You sure it's not high water? Or water is too low? Counter intuitive
(another phrase for wrong?), but if you tuned with some water in the
source--then take it away--things will behave differently. Also if you
do have trace water in your samples, going from 100 mV to 1100 mV (m/z18
in middle cup) tends to cause problems. Going from 1000 mV to 2000 mV
tends to be more stable (yes it will get bad if you end up with too much
water)... That's probably a function of the tune (and surface effects,
Time to change the oil wick on the turbo--or flush out old oil depending
on our turbo. (the one thing not explicitly mentioned ;)
I've recently had problems with valves leaking on the back side. A short
pulse of gas going into the source when the DI was switched over--even
though bellows and lines were pumped out.
On 5/24/2016 5:04 PM, Ross Beaudette wrote:
> Howdy Everyone,
> I am soliciting suggestions and ideas for an hydrogen source within our mass spec. We've been having an ongoing mystery concerning a large amount of H2 in our 252 since an inlet venting failure. To make a long story very short:
> The cause:
> -We have 120V scrolls as the backing pumps, which means when the inlet vented, the scrolls never turned off because they are not a function of the 230V inlet power control switch. Therefore, it was believed that the oil from the wasteline Pfeiffer turbo felt pads had contaminated our machine with hydrocarbons since it was under vacuum for some time, and hence, our H2 problem.
> The solution:
> -Subsequent B scans confirmed hydrocarbons, and we baked out the entire machine; source, COV, and inlet (but not the flight tube).
> The mystery:
> -After the bakeout, the hydrocarbons were all but gone, our 252 had a clean bill of health. Then we added standard gas, the H2 returned but NOT the hydrocarbons. (The standard gas was proven to be hydrogen-free).
> Troubleshooting steps:
> -It was thought that perhaps we baked ON the oil, so we changed the capillaries to be sure. This has made no difference.
> -Next steps might be to bake the flight tube, although a longshot, since we analyze only N2 and Ar.
> -Rebuild and clean the COV
> The issue is there is too much interference going on from the hydrogen, which affects our 29/28 ratio and the subsequent statistics prove this to be true. Does anyone have experience with this kind of problem? Many thanks for your time.