Chromatography Forum

I am using the Phenomenex EZ:Faast kit for GC-FID and I am getting variability in my peak areas for my standards. They are pre-made stds that come with the kit and are prepped the same way everytime. Can anyone help me out with this? Or has anyone else experienced this?

Hi jburton

First of all what % variation in peak area are you experiencing? Of course you are using Norvaline as the internal standard (contained in reagent #1 of EZ:faast kit) and so you can caluclate the response factors for each amino acid, these should not vary regardless of some variation in peak area.

The rate you draw the standard thru the SPE tip will affect the retention of the amino acids on the sorbent and thus apparent "recovery", in addition, the mixing/emulsion steps are important to ensure adequate mixing and derivitisation as well as waiting at least the required time for complete reaction (stated as > 1 minute, then mix again then wait > 1 minute. )

We run EZ:faast for wine and plant samples, and have great reproducibility of peak areas and of course response factors, but i have seen some new people to GC and SPE come up with some crazy standard chromatograms where there are very small peaks indeed, this was due to namely the speed at which they draw the sample thru the SPE tip in steps #3 and 5 of the EZ:faast instructions as well as poor non reproducible mixing/emulsion. Also ensure all the SPE sorbent is expressed into the vial at step#10 as this will also affect amino acid "recovery"

Hope that helps some

Greg