Acetic acid-d4 (Tetradeuteroacetic acid), a deuterated carboxylic acid, is the tetradeuterated form of acetic acid. Its dissociation constant has been evaluated in deuterium oxide (D2O) by an emf method.Acetic acid-d4 has been used as a deuterated solvent for the dissolution of internal standard in qNMR (Quantitative Nuclear Magnetic Resonance) quantification experiments. Acetic acid-d4 may also be used as a deuterated solvent in the 1H NMR spectral studies of the following: · CB2, a CNBr peptide · α - tocopherol succinate hydrophobically modified chitosan(CS-TOS)