I set up a qualitative, polarity swtiching method to detect diuretics and laxatives in human urine. The ion ratios of 2 mass transitions fluctuate in many analytes. I used different source conditions for positive and negative ionization experiments in the method (with no scheduled MRM). The analyzer used is Sciex 4000QTrap. The source temperature, GS1, 2, IS used are different for the 2 experiments in this method. I wonder if changing source parameters will affect the ion ratio stability as well. Since ion ratios are not stable, I used 2 mass transitions to identify the analytes. I ran 25 blank matrices to check the background signal and adjust the integration area count accordingly. Some mass transition of some of the analytes has high background counts indeed. For these, I confirm with MRM-IDA-EPI full mass spectrum in another injection.
The service engineer told me that the temperature cannot be changed swiftly enough to follow the method and the source heater will easily break down.
Therefore, I tried to unify the source conditions but some analytes' response drop to 20% of original method while some were not affected.
I wonder if I need to start the whole validation again if I change the source parameters. If so, what is the minimal experiments I need to perform for this method change?
Any experts please kindly enlighten me. Thank you very much.