Early in 1989, the pressure transducer in the osmometer failed and was sent overseas for repair. The osmometer was returned in early 1990 with a new pressure transducer; however, upon receiving the instrument we attempted to calibrate it by using a hydrostatic pressure head and after a great deal of effort discovered that the base line had become extremely unstable. The osmometer was returned to the manufacturer for additional servicing and is currently being calibrated by the U.S. dealer and is to be returned soon. As a result, during this fiscal year no new measurements have been carried out. Thus far, 14 lots of dextran 70 from 4 manufacturers have been studied, and we wish to look at a total of 16 lots of dextran 70 (4 from each manufacturer). We have started a systematic study of hetastarch (high molecular weight hydroxyethyl starch) and have carried out measurements on 5 lots from the single manufacturer. In addition, 2 lots of dextran 40 from 2 manufacturers have been investigated. We plan to continue all these studies with the return of the osmometer in order to obtain the number average molecular weight and second and third virial coefficients for each lot. Due to the unavailability of the osmometer, no additional light scattering experiments have been performed on any of these materials in order to obtain complementary weight average molecular weights. The ratio of these molecular weights provides a measure of the polydisperity of these products, which relates to clearance properties of these materials.
