Safety GC-MS with hydrogen

[nbellora]

Hi at all,
I'm working with a GC-MS with hydrogen to develop a method.
I know that some labs have installed tubes on the split and purge valve and also on the pump for reasons of safety.
I wanna know how to know if it is mandatory or it depends on lab air circulation.


thanks in advance

Nicolò

[benhutcherson]

If you want to do it, you can.

My take on the issue has always been that hydrogen effuses so fast through the air, particularly regularly exchanged lab air, that it's extremely difficult to reach 4% hydrogen in your lab air.

At least on Agilent systems, there are a few precautions recommended, including that you don't try to pump down if the carrier has been allowed to build up in the MS for any amount of time(shut it off and let it clear out before pumping down), that you remove the front cover of the MS, and that you LIGHTLY screw down side plate cover to keep it from flying open in the event of an explosion.

The Agilent EPCs will generally shut off if they can't reach the setpoint pressure within a couple of minutes, which also makes things a bit safer.

[James_Ball]

If you want to do it, you can.

My take on the issue has always been that hydrogen effuses so fast through the air, particularly regularly exchanged lab air, that it's extremely difficult to reach 4% hydrogen in your lab air.

At least on Agilent systems, there are a few precautions recommended, including that you don't try to pump down if the carrier has been allowed to build up in the MS for any amount of time(shut it off and let it clear out before pumping down), that you remove the front cover of the MS, and that you LIGHTLY screw down side plate cover to keep it from flying open in the event of an explosion.

The Agilent EPCs will generally shut off if they can't reach the setpoint pressure within a couple of minutes, which also makes things a bit safer.

I have never understood the warning to remove the front cover on the Agilent MS when using Hydrogen, you would think if it is going to explode and break the front glass you would want something there to help catch it.

With Hydrogen carrier in an MS, you are going to want to keep the flow down to about 1ml/minute to be able to maintain proper vacuum, less flow the better with Hydrogen. You can't actually take advantage of the higher flow rate/sharper chromatography that you would with other detectors when using Hydrogen because the extra flow will kill the sensitivity of the MS. So with Hydrogen on MS there should be no difference in safety than using Hydrogen carrier on a GC/FID or GC/ECD if you are at the same split flows on the inlet since you will be normally using lower column flow rates than other detectors. The FID with Hydrogen would burn it away, but any other detector will still vent it to the room unless you use tubing to route it outside or to a hood.

[LALman]

'Remove the front cover' is just for access so you can lightly screw down the side plate, no other reason. You can put the front cover back on afterwards.

[James_Ball]

'Remove the front cover' is just for access so you can lightly screw down the side plate, no other reason. You can put the front cover back on afterwards.

Actually you have to open the side cover to do that, at least on the 5975, it would be difficult to do it on the 7000 just with the front cover off also.

I wonder if it is in case of a power failure, if there is a leak it helps prevent hydrogen from building up in the electronics area?

[LALman]

Ah, I was thinking only of my 5973. That cover sort of wraps around from front to side. It just pops off but gives access to the sideboard scews.

[James_Ball]

I found this in the manual

"You must remove the plastic cover over the glass window on the front of a 5975
MSD. In the unlikely event of an explosion, this cover may dislodge."

I would think a flying plastic cover would be less dangerous than flying glass shards from the front window, since that would have to fracture to dislodge the plastic cover.

I guess it is akin to the warning sticker to not use a hair dryer in the bath tub.

[benhutcherson]

I seem to recall the plastic cover(the small one) on the front of the 5975 having a warning on the top of it to remove it when using H2 also.

Aside from the claimed fly-off risk, I'd assumed also that it was to help prevent build-up in case of a leak. I agree, though, that if that did happen I'd rather it hopefully hold back the glass window than worry about it flying around.

I ran hydrogen some on my Varian 300, which relies on a 1/2" thick piece of glass to seal the top of the manifold. It makes a fun showpiece since you can see the source, quads, and even the top of the turbo when it's in operation(although the turbo even at about 30% speed doesn't look like it's moving since you only see the stationary rotor under the top rotating one) and all works well, but that glass is nice heavy piece to remove even to change a filament. There's also I think either a sheetmetal or plastic cover(never had one, but I've seen them on Ebay) that you're supposed to lay on top of the glass when baking out the manifold supposedly to provide protection if the glass did break, but I never worried about it given that the manifold bake-out temperature was 10ºC higher than the normal operating temperature(50º vs. 40º) and the source temp was actually lower than where I kept it in normal operation.

In any case, I switched that one over to H2 when I was using the beastly 50m x .15mm column(never use a column like that if you can avoid it-.15mm is good, but 15-25m is plenty for most purposes) to avoid going over what the EPCs could handle. I never worried about H2 explosions with that one, especially since I figured in the worst case if I thought if I had a bunch of H2 in the manifold it was a mouse click away to flood it with Ar in a few seconds(whether under vac or vented). That would have been...scary...to have that glass cover blow, though.

[LALman]

I forgot the 5975 had a front viewing window. Conjecture: they don't think the window will fragment (safety glass maybe?) but just crack and stay in place, but escaping gas would make the plastic cover fly.

[benhutcherson]

Getting the 5973 up and going now has made miss some of the nice features of the 5975. Not having to take the whole top cover off is nice, although it's kind of not a big deal on a 73.

I always had thought the window on the 5975 was kind of gimmicky(albeit nice to see if the filament is on and also show people that it is actually a glowing filament) but it does have one very functional use for me. It makes it REALLY easy to see the transfer line tip so that you can get the column placed 1-2mm out.

Of course, the 73 is still easier than a 71/72 with the SIS hollow tip, which I seem to remember you're using(I had one on my 71/72). I'm not sure if I ever managed to actually pull the transfer line out, position the column by eye, and then manage to get it settled back correctly without breaking the end of the column. I finally started swaging the ferrule on with the transfer line out, undoing the nut and retracting the column, and then reinstalling it once I had the transfer line in place.

[LALman]

You are right its a pain to put in. I gave up worrying about it. RE the preswaging the column nut... Don't you still run a chance of chipping the column end? My straight through fitting has got a tiny lip on it.

[benhutcherson]

You're right about the lip/potential to damage the column tip.

I've yet to observe one chipped when I removed it after installing this way, although of course I don't have any way to see it until I pull it out again, and I get into the issue again of almost inadvertently breaking it if it's out of the transfer line when I try to install it. It would be interesting to me to intentionally chip the end and see if you were better off with a chipped end vs. the original style side exit...

On the Varian Saturn, there's no practical way to view the column end with the transfer line installed, so I like that they made it such that you could fit with the transfer line removed and then safely put the transfer line back in place. There transfer line tip on those is a big piece of rounded vespal that helps guide it into place before the column goes anywhere, and unlike the 5971/2 there's no real "flex" in the line or other jiggling positioning to get it lined up. When I first installed the 300-TQ, the instructions say to pull the ion volume out a bit, put the column in until it bottoms out, and then pull back a bit(just like a 5971 with the standard tip). Unfortunately, I didn't have a good grasp of just how much to pull out the volume and also didn't have the designated tool at the time, and ended up putting the column all the way through the source. I was ready to complain loudly about the fact that the thing wouldn't tune until I rechecked and realized this(the whole idea of retracting the volume is to hit the solid side of it rather than the hole).

I got the pre-swaging idea from a tool Varian use to sell-a ruler that had what was basically the threaded GC end of the transfer line grafted onto the end of it. I didn't have one, but it was a tool that worked for virtually any Varian column application and would let you measure the length then swage the ferrule on. Unfortunately, it wouldn't work with Agilents since the Varian column nut(at both ends) is larger than Agilent.

[James_Ball]

Getting the 5973 up and going now has made miss some of the nice features of the 5975. Not having to take the whole top cover off is nice, although it's kind of not a big deal on a 73.

I always had thought the window on the 5975 was kind of gimmicky(albeit nice to see if the filament is on and also show people that it is actually a glowing filament) but it does have one very functional use for me. It makes it REALLY easy to see the transfer line tip so that you can get the column placed 1-2mm out.

Of course, the 73 is still easier than a 71/72 with the SIS hollow tip, which I seem to remember you're using(I had one on my 71/72). I'm not sure if I ever managed to actually pull the transfer line out, position the column by eye, and then manage to get it settled back correctly without breaking the end of the column. I finally started swaging the ferrule on with the transfer line out, undoing the nut and retracting the column, and then reinstalling it once I had the transfer line in place.

Another reason for the glass window is so you can visually see which source you are using, either EI or CI, without having to vent and check. That is why the label on the source is facing the window.

Those open tip transfer lines on the 71/72 I used to put the column through then cut it at the end of the tip which would leave about 1mm extension then install the transfer line.

[LALman]

Getting the 5973 up and going now has made miss some of the nice features of the 5975. Not having to take the whole top cover off is nice, although it's kind of not a big deal on a 73.

I always had thought the window on the 5975 was kind of gimmicky(albeit nice to see if the filament is on and also show people that it is actually a glowing filament) but it does have one very functional use for me. It makes it REALLY easy to see the transfer line tip so that you can get the column placed 1-2mm out.

Of course, the 73 is still easier than a 71/72 with the SIS hollow tip, which I seem to remember you're using(I had one on my 71/72). I'm not sure if I ever managed to actually pull the transfer line out, position the column by eye, and then manage to get it settled back correctly without breaking the end of the column. I finally started swaging the ferrule on with the transfer line out, undoing the nut and retracting the column, and then reinstalling it once I had the transfer line in place.

Another reason for the glass window is so you can visually see which source you are using, either EI or CI, without having to vent and check. That is why the label on the source is facing the window.

Those open tip transfer lines on the 71/72 I used to put the column through then cut it at the end of the tip which would leave about 1mm extension then install the transfer line.

James how do you account for the shortening of the transfer fitting as the bellows compresses under vacuum. Do you pre-compress it when installing the column?

[James_Ball]

The tube that the column slides through it attached to the end of the bellows that has the column nut on it, so the tube(with tip) and column both move together as the bellows contract. The gold fitting that screws into the side of the analyzer will limit the in travel of the tip so it will always position the tip correctly inside the source.

Under vacuum the bellows allow the tip to make firm contact with the gold fitting which is how the source is heated on the 71/72, indirectly by the transfer line.