Stable Isotope Geochemistry


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Eva Stüeken <[log in to unmask]>
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Stable Isotope Geochemistry <[log in to unmask]>
Fri, 3 Jun 2022 04:09:07 -0400
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Hi Dana,

I don't have much experience with the MAS autosampler myself (I have an EA Isolink from Thermo with a Costech zero-blank autosampler, using the control box that somebody else mentioned already), but in this paper below we compared data from our EA to an EA in Thermo's lab in Milan, which does have a MAS, and they obtained very comparable data for CNHS abundances:

Stüeken, E.E., de Castro, M., Krotz, L., Brodie, C., Iammarino, M. and Giazzi, G., 2020. Optimized switch‐over between CHNS abundance and CNS isotope ratio analyses by elemental analyzer‐isotope ratio mass spectrometry: Application to six geological reference materials. Rapid Communications in Mass Spectrometry, 34(18), p.e8821.

An advantage of the MAS is that you can add samples to it on the fly without having to vent anything, which is tremendously useful during trouble-shooting. You can also expand that size of the MAS with additional carousels. Furthermore, I think it allows you to take better advantage of the helium-management system that Thermo designed for the EA Isolink. Using the zero-blank AS instead, I currently have 10ml/min of He constantly venting into the room. With the MAS, I believe those 10ml/min would be recycled. Though somebody else would need to chip in to comment on how significant this saving is. I don't know. 

The reason why I nevertheless switched to a zero-blank AS is because I often analyze rock samples with several 10s of mg in mass, and I was worried that those would not be sufficiently purged by the MAS. In the zero-blank AS, one can pressurize the chamber up to 2-3 bar with He and then vent it quickly and repeat that several times, which I imagine to be a very effective way of forcing air out of pore spaces within the fine powder of the sample capsules. However, I have not actually made the quantitative comparison with the MAS to test if this is indeed an important difference. I've been meaning to do that, but haven't had time. 

I hope, this helps a bit in any case.