A chromatographic objective function to characterise chromatograms with unknown compounds or without standards available

• New approach not requiring standards to characterise chromatographic performance.
• Approach based on automatic measurement of chromatographic peaks protruding part.
• Characterisations carried out based on peak count and global resolution.
• Advantages and limitations appraised in comparison to the peak purity criterion.
• The approach is successful when applied to chromatograms with unknown compounds.

Getting useful chemical information from samples containing many compounds is still a challenge to analysts in liquid chromatography. The highest complexity corresponds to samples for which there is no prior knowledge about their chemical composition. Computer-based methodologies are currently considered as the most efficient tools to optimise the chromatographic resolution, and further finding the optimal separation conditions. However, most chromatographic objective functions (COFs) described in the literature to measure the resolution are based on mathematical models fitted with the information obtained from standards, and cannot be applied to samples with unknown compounds. In this work, a new COF based on the automatic measurement of the protruding part of the chromatographic peaks (or peak prominences) that indicates the number of perceptible peaks and global resolution, without the need of standards, is developed. The proposed COF was found satisfactory with regard to the peak purity criterion when applied to artificial peaks and simulated chromatograms of mixtures built using the information of standards. The approach was applied to mixtures of drugs containing unknown impurities and degradation products and to extracts of medicinal herbs, eluted with acetonitrile–water mixtures using isocratic and gradient elution.