Helium woes

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

19 posts Page 1 of 2
I wanted to run a fresh calibration for 525, and started with a tune. Found roughly 400% N2 with almost no O2. Checked every place for a leak and found none Plugged the inlet end of my column and N2 dropped like a rock.
Agilent engineer on site and re did everything I did with the same results.
He changed all the gas traps and copper lines, and even connected to a different tap on our manifold. He also fed the instrument directly from a tank.
The only thing I can come up with is that we have at least one contaminated tank. This am I switched to the other bank of tanks on our manifold.
Anyone else seeing issues like this? Our tanks are filled in Mass.
Our volatiles chemist spent the entirety of last week chasing an air leak in a GCMS. (I'm still not sure if this followed some major purge-and-trap maintenance, or if the purge-and-trap maintenance was part of the same problem.) Finally on Thursday he swapped in a new tank of helium. Air was at normal operating levels by Friday morning.

This was ambient air, however (4:1 N2:O2 with trace argon) and I'm still not 100% convinced it was the tank. We probably wont know until/unless Airgas recovers and tests the remainder of the tank. Anyone ever seen ambient air contamination in a UHP helium cylinder?
I had a bad tank of UHP-5 Helium. I was seeing 90,000 counts of Mass 40. Normally see 800-2000 counts of mass 40 and 44. The provider said if I could prove it was bad they would replace it. I sent a sample of it to ORS. I was surprised when I got the results back...
16 ppm Argon
192 ppm Nitrogen
3 ppm hydrogen
99.957% helium
The provider said they would comp me if Praxair agreed with the analysis. But it got ignored by Praxair. Distributor said hands were tied. I quit using the helium from that distributor.
Update
After the change to "fresh" tanks yesterday we had ! 500K N2, set the instruments to a high split flow over nite. This am I had ~40000 counts.
Ran an autotune and the N2 came out at 6%. In my case it was the tanks, which one of 4 it's up to the distributor to deal with.
With helium supply getting tight I am afraid we will be seeing this more often.

I heard Airgas got a huge contract with NASA to supply them with helium, we have been seeing difficulty getting gas from them lately too.

A few weeks ago Airgas had to search around at four separate locations nearby just to find us the two extra UHP Nitroge we needed.
The past is there to guide us into the future, not to dwell in.
When they switched SDS formats a few years ago the workers at my supplier got confused and I got 2 tanks with large amounts of Argon mixed in and one with large amounts of nitrogen mixed in. Since then I haven't had any issues except the continuing price of about $500 a cylinder. I looked at switching to hydrogen a few years back but for GC/MS I rely heavily on library searches and a lot of my compounds (monoterpenes sesquipterpenes) have very minor differences in the ion abundances that would get mucked up with hydrogen shifting some them to +1 amu peaks.
MSCHemist wrote:
When they switched SDS formats a few years ago the workers at my supplier got confused and I got 2 tanks with large amounts of Argon mixed in and one with large amounts of nitrogen mixed in. Since then I haven't had any issues except the continuing price of about $500 a cylinder. I looked at switching to hydrogen a few years back but for GC/MS I rely heavily on library searches and a lot of my compounds (monoterpenes sesquipterpenes) have very minor differences in the ion abundances that would get mucked up with hydrogen shifting some them to +1 amu peaks.


Have you tried nitrogen carrier? Shimadzu has a power point on it I found somewhere not long ago. I have tried it, you will have longer runs and have to keep the flow low, but they suggest a 0.15mm ID column. I was able to run a 0.18mm ID column at 0.3ml/min and get decent peak shapes. You also lose some sensitivity just as with hydrogen, but no mass shifting from the CI that hydrogen causes. I did see a lot of mass 42, which seems to be coming from N3 forming in the source, I am going to try a few other things to eliminate that.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
With helium supply getting tight I am afraid we will be seeing this more often.

I heard Airgas got a huge contract with NASA to supply them with helium, we have been seeing difficulty getting gas from them lately too.

A few weeks ago Airgas had to search around at four separate locations nearby just to find us the two extra UHP Nitroge we needed.


Weirdly enough, Airgas has been "courting" us for a month and a half or so, and actually a few weeks back were able to come up with 100L of LHe for us when our regular supplier(Praxair) allocated us to 60L. When you have 4 magnets to take care of, 60L just scratches the surface and gets them up to safe levels.

I'm a bit worried about N2 in He, but fortunately I haven't seen it yet from the local supplier we use(Welder's Supply/Specialty Gases out of Louisville).
James_Ball wrote:

Have you tried nitrogen carrier? Shimadzu has a power point on it I found somewhere not long ago. I have tried it, you will have longer runs and have to keep the flow low, but they suggest a 0.15mm ID column. I was able to run a 0.18mm ID column at 0.3ml/min and get decent peak shapes. You also lose some sensitivity just as with hydrogen, but no mass shifting from the CI that hydrogen causes. I did see a lot of mass 42, which seems to be coming from N3 forming in the source, I am going to try a few other things to eliminate that.


I was under the impression nitrogen carrier for GC/MS was not feasible. An agilent seminar quoted it is like having basketballs bouncing arround in your MSD (too big a molecule). I've considered it for my FID though.
MSCHemist wrote:
James_Ball wrote:

Have you tried nitrogen carrier? Shimadzu has a power point on it I found somewhere not long ago. I have tried it, you will have longer runs and have to keep the flow low, but they suggest a 0.15mm ID column. I was able to run a 0.18mm ID column at 0.3ml/min and get decent peak shapes. You also lose some sensitivity just as with hydrogen, but no mass shifting from the CI that hydrogen causes. I did see a lot of mass 42, which seems to be coming from N3 forming in the source, I am going to try a few other things to eliminate that.


I was under the impression nitrogen carrier for GC/MS was not feasible. An agilent seminar quoted it is like having basketballs bouncing arround in your MSD (too big a molecule). I've considered it for my FID though.


Well they use it as the collision gas in the MS/MS so I tried it in our 7000. We have another lab that is going to try it in a 5977 soon to see if it takes a 7000 vacuum system to pump it out fast enough or not.

I found the presentation here

https://apps.nelac-institute.org/nemc/2 ... -Macek.pdf

Interesting read for certain. I had tried it years ago with a 5973 using a diffusion pump but that just can't pump the nitrogen out fast enough. With the 7000 I was running 0.5ml/min and had a pressure near 5x10^-6torr, at 0.3 I was getting close to the -7s torr. I wish I had a spare instrument so I could do more than a single day's worth of experiments.
The past is there to guide us into the future, not to dwell in.
I run Nitrogen as a rest gas two instruments(5971, 5975) and have never been able to get a satisfactory tune on nitrogen. It's worth mentioning that these both are diffusion pump instruments, but I've been afraid to even try running them due to the terrible tune.

At least on HP/Agilent stuff, it's worth noting that the vacuum gauge is calibrated for nitrogen. Helium will cause the gauge to read low-in fact the manuals will tell you to multiply the gauge reading by 6 to get the "true" vacuum. The main value in a vacuum gauge for me at least is that even if it's inherently inaccurate under the conditions where it is being used, it is precise, so a change in gauge reading can indicate abnormal conditions in the instrument.

I mention all of that because at first glance the vacuum readings with N2 look terrible on my instruments. If I see 2x10^-5 on He, I might see 4x10^-4 on N2(actual numbers I've observed) with the same column head pressure. If you apply the 6x correction factor, you see that the vacuum is still somewhat worse on N2, but not as bad as the gauge readings taken at face value might lead you to believe. Also, don't forget that, even though the head pressure is the same, the flow rate will be different(don't forget to tell the instrument you're running N2 vs. He so that it can correctly calculate the flow).

My Varian 1200L should be here in a week or two, so once I get it installed and running, I'll be interested to see how the turbo pump in it does with N2. It's getting plumbed separately from the other two GC-MSs, but I'm plumbing in an N2 rest valve for it also.
benhutcherson wrote:
I run Nitrogen as a rest gas two instruments(5971, 5975) and have never been able to get a satisfactory tune on nitrogen. It's worth mentioning that these both are diffusion pump instruments, but I've been afraid to even try running them due to the terrible tune.

At least on HP/Agilent stuff, it's worth noting that the vacuum gauge is calibrated for nitrogen. Helium will cause the gauge to read low-in fact the manuals will tell you to multiply the gauge reading by 6 to get the "true" vacuum. The main value in a vacuum gauge for me at least is that even if it's inherently inaccurate under the conditions where it is being used, it is precise, so a change in gauge reading can indicate abnormal conditions in the instrument.

I mention all of that because at first glance the vacuum readings with N2 look terrible on my instruments. If I see 2x10^-5 on He, I might see 4x10^-4 on N2(actual numbers I've observed) with the same column head pressure. If you apply the 6x correction factor, you see that the vacuum is still somewhat worse on N2, but not as bad as the gauge readings taken at face value might lead you to believe. Also, don't forget that, even though the head pressure is the same, the flow rate will be different(don't forget to tell the instrument you're running N2 vs. He so that it can correctly calculate the flow).

My Varian 1200L should be here in a week or two, so once I get it installed and running, I'll be interested to see how the turbo pump in it does with N2. It's getting plumbed separately from the other two GC-MSs, but I'm plumbing in an N2 rest valve for it also.


Hydrogen causes the same problems as far as gauge readings go, so none of the numbers directly relate, but the gauge is a good way to know what "normal" should be once you get things going.

I doubt the 5971 would have enough pumping capacity to handle nitrogen carrier, or you will need to go to the smallest ID column possible to keep flow down and linear velocity up, if staying within the limits of the pumps. The 5975 may handle it but I would definitely be running at least an E2M2 rough pump, those little ones just won't do it. The 7000 has an RV5 so roughing is well sized for nitrogen, I am running E2M2s on the 5973/5975s I have also, it just helps keep things pumped out better even on helium.
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
benhutcherson wrote:
I run Nitrogen as a rest gas two instruments(5971, 5975) and have never been able to get a satisfactory tune on nitrogen. It's worth mentioning that these both are diffusion pump instruments, but I've been afraid to even try running them due to the terrible tune.

At least on HP/Agilent stuff, it's worth noting that the vacuum gauge is calibrated for nitrogen. Helium will cause the gauge to read low-in fact the manuals will tell you to multiply the gauge reading by 6 to get the "true" vacuum. The main value in a vacuum gauge for me at least is that even if it's inherently inaccurate under the conditions where it is being used, it is precise, so a change in gauge reading can indicate abnormal conditions in the instrument.

I mention all of that because at first glance the vacuum readings with N2 look terrible on my instruments. If I see 2x10^-5 on He, I might see 4x10^-4 on N2(actual numbers I've observed) with the same column head pressure. If you apply the 6x correction factor, you see that the vacuum is still somewhat worse on N2, but not as bad as the gauge readings taken at face value might lead you to believe. Also, don't forget that, even though the head pressure is the same, the flow rate will be different(don't forget to tell the instrument you're running N2 vs. He so that it can correctly calculate the flow).

My Varian 1200L should be here in a week or two, so once I get it installed and running, I'll be interested to see how the turbo pump in it does with N2. It's getting plumbed separately from the other two GC-MSs, but I'm plumbing in an N2 rest valve for it also.


Hydrogen causes the same problems as far as gauge readings go, so none of the numbers directly relate, but the gauge is a good way to know what "normal" should be once you get things going.

I doubt the 5971 would have enough pumping capacity to handle nitrogen carrier, or you will need to go to the smallest ID column possible to keep flow down and linear velocity up, if staying within the limits of the pumps. The 5975 may handle it but I would definitely be running at least an E2M2 rough pump, those little ones just won't do it. The 7000 has an RV5 so roughing is well sized for nitrogen, I am running E2M2s on the 5973/5975s I have also, it just helps keep things pumped out better even on helium.


I supposed I should play with N2 more on both instruments.

I run a .18mm column on the 5971, and have it backed by a Varian DS102. The latter really does make a difference-I ran it on the 5975 for a few months while I was waiting on a pump rebuild(we do it in house, but I don't do it personally, and it sometimes take a bit of prodding to get one bumped up) with both better foreline pressures and better chamber pressures for a given column flow rate.

Unfortunately, I'm still with the E2M1.5 on the 5975. I'd really like to put a better pump on it-I actually keep my eyes open for those DS102s since I've had amazingly good luck with them(they don't seem to spring leaks every 5-10 years like the Edwards pumps do). I'm guessing Agilent liked them too since they still sell that line of pumps, although I don't think they spec it with any instruments. The specs on it claim 114 l/min(60hz), which puts it somewhere between the Edwards E2M5 and E2M8 in pumping capacity. In all honesty, it's probably overkill. I needed a pump in an emergency, and had it lying around from a retired Varian Saturn, so on it went and I liked the results. The only potential downside is that it pulls enough current that it needs to be plugged in separately from an Agilent/HP MS(not into the outlet on the back), although I actually prefer doing it that way anyway.
We've had so many helium tanks contaminated with nitrogen that we intentionally monitor for it when hooking up a new tank. Interesting note about Airgas sending our helium supply to NASA. I'm in the process of switching from helium to hydrogen or nitrogen where possible.
Regards,

Christian
MSCHemist wrote:
James_Ball wrote:

Have you tried nitrogen carrier? Shimadzu has a power point on it I found somewhere not long ago. I have tried it, you will have longer runs and have to keep the flow low, but they suggest a 0.15mm ID column. I was able to run a 0.18mm ID column at 0.3ml/min and get decent peak shapes. You also lose some sensitivity just as with hydrogen, but no mass shifting from the CI that hydrogen causes. I did see a lot of mass 42, which seems to be coming from N3 forming in the source, I am going to try a few other things to eliminate that.


I was under the impression nitrogen carrier for GC/MS was not feasible. An agilent seminar quoted it is like having basketballs bouncing arround in your MSD (too big a molecule). I've considered it for my FID though.
Hydrogen makes a great carrier for FID. I use nitrogen for the makeup gas.
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