Stability of human insulin in solutions containing sodium bisulfite

The stabilities of human insulin (HI) in aqueous solutions were investigated in the pH range of 4.0-7.0 in the presence (1.0-3.0 x 10(-3) M) and absence of sodium bisulfite (SBS) both in the dark and under scattered light (1000 lux) using high performance liquid chromatography. Increasing concentrations of SBS tended to degrade HI. In the presence of SBS, with an increase in the pH value, the stability of HI decreased in the pH range of 4.0-7.0. There was a partial difference in the stability of HI in the presence of SBS in the dark and that under scattered light. HI was stabilized by glucose in the presence of SBS in the dark, and the stability of HI was revealed to depend on the concentration of free SBS. The reason for this phenomenon was postulated to be the formation of bisulfite-glucose adduct.