Chromatography Forum

I need to calculate the resolution (rel. resol. or USP resol.) of a peak which elutes on the tailing of the main component. This peak is integrated using a tangential skim. However, Empower does not calculate any resolution for the skimmed peak. Is this a bug in Empower or am I doing something wrong?

No one has replied, so I'll try to chip in, but this may not be a very accurate reply.

I don't know if Empower can calculate what you're asking for, but I personally don't think it should, as it isn't really something that can be evaluated from the data available. Resolution is separation of two peaks divided by average peak-width, but by definition, if the peaks are not resolved, it's impossible to know the peak-width accurately. You can estimate the peak width by measuring from the start of the first peak to its middle, and from the middle of the second peak to its end, but if either peak suffers from asymmetry the measurement won't be correct. If a peak is on the tail of another peak, its whole shape will be very non-Gaussian because the Gaussian peak has been added to a steep (and curvy) slope, so finding its genuine width will be a challenge.

If the peaks are not resolved, then the calculated value of the resolution isn't very valuable. If you want to quantify the resolution with a view to ensuring that a best-you-can-do-but-not-very-good method isn't getting worse, or because you want to compare different methods, none of which gives good resolution, in order to pick the best (for example during method development) then maybe, perhaps, some other measure, such as the valley-height above baseline might be a better measure?? I'm not sure. Someone tell me I'm wrong, please!

Can you post an image of the chromatogram?

From the Empower help:

Resolution is calculated for both named and unnamed peaks, where the appropriate peak width can be calculated. Resolution is not calculated for skimmed peaks.

So I guess the appropriate peak width cannot be calculated for skimmed peaks.

Check this article for more background on this whole topic:
http://www.chromatographyonline.com/est ... ed-peaks-0

I've found out that the resolution of skimmed peaks will not be calculated.
From the help function:

Resolution is calculated for both named and unnamed peaks, where the appropriate peak width can be calculated. Resolution is not calculated for skimmed peaks.