PAH analysis

[Ruben]

Hi. I am using a Varian Saturn 2000 GC/ion tap MS system to analyse for PAHs. I am able to get all peaks except the last 4 peaks of an EPA 17 component test mix. Theseae are the benzo(b and K)fluoranthene, benzo(a) pyrene, and the indeno upto dibenzo(ghi)perylene compounds.

I am using a a VF5 column (30m x 0.25um ft x 0.25um duiameter. In addition there peaks often seem to be shifting. AM not sure if it is a method setup or extraction setup.

Can anyone advise why I am unable to elute the last 4 peaks(m/z 252,252,276,278).

Thanks

R

[Don_Hilton]

What is the upper temperature of your temperature ramp and what is the temperature of your transfer line to the MS?

[Ruben]

The instrument settings are: trap = 150 deg celc, t/fer line = 180 and manifold 170 deg celc.

I am certain these temperatures can be increased, but it was recommended during a routine maintenance by our supplier to keep the instrument settings as above.

Thanks

[Ruben]

Apologies, typing error, manifold is set at 70 deg celcius...

[Don_Hilton]

If the end of your chromatographic column passes throug the transfer line, high boilers may be trapped in a cold sport at 180 degrees. I am not familiar with your instrument, so I can not make specific reccomendations.

[MX304]

If the end of your chromatographic column passes throug the transfer line, high boilers may be trapped in a cold sport at 180 degrees. I am not familiar with your instrument, so I can not make specific reccomendations.

That would be my thought as well. We normally go to 280 deg. on the transfer line.

[RobPelot]

I am beginning some work on PAHs right now as well. Just curious, what type of ionization source are you using on your MS?

We were having a similar problem not getting the chrysenes, while having no issue with our lower MW PAHs.
It ended up being our extraction procedure. The method we got from the literature did not have us collecting enough from an Alumina and then a Silica Column. We were leaving the higher MW compounds behind

[boris_gto]

what you temperature program and you column. I go to 300 degrC for db-5MS UI

[jarodw]

difficult to say definitively as gc paramters unkown but t/f line T seems way too low for heavy PAH.