VI. STANDARDIZATION OF ACTIVITY 259 



tweeii ascorbic acid and either perinaphtliindanetrionc hydrate or the de- 

 rivative 2-nitroperiiuiplilhiiidanetrioue hydrate has recently been pro- 

 posed.'^' Reductones, reductic acid, and cysteine may cause interference, 

 but it is churned that, for the estimation of ascorbic acid in pure solutions, 

 blood plasma, and urine, this method is as accurate as, but simpler and 

 quicker in operation than, the Roe and Kuether method. 



Further developments of physical methods for the estimation of ascorbic 

 acid are awaited with interest. It is doubtful, however, whether any of those 

 already described will have wide application, except possibly for phar- 

 maceutical preparations, unless they are modified to give greater specificity 

 compared with the chemical methods of ascorbic acid assay. 



VI. standardization of Activity 



MAMIE OLLIVER 



In 1931 the Permanent Commission on Biological Standardization of the 

 League of Nations adopted 0.1 ml. of freshly expressed lemon juice, Citrus 

 limonum, as the unit of vitamin C acti\'ity. The possible variation in as- 

 corbic acid content of this juice was subsequently emphasized however,' 

 and in 1934 the Commission recommended the adoption of L-ascorbic acid 

 as a standard of reference. However, in order to maintain the biological 

 value of the unit, the Commission approved 0.05 mg. of L-ascorbic acid as 

 the international unit (I.U.) of vitamin C activity, since this is the approxi- 

 mate average content of 1 ml. of lemon juice. Hence, by definition 1 g. of 

 L-ascorbic acid is equivalent to 20,000 I.U. 



The criteria of purity laid down for this international standard by the 

 International Conference in 1934 and the findings of Haworth on a sample 

 prepared by Szent-Gyorgyi are quoted by Coward:- 



Melting point 



Specific rotation in water [alo" 



(Concentration, g./ml. 

 Amount in milliliters of 0.01 A" aqueous iodine 



required by 10 mg., the titration being carried 



out with starch as indicator 11.4 11.4 



1" M. S. El Ridi, R. Moubasher, and Z. F. Hassan, Biochem. J. 49, 246 (1951). 



1 A. L. Bacharach, P. M. Cook, and E. L. Smith, Biochem. J. 28, 1038 (1934). 



2 K. H. Coward, Biological Standardization of the Vitamins, 2nd ed., p. 87. Bailli- 

 6re, Tindall and Cox, London, 1947. 



