ANEURINE (thiamine) 



in isobutanol. Maximum fluorescence occurred at pH ii. D. F. 

 Clausen and R. E. Brown ^^ attributed certain of the errors in the 

 thiochrome method to the effect of dissolved oxygen and changes of 

 temperature on the quinine standard generally employed, and advo- 

 cated the use of glass standards and a constant temperature. Certain 

 foodstuffs may contain substances that interfere with the quantitative 

 adsorption of aneurine on Decalso.^i 



An alternative oxidising agent to potassium ferricyanide was 

 suggested by W. I. M. Holman,^^ ^j^q claimed that a saturated solution 

 of mercuric oxide in alkaline potassium chloride solution gave more 

 satisfactory results, especially when applied to Decalso eluates. 



C. A. P. Carbajal,33 instead of estimating the thiochrome fluori- 

 metrically measured the ferrocyanide simultaneously formed by 

 titration with eerie sulphate solution. Little information is available 

 as to the merits of this method, which is claimed to be capable of 

 estimating as little as 5 /xg. of aneurine. 



In addition to ensuring that the conversion of aneurine into thio- 

 chrome is not inhibited or the fluorescence enhanced by the presence 

 of other impurities, satisfactory assays also necessitate the complete 

 extraction of the aneurine from the material being tested with, at the 

 same time, the minimum of substances likely to interfere with the de- 

 velopment of the fluorescence. A large variety of methods exist for 

 extracting aneurine from foodstuffs but, in general, these resolve 

 themselves into extraction with acid, digestion with enzymes or a 

 combination of the two. According to R. G. Booth,^* extraction with 

 acid is as efficient as is enzymic digestion, but most workers appear to 

 prefer the latter method. L. J. Harris and Y. L. Wang ^^ used a 

 combination of takadiastase and papain, whilst takadiastase alone 

 was used by E. C. Slater ^^ for milk and cereal products, by Brown 

 et al.,^"^ who claimed it to be the best of the enzymes for cereal products, 

 and by A. Z. Hodson ^^ for milk. R. T. Connor and G. J. Straub ^^ 

 digested the material for one hour with dilute sulphuric acid and then 

 incubated with clarase. 



The thiochrome method can also be used for the estimation of 

 aneurine pyrophosphate (cocarboxylase), and it is possible to obtain 

 an estimate of the free and combined aneurine in the same solution. 

 On oxidation with ferricyanide, aneurine pyrophosphate and ortho- 

 phosphate give derivatives insoluble in isobutanol, 22 but by incubation 

 with a kidney phosphatase preparation, both esters are converted 

 into free aneurine, which can then be estimated by conversion to 

 thiochrome. H. G. K. Westenbrink and B. C. P. Jansen *^ used a 

 different method for the fluorimetric estimation of aneurine pyro- 

 phosphate ; after oxidation with ferricyanide, they evaluated the 

 fluorescence in the isobutanol layer to estimate the free aneurine, and 



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