Problems with getting a stable PFPD signal

[big boss 88]

Peter,

I cooled down the instrument then switched it off.

I only removed the ignitor cable from the detector top mount.

I did check for the other cables but did not removed any of them.

[Peter Apps]

As long as the instrument was switched of you are OK, if you open up with power to the photomultiplier you will cook it.

Peter

[big boss 88]

What about the sulfur filter inside the photomultiplier tube, is it really sensitive to light??

My colleague previously opened it to check if it is for sulfur or phosphorous, he wiped it with methanol and put it back, was this a bad action?

[Peter Apps]

As far as I know the filters in the Varian PFPD are just coloured glass, so it should be OK.

It would be a good plan to run the test mix specified in the detector manual to check sensitivity.

Peter

[muGC]

For the tubing, I am not suing the recommended PEF tubing as they are not available and instead I am using he normal tubing and I tried to minimize the lengths as much as possible,

Your use of bare stainless steel is certainly part of the problem, but maybe not the entire problem (I still think you need a new combustion tube). You cannot be performing trace sulfur analysis without using inert/treated steel. Your method, ASTM D6228, states in sections 4.1 and 6.1.1 that all of your equipment must be inert/passivated. See http://www.silcotek.com/silcod-technolo ... rt-coating.


I recommend the following:

1) Purchase a Sulfinert treated gas sampling loop. http://www.restek.com/catalog/view/2352

2) Purchase Sulinert treated stainless steel tubing for your sample inlet lines and valve->GC inlet line. http://www.restek.com/catalog/view/2351