80, Ar2+ is an interference for the major isotope of selenium (Se).  With a mass of 56, ArO+ is an interference for the major isotope of iron (Fe).  In traditional ICPMS, these interferences are the reasons that less abundant isotopes of Se and Fe are used.   

Using isotopes with lower abundances results in lower sensitivities and thus higher detection limits.  With traditional 

 ICP-MS, detection limits for both Fe and Se were approximately 2-20 ug/L due to the argon plasma background and these polyatomic interferences. With reaction or collision cells, detection limits can be reduced to <1 ug/L.

Other polyatomic species which present problems for traditional ICP-MS are as follows:

Interference Analyte
38Ar1H 39K
40Ar 40Ca
35Cl16O 51V
40Ar12C 52Cr
23Na40Ar 63Cu
40Ar35Cl 75As

ELAN 6100 DRC and
Agilent 7500ce

The PerkinElmer ELAN 6100 DRC features a Dynamic Reaction Cell (DRC) while our Agilent 7500ce and -cx systems have dual reaction/collision cells.  Both are effective at minimizing polyatomic ions from the plasma.  Reaction cells may have reaction products that interfere with certain elements. Therefore they are most useful for a limited target list, but may also reduce the interference better than a collision gas.  A collision gas such as He does not produce unwanted reaction products and allows the analysis of the broadest range of elements with minimal interference.

Agilent 7500cx

Reaction and Collision Cell

The cell is part of the ion optics bench which is under vacuum between the focusing lenses and the analyzing quadrupole (where the isotopes are separated).  The cell contains a separate quadrupole or octapole to keep the ions focused, and the cell is slightly pressurized with a reaction or collision gas gas.

In the case of Fe and ArO+, the interference is remove by using a reaction gas of ammonia:

ArO+ + NH3 -----> ArO + NH3+

With the ArO+ removed in the reaction

cell as a neutral species, 56Fe+ can be determined with much better sensitivity and lower detection limits.

Additional ICPMS publications by WCAS:

Metals Analysis by ICPMS, ICPMS vs.GFAA, ICPMS Metals Screens, Lead (Pb) by Isotope Dilution ICPMS, and "Environmental Analysis Using ICP-MS", Environmental Laboratory, August/September 1993, pg. 44-49. "ICP-MS for the Analysis of Metals on Membrane Filters", American Industrial Hygiene Association Journal, 48(2), pg. 977-979, (1987).

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