Bioequivalence and Bioavailability Forum

Dear all,

I played around with the last example. Since I had no access to the peak slices, I fired up SigmaSCAN Pro 5 to extract the chromatogram from the report. Next I used PeakFIT 4.12 with the EMG (exponentially modified Gaussian) model to deal with tailing peaks:



Interesting results. The tangential integration method of the original chromatogram (red line) overestimates the tailing of the first peak. The system has no other choice, because the baseline is established with the end of the second peak. The enantiomeric ratio is given with 54.2%/45.8%. The perpendicular drop at the valley (blue line) would give a ratio of 51.7%/48.3%. If we calculate the areas of EMG-fitted peaks we get 52.0%/48.0%. Assuming a theoretical ratio of 50%/50% for the racemate, we get biases of 8.35%, 3.39%, and 4.01% for the three methods (since I don’t know the enantiomeric purity of the standard, this claim is rather specultive). But it’s clear, that the tangential integration performs worst and should be avoided.

Unfortunatelly no (!!) current commercial CDS allows peak fitting. Merck/Hitachi’s mid-1990s D-7000 HPLC system manager (HSM v4.1) allowed deconvolution of two merged peaks based on the EMG model. Hillebrand* showed for a large combination of parameters (resolution, tailing, theoretical ratios of merged peaks, noise) that both the HSM and PeakFIT gave unbiased results in all cases, whereas all conventional integration methods performed worse in all cases. Though SigmaFIT is able to import AIA chromatography files, it’s unclear whether it’s application would be acceptable in a regulated environment.

A close-up of the intersection is given below:

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• Hillebrand H. Deconvolution. In: Kuss H-J, Kromidas S (eds.): Quantification in LC and GC. Wiley 2009:p123–51.