Solid Fat Content and Relaxation Time Measurement of Petrolatum Using Time-Domain NMR, and the Correlation with Viscosity and Crystallinity

This study aimed to clarify the relationship between the NMR parameters of petrolatum obtained using the time-domain NMR (TD-NMR) technique and the physical properties obtained using conventional methods. Six commercially available drug-free petrolatums were used. First, the physical properties of these samples were recorded by conventional methods: polarized light microscopy, viscometry, and X-ray diffraction (XRD). The XRD pattern showed a characteristic diffraction pattern corresponding to the crystallization of paraffin wax. Next, the TD-NMR technique estimated the solid fat content (SFC) and T₂ and T₁ relaxation times as NMR parameters. The free induction decay of petrolatum showed the characteristic biphasic decay, while the SFC value was estimated from signal intensities. Finally, a scatterplot matrix was drawn to clarify the relationship between the NMR parameters and the physical properties. Using the Spearman rank-order correlation, the SFC showed a strong and positive correlation with the crystallinity (ρ = 0.855), and the T₂ relaxation time showed a moderate and negative correlation with the viscosity (ρ = -0.707). In conclusion, this study clarified which NMR parameters correspond to the conventional physical properties: the SFC corresponded to the crystallinity and the T₂ relaxation corresponded to the viscosity. Utilization of the TD-NMR technique to evaluate molecular mobility may be useful in terms of complementing the conventional physical characterization of petrolatum.