Quality control question

[chemwipe]

Haven't posted here in years, but figured this was the best place for some feedback.

I run PCB screens by ECD and start every morning with a hexane (with surrogate) and a 1 ppm Aroclor 1016/1260 standard before running samples.

Is there ever reason why this should not be done? I've encountered resistance saying this is not necessary.

There is a host of other things, but I'll put this out there for now.

Thanks!
John

[tom jupille]

I can't think of a reason not to do it. Whether it's absolutely "necessary" or not is a judgement call. It's a form of "system suitability" test; you have to weigh the cost of spending the time to test every day versus the risk that the system will malfunction some day.

[LALman]

Back when I ran PCB's by GC-ECD, I did the same. The first injection of the day may be a little off because of active sites or carrier gas contamination accumulating in the inlet or front of column. A quick run clears all that out and then your CC and blank and the rest of the run are all happening in a continuous sequence which works best.

[James_Ball]

Haven't posted here in years, but figured this was the best place for some feedback.

I run PCB screens by ECD and start every morning with a hexane (with surrogate) and a 1 ppm Aroclor 1016/1260 standard before running samples.

Is there ever reason why this should not be done? I've encountered resistance saying this is not necessary.

There is a host of other things, but I'll put this out there for now.

Thanks!
John

If this is the only standard you are running then I would say yes, because you would not know if the instrument has changed in sensitivity or not. Most EPA methods require it before and after every 10 injections to make sure the instrument stays in calibration. A dirty sample, or leaky septum or other problems can cause a shift in either retention time or response that needs to be validated often.

[chemwipe]

Thanks for the replies.

I'm being told that running standards daily is unnecessary and to use a blank with surrogates to evaluate PCBs.

I've been doing GC work for 17 years and I don't agree with that at all!

[James_Ball]

Thanks for the replies.

I'm being told that running standards daily is unnecessary and to use a blank with surrogates to evaluate PCBs.

I've been doing GC work for 17 years and I don't agree with that at all!

Are these just for internal quality control or are the results reported as a compliance sample? If you reference any EPA or ASTM methods then you have to do the QC listed in the methods, if it is an in-house screen method then whatever works. The question for those above is, will there ever be a possibility any result could be challenged in court, and if so, would they want to be on the witness stand to defend the validity of the data? That alone drives me toward more QC than less.