Helium woes

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

25 posts Page 2 of 2
I tend to sporadically use my GC's, mostly during the day. Another option would be to put manual switching valves before each inlet feed and have nitrogen or hydrogen pumping through when not in use and switch to helium about 30 minutes or so before running the instrument.
MSCHemist wrote:
I tend to sporadically use my GC's, mostly during the day. Another option would be to put manual switching valves before each inlet feed and have nitrogen or hydrogen pumping through when not in use and switch to helium about 30 minutes or so before running the instrument.


I have this setup on my 7000QQQ for research purposes so I can switch between gases quickly. It works well, just have to remember to make the switch, but if you run the line just above the back of the instrument so you see the valve from the front and at eye level you can tell what gas is flowing easily when setting up the samples.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
MSCHemist wrote:
I tend to sporadically use my GC's, mostly during the day. Another option would be to put manual switching valves before each inlet feed and have nitrogen or hydrogen pumping through when not in use and switch to helium about 30 minutes or so before running the instrument.


I have this setup on my 7000QQQ for research purposes so I can switch between gases quickly. It works well, just have to remember to make the switch, but if you run the line just above the back of the instrument so you see the valve from the front and at eye level you can tell what gas is flowing easily when setting up the samples.


I've posted about running the same set-up(N2/He) with my 5971 and 5975, which are both on the same carrier gas line so both get the same gas.

The quick and dirty check that I actually tell people to use is to look at the hi-vac gauge on the 5971. If it's in the ~10^-4 torr range, the nitrogen is still high while 10^-5 means that it's purged with helium. Due to the way the plumbing is laid out in the room, if the 71 is good to go, the 5975 is also.
I've switched my 5971 system to H2. I'm using a DB624 20m x 200um x 1.12um (cut down from the 24m). Helium would let me go down to 0.3mL/min. But hydrogen flows so freely that I can only go down to 0.7 psi on the flow controller which corresponds to 0.82 mL/min at 40C. That gives me a reading of 7.9 E-05 Torr on the vacuum meter. Opening the tune vial bumps that up to 1 E-04 Torr.
Jotting this down here for my own reference as much as anything-

Granville-Phillips(who made/makes the ion gauge and controller on every Agilent MSD I've ever used) gives a table of "sensitivities" for different gases at this link

https://www.mksinst.com/mam/celum/celum ... 04-MAN.pdf

on page 36.

The relevant values-Nitrogen is given a value of 1.00, as we know. Helium is .18, which corresponds with the 6x factor that Agilent tells us.

H2 is given as .46. Some quick math tells me that 7.9x10^-5 on H2 is a "real" value of 1.7x10^-4, which would also correspond to a gauge reading of 3.09x10^-5 for He. That sounds reasonable for me for a 20m x .2mm column at ~.85mL/min.

BTW, does your 5890 have an EPC module or does it have the good old trusty regulator knob and gauge on the front? I've used the gauge and knob a whole lot, but the one I work with most now has an EPC and I wouldn't trade it for anything. Among other things, it's nice to get a consistent flow rate in a temperature program.
For Hydrogen I used a 40m x 0.18mm column on the 5973, which allowed enough head pressure to keep it steady even at low flows.

The early 5890s with EPC were not so good as some of the later ones. Our first one we went through several flow controllers as the methylene chloride kept eating up the o-rings in them. They finally upgraded to a more resistant material for the o-ring which helped a lot.
The past is there to guide us into the future, not to dwell in.
benhutcherson wrote:
....
BTW, does your 5890 have an EPC module or does it have the good old trusty regulator knob and gauge on the front? I've used the gauge and knob a whole lot, but the one I work with most now has an EPC and I wouldn't trade it for anything. Among other things, it's nice to get a consistent flow rate in a temperature program.
My 5971 MS is paired with a 5890 series II with EPC. No gage on the front just a needle valve controlling total flow a split vent and a septum purge vent. On the keyboard display you set the flow and then I can read the corresponding pressure that the GC calculates for that flow.

I do have another 5890 series II with EPC (allows pressure pulses and control by flow or by pressure over a temperature interval) with an FID detector. I've wondered how hard it would be to pair it with the 5971. But I figure there may be firmware problems. Also, I would need to swap the inlets (which probably would not be that much trouble). I'm pretty sure an inlet used for DRO by GC-FID for 20 years would be too dirty to switch over to 8260 VOC's.
LALman wrote:
benhutcherson wrote:
....
BTW, does your 5890 have an EPC module or does it have the good old trusty regulator knob and gauge on the front? I've used the gauge and knob a whole lot, but the one I work with most now has an EPC and I wouldn't trade it for anything. Among other things, it's nice to get a consistent flow rate in a temperature program.
My 5971 MS is paired with a 5890 series II with EPC. No gage on the front just a needle valve controlling total flow a split vent and a septum purge vent. On the keyboard display you set the flow and then I can read the corresponding pressure that the GC calculates for that flow.

I do have another 5890 series II with EPC (allows pressure pulses and control by flow or by pressure over a temperature interval) with an FID detector. I've wondered how hard it would be to pair it with the 5971. But I figure there may be firmware problems. Also, I would need to swap the inlets (which probably would not be that much trouble). I'm pretty sure an inlet used for DRO by GC-FID for 20 years would be too dirty to switch over to 8260 VOC's.


You can pull the weldment and sonicate in hexane and scrub out the inside and the split vent with swabs and abrasive like Bar Keepers Friend and bake it out in the oven and it would probably clean up really well. Be sure to replace the copper split vent line and it should be good to go.
The past is there to guide us into the future, not to dwell in.
Yeah Agilent sells a helium conservation module that lets you plumb both N2 and He to the conservation module, and then connect the module to the inlet pressure supply. You can flip between Helium and Nitrogen on demand via the software. Alternatively, tee both gases to the EPC and use shutoff valves. Just make sure you correctly set the gas type in the EPC config because if you specify helium and run nitrogen and measure the split flow you will find it is wildly wrong. The helium conservation module handles this for you I think.

I've seen helium contaminated with lots of things, the best (worst) thing I've ever seen was a tank with trace HCl gas in it. I spent several days working to figure it out and eventually we noticed Cl isotopes observed in the background of blank runs, multiple columns and filaments ruined before we figured it out. It was a police lab and I got to listen when they called their gas supplier hahahaha, it was wonderful.

CO2 could be a contaminant in helium, but keep in mind you will also get mass 44 CO2 off gassing from vespel. Vespel/graphite ferrule on the end of the column will get you a very tiny bit. The vespel lens stack insulator in the source will get you some. If you have an HES source there is some additional vespel around the source so I have seen more 44 on those systems. I just exclude 44 any time I'm doing deconvolution or library matching. This occurs I believe due to a chemical reaction in the Vespel that forms CO2, and so it occurs more at source temp of 300 or 350 C. If you run your source all the time at 300 (say.. PAHs..) you'll eventually find that the lens stack insulator becomes very brittle and crispy. I recommend loading an idle method with a source temp of say 280 or 250 C when the system is not going to be run for a while if you're using a high source temp for acquisition. Just let it stabilize for 30 min or so before running when you heat it back up.
aldehyde wrote:
Yeah Agilent sells a helium conservation module that lets you plumb both N2 and He to the conservation module, and then connect the module to the inlet pressure supply. You can flip between Helium and Nitrogen on demand via the software. Alternatively, tee both gases to the EPC and use shutoff valves. Just make sure you correctly set the gas type in the EPC config because if you specify helium and run nitrogen and measure the split flow you will find it is wildly wrong. The helium conservation module handles this for you I think.


When I do N2 "helium conservation" I don't bother with changing the gas in the instrument configuration.

My "rest" method on both my instruments(5890/5971 and 7820/5975) is set to 50º column, 150º inlet with a(computed) .5mL/min flow rate. I then manually set the head pressure to 1.5psi(front panel on the 5890, front panel software on the 7820), which gives about .5mL/min N2 at 50ºC. Since I set things to splitless to also save gas, I don't worry about that.

When I do it that way, all I have to do is flip it back over, and when I load the running method of the day it will return the flow rate to "correct" for He. I give 30 minutes-1 hour to switch over completely-sometimes I crank the flow rate way up to speed this up.
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