By Anonymous on Thursday, June 19, 2003 - 04:37 am:
I have had separation on a standard and sample using a normal phase setup and, after running the standard on two consecutive days following this analysis, I have seen the smaller peak merge with the larger (but still distinguishable) and then totally disappear.
After I had seen the spearation was less distinct (2nd run) I remade the mobile phase and made up the standard again.
Does anyone have an answer?
By Chris Pohl on Thursday, June 19, 2003 - 08:32 am:
What is your mobile phase? Since you're using normal phase it's crucial that you control the water content of your mobile phase. Your problem could be caused by slow contamination due to excessive water in your mobile phase or some other polar component in one of your mobile phases. For example, chloroform typically contains polar stabilizers.
By Anonymous on Thursday, June 19, 2003 - 01:08 pm:
I like Chris's answer, but lately I've seen big selectivity changes with a normal phase chiral method due to the uncontrolled column temp. Maybe a factor for you?
By Tom Mizukami on Thursday, June 19, 2003 - 10:52 pm:
The USP has some definitions for controlled room temperature, etc. Most pharmaceutical labs have an SOP allowing ambient methods to be run temperature controlled in the range of controlled room temperature, or something like that.
By Tom on Friday, June 20, 2003 - 02:42 am: