The assay method of “The Japanese Standards of Food Additives, 1st. Ed., 1960”, is as follows:
Dissolve about 0.5g of nitrofurazone, dried at 105° for 1 hour and accurately weighed, in aldehyde-free alcohol to produce a 1000ml solution, To 20ml of the solution add sufficient water to make the colume to 100ml. To 5ml of the solution add 4ml of aldehyde-free alcohol, and dilute to 100ml with water. Determine the absorbance A of this solution in a 1cm cell, at a wave length of 375mμ. Calculate the purity of nitrofurazone by the following formula. Correct the result by the control test.
Content=A/0.398×500/Weight of sample (mg) ×100 (%)
However, the data obtained by this method are not always precise.
In this report, the new method is described, in which another compound of high purity listed in the official book is adopted as the control standard substance.
In this case,
p-nitrophenylhydrazine is suitable for this purpose. The purity of nitrofurazone is calculated by the following formula.
Content (%) =Absorbance in ca. 5ppm nitrofurazone in 1% glycine aqueous solution/Absorbance in ca. 5ppm
p-nitrophenylhydrazine in 1% glycine aqueous solution×0.901×Weight (mg) of
p-nitrophenylhydrazine/Weight (mg) of the Sample
By this method, the discrepancy of absorbances due to difference in kinds of instruments or cells is able to be compensated, and the results of determination are almost constant.
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