Undiluted toothpastes and creams by NMR

The active components in viscous formulations like toothpastes, cosmetic creams and pharmaceutical gels can be analysed by high-resolution-magic angle spinning NMR spectroscopy with minimal sample preparation, say scientists in Switzerland. When viscous substances are subjected to conventional solution NMR, the restricted mobility of the components leads to broad resonances which are not particularly useful. This limitation can be circumvented by time-consuming sample processing.

As a new alternative, Martina Vermathen and coresearchers from the University of Bern have shown how simple dilution with D₂O allows good spectra to be recorded by ¹H HR-MAS NMR spectroscopy. Writing in Analytical Chemistry, they illustrated the procedure by analysing chitosan in toothpaste, the anti-inflammatory dexamethasone acetate in a cream, and the local anaesthetics lidocaine and prilocaine in a gel and a cream.

Using a deuterated reference compound, levels of the active components down to 0.01% by wt. could be measured, which is sufficent to cover most common additives.