Chromatography Forum

I do method 525 and use triphenylphosphate ( TPP ) as one of my surrogates. Most of my TPP recoveries are in the range of 130% and a few go over 150%. Section 10.3.4 states that monitor areas of Is and surrogates, and only be concernet when they fall by more than 50% of the calibration average. I can hear my auditors now!
I do SPE using an old Autotrace extractor and Resprep cartriges.
Anyone else have this issue?

Thanks