<[log in to unmask]>, Michael
Murphy <[log in to unmask]> writes
>Once again the dunce cap is on and I return to the classroom (virtual
>in this case). While setting up a new ICPMS instrument a "random"
>sample of tap water (this is well water) was analyzed and showed strong
>values and nice peaks for barium and strontium. This holds for Ba at
>mass 137 and 138 and for Sr at mass 88 and 86 in no-gas mode, H2 mode,
>and He mode. "Apparent" concentration is ~ 2300 ppb Sr and ~90 ppb Ba
>(the concentration for each analyte is the same at both masses).
>This was confirmed on a second ICPMS (no cell installed) but,
>fortunately, the ICPOES did not see Ba or Sr.
>Relieved as I am that I am not working overtop a future Superfund site
>I admit that I cannot see what species are causing these rather
>consistent readings (e.g. Ba138 = 607596 counts = 89.9 ppb, Ba 138 =
>3874062 counts = 90.2 ppb, Sr 88 = 94962677 counts = 2390 ppb and Sr 86
>= 10714443 counts = 2320 ppb). If it is a polyatomic problem I cannot
>find a structure(s) that make sense.
>I am assuming that some of you know these interferences by heart, so
>any insight would be much appreciated.
Not by heart but I have a program that will solve the knapsack problem
to look for vaguely plausible interferences on the assumption that they
are a single species.
I have to say there are not too many candidates likely to be in drinking
water that would replicate the Ba and Sr isotope patterns, and the
simplest solution would be that they are real but it might be worth
measuring masses 84,87,90 and 135,136, 140 as a cross check on the ICP.
The suggestions of my program are pretty wacky but offered anyway since
they might just be relevant or assist with interpretation of your ICP
data. I suspect your OES may be telling fibs.
Approx Sr mimics
KrHe 84: 2.3 86: 11.6 87: 11.6 88: 56.9 90: 17.4
ArTi 84: 0.3 86: 8.0 87: 7.7 88: 73.16 89: 5.5 90:
FeS 86: 5.6 88: 87.2 89: 2.8 90: 4.1 91: 0.1
LiBr, GeN would hit 86, 88 but the ratio is wrong.
Approx Ba mimics
ArNKr 134: 2.5 136: 11.6 137: 11.5 138: 56.5 139: 0.2 140:
17.23 141: 0.1
ArCuCl, InNa, PdS will hit 138
That isn't an exhaustive list, but the others really are far too crazy
and a bad fit. A semiquant would identify what majors are present.
Nezumi Scientific Software
North Yorkshire, UK