Organic modifier compatible with MS

[Jo]

Dear all,
I would like to know which, apart from the commonly used acetonitrile and methanol, are other organic modifier suitable for UV detection and compatible with MS? My aim is to have a selective LC method suitable for UV detection (organic modifier such as tetrahydrofuran or dioxan may be needed), which is also compatibe with MS.
Any help will be greatly appreciated

[MG]

I've used THF up to 30% with LC/MS, and it works. However, I once attempted to spray a sample dissolved in 100% THF and got no electrospray current. So if you're using high concentrations of THF, you'll have to experiment. Isopropanol can be used, but higher concentrations will cause pressure issues due to the viscosity. Acetone can be used with LC/MS and works fine, but not with UV. Many other solvents can be used under certain conditions, even normal-phase solvents although post-column addition of a polar solvent may be required; search the literature for more details. Exercise all reasonable precautions when spraying flammable solvents into a heated zone!

[Jo]

Thanks MG for ur comments.
Meanwhile I would like to have more information regarding spraying flammable solvent into a heated zone. Thanking u before hand

[MG]

Well, unless you're doing nanospray work, your LC/MS is going to involve spraying solvents into a area bathed in a heated gas, probably 300°C or hotter. Usually, the heated gas is nitrogen, but some manufacturers have recommended the use of air rather than nitrogen.

I don't know about you, but I don't like the idea of spraying high concentrations of acetone, hexane, or other flammable solvents into a heated air atmosphere, where a spark could occur (corona discharge can happen even in ESI). By "taking precautions", I meant to be aware of what vapors you are mixing in the heated zone, and keep safety in mind when planning your experiments.

[JA]

MG can you elaborate on what kind of safety precautions you take in your lab when planning and executing experimental work using flammable solvents with an LC-electrospray/APCI-MS?

I got the impression most organic solvents used are flammable and have a flash point below the typical source and desolvation temperatures used in these instruments, so what is it we can actually do to minimise fire risk?

TIA

[MG]

I don't use compressed air in my ion sources. I use nitrogen.

Since certain MS manufacturer(s) recommend the use of air, I can only guess that many people have used air (at least with RP-LC) without launching their ion sources across the lab. If your MS manufacturer recommends the use of air, you have to decide whether you think this is safe given the types of solvents you'll be spraying.

Here's a document that mentions the explosion hazard when working in normal phase LC/MS.

http://www.appliedbiosystems.com.au/114AP12.pdf

[JA]

thanks MG, that was my bad thinking that all API instruments would utilise Nitrogen as the nebulising & cone gas; couldn't imagine otherwise
'Least it was a good chance to highlight the general necessity for a non-oxidising source atmosphere..