James_Ball wrote:liyanghenry wrote:LWC wrote:
Was anyone able to come to a conclusion about the loss of PAHs?
I am having the same problem with my SUR Benzo[a]pyrene-d12 in EPA 525.3. For all of my extracted samples Benzo[a]pyrene-d12 come out to 50-65% recovery.
I have tried traditional and matrix matched calibration standards and they are almost identical.
I have tried extracting these in the dark- no improvement
I used a better quality Methanol- no improvement
The matrix match cal std use the same solvents so I don't expect those to be the culprit
All samples/std are stored in the same freezer.
I am following the EPA method as instructed for DVB disks and I cannot understand why my Benzo[a]pyrene-d12 SUR recovery is consistently low?
Any help would be appreciated, thank you!!
Thank God I find this post, I am also doing 525.3.
I am having the similar issue with low Benzo[a]pyrene-d12 SURR and it is driving me crazy!
My problem is that the QCs (MB, RL and LFB) injected after ICAL and QCS are having low Benzo[a]pyrene-d12 SURR recovries (60%-70%) but most of my samples are above 80%. If I re-injected the same QCs after 20 injections of sample extracts, recovery would jump back to 80% but analytes like Tebuthiuron and Prometon would break down.
Any ideas how to solve this? Appreciate!
We are running this analysis also and had similar problems with the Benzo[a]pyrene-d12. We had to extend the drying step to remove more water from the extraction cartridges ( using the Waters XLB) and that helped a lot with the recovery. I was having half of my batch fail low, and when the Blank or LFB would fail, that would take out the whole batch QC wise.
When we had trouble this summer with the HVAC, and I did some extraction batches with the building humidity near 80%, almost every one would fail, once that was under control and I could pull dry air through the cartridges for 20-30 minutes my recoveries improved and I had several batches pass without a single failure. Experiment with dry times. The method says to dry 10 minutes at 20 inches vacuum, but it can be difficult to reach 20 inches when you are pulling air through so many cartridges. If recovery increases as dry times increase that could be the problem. Just keep an eye on the first surrogate the elutes, as once you get to a certain point it can begin to decrease recovery with longer dry times. At one hour we had unacceptable recovery of that early surrogate but good recovery of the Benzo[a]pyrene-d12.
We had a conference call with EPA about method 530 problems and I asked about dry times for 525.3 and they said it could be extended within reason. We also had to use matrix matched standards to achieve good recoveries near the MRL since for some analytes there is a lot of background from the preservatives, it can affect the surrogates slightly also.
Thank you for your reply.
I think my problem was mainly due to the instrument. The Benzo[a]pyrene-d12 SURR that failed low around 50-70% for my QCs will always increase by 10-20% if I reinjected them after the whole run(20 injections between). That means any extracted samples that injected after my non-extracted ICAL and QCS would fail the Benzo[a]pyrene-d12 SURR. I also noticed the target ion 264 would break down to 263 when SURR recovery is low.
I suspected the matrix affects the system resulting in the degradation of ion 264, as more extracted samples (at least 10 injections) runing through the GC/MS, the system is kinda conditioned well enough for that SURR. But the sensitivity near the MRL for some early eluting compounds would go bad. What a Dilemma!
As for drying time, we've been doing ten minutes with nitrogen flowing through the system. Room humidity seems to be an issue but that can't explain why SURR recovery would come back for my reinjected QC and never fail for my samples.
I had no problem using non-extraced ICAL and QCS for the past two years, so matrix matched ICAL would be my next move if Benzo[a]pyrene-d12 SURR issue not resolved.
Where would the active site be if the instrument cannot reproduce the abdunce of 264 for the Benzo[a]pyrene-d12 SURR?