The aim of the project is to deepen the understanding of chromatographic retention, especially for separation of complex samples, by modeling retention time shifts as a function of small perturbations of the gradient, mobile phase pH, temperature, etc. A better understanding of the retention behavior of peaks can be used to improve chromatographic separation of complex samples, pinpoint the cause of observed peak shifts to get a chromatographic system under control, improve alignment of data on complex samples, and enhance mechanistic understanding of the retention time mechanisms.