Agilent 5975C Calibration Valve Issue

[mbpastor]

Hello,

I am working on a Agilent GC-MS system. I have run into some issues regarding the calibration valve. I typically run an analysis and open up my calibration valve for calibration with PFTBA at 55 C after my analysis. I noticed the signal from the PFTBA was slowly dying out. Eventually, the signal was so bad that the air leak at the end of our run was drowning out the PFTBA signal.

I checked the calibration vial. My initial thoughts were that it was running low. I refilled it and purged the calibration vial. I ran again and saw essentially no signal when the valve was programmed to be open. I have removed the calibration vial and reinstalled. I get some signal initially (not of PFTBA) but then it plateaus with no PFTBA detected.

Is my expired PFTBA bad? Is this an issue of the calibration valve itself? Any thoughts would be helpful.

[Peter Apps]

Welcome to the forum.

On the 5973s that preceded your instrument the calibration gas valve would sometimes stick closed. I gave it a gentle tap with a screwdriver handle to get it to open.

Peter

[James_Ball]

On the 5973 I also had to replace a valve because it would open, then slowly close while tuning. They are solenoids so they can go bad, or just get gummed up over time, and the valve is essentially the same on the 5973 and 5975, just the 5975 it on top and mounted sideways so they could put the glass on the front. If it doesn't begin to work after tapping on it, you may just need to replace it.

[mbpastor]

Update:

I have been able to get the valve to work after emptying some of the PFTBA solution and reinstalling it ensuring a proper seal. I am now running into issues of an air leak drowning out my PFTBA signal.

This air leak is most apparent after cooling the GC oven. I will see this tailing at the end of each acquisition (heating to 250 and cooling to 55 for PFTBA) as well as at the beginning of my following samples. I was able to see a small peak standing out of the rising baseline which corresponds to PFTBA. Unfortunately I need stronger signal from my PFTBA vs air.

I do not know much about testing for leaks but I am assuming it is related to some of the components going bad with heating and cooling.

[James_Ball]

Update:

I have been able to get the valve to work after emptying some of the PFTBA solution and reinstalling it ensuring a proper seal. I am now running into issues of an air leak drowning out my PFTBA signal.

This air leak is most apparent after cooling the GC oven. I will see this tailing at the end of each acquisition (heating to 250 and cooling to 55 for PFTBA) as well as at the beginning of my following samples. I was able to see a small peak standing out of the rising baseline which corresponds to PFTBA. Unfortunately I need stronger signal from my PFTBA vs air.

I do not know much about testing for leaks but I am assuming it is related to some of the components going bad with heating and cooling.

The easiest way to find a leak is to use Dustoff (computer duster in a can) and spray it around the seals and fittings while scanning with the cal valve closed. It will give peaks just above 50 mass units, but I can't remember the exact masses.

The leak you describe sounds like the ferrule on the column where it enters the mass spec. When the oven heats up it will seal, when it cools it will leak. This often happens because the vespel ferrule will shrink when heated several times, usually you just have to go another 1/8 turn of the interface nut to get it tight enough.