Analysis of Lactulose Preparations by Spectrophotometric and High Performance Liquid Chromatographic Methods

Spectrophotometric methods of analysis were applied to sugar mixtures produced during isomerization of lactose to lactulose.A combination of four established spectrophotometric methods was used to quantitate galactose, tagatose, lactose, and lactulose, the four major sugars present.In addition, a method originally developed for determining lactose with methylamine at 65°C and pH MATERIALS AND METHODS Sugar StandardsReagent grade anhydrous glucose, fructose, tagatose, galactose, &-lactose monohydrate, and lactulose were dried under vacuum at 65°C for 16 h and then used to prepare 100 mg/ml stock solutions.Lactulose syrups were either purchased (Cephulac, Merrell-National Laboratories a) or prepared by isomerization of lactose with calcium hydroxide (15), triethylamine (18), or sodium aluminate (11).The syrups, stored as 70 to 80% solutions, were diluted to the appropriate concentrations prior to analysis.