One pair of to be compared samples - an authentic one (named A) with a questionable one (named Q) - is sampled and focused in such a way, that about 10 to 20 % of the sample bows overlap. Note: per plate three of such compare pairs could be sampled or two differing samples Q touching one sample A - but see the figure below. The chromatographic separation is selected in such a way, that important parts of the compare samples reach a relative position
Pr of above 0.2 and below 0.8. NOTE: Pr is used instead of the classical Rf. Pr means relative position. The radius of the circular chromatogram has the value Pr = 1.0
In the “overlap area” of the chromatograms there exists a special analytical condition not available by any other analytical procedure (at least not known to the author prior to 2009), where all physical and chemical conditions are strictly equal to the overlapped substances. As the separation is strictly simultaneous, there is also no any time effect active, which otherwise could easily produce systematically falsifying effects to the compare samples. If the chromatograms for the questionable sample differs qualitatively and / or quantitatively from the authentic sample, sample Q is NOT equal to the sample A. Product Q differs from product A.
This result has the highest possible safety: it is 100 % sure. No repetition, no statistics necessary in case the samples have been taken, prepared and given totally error free. This however is the professional condition sine qua non for a trained analyst, as everything he/she has to know about correct sampling is standard knowledge since more than hundred years,