Chromatography Forum

I am new and running EPA 300.0 on an ICS-6000 and I'm trying to make sure the processing methods are following the DEP guidelines. After calibration, the current retention times are set in the component table tab. But as far as the retention time windows, how is that set? The method states "3 times the standard deviation of the retention time" so am I adjusting this percentage each time as well to that result? Or is that formula for something else?
Forgive my inexperience but I can't seem to find an answer in the software or elsewhere.

Please include a mention of the data system you're using. ICS 6000 speaks to several CDS platforms...

My suspicion is that you make 3 or 4 injections, calculate a mean value and standard deviation for each peak of interest and set your retention window to be approximately RT±3sd, and then you can forget it.

Depending on your CDS, there may be a convenient box to check to accomplish this in your processing method.

The method is only suggesting how to set retention times, not mandating it.
"The width of the retention time window used to make identifications should
be based upon measurements of actual retention time variations of standards
over the course of a day. Three times the standard deviation of a retention
time can be used to calculate a suggested window size for each analyte.
However, the experience of the analyst should weigh heavily in the
interpretation of chromatograms."

When they use the word should that means it is just a suggestion and it's not mandatory. If the method says 'shall' then it is mandatory.

I generally set a wider window for sulfate and nitrate because the retention times shift the most for those when the concentration is high on the AS-18 column that I am using. You still have to be careful about high nitrates getting identified as sulfate because of the retention time shift. High sulfates get misidentified as bromide or even carbonate. My rule is that any time there is a large peak after chloride I make a dilution to confirm peak identities.You don't want to miss a high nitrate. I have seen them over 50 mg/L. Chlorate peaks can sometimes be misidentified as nitrate even if they are not that large. You just have to closely examine all chromatograms to make sure the peaks are what the instrument says they are. You can also spike samples with low level anions to confirm what anion retention times are in the sample being tested.

Thank you for your insight! This has been very helpful.