We have applied a combination of H quantitative NMR spectroscopy (H-qNMR) and chromatography (GC or LC) to establish reliable analytical methods (qNMR/GC and qNMR/LC) for organic compounds. In this method, a reference standard is used as an internal standard for both H-qNMR and chromatography to estimate relative molar sensitivity (RMS) for analytes. The RMS values are calculated from the molar ratios between analytes and the reference standard obtained byH-qNMR; and the response ratio between them obtained by chromatography. Concentrations of analytes in the organic solution can be simultaneously determined from the RMS and amount of the reference standard added in the sample solution. This analytical method is an innovative one because only one reference standard with International System of Units (SI)-traceable property value, purity, or concentration, is necessary to determine accurate concentrations of multiple organic components in organic solutions, without the respective certified reference standards for various analytes. To verify this method, a certified reference material, NIST SRM 1647f, was used. Among the 16 polycyclic aromatic hydrocarbons (PAHs) included in NIST SRM 1647f, naphthalene and benzo[a]pyrene were selected as analytes for this method, using 1,4-bis(trimethylsilyl)benzene-d as the reference standard. Each quantitative value obtained by qNMR/GC and qNMR/LC agreed with each certified value within its expanded uncertainty.
Classical selective homodecoupling was used in a 1 H NMR purity assay to improve accuracy by overcoming spectral overlaps due to 1 H− 1 H spin coupling. Dummy irradiation at a specific frequency was used in addition to irradiation at a 1 H resonance of the analyte to avoid irradiation bias. The method was validated in a 1 H NMR purity assay of highpurity 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 1 H 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%.
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