Greeting forum denizens. I’m running organochlorine pesticides on an Agilent 7890B with micro-ECD detectors, and I’m having a problem with the results on my rear column. The rear column is a Restek CLPesticides column and the maximum program temperature on this is 340 C. My oven ramp varies from a low of 210 C to a high of 320 C. My detector temperature is 320 C and the temperature on the injection port is 160 C.
When the instrument has not been used for a day or so I start off with injecting a 2.00 ppm pesticide mix to prevent adsorption on the column, followed by two hexane rinses. For some time I have been having a problem with my resulting peak areas. They vary quite a bit. To use one compound as an example (a-BHC, the first eluting pesticide), my first injection has an area of 11679.2. My second injection has an area of 31087.8, and the third injection has an area of 22964.8. In all cases the peaks look nice and sharp with no tailing. They are noticeably smaller in height.
The next day I switched the front and rear injectors to check for possible problems with them. I figured if the injector was the problem then my issue should follow it and I should then see this problem on the front column and not the rear. But the problem seems to he stopped. Does anybody know why this would happen? Was it just that I didn’t sufficiently prime the column the previous day? Why would I only have this problem with the rear and not the front. This is very confusing to me.
Additional info: The front column is a Restek CLPesticides 2 column run under identical conditions. Again, it is not having this problem. All three injections are consistent.