First, a series of stock solutions are made. Stock Solution 1: 2.18 g of recrystallized insulin are dissolved in 25 ml of 0.1
N hydrochloric acid, and distilled water to a volume of 125 ml is added. Stock Solution 2: To 20 ml of an aqueous zinc chloride solution containing 1%
zinc is added distilled water to a volume of 125 ml. Stock Solution 3: 1.36 g of sodium acetate with 3 mols crystal water are
dissolved in distilled water to a volume of 100 ml. Then, 1.3 ml of glycerine are mixed with 0.5 ml of a 25% solution of methyl
p-hydroxybenzoate in ethanol, and 50 ml of distilled water are added. To the
produced mixture are, after sterile filtration, added 10 ml of the stock solution
1, 2.5 ml of the stock solution 2 and 10 ml of the stock solution 3, after which
3.0 ml of sterile 0.1 N sodium hydroxide are added, and the mixture is filled
up with sterile distilled water to a volume of 100 ml. The insulin will be
precipitated amorphously by the admixture of the sodium hydroxide, and the
produced suspension acquires the pH value of 7. It will contain approximately
1 gamma zinc per insulin unit.
