Molecular mass estimation of derivatized compounds: a PFG NMR study

Pulsed-field gradient (PFG) 1H and 31P NMR methods were developed to quantitatively estimate the molecular mass of compounds, derivatized with either trichloroacetyl isocyanate (TAI) or 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane (chlorophospholane). These agents provide selective analysis with high sensitivity for molecules containing alcohol, amine, carboxylic acid, or thiol functional groups. Tetramethylsilane (TMS) or bisphenol A was used as internal diffusion reference. The empirical relationship between relative diffusivity and molecular mass was established for a set of mono- and difunctional compounds with molecular masses in the range 32-330 g/mol. The utility of the method was demonstrated by analyzing alcohol, phenol, and carboxylic acid components in lubricating oil.