Drifting organochlorine pesticide calibration when the instrument is not in use for a day


I'm running Openlab CDS Chemstation version C.01.10[201], and I'm having a problem maintaining my calibration. He's the deal:

On 1/11 I ran my cal curve overnight. The following day I entered the curve. The fit was great, and my check standard (0.20 ppm, 22 compounds) came right in on both the front and the rear. On1/13 I ran the check standard again. Once more both the front and rear results came in very nicely. Two days later, during which the instrument was not in use, I ran the same standard. As I had been off for a day, I ran a 10.0 ppm as a primer. I had been told this was a good idea as it prevents adsorption on the column. So, I ran the primer, a hexane to rinse. The results from the rinse showed no carry over from the primer.  Then I ran the check standard. It came in too high. So did the curve standard I ran four days prior. The problem is that, while the front column results were too high, the rear column results came in nicely. When results from 1/11 and 1/15 ae overlaid, the front column peaks are higher, but the baseline on the front is no higher or lower than it was several days ago. The resting signal doesn't seem to have risen during the last few days and the peaks maintain a nice and sharp shape. Does anybody have any idea why the front column results would be shifting like this? While I'm not sure the instrument model matters, I am running on a 7890B with the Restek CLPesticides 2 column on the front and the CLPesticides on the rear.


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