Chromatogram explainer
A main peak at 6.0 minutes holds 97.0% of the area and an impurity peak 1.20 minutes later holds 3.0%. With a resolution of 1.67 a valley separates them, so each peak gets its own area and purity reads 97.0%.
Illustrative model with two peaks. Not data from any lab or product.
True purity
97.0%
Reported purity
97.0%
Resolution (Rs)
1.67
Peaks separated
How this works
The model draws two Gaussian peaks of equal width. Resolution is the gap between their centres divided by four times the peak's standard deviation, the usual definition for equal-width peaks given in the pharmacopeial chapter on chromatography. Below a resolution of about 1, a simple integrator cannot draw a valley between them and reports one peak.
Real chromatograms have many peaks, different shapes and integration settings, and labs validate methods so that likely impurities are separated. That is why a certificate should name its method, and why mass spectrometry across the main peak, as described in LC-MS, is a useful second check.
Questions
- Does 99% purity mean 1% impurities?
- It means 99% of the peak area the detector recorded, under that method. Impurities that co-elute with the main peak, or that the detector cannot see, are not in the 1%.
- Is this real data?
- No. It is an illustrative model to show the principle. It does not represent any lab, product or certificate.