Difluoroacetamide: A Selectively Tunable, Universal 1H and 19F Quantitative NMR Calibrant

Quantitative NMR (qNMR) is a robust technique used in a variety of chemical industries due to its numerous analytical advantages. It exhibits a universal response, a broad linear range, diverse compound applicability, and allows for facile method development. The most accurate qNMR results are obtained with an internal calibrant, but no truly universal calibrant currently is known that is stable, non-toxic, commercially available, exhibits a unique chemical shift, is highly soluble in both aqueous and non-polar solvents, and exists as a non-hygroscopic solid for accurate weighing. In this study, we investigated several potential qNMR calibrants and identified 2,2-difluoroacetamide (DFA), which meets all the aforementioned criteria. This calibrant is soluble in a wide polarity range of both protic and aprotic solvents from D2O to CD2Cl2, and it exhibits selectively tunable 1H and 19F chemical shifts via decoupling that resonate in sparse regions of the typical NMR spectrum. We evaluated the broad utility of this calibrant by assaying 13 active pharmaceutical ingredients in 12 different deuterated solvents. Our results demonstrate excellent measured accuracies and precisions of 100 ± 1% and % RSD (n=3) less than 1%, respectively. Therefore, we recommend difluoroacetamide as a reliable and generally applicable internal calibrant for qNMR analysis.