Retention time variation and peak identification

[C.Bourque]

Hi all

Please let me know if I have missed any previous posts regarding this issue. I've been searching as best I can, but havn't found anything definitive.

In very general terms: I am wondering if there are any guidelines or processes which outline a general method for determining acceptable ranges of peak retention times in order to confidently identify sample analytes? In other words, if a peak shifts (up or down), how much is enough to say "this peak is absolutely NOT what I am interested in"?

I would like to be able to reference a known (generalized, of course) guideline if I could, such that I have some kind of reasoning to reject seemingly aberrant analyte peaks and not reject others. I guess this stems from the idea of having a known and rigid set of guidelines to a myriad of statistical analyses, and having the almost unanimous rule of requiring p<0.05 to accept or reject statistical hypotheses. Similarly, is there some way of calculating or assessing retention times, such that under a certain set of controlled conditions, tR's outside of a certain range can be regarded as something other than your analyte of interest?

I've searched this forum as much as I could, but have found no real consensus on this matter, other than a few comments which insinuate there are no real guidelines, as it can vary depending on the method being utilized. Does this mean it is truly and completely at the discretion of the analyst?

Thanks so much in advance for any and all input!

[tom jupille]

That's why you evaluate robustness as part of method validation. The consequences of changes in retention vary tremendously from one method to another, so rather than try for "one size fits all", you purposely vary the conditions to see what happens, and you set the system suitability requirements accordingly. In my experience, resolution between critical pairs of peaks is a more sensitive metric than is retention time.

[bisnettrj2]

A lot of EPA methods have a retention time study requirement, where you take retention time measurements from several injections of a standard injected over several days, get the standard deviation to derive your retention time window, and then you update the absolute retention time at the beginning of the analytical run or from the mid-point calibration standard.

11.6.4 The width of the retention time window for each analyte, surrogate, and major
constituent in multi-component analytes is defined as ± 3 times the standard deviation of the
mean absolute retention time established during the 72-hour period or 0.03 minutes,
whichever is greater.

http://www.epa.gov/osw/hazard/testmetho ... 00c_v3.pdf

[C.Bourque]

Great! Thank you both very much for your input, it's much appreciated!

[cody84]

We compare the retention time of the analyte to that of the standard (if they're the same compoung). Must be within +- 0.1 min of the nearest standard injections RT. This is also used as an ID test.

[C.Bourque]

http://www.epa.gov/osw/hazard/testmetho ... 00c_v3.pdf

Where is this document from? I can't find the reference information. Is it an EPA publication?

Also, thank you cody84 for your input!

Thanks!

[bisnettrj2]

Yes, this is an EPA publication. It is the quality control guideline document for the EPA 8000-series (solid waste/RCRA) methods. See the description below (from the first page of the document):

http://www.epa.gov/osw/hazard/testmetho ... .htm#8000C

"Method 8000C (PDF) (66 pp, 250K) [March 2003]
Determinative Chromatographic Separations

Method 8000C is not a determinative method, but instead provides updated guidance on analytical chromatography and describes calibration and appropriate quality control procedures that are common to all SW-846 chromatographic methods. However, more specific quality control requirements that are provided in the applicable determinative method will supersede those noted in Method 8000C. Method 8000C should be applied in conjunction with all SW-846 determinative chromatographic methods."

See also http://www.epa.gov/wastes/hazard/testme ... /index.htm for a compendium of all the EPA analytical methods for RCRA (Resource Conservation and Recovery Act) methods.