Page 1 of 1
GC/MS with low sensivity
Posted: Tue Aug 25, 2009 12:56 pm
by astroguille
Hi people!
I work at a GC6890/MSD5973 (with a turbo pump and cuadrupole).
The column is a HP 5ms. The flow is 0.8, He.
I have a problem.
The system worked good 2 weeks ago. Then, I shutted off the system and installed a UPS. After that, the system's sensivity fall a lot.
The autotune is OK (EMV 1700, Repeller 31)
I changed septum and liner.
The gold seal was changed 1 month ago.
What can the problem be?
Thanks
Posted: Wed Aug 26, 2009 1:39 am
by Don_Hilton
YOu indicate that autotune is 1700 V. What was it before? (If it has not changed, the mass spec is fine and you need to look for a chroamtography issue - like column installation or inlet issues.)
How is the background air? (Leaks kill sensitivity)
Also, what are you using to measure the sensitivity of the gc/ms system?
Posted: Thu Aug 27, 2009 8:31 am
by thohry
If you did not do anything except shutting down the instrumen (to put in the UPS) and the sensitivity reduced a lot, the thing may be that you did the shutdown not properly. Or if you have reinstalled the column (in the MS side), that could be the culprit.
One more thing: you shoud check the groundness of the lines after the UPS.
Posted: Tue Sep 15, 2009 3:10 pm
by astroguille
YOu indicate that autotune is 1700 V. What was it before? (If it has not changed, the mass spec is fine and you need to look for a chroamtography issue - like column installation or inlet issues.)
How is the background air? (Leaks kill sensitivity)
Also, what are you using to measure the sensitivity of the gc/ms system?
I use the usual standard, and the abundances falled 90%
Posted: Tue Sep 15, 2009 3:11 pm
by astroguille
I used the usual standard, and the abundances falled 90%.
Posted: Tue Sep 15, 2009 11:02 pm
by Don_Hilton
Because the 5973 adjusts the detector voltage to adjust for sensitivity changes in the mass spectrometer, I would say that the problem is chromatographic. Check the connections you made while doing inlet maintenance to be sure that you do not have a leak. (A leak can result in loss of sample by splitting flow between the column and the outside of the instrument.) Also be sure that you are using a good syringe. While it does not happen often they can wear enough that the sample can blow back past the plunger.
Also, be sure of the standard. Some do not keep well and sometimes standards that keep well are accidentally spoiled.