Validated quantitative ³¹P NMR spectroscopy for positional isomeric impurity determination in...

In this study a quantitative ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy method was described to determine positional isomeric impurity β-GPC in commercial products of L-α-GPC. The samples were dissolved in D₂O and trimethyl phosphate (TMP) was selected as an internal calibrant. The measurements were performed on a Bruker 500 MHz spectrometer and the spectra were recorded under optimized process conditions. A good linear relationship was constructed for β-GPC in the range of 62.7-528.0 µg·mL^-1, i.e. 0.03-0.25 % (w/w %, in relative to L-α-GPC) with a correlative coefficient of 0.9996. The limit of quantification (LOQ) and limit of detection (LOD) were 62.7 µg·mL^-1 and 20.9 µg·mL^-1 with signal to noise of 3 and 10, respectively. The spiked recoveries were in the range of 98.17-99.78 % with the relative standard deviation (RSD %) less than 1.0 %. Therefore, it could be supposed that the ³¹P NMR was a promising alternative method for sensitive determination of β-GPC for strict quality control of L-α-GPC.