Determination of the presence of hyaluronic acid in preparations containing amino acids: the molecular weight characterization.

Several pharmaceutical preparations contain hyaluronic acid in the presence of a large variety of low molecular weight charged molecules like amino acids. In these mixtures, it is particularly difficult to determine the concentration and the molecular weight of the hyaluronic acid fragments. In fact zwitterionic compounds in high concentration behave by masking the hyaluronic acid due to the electrostatic interactions between amino acids and hyaluronic acid. In such conditions the common colorimetric test of the hyaluronic acid determination appears ineffective and in the (1)H NMR spectra the peaks of the polymer disappear completely. By a simple separation procedure the presence of hyaluronic acid was revealed by the DMAB test and (1)H NMR while its average molecular weight in the final product was determined by DOSY NMR spectroscopy alone. The latter determination is very important due to the healthy effects of some sizes of this polymer's fragments.