Quantitative 13C NMR spectroscopic studies on the equilibrium of formaldehyde with its releasing cosmetic preservatives

The aim of our study was to show that NMR spectroscopy is an excellent method to obtain reliable information about the equilibrium between free formaldehyde and its formaldehyde releasers. For this purpose, we compared several O- and N-formal-based formaldehyde releasers used in industrial and consumer products. The underlying chemical structures as well as the release of formaldehyde were followed quantitatively as a function of the pH and dilution. It was shown that only the amide-based N-formals are a reservoir for formaldehyde in the concentrations normally used in cosmetic products, whereas O-formals and the amine-based N-formals decompose completely. Since NMR spectroscopy does not affect the equilibrium between free and bound formaldehyde, we think that it is the only method for unequivocal determination of free formaldehyde. Measurements on finished products showed that free formaldehyde can be quantified down to concentrations as low as approximately 0.002 wt % in an acceptable measuring time.