21 Oct
1998
21 Oct
'98
1:09 p.m.
When I was a lad, we used to use a fine jet of helium and spray that
round any possible leaks. It shows up very clearly on a mass spectromter.
Some of them even had a setting on one of the controls to look for the
appropriate peak (4, I guess).
Virtually all the instruments I am involved with have a GC for sample
introduction so there is helium present all the time. Do they ever think of
using the tank of argon sitting off to the side? Much less know the mass of
argon? (40) Do they ever think of using any of the gallons of methanol
present in all the labs? or even know offhand what mass to look for. (31
there is to much 32 from the leak - O2)
The heliun/argon works on the source region but on the analyzer region you
have to resort to numerous other methods - there is nothing to ionize the
gas. Instead you have to use solvents and look for the pressure burst when
the liquid volitizes in the vac. I have had to even pressurize the system
with heliun and use a gas leak detector to find some. - A bad weld on a
diffusion pump is the worst to find. At hi vac. it is extremly hot when it
is cold the pump oil seals the leak.
What makes it even more fun is I have no diploma other than high school. I
have taught numerous classes in mass spec to masters and phd's on operation,
maintenance and troubleshooting. It gets really funny when they find out I
have had only 1 university course - sociology.
Dan