****************************************************************************** From: Paul Servizio Date: 14 Oct 1998 11:52:36 -0400 Subject: methane quality Organization: * While we're on the subject of gases, I want to determine the quality needed for methane reagent gas for CI on the HP 5973. I was recently told to use 5 nines, but my supplier can only get 4 nines grade (4.5) Should that be adequate. Do I need a scrubber. This is for a new installation. What grade are people using? I have 5 nines helium for GCS. This is for a new set up. paul.servizio@state.ma.us ****************************************************************************** From: "Stuart Coleman" Date: Fri, 16 Oct 1998 19:14:16 +1000 Subject: Re: methane quality Organization: Prodigy Services Corp Paul, I would suggest 4.5 should be adequate for positive CI, but for negative CI, either add a good scrubber or use the higher grade methane. Stuart Coleman ****************************************************************************** From: A.P.Bruins@farm.rug.nl Date: Mon, 19 Oct 1998 9:51:38 MET Subject: Re: methane quality Organization: Pharmacy Dept Groningen University Hello Paul, The level of impurities is not so important. The kind of impurities is very important. For example, methane that contains 10% nitrogen will work fine, but methane that is contaminated with moisture cannot be used for methane CI. In my experience Matheson grade 4.5 in lecture bottle has been entirely satisfactory. You should always check the low mass region down to m/z 10 for unexpected background ions. In a correct methane CI spectrum you should get m/z 17 (100%) m/z 29 (abundance depending on source pressure) and m/z 41. Other alkenyl and alkyl ions can be found at 55, 57, 69, 71. The level of these ions may depend on the quality of methane, by is even more dependent on the cleanlyness of your gas regulator and gas lines. Avoid contamination by hydrocarbons. It is a good idea to evacuate gaslines periodically by use of a rotary pump, but do not do this for a longer time period than necessary for just removing the methane you use for flushing the lines. Backstreaming of rotary pump oil vapour will increase the background level. Make sure your regulator and gas lines are dry, and flush + evacuate them with methane. Use a diffusion-free regulator. In my experience the old Matheson lecture bottle regulators, equipped with a rubber membrane lead to water vapour in methane, which gives you an abundant ion at m/z 19 H3O+. You do not want this, since you want proton transfer from CH5+, not from H3O+ to your sample. Other oxygen and nitrogen containing organic contaminants should be kept out of the system, since such compounds are readily ionized under methane CI conditions. Another common-sense advice: you need only a trace of ammonia gas in mathane to convert CH5+ into NH4+. So if you have to do both methane and ammonia CI, first use methane, and then ammonia, and finally pump and flush out your gas lines several times before using methane again. Good luck, Andries Bruins Dr. A.P. Bruins University Centre for Pharmacy A. Deusinglaan 1 9713 AV Groningen, The Netherlands phone +31-50-363-3262 fax +31-50-363-3311 a.p.bruins@farm.rug.nl ****************************************************************************** From: Patrick_Calway@hc-sc.gc.ca Date: Thu, 22 Oct 1998 18:44:49 GMT Subject: Re: methane quality Organization: Deja News - The Leader in Internet Discussion I strongly recommend the use of scrubbers on both your CI and carrier gases. The problem is usually not the quality of the gases but the quality of the tanks the gases are in. We have had too many instances where the tank was the problem. In one case, we had a lecture bottle of Matheson research grade methane put our system down so badly that I refused to allow the regulator to be reused. Since other bottles of gas were fine, I am assuming the problem was the individual bottle. Several years ago, we had switched to a new gas supplier (gov't buys from low bidders) just as we were commissioning 4 brand new GC systems. We sent the first two high purity(?!) helium tanks back because there was visible grease in the throat of the tank valves. The next four tanks took out all 4 GC's before the commissioning process was completed. We were able to tentatively identify a type of grease as the contaminant. How it migrated through 25-50ft of gas line in that short a time, I don't know, but it did. It contaminated the systems so severely that all four had to be returned to the manufacturer for a complete replacement of the pneumatics. Lots of dollars and months of production lost. For our current system, we buy ECD grade helium for carrier gas, analysed by the tank if we can get it. We use a heated Supelco scrubber in the line.These scrubbers do a fairly decent job and don't have to work too hard with this gas. If there is a tank problem the scrubber will likely protect the system. (I once goofed and put a regulator with a neoprene diaphragm on a GC/Hall detector system. The system went down within a couple of hours, but recovered on its own overnight once the regulator had been changed. I don't believe recovery would have been that easy without the trap in place. The scrubber paid for itself with this one incident.) Since the methane incident, we have added a UOP mat/sen scrubber to the CI line (available through HP). We have actually been able to stop using the research grade methane at $hundreds per bottle and go to a MUCH cheaper grade of methane and still get good performance. Again, the scrubber pays for itself.