Quantitative quadrupolar NMR (qQNMR) using nitrogen-14 for the determination of choline in complex matrixes

NMR offers the unique potential to selectively excite the chosen nuclei avoiding in an extraordinary way the matrix effect. Quantitative Nitrogen-14 NMR (N-14 qNMR) spectroscopy has been introduced for the first time as a robust and validated method to determine choline in a variety of matrixes including quinoa grains, instant coffee and food supplements. A study about the ion pairing of choline bitartrate in aqueous solution by means of diffusion PGSE, NOESY and HOESY NMR have been also provided. Validation of the method within eight concentrations levels (from 1.58 to 79.0 mM) afforded a limit of detection of 400 mu g/mL (1.58 mM), a quantification limit of 1000 mu g/mL (3.95 mM), excellent linearity (R-2 higher than 0.999), intra-/inter-day precisions lower than 1.24% (CV), recoveries of 93.5%-102.5%, and complete absence of matrix effect. The fast and reliable quantification of choline together with the accuracy and simplicity of this new approach make it useful in the development of analytical procedures that could dramatically affect traditional analysis.

Automated summary

NMR offers unique potential for selective excitation of specific nuclei and avoiding matrix effects; Quantitative N-14 qNMR spectroscopy is a robust method for determining choline in various matrices; Study of ion pairing of choline bitartrate in aqueous solution and fast, reliable quantification of choline were also provided.