Quantitative analysis of D-(+)-glucose in fruit juices using diffusion ordered-¹H nuclear magnetic resonance spectroscopy

This study works on D-(+)-glucose quantitative analysis using diffusion ordered-quantitative ¹H nuclear magnetic resonance spectroscopy (DOSY-qNMR), by which an analyte could be distinguished from interferences based upon a characteristic diffusion coefficient (D) in gradient magnetic fields. The D value of D-(+)-glucose in deuterium oxide at 30°C was 5.6 × 10^-10 m²/s at a field gradient pulse of between 5.0 × 10^-2 and 3.0 × 10^-1 T/m, distinguished from fructose, sucrose and starch. Good linearity (r² = 0.9998) was obtained between D-(+)-glucose (0.5-20.0 g/L) and the ratio of the resonance area of a-C1 proton (5.21 ppm) in D-(+)-glucose to that of the β-C1 proton (5.25 ppm) in D-glucuronic acid (50.0 g/L) as an internal standard. The DOSY-qNMR method was successfully applied to quantify D-(+)-glucose in orange juice (18.3 ± 1.0 g/L), apple juice (26.3 ± 0.4 g/L) and grape juice (45.6 ± 0.6 g/L); the values agreed well with a conventional F-kit glucose method.