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- Posts: 1
- Joined: Wed Apr 29, 2009 6:33 pm
Hello! I stumbled upon this forum while looking for solutions to a problem my lab has been having with a pegged (offscale max) signal on our Perkin-Elmer Autosystem GC-ECD. Using some info from a thread from 2004 (since locked, or I'd give acknowlegement there), we managed to get it working again. I thought I'd give a little summary just to help out anyone else in my same situation.
Upon running a sample on our standard sample method (ramp from 150C to 300C), the signal would start out at maximum and remain there, flat, until a few minutes into the run. It would then drop immediately down to zero (we were running straight toluene) and remain there for the duration of the run. Blanks were normal (blank method is 300C for the entire duration).
It turned out that the detector was poorly seated, possibly due to a buildup of graphite from ferrules at the detector end of the column, and was touching its surroundings in such a way that it grounded itself, affecting the signal. However, it seems that thermal expansion was breaking the contact at higher temperatures, resulting in normal operation during the hotter parts of the sample method and during the blanks. It's a pretty singular problem, but just in case anyone else sees this happen, cleaning out all the graphite and re-seating the detector may help!
Upon running a sample on our standard sample method (ramp from 150C to 300C), the signal would start out at maximum and remain there, flat, until a few minutes into the run. It would then drop immediately down to zero (we were running straight toluene) and remain there for the duration of the run. Blanks were normal (blank method is 300C for the entire duration).
It turned out that the detector was poorly seated, possibly due to a buildup of graphite from ferrules at the detector end of the column, and was touching its surroundings in such a way that it grounded itself, affecting the signal. However, it seems that thermal expansion was breaking the contact at higher temperatures, resulting in normal operation during the hotter parts of the sample method and during the blanks. It's a pretty singular problem, but just in case anyone else sees this happen, cleaning out all the graphite and re-seating the detector may help!
