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- Posts: 45
- Joined: Thu Nov 05, 2009 6:28 am
I would like to ask you one (probably) easy question. I realize an analysis of Chlorogenic acid by GCMS. I derivatize the acid with MSTFA, dilute it with dichloromethane, and then inject the mixture.
I noticed, that the area of late eluting peaks is not stable. It can change quite strongly (1,5 times) from injection to injection. Early peaks have the same integral from injection to injection - everything is fine here! For peaks in the middle of the chromatogram, the area also tends to change, but not so much (1-2%). And late eluting peaks change quite a lot, as I have already noted.
Thus, there is an obvious dependence of the area change on the thermostat temperature. The injection is in Splitless mode (300'C). The Oven program is 50'C (0.7 min) and then 10'C/min to 310'C (5 min). Chlorogenic acid is eluted at about 310'C. The signal is clear and has good intensity. But reproducible is poor.
I see, that the answer is very easy, but I can't find the problem. Why the strength of the effect is so dependent on the Oven Temperature? Can you help me?
Thank you!