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- Posts: 12
- Joined: Thu Dec 14, 2017 1:35 pm
I am developing a method for the determination of some psychiatric drugs through UPLC-MS/MS. There is a good sensitivity and separation for my analyses. When I proceed to do a 10-time repeatability by injection the same standard in succession, the trouble appears: the peak area of some of analyses may drop dramatically (10-time or 100-time lower than other injection) randomly in one or two injection out of the 10. And the peak-area dropping analyses are not the same in the 10 injections. And my internal standards do not go up or down with my native compound standards which results in a poor repeatability of Native/Internal standard value as well as poor R square of the calibration curve.
I have confirmed it is not a problem of the mass spec or the liquid nitrogen because other colleagues have just tried their method and the repeatability is quite good (less than 5%).
Has anyone who has encountered this problem? Or any suggestions?
Thanks so much for your attention.
Kenny