Stability of galactose in aqueous solutions

The stability of 5%-30% w/v galactose in sterile water for injection and acetate and phosphate buffers was studied. The concentration of galactose was determined after each sample was diluted to a nominal concentration of 0.5% (w/v); for purposes of data analysis, the concentration as measured in the diluted sample was multiplied by a dilution factor to obtain the true concentration in the sample. The concentrations were determined from the regression line obtained by plotting the peak-height ratios (for various concentrations of galactose and the internal standard cellobiose) versus the galactose concentrations. Triplicate samples were quantitatively analyzed for galactose content by high-performance liquid chromatography. The stability of the samples was then studied in relation to buffer concentration; pH; storage at 25, 45, and 65 degrees C for six weeks, and autoclaving at 121 degrees C for 30 minutes. Galactose degradation increased in relation to its concentration, increasing temperature, and buffer concentration. Galactose solutions in water and phosphate incurred less than 5% degradation on autoclaving; however, the 30% solutions in acetate buffers lost up to 21% of initial content. Yellow discoloration of solutions was associated with autoclaving and prolonged exposure at 65 degrees C and appeared in some solutions that did not exceed the USP XXI limit of 5-hydroxymethylfurfural and related compounds in dextrose injection. The estimated room temperature shelf-life of galactose in sterile water for injection sterilized by 0.45-micron-porosity membrane filtration is four and one-half months. Solutions may also be sterilized by autoclaving at 121 degrees C for 30 minutes; galactose solutions containing pH buffers should not be sterilized by autoclaving.