Chromatography Forum

Hello everybody

How bad is ACN realy as solvent vor GC-MS?

Expecially when using PTV Solvent-Vent-Mode.

What do i have to expect?

many thanks in advance

As long as you do not have expansion volume that overfills the inlet liner and in PTV is sufficiently below the boiling point of analytes, it should work. If that is what it takes to get your sample on the column - it is what you need.

AcN can pick up water - but you don't have to let it do that. And I suppose that if you use a poor quality of AcN, you can have some of the nitrile hydrolize -- but use high quality solvent and you should be good. If you pick up salts in the AcN, you will deposit them in the GC liner and, perhaps, on the head of the column. This is bad. But, you need to avoid this with other solvents as well.

We have done injections of Acetonitrile before on GC/MS to do confirmation on HPLC analysis and it has worked well, but we were using split/splitless injection ports. For the PTV in solvent vent mode, as Don mentioned, should only be a problem if your lightest analyte has a boiling point near that of Acetonitrile, which is rather high compared to most solvents used for the same type of analysis.

Thanks for your insight

The reason why i ask is that i was told by our Instrument supplier that ACN is bad for the MS.

However i have seen some GC-MS Methods where ACN is used.

I would be curious about why the vendor would say that. LC/MS has a good bit of acetonitrile going into the system - and those systems do just fine. The LC/MS system does get oil changed more often - but that is because of the quantity of solvent going into the system. And the GC/MS ion source should be able to handle acetonitrile just as well as it handles any other solvent...

If it is a matter that Acetonitrile elutes later than some other solvents - you drop the ionization voltage to the filaments as the solvent peak goes past -- just like you often do for propylene glycol and glycerin peaks when analyzing flavorings.