Molecular Spectroscopy of Anionic Surfactants II—Nuclear Magnetic Resonance Spectroscopy

Nuclear magnetic resonance (NMR) spectroscopy is an analytical technique that is used routinely for the identification of organic compounds. Chemists apply H and carbon (C)-NMR spectroscopy to determine the structure of synthetic organic molecules and natural products. Liquid chromatography has been interfaced with NMR spectroscopy (LC-NMR), which allows the separation of mixtures into individual anionic surfactants and their subsequent detection by means of proton NMR spectroscopy. The application of LC-NMR requires specialized equipment such as an NMR probe with a flow cell. NMR may be used to quantify the relative ratios of the individual components in mixtures or to measure the average alkyl chain length or the number of ethylene oxide units present in a surfactant. The assignment of fatty acid salts by means of NMR spectroscopy relies mainly on the resonance frequency of the C nucleus of the carbonyl moiety. The signals of the fatty acid chain will provide information on the average chain length of the fatty acid.