NMR spectroscopy is widely used for structural determination of a molecule. Recently, the quantitative aspect of NMR has been focused. The signal intensity under NMR is known to be proportional to the number of nuclei contributing to the signal.
19F is expected to observe the accurate quantitative result because of the sensitivity is similar to that of 1H. Moreover, 19F NMR has a wider frequency range whose signal dispersion is advantageous for the signal separation. On the other hand, the wider frequency dispersion may cause a problem on a uniform signal excitation, so called off-resonance effect, for targeted signals. We had established with 19F qNMR which has 1 % or less accuracy of measurement by avoiding the off-resonance effect .
In this research, we report a development of accurate quantification of for 1H and 19F qNMR using 3,5-bis(trifluoromethyl)benzoic acid (3,5-BTFMBA) as an internal standard. The purity of 3,5-BTFMBA was determined by a subtraction method with analysis of impurities. Two analytes used in this reseach, chlorfenapyr and diflubenzurone which are reference materials.
All NMR spectra were obtained by using a Varian VNS 600 spectrometer at 595.238 MHz. The probe used was a Varian 15N-31P/1H-19F PFG dual-broadband probe. All the data were processed using MestReNova. The detailed process conditions were described in ref. 2 for 1H NMR and ref.1 in 19F NMR, respectively.
As results, purities of analytes were determined with repeatability of <0.2 % in 1H NMR and <1 % in 19F NMR, respectively. These quantitative values were agreement with their reference values. In this method, accuracy of the quantitative value was confirmed by only qNMR with mutual validation by 1H NMR and 19F NMR spectroscopy.