Hi at all,
For the analysis of polycyclic aromatic hydrocarbons in urban air we used a method that involves a liquid chromatographic separation with a hypersil PAH column and gradient elution (water-acetonitrile).
The HPLC used is HP 1090 with fluorimetric detection and the method is optimised for separating 16 PAH (EPA 610 mixture).
Unfortunately, the HPLC is used for other analysis too (the last case is aldehyds as DNPH derivatives) and, when returning to PAH analysis response of standard solution result changed for benzo(a)pyrene peak.
In particular the benzo(a)pyrene peak show a substantial decrease with respect to benzo(b)fluoranthene and benzo(k)fluoranthene that immediately preceed benzo(a)pyrene peak in chromatogram and are detected in the same conditions (Ex 255 nm; Em 420 nm).
Usually, response of benzo(a)pyrene peak is restored to original value by two or more injections of the same standard solution.
Have anyone experience with this behavior?
Note that HPLC plumbing is extensively washed with acetonitrile-water before analysis.
Thanks in advance