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GC/MS response decreased 4 times
Posted: Tue Apr 26, 2005 3:19 pm
by wl_yang
Hello,
I have a problem again. I was running some herbicides using GC/MS half year ago, and now the responses decrease about four times for each compound! What happened? Please help me. Thank you.
Posted: Wed Apr 27, 2005 6:21 am
by jimmyhu
The response of GCMS does change over time, it may depend on: (1) instrument tuning, (2) instrument setup parameters, (3) standards degradation, (4) etc, So an employment of internal standard can minimize the variation of the GCMS response if it is not controlled.
Re
Posted: Wed Apr 27, 2005 1:58 pm
by wl_yang
Thanks a lot, Jimmy.
The solutions I analyzed are standard solution I made. The response for each compound decreased after several months later using the solution from the same source. Then I made a new stock solution and new standard solutions, and they could not give me higher responses. I autotuned and the result is good. I am changing the inlet septum now.
Posted: Wed Apr 27, 2005 2:44 pm
by Consumer Products Guy
You need to first determine whether the low response is a GC issue or an MS issue.
I think it is a GC issue
Posted: Wed Apr 27, 2005 3:25 pm
by wl_yang
because the tuning of MSD looks good.
Posted: Fri May 06, 2005 3:24 am
by Ron
If there has been no instrument maintenance performed in the last 6 months the instrument may need some work. As Consumer Products Guy pointed out the first step is to determine if the problem is in the GC or MS. Do routine maintenance of the inlet and column and see if response goes back up. If not, the ion source and lenses probably need to be cleaned. The tune may still look good, but have the repeller, focusing lens, or detector values changed significantly? If so the MS probably needs cleaning even though it tunes properly.