[Claude Pelletier]

Hi!

My name is Claude Pelletier.  I'm an analytical chemist working for the Coastal Zones Research Institute in New Brunswick Canada.  We do PAH analysis now for more than 10 years and recently got very low recovery on benzo(a)pyrene and perylene-d12, but not on other PAH.  We add to the sample before extraction 50mg of sodium sulfite to reduce residual chlorine.  If we analyze and extract that was good after 2 or 3 days, the signal for perylene-d12 (surrogate) decrease, showing that something append in the extract.  In the worst case, 5ppb of perylene-d12 totaly desapear.  Nothing have change in our method and find it hard to locate the problem.  Any help will be appreciate.

Thanks!

Claude Pelletier

[chiralic]

Did you check you equipment? HPLC? or GC-MS? How old is your column?

[Borek]

Have you changed any of the reagents used (changed like in opened a new bottle, mixed new batch)?

[Claude Pelletier]

We changed our GC column about 8 months ago.  The GC-MS seems to work fine.  We got good signal for standards.  The problem start when we did analysis on CAEAL (Canadian Association of Environmental Analytical Laboratories) samples.  We got very low recovery on benzo(a)pyrene but not on the other PAH who elute around benzo(a)pyrene. It seems that a specific reaction took place for benzo(a)pyrene and perylene-d12 but not on other PAH.  I will look to see if one of the reagent was change (new bottle).  At first we suspect our sodium sulfite used to reduce residual chlorine, and we verified before acidification and addition of surrogate that no residual chlorine was present.  We also notice that when the recovery is acceptable, after only a few days, the surrogate seems to disappear.  For now it is hard to say if it is adsorb on the vial surface, or chemically transform.  Visually, the fluorescent yellow color of perylene-d12 seen just after extraction and concentration seems to loose it's fluorescent color and is now just yellow.

[Ψ×Ψ]

I seem to remember something similar happening in a lab where I used to work, and IIRC perylene was one of the standards that was acting strangely.  Are any new and curious peaks appearing?

[Claude Pelletier]

Yes, there is some small peaks that elute at high temperature.  Being not a specialist in mass spectrometry, it is still visible by the mass spectra that those compounds contain bromide.  When at first perylene disappear, the recovery for pentachlorophenol-c13 was good.  Last week, because of high noise (mostly column bleed) I concentrated my extract to 200µl instead of 500µl.  When I did the integration, I noticed that perylene totally disappear but also that pentachlorophenol-c13 recovery was very high.  We use as internal standard for pentachlorophenol 2,4,6-Tribromophenol.   Now,  the 2,4,6-Tribromophenol recovery is very low, putting high the recovery of pentachlorophenol-c13.  It seems that there is a chemical reaction between 2,4,6-tribromophenol and perylene-d12, but only in the extracts and not in the standards.