Unique Usage of a Classical Selective Homodecoupling Sequence for High-Resolution Quantitative ¹H NMR

Classical selective homodecoupling was used in a ¹H NMR purity assay to improve accuracy by overcoming spectral overlaps due to ¹H–¹H spin coupling. Dummy irradiation at a specific frequency was used in addition to irradiation at a ¹H resonance of the analyte to avoid irradiation bias. The method was validated in a ¹H NMR purity assay of high-purity diethyl phthalate (National Metrology Institute of Japan Certified Reference Material (NMIJ CRM), purity: 99.98%). The obtained purity value biases were 0.27% or less. The utility of the method was demonstrated in another ¹H NMR purity assay of dipropyl phthalate (NMIJ CRM, purity: 98.41%), which contained a tiny amount of the structurally similar compound methyl propyl phthalate as an impurity. An accurate assay was achieved with the method, giving a purity of 98.39%, whereas the conventional method gave a purity 99.13%.