New in GC-MS

[Aleugz1101]

We just acquired a new GC-MS equipment and we would like to do the PAH analysis in our equipment. When running the standard for PAH we are not getting the othe components of the standard. Our equipment is using 100% Dimethyl Polysiloxane column with 30m x 0.25 mm ID x 0.25µmdf. We have another column for FID with 60m x 0.32mm ID x 1µmdf. The reading of the PAH standard is erratic which difficult to read. Please guide us regarding this matter. We are adviced to purchase another column for the analysis of PAH. Than you very much

[Don_Hilton]

Are you following a standard method or are you trying to devlop your own. Also what is your sample matrix? Air? Petroleum?

I would suggest against using a 0.32 ID column on your mass spec. (It can be done but there are flow issues.)

And how much experience do you have with gas chromatography and with GC/MS?

[Aleugz1101]

Thank you Don...

We are following EPA SW 846 8270D and using the standard PAH - 471 in acetonitrile matrix of Ultra Scientific. We have run 100ppb and 1ppm in ultrapure water. We are only new in using the GC/MS and we really appreciate your advises regarding our concern.

[Don_Hilton]

The method calls for a 30 m DB-5 (or equivalent) column. They specify 0.32 or 0.25 mm id. and a 1 micron film.

Are you passing DFTPP tune checks? At what voltage does the mass spec autotune? At what voltage are you running the detector for the method?

As you say the reading of the PAH standard is erratic - is this in retention time? Area? Ratio to internal standard? (And how do the internal standards look in the chromatogram?)

[AICMM]

Aleugz1101,

The column you are using is fine for this analysis. The only issue you might eventually find is that you don't get good peak shape at high concentrations due to column overload. But that is a tomorrow problem from the sound of things.

Don is right, you want to avoid the 0.32 id column if you can.

All of which means something else is going on but you need to provide more information about what is wrong and how you are set up. Oven temperature profile, inlet temperature, liner type, etc., etc., will prove very helpful. Likewise, if you can post a chromatogram that is also very helpful.

best regards.