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- Posts: 12
- Joined: Thu Dec 14, 2017 1:35 pm
I am developing a method for determine a group of pharmaceuticals using C18 column. But I just can't make it pass the 10-time repeat. The intensity of some of the compounds decreased dramatically (2 times to 100 times) or just split completely in a random way, without knowing which compounds might behave in this way in the following injection (both native compounds and internal standards), just what I said in my very first post.
It is not a problem of resolution setting, since I set it as "Unit". And I tuned it again by using the same organic solvent as my mobile phase (B) under the same flow rate. It turns out to be better for some compounds. But the problem still existed. One day, I just switched to a new liquid nitrogen as the original one was run out of. Then the vacuum gauge value went to 3.8 (normally it was 3.1). And I did a 5-time repeat whose repeatability was fine for all the compounds. Then The instrument was used by other staff with different methods and target analyses overnight. The next day, I thought yesterday's repeatability seemed good. I could adjust the gradient a little bit to separate the analytes more. But during the adjustment trials, the peak of some analytes either split completely or decreased dramatically in a random way (At this time, the vacuum gauge decreased to 3.4). And then I thought is it a problem with the gradient. So I did a 10-time repeat using yesterday's gradient, and the problem still existed, even though much better than what it appeared at the very beginning I posted my first post here. So I started to think would vacuum possibly be the cause? If so, how? And how could I adjust the value of the vacuum gauge?
Another cause I suspect is when I do the compound tuning (syringe), the TIC is not very stable, went up and down. (Some of them are relatively stable, some of them are not). Actually this is what I really suspect. Maybe I should do compound tuning again with those trouble compounds.
What's your opinions? I appreciate your wisdom a lot. Thanks for your attention.
Best regards,
Kenny