Reduced peak sensitivity
Posted: Wed Jan 26, 2011 8:13 pm
I am doing headspace analysis using a CombiPal attached to a GCMS. Three weeks ago, I was seeing reasonable reproducibilty among multiple samples on a DB-624 column, 50:1 split, 1 ml injection volume. Since then, the reagent has dropped from 80,000 abundance to 15,000 abundance. Other compounds in the sample (all with higher bp) have not changed dramatically. Retention times remained the same. I changed the liner and the gold seal in the GC, and remade the standard. I still see the reduction in peak concentration. I injected the standard, old and new, one right after the other to see any changes in concentration or decomposition peaks. Both looked the same. I changed the syringe on the Combipal and did not observe any increase.
Any suggestions would be appreciated.
Another note: Upon checking my logs, I realized I had changed a tank of He prior to the problem. I typically use 1 tank every 2.5 months and in the past two months I had been using 1 tank every 3 weeks without any change in GCMS parameters. I had checked for leaks and switched the regulator, but the problem didn't stop until this last tank change. I don't know if this is random coincidence but thought I would mention it.
Any suggestions would be appreciated.
Another note: Upon checking my logs, I realized I had changed a tank of He prior to the problem. I typically use 1 tank every 2.5 months and in the past two months I had been using 1 tank every 3 weeks without any change in GCMS parameters. I had checked for leaks and switched the regulator, but the problem didn't stop until this last tank change. I don't know if this is random coincidence but thought I would mention it.
