168 Proceedings of the 1 st International Conference on Polymer Development and Applications, University of Nigeria, Nsukka, Nigeria, March 18 – 21, 2009 MOLECULAR WEIGHT DETERMINATION OF SOME NATURAL GUMS BY DILUTE SOLUTION VISCOMETRY Uzor P. F. 1 ’*, Agbo I. U. 2 , Omeje E. O. 1 , David E. K. 1 , Attama A. A. 3 and Adikwu M. U. 3 1 Department of Pharmaceutical and Medicinal Chemistry, Faculty of Pharmaceutical Sciences, 2 Department of Pure and Industrial Chemistry, 3 Department of Pharmaceutics, University of Nigeria, Nsukka 41000, Enugu State, Nigeria. * To whom all correspondence should be addressed. E-mail: philuzor4u@yahoo.com ; Tel.: +234 803 7008 294 Abstract: The objective of this work was to determine the molecular weight of the natural gums from the following plant sources using dilute solution viscometry method: pods of Albemoschus esculentus, empty pods of Cola acuminata, corms of Colocasia antiquorum and seeds of Detarium microcarpum. By means of the Ostwald U-tube viscometer, the relative viscosities of the standard polymers of molecular weight-low, medium and high grades of sodium carboxymethylcellulose were determined using water as the solvent. The relative viscosity data were used to determine their intrinsic viscosities from the straight line graphs plotted according to the Huggins’s law. Subsequently, the natural gums were extracted and their intrinsic viscosities similarly determined. Using the molecular weights and the intrinsic viscosities of the standard polymers, a calibration curve was fitted from where the empirical Mark Houwink’s constants were determined. The constants were used to calculate the molecular weight of the natural gums according to Mark Houwink’s equation. The results showed that the molecular weight of Albelmoschus esculentus gum was 143,396; that of Cola acuminata gum was 77,792; that of Colocasia antiquorum gum was 17,767 while that of Detarium microcarpum was 63,389. The conclusion was that the viscosity average molecular weight of the natural gums from Albelmoschus esculentus, Cola acuminata, Colocasia antiquorum, Detarium microcarpum were143 396, 77 792, 17 767 and 63 389 respectively. Keywords: molecular weight, natural gum, polymer, dilute solution viscometry, Albelmoschus esculentus, Cola acuminata, Colocasia antiquorum, Detarium microcarpum [ICOPDA, 2009, VOL. 1,168-176] INTRODUCTION Gums may be natural polymers such as proteins and carbohydrates, derived polymers obtained from natural polymers by chemical modification such as methylcellulose; or synthetic polymers obtained by synthesis from low molecular weight substances such as polyvinyl alcohol (Encyclopedia Americana, 1993). In terms of origin and sources, natural gums are usually obtained from seaweeds, buffalo hides, pig skins, wounded trees, cereal grains, plant seeds and other common as well as bizarre material (Claus et al., 1970; Ajali, 2004). Being polymers, gums find extensive use in many fields such as thickeners, adhesives, gelling agents. In pharmaceutical preparations, they are used as emulsifiers, stabilizers, binders, disintegrants, suspending agents, etc. The synthetic and semi-synthetic gums are not only expensive but not always available to the local industries especially in developing countries (Ezehi, 2008). These add to the cost of pharmaceuticals and other industrial products which are produced with these gums. The search for cheaper, easily available, yet high quality gums has led to more studies in recent years on the characterization of the locally available natural gums. The natural gums chosen for this study are from the pods of Abelmoschus