Problem with internal standards using the purge and trap

[marie0213]

Hello,

I have so much problems with the purge and trap these past months and I can't get help from anyone so I'm taking a chance here. I'm analyzing volatiles in water on a purge and trap (trap #9) connected to a GCMS. I'm using the P&T to add my IS and surrogates and to do my calibration curve. Everything was working fine for 3 years. Now, I can't do a curve from 1 to 20 ppb. I tried changing the trap, manually doing the curve myself, adding the IS myself, injecting using the water method and the soil method because they have a different flow path... Nothing works, I get a parabola as a calibration curve for the less volatile compounds. The other day, I was rushed and only injected a calibration curve without adding IS nor surrogates. Everything was perfect. I did multiple tries and it seems that the IS/surrogates affect my analytes responses... I injected a curve without IS and one with IS one after the other and both were fine.. I'm thinking maybe I have an active site but can't determine where and why it only affects my IS/surrogates.?? Any clues?? Thank you very much for your time. Marie

[mckrause]

Have you tried switching IS/surrogate standards?

[Steve Reimer]

This is a common problem. There are several threads about this on this site.