Examination of insulin formulations using quasi-elastic light scattering

A selection of neutral insulin formulations from commercially available vials was examined by quasi-elastic light scattering. In preliminary investigation, significant differences in the particulate nature of insulins from different manufacturers were apparent. Some preparations contained only small diameter species believed to be insulin hexamer while others showed evidence of larger aggregates and microcrystals. Addition of small amounts of bicarbonate had no detectable effect on the small species but dissolves the microcrystals. Speculation on further and more quantitative use of this new technique for analysis of insulin solutions is reported.