I'm running PCB's on our good ole 6890N with micro-ECD detectors. It's a great machine, but this a few days ago I noticed something. After not being run during the night (or over the weekend), I noticed that, when I run my opening standard the next day, the standard comes in high. Either near the high end of our acceptance limits or above the allowable range. During the course of the day the standard then drifts lower. For example, our standard is 1.00 ppm with an acceptance limit of 0.85-1.15 ppm. After not being run for the weekend it might start out about 1.13 then, during the course of a few hours of being run, drift down to 1.06.
This is a very new phenomenon. Until this problem started, it came in at right around the expected value throughout the day with no drifting. But I'm afraid it may soon drift to where my opening standard will be out of range until I run hexane rinses for a few hours at the start of a run.
So my question is obvious: Does anybody know why this is suddenly happening and what I can do to remedy/ prevent this? The calibration is very recent and the standards are recently made as well, so I don't believe those are the problem. HAAAAAAALP!!!