Dear all,

i hope someone has an idea what i might have overlooked in appliying the H3 correction to the water samples i am trying to analyse for my diploma thesis... I am working on a GVI isoprime mass spectrometer coupled to a vario EL III (elementar) and measure a stable H3 factor of around 11 ppm/na. The linearity test for the reference gas shows no variation of the mass3/mass2 ratio with varying signal intensity.

However, i see vast nonlinearity when analyzing a water sample. Reference and sample peaks look fine and sample peak intensities are as expected for the sample weight. It seems like, in contrast to the reference gas ratio calculations, the H3 factor is not included in the ratio calculations for the samples. The technician and I have no more ideas. It is the first time D/H is measured on this machine.

My question are:

First of all: Is the H3 correction for the samples commonly calculated automatically by the mass spec software or do you have to correct the sample ratios manually for the H3 contribution?
(Perhaps there is someone using the same isoprime mass spec and could tell me about some hidden places in the Ion Vantage software where a simple tick could solve all my problems...??)

Secondly, if the Reference gas linearity is good, what might be causes for the nonetheless observed sample nonlinearity in the water samples (apart from calculation errors)?

...A third "bonus" question out of mere interest: What is the problem with high H3 factors (e. g. 50 ppm/na) as long as linearity stays good for the reference gas...?? Or is it simply "the smaller the H3 factor the better the linearity"?

PS: I already searched the archives but could not find anything suitable...

Thanks a lot in advance for the help! Its great to learn from the pros with the help of this list...

Marc Ruppenthal