[crosemeyer]

I'm working at an analytical lab in CA running a couple of GCs, looking at Diesel, Gasoline, and Fuel Oxygenates.
 
I'm having some issues with Diesel.  We run a surrogate with all samples (Octacosane C28), and our recovery leaves something to be desired.  California regs let us use the last six months' recovery to establish control limits, but Arizona does not (we do some AZ work), and some clients want us to get our limits within the range of 70-130%.
 
I was hoping someone here might have some advice, or know where I can get some.  I'm thinking we can likely resolve the issue by raising the peak detection parameters, but I'm not 100% sure where to start.

[Mitch]

Are you extracting C28 from diesel? The reason I ask is because I'm not sure what you mean by recovery?

[marquis]

A couple of questions. 

Are your peaks symetrical and sharp?

Most integration software marks where integration starts on the peak.  Does the integration start at the base of the peaks?

You hope that integration issues will resolve recovery.  That is usually not the case.

Good luck.

[crosemeyer]

Hi.

No, we're looking at diesel with an FID, so peaks are anything but sharp and well defined.  I'm worried that the surrogate is getting lost in noise and/or an elevated baseline.

Could the fact that we are also defining a group (C₂₇-C₃₀) in this range affect integration of the surrogate?

[marquis]

Yes, it could. 

But it sounds like better chromatography is the best answer.  If you are testing to a standard method, changing the chromatography may not be possible.