Novelly quantitative analysis on mixtures of food supplements containing amino acids via high-resolution pure shift 1H NMR spectroscopy

Identifying and quantifying amino acids in complex systems of food supplements by conventional ¹H NMR spectroscopy is a challenging task. Extensive signal overlaps of a variety of amino acids in ¹H NMR spectra limit its application in the analysis of the complex amino acid systems. Triple spin echo PSYCHE (TSE-PSYCHE), a pure shift NMR analytical technique, can provide a simplified and high-resolution proton spectrum by removing the ¹H–¹H homonuclear couplings. Hence, this TSE-PSYCHE NMR method can substantially alleviate the overlap problem so that it has a great potential for quantifying complex amino acid mixtures. Moreover, based on TSE-PSYCHE NMR we successfully quantified the components of two commercial amino acid nutrition tablets: the quantification regression analysis affords a satisfactory linearity with correlation coefficients higher than 0.9910 for all analytes, limit of detection (LOD, 0.075–0.66 mg/mL), limit of quantification (LOQ, 0.25–2.21 mg/mL), accuracy (bias %: 0.06–3.4), the recovery values between 92.38 and 109.0 %, and precision (the relative standard deviations, RSD %) at the range of 0.48–3.50. In this work, we developed a novel quantitative NMR for a global and direct analysis of amino acids of food supplement content.