DEVELOPMENT OF A PREDICTIVE MODEL FOR CALCULATION OF MOLECULAR-WEIGHTOF HUMIC SUBSTANCES

Size exclusion chromatography (SEC) is a powerful tool for the determi nation of molecular size of compounds. However, the conducted SEC anal ysis of 35 humic substances (HS) samples demonstrated, that it has som e severe pitfalls fur the molecular weight characterization of HS resu lting from a lack of appropriate standards. To overcome this problem. a new approach to calculation of molecular weight from the SEC data wa s developed. It is based on the correction of the experimentally deter mined distribution coefficient (K-d) values according to the predictiv e equations derived tither from the data on charge density and hydroph obicity of the analyte or from the values of its characteristic struct ural parameters. Verification of both predictive equations using model compounds has displayed much better prognostic potential of the polyn omial equation developed with a use of integral structural parameters of the analyte. Application of this predictive equation to synthetic p olyelectrolytes gave satisfactory estimates for all the polymers with K-d>0.15. The model calculation for an averaged sample of HS allowed t o estimate a difference between the ideal and experimental values of K -d(Delta K-d) by a value of 0.02. The correspondent correction of the SEC-data of 35 HS samples showed overestimation of the values of molec ular weight of HS determined by the standard data handling technique. The obtained model estimations are to be verified along with the furth er development of the model based on the adjustment of the model assum ptions to specific polyelectrolytic properties of HS. (C) 1998 Elsevie r Science Ltd. All rights reserved.