A natural crystal growth retarder in lactose
1980
Visser, R.A. (Cooperatieve Condensfabriek Friesland, Leeuwarden (Netherlands))
Growth experiments were made with single crystals of alpha-lactose hydrate in supersaturated solutions in accordance with a method described by van Kreveld and Michaels. We found that the results of our growth experiments strongly depended on the origin of the lactose that was used for the solution. To obtain an "absolute blank" for our growth experiments, we tried to purify the lactose further by recrystallization. After every recrystallization the lactose obtained had a lower pH and a smaller growth rate than its starting product, even when the latter had been previously neutralized. Fractional recrystallization showed a gradually increasing pH of the fractions; finally a neutral lactose could be obtained. With ion exchange we succeeded in making a non-ionic lactose; it was thus proved that the acidity is not a property of the lactose itself. Growth experiments with this non-ionic lactose gave the "absolute blank". Growth rates with this lactose were found to be much higher than with pharmaceutical-grade lactose from different sources. This was especially the case for the (010) and (110) faces. From the anion exchanger used an acid solution was obtained, which appeared to have a strong growth-inhibiting action. This demonstrates that pharmaceutical grade lactose contains an accompanying substance with an acid character, which crystallizes persistently together with the lactose and which slows down the rate of growth. In a subsequent paper the isolation and the identification of this product will be discussed.
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