What are the limitations and disadvantages of an ICP-MS with helium plasma compared with ICP MS with argon plasma with colision cell technologies?
First of all there is no commercial He-ICP-MS. The reason for this is mainly the costs for He vs. Ar. I dont think that you can convince any lab manger to get an He ICP…
Secondly – you mixing things here the correct way would be rather to ask what is the advantage of high-resolution-MS vs. Collision cell for interference management.
Coming back to the He-ICP – ther might be some advantages over a Ar ICP – no Ar polyatomics (e.g. ArC on Cr, ArCl on As and ArO on Fe) but hese are normally good manageable with He collision cell or HR. Also with He ICP the mass 40 (and 80) would be free – but also this can be managed with H2 reaction cell… Another thing would be the higher IP of He and a good CT between He and halogens – you can find that in literature on MIP plasmas from 1980-1990th…. Also the He ICP has been described in the 1988 with some comparison (you can start with Dave Koppenaal 1988 JAAS and go from there….)
Cheers…
Dear Daniel,
Thank you a lot for explanation. I have read some articles about this subject written by Arkbar Montaser's group (Sang-Ho Nam et al, 1994, Morajev, et al, 2004, etc), however, it was unclear to me if there was analytical applications in routine analysis.
Best regards
Rodrigo:
If you actually need, you may use ANY commercial ICP-MS spectrometer
with Helium plasma. You just need a proper nebulizer, torch, etc.
(probably some tuning of your plasma ignition system)...
With He you get around some common interferences that cause you grief in Ar plasmas (ArCl, for example). That said, the cost of He is prohibitive.
In Argon plasma it having poly atomic interfierence that is ArAr mass 80 in Se metal where as helium plasma it is not there.
Actually in collision cell technology it self used He + H2 mixture ( 8% H2 rest of He) gas for removal polyatomic species like above Ar Ar.
Ramaswamy, you mix something here. He is used for collision cell, discriminating interferences by inducing a kinetic energy difference between single atomic ions and polyatomics. then there is a energy barrier which the polyatomics can not overcome at the end of the cell since they lost too much energy by collision with He. Pure He in a collision cell however will not help you for Se... here you need a reactive gas such as H. here you do gas phase chemistry between H and ArAr+.... BUT all this has not much to do whether in a He plasma one has an interference on 80 or not. Also again - He plasmas are not practical due to the price of He and also in the isotope community people discussing the possibility that He may run short and several labs have received only limited/delayed pure He shipping. Also He may have other interferences such as double charged since it ahs a much higher first IP compared to Ar... A good source for the principles of collision and reaction cells is: Tanner SAB 2002, 1361-1452 ;-)
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