VIII. STANDARDIZATION OF ACTIVITY 453 



The (.iitTercnt methods of estimation vary widely in pi-iiicij)!*' and even 

 the same method (chemical, biological, etc.) may be carried out in different 

 ways. Thus, for obtaining a reliable extract, different proteinases may be 

 used, combined with extraction with diluted hydrochloric acid, sulfuric 

 acid, or sodium acetate solution. The extracts may be purified for removal 

 of interfering substances in different ways. Several different methods are 

 used for the oxidation of thiamine to thiochrome. Therefore it is possible 

 that the results of the thiamine estimation of one laboratory do not agree 

 very well with those of another institute. 



Therefore in man}'' countries the results of different laboratories have 

 been compared. The most recent investigation in this respect probably is 

 that of the Aneurine Panel of the Subcomittee on Vitamin Estimations of 

 the British Analytical Methods Committee of the Society of Public Analysts 

 and Other Anal>^ical Chemists.-^ The panel prepared large homogeneous 

 amounts of malt extract, wheat germ, wheat flour (85% extraction), yeast 

 extract, and three different samples of dried yeast. Representative samples 

 of these thiamine-containing foodstuffs were sent to the collaborating lab- 

 oratories in England and in the Netherlands. A detailed description of the 

 recommended thiochrome method was given. ^^ For the results, see Tables 

 IV and V. 



From these results we see that the various results in the different labora- 

 tories are not in perfect agreement. Particularly the biological methods 

 gave divergent results. On the other hand the agreement of the results of 

 the thiochrome and the microbiological methods was not too bad. 



VIII. Standardization of Activity 



B. C. P. JANSEN 



Before the large-scale production of pure, crystalline thiamine hydro- 

 chloride, it was decided at the Vitamin Standards Conference of the Com- 

 mission on Biological Standardization of the Health Organization of the 

 League of Xations held at London in 1931 that a certain quantity (10 mg.) 

 of an acid clay activated by an extract from rice polishings should be used 

 as an international unit of antineuritic vitamin Bi (at that time the name 

 of thiamine).' This activated acid clay was prepared in the Medical Labora- 

 tory at Batavia (now Djacarta) and had ah'cady been shown to l)e a very 

 stable material. In experiments with pigeons and rats it appeared that 10 

 mg. of this activated acid contains about 3 y of thiamine hydrochloride. 



'" .Analytical Methods Committee, Anabist 76, 127 (1951). 



'Medical Research Council, Vitamins: .\ Survey of Present Knowledge, p. 313. 

 His Majesty's Stationery Office, London, 1932. 



