MOLECULAR WEIGHT MEASUREMENTS OF POLYCARBOXYLIC ACIDS IN WATER BY VAPOR PRESSURE OSMOMETRY

Number-average molecular weight determinations of polycarboxylic acids in water by vapor pressure osmometry may yield erroneous results owing to dissociation. Based on experimentally determined values of Mn and pH, a correction system is described which makes possible calculations of accurate Mn values. The applicability of the correction system is demonstrated for 15 known aliphatic and aromatic compounds, containing between one and six carboxyl groups per mole and to water-soluble humic compounds of widely differing molecular weights, containing relatively high concentrations of carboxyl groups. This method may be especially useful for naturally occurring water-soluble organic compounds which are insoluble or only very slightly soluble in organic solvents. © 1969.