a Liquid-Phase Infrared Strategy for Quantification of Surface Alkanoate Ligands on Colloidal Nanocrystals

A liquid-phase IR strategy based on bi-phase HCl digestion of colloidal nanocrystals is developed for quantitative determination of their most common surface ligands─alkanoate ones─in a broad range of concentration (4.03 × 10–2 and 7.68 × 10–5 mol/kg). Digestion converts all alkanoate ligands to the corresponding fatty acids, which share the same carboxylic vibration modes (dimer and monomer) for liquid-phase IR measurements in dodecane (the non-polar phase for digestion). Albeit with structure-dependent equilibrium constants between the dimer and monomer, a universal extinction coefficient in the IR window covering both vibration bands is confirmed. Different versions of the liquid-phase IR strategy are developed for alkanoate ligands with significant solubility in the aqueous phase (such as acetic acid), low solubility in either phase (e.g., stearic acid), and in the presence of common chemicals for synthesis and processing of colloidal nanocrystals.