James_Ball wrote:LALman wrote:I also, am using nitrogen from a dewar as my purge gas and general use gas.
Steve Reimer wrote:
James:
We are still looking in to switching to hydrogen and already have switched everything but the GCMS units. 8260/624 is almost impossible until some allowances are made from EPA.
What is the main problem with 8260? Tuning or reactivity? The tune criteria were adjusted in 8260D to allow hydrogen but there wasn't much input on problems labs were facing.
Reactivity is another can of worms all together.
Its the 96 mass in BFB that gets too large at the expense of mass 95 which becomes proportionally lower and that affects the 174/95 ratio. I assume the hydrogen is adding a proton to the 95 mass. The other losses were as I said for brominated and chlorinated compounds about 25% of the signal area you would get with helium. It helped me to purge with argon or nitrogen and then dry purge with helium for 1 minute before desorption. In my experience hydrogen reacts more with the 8260 analytes under argon or nitrogen but less so with helium; that helped the recoveries of halogenated compounds.
This was the main problem for us also. If we could switch to 8260D it would be great but we do as many or more 624.1 samples and 524.2 and 524.3. I didn't lose that much 95 to affect the 174 ratio, but could almost never get the 96 down low enough. The longer I ran hydrogen the better it got, but I went from 96 being almost 85% versus 95 down to about 20% which was still too high for most methods. Someone from Tekmar said they made it pass with a flow rate of 0.3ml/min carrier, but that is barely 2 psi even with a 30mx0.18 column, very difficult to maintain at a steady flow.
Also as above I have seen problems with active compounds in 8270/625, but I think if I can burn out all the hydrocarbon background the hydrogen releases from the flow path I might get some of them back. I am also looking to see if solvent evaporation using the MultiMode injection port in solvent vent mode will help. Maybe inject cold then flash onto the column will cause less breakdown. I have used this LVI type injection with even 1ul injections for other tests and it works well, just haven't tried it with hydrogen carrier yet.
We are also working to switch to nitrogen purge for volatiles but have to plumb in the nitrogen, I don't know why when we designed the lab we put everything but nitrogen on the benches in the volatiles room.
I have been playing with nitrogen and vacuum chromatography; it is quite nice, to be honest. I've mostly played with pesticides but I have done some work with phenols and PAHs, and it works quite well. If you get a chance to play with it you should; nitrogen is cheap and doesn't give you the system issues that hydrogen does.
We have gone to N2 for purge gas for volatiles. It's just so much more efficient than He for the heavier compounds. I don't run much in the way of light ends, so it would be interesting to see how it works for you at the front with the gases.
