HPLC-UV Detection Methods for Hydrophilic Compounds Using On-column Complexation with Metal Ions

High hydrophilic compounds are difficult to separate by conventional reversed-phase chromatography. When they lack chromophores, they are also difficult to detect by ordinary UV detection. However, the complexation of hydrophilic compounds with metal ions can greatly change their steric and electrostatic properties, which would facilitate their separation by reversed-phase chromatography or ion-exchange chromatography. Complexation can also shift their absorptions to longer wavelengths and increase their extinction coefficients, which would facilitate their detection in UV. Here, we show that hydrophilic compounds can be separated by reversed-phase chromatography or ion-exchange chromatography by on-column complexation with metal ions added to the mobile phase, and can be detected by UV detection. Thus, the coordination ability of hydrophilic compounds provides new ways to separate them. We also apply the methods to measure hydrophilic compounds (e.g. sequestering agents, carboxylic acids, alcohols and sugar alcohols) in environmental water samples, common commodities and foods.