When using eazy chrome elite on a Agilent 7890A and using an EC wax column, I am constructing a simple method using 5 levels of IPA and DI Water as external stds. I am able to get a linear fit type of 0.999 and greater when constructing the calibration table. When I re-run the level samples as an unknowns (same vials), my % recovery is up to 2% off of what it was when it was run as an external calibration std. you can also tell in the reports that the peak area calculated for the samples, when run as unknowns, are at least 3-400,000 less than when those same samples are run as external stds. The integration is exactly the same as are all other parameters in the method.
Would it be acceptable to run the samples as external stds to show system suit passes and then re-run the middle level external std and unknown samples together to do a one point calibration update of the original table? This would slightly change the fit.
Also, does anyone have any better suggestions as to what kind of column to use when testing product with water and IPA in it. I heard DB-1 are good.