Quantitative NMR (qNMR) is a powerful tool to quantify an analyte without the need for an identical standard, which is considered to be a primary ratio method. In particular, the use of 1H NMR has been widely applied in the quantification of medicines, beverage components, and natural products in medicinal plant extracts because of its high sensitivity and the widespread presence of 1H nuclei in organic molecules. Our group has previously reported a novel 1H qNMR technique that is able to determine quantitative values of the analyte with metrological traceability to the International System of Units with a certified reference material as the internal standard (IS); this is called AQARI (accurate quantitative NMR with internal reference substance).
There are other advantages to qNMR using 1H such as simple sample preparation, low sample consumption, and rapid, non-destructive measurement. Furthermore, it is widely recognized as a reliable technique due to the development of high-field magnets, and improvements in probe technology and gradient shimming techniques contributed to the enhancement of sensitivity, resolution, and precision. In Japan, qNMR using 1H NMR has been set as an official method for assessing the purities of reference substances for pharmaceuticals and food additives.
In this review, we describe our recent studies regarding the applicability of qNMR using 1H NMR for the purity assessment of organic compounds and the analysis of complex mixtures. The first half of the review introduces qNMR using 1H NMR with IS, while the second half describes our recent purity assessments of commercial reagents for food analysis, and the quantification of several preservatives in processed foods by qNMR.
Keywords: AQARI, Acesulfame potassium, Acetamiprid, Carminic acid, Carthamin, Dichlorvos, Food additives, Flavonoid, Isoxathion oxon, Metrological traceability, Pesticides, Preservatives, Quantitative NMR, Steviol glycosides, Trichothecene mycotoxin.