Chromatography Forum

Hi all,

I'm new here so please excuse my ignorance!
Through a friend of a friend I've been offered a Thermo GC-MS EI only system including the PC with mass spec data system and a liquid auto-sampler. It's going to cost me almost $10k so as a total GCMS virgin noob, I could really use some advice so as to avoid an expensive mistake. My background is "advanced hobbyist" and in times past I've been using the old traditional techniques of bench or "wet" chemistry to perform analysis, using the old tried and trusted methods such as melting point/boiling point determination and a shelf full of all manner of analytical test reagents; really old-time stuff which I have to say, has been incredibly useful for learning purposes over the years. However, I feel the time has come to jump into something a bit more 21st century.
Can anyone tell me if these machines have any known issues I should be checking for? How are they regarded within our field? And also whether it's possible to use Argon instead of the specified Helium for the carrier gas, since I can get a free supply of the former; not so the latter.
The model I'm considering is the same one (I think!) as is shown on the upper right photo of the Wikipedia page on CGMS machines:

https://en.wikipedia.org/wiki/Gas_chrom ... ectrometry

Thanks in advance for any informed advice!

For GCMS EI I doubt Argon would work. Nitrogen and Argon soak up much of the energy used for ionization from the filaments and give very low sensitivity. Normally Helium is the best carrier for ionization purposes, but Hydrogen can be used with good results also, as long as you are not trying to pass the strict EPA tune criteria for Bromofluorobenzene. I believe that is a quadrupole unit so the hydrogen is compatible, but if it is an Ion Trap mode then I am not sure it will, I know the Varian Ion Traps can only use Helium. You can use a hydrogen generator which you can probably get at a reasonable price used, if you don't want to bother with hydrogen cylinders( though unless you are using it hard every day, a typical cylinder will last you for months).

I am not familiar with the Thermo GCMSs so can't say much more about reliability or ease of use.

For GCMS EI I doubt Argon would work. Nitrogen and Argon soak up much of the energy used for ionization from the filaments and give very low sensitivity. Normally Helium is the best carrier for ionization purposes, but Hydrogen can be used with good results also, as long as you are not trying to pass the strict EPA tune criteria for Bromofluorobenzene. I believe that is a quadrupole unit so the hydrogen is compatible, but if it is an Ion Trap mode then I am not sure it will, I know the Varian Ion Traps can only use Helium. You can use a hydrogen generator which you can probably get at a reasonable price used, if you don't want to bother with hydrogen cylinders( though unless you are using it hard every day, a typical cylinder will last you for months).

I am not familiar with the Thermo GCMSs so can't say much more about reliability or ease of use.

I tried this. It absolutely does not work. Intensities dropped drastically and ion ratios were wrong. It takes quite a while to get the Argon out of the system enough to restore sensitivity. Its also one reason I get peevish when I get a UHP helium cylinder that has strongly elevated mass 40 counts.

However, argon works fine as carrier for GC-FID.

I've never run argon in GC-MS, but can tell you that nitrogen is useless. I use it as the "rest" gas on my instruments, but it's difficult to get anything remotely close to a good tune with nitrogen as it just gets in the way of the large masses too much. Argon would have similar issues, and I've also heard of issues with it and certain types of electron mulitpliers.

I don't have any hands on experience with Thermo GC-MSs, although I know of two in our department-one a quadrupole and one an ion trap. Many of Thermo's staple chromotagraphy MS products are derived from Finnigan instruments, a brand that they bought in the late 90s(I think). Finnigan was one of the pioneers in coupled chromatography-MS techniques, and especially commercializing them. My LC-MS(c. 2000) is actually branded Thermo-Finnigan. So, in that sense, I consider them basically sound instruments.

I've never run argon in GC-MS, but can tell you that nitrogen is useless. I use it as the "rest" gas on my instruments, but it's difficult to get anything remotely close to a good tune with nitrogen as it just gets in the way of the large masses too much. Argon would have similar issues, and I've also heard of issues with it and certain types of electron mulitpliers.

I don't have any hands on experience with Thermo GC-MSs, although I know of two in our department-one a quadrupole and one an ion trap. Many of Thermo's staple chromotagraphy MS products are derived from Finnigan instruments, a brand that they bought in the late 90s(I think). Finnigan was one of the pioneers in coupled chromatography-MS techniques, and especially commercializing them. My LC-MS(c. 2000) is actually branded Thermo-Finnigan. So, in that sense, I consider them basically sound instruments.

Maybe that is why Agilent uses the ETP type multipliers in their ICP/MS as it will work with Argon while others won't. Everything else they have come stock with the monolithic type multipliers.

If it is a quadrupole instrument and I wasn't doing any regulated EPA work, I would go with hydrogen carrier, unless needing the absolute most sensitivity possible.