Chromatography Forum

I am currently using a full evaporation technique (FET) and inject the headspace using an ITEX method I have developed.

I have a 1000ppm solution in water. I am taking 50ul of this solution into a 20ml headspace vial and evaporating using an agitator set at 150 degree C.

How do I work out what the concentration of this will be in the gas phase when fully evaporated?

Thanks,
Rebecca

Since it is fully evaporated, isn't it as simple as

1,000 µg/mL x 0.050 mL = 50 µg

in the vial? What are the remaining details of your method? Are you pulling all of those vaporized molecules through your ITEX device and trapping them on a sorbent? I'm not an authority on the ITEX device/technology but it looks like a variation on the theme of thermal desorption.

I'd say your calibration curve is likely going to be some plot of mass of analyte correlated to instrument response. Once you know the mass of your analyte in the unknowns, you'll calculate the concentration in the sample from the amount of sample you vaporized in the first place.

No need to calculate the HS concentration. Derive your calibration in terms of the concentration in the liquid phase, keep your volumes constant and you won't ever need to know the actual gas phase concentration.