A general formalism describing the main conditional and non-conditional probabilities as well as their corresponding information entropies that can be assigned to analysis by high-performance liquid chromatography with diode array and fluorescence detection is discussed. Some quantitative parameters of the detection (absorbance, fluorescence, peak height, data acquisition rate) are used in order to estimate these probabilities. The events within chromatographic peaks are conditioned by their maximum (peak height). Several examples are discussed and conditional and non-conditional information entropies by Shannon's formula are evaluated by given relationships.