VITAMINS AND HORMONES 163 



VITAMINS 



Vitamin C yields an anodic wave and this has been used for determination 

 of the vitamin but the oxidised form is not reducible at the dropping electrode. 



Lingane and Davis have obtained some interesting results with the vitamin B 

 group. Half-wave potentials (with the saturated calomel electrode as the reference 

 value) in 0-lN KC2 or 0"1M tetramethyl ammonium bromide were as follows : — 



Kiboflavin -0-35 v. 



Thiamin 

 Nicotinic acid 

 Pyridoxin . . . 

 Pantothenic acid 



-1-25 

 -1-7 

 -1-8 

 -2-0 



Anomalies in the case of riboflavin have been ascribed to the presence of surface 

 inactive tautomers. Brdicka (1941, 1942), has studied the polarographic behaviour 

 of riboflavin. 



SEX HORMONES 



Sex hormones containing a double bond conjugated with the ketone group 

 (CH : CH.C : 0) give a wave at — 1 -7 volts, the height of the wave being proportional 

 to the hormone concentration. These experiments were conducted in 90 per cent, 

 ethyl alcohol containing lithium chloride. The half- wave potential of cholestenone 

 in ammonium chloride solution is — 1-25 volt (versus normal calomel electrode) 

 (Adkins and Cox, 1938.) 



It has been shown by Wolfe, Hershberg and Fieser (1940), that 17-ketosteroids 

 treated with tetramethylammonium acethydrazide chloride (Girard T reagent) give 

 hydrazides with a characteristic polarographic wave (half- wave potential at — 1-4 

 volts). This has been used for the determination of urinary ketosteroids (Barnett, 

 Henly and Morris, 1946). 



The polarograms of the steroid hydrazones are all similar to that given with the 

 Girard T reagent (with a half- wave potential at about — 1 -3 volt) except in the case 

 of sulphur-containing analogues which have a lower potential (Barnett and Morris, 

 1946). 



FISCHER TITRATION METHOD FOR WATER DETERMINATION 



The Fischer (1935) reagent provides a convenient method for the determination 

 of small amounts of water. In an anhydrous solvent iodine and sulphur dioxide do 

 not react, but when water is added reaction occurs : — 



2H2O + SO2 + I2 = H2SO4 + 2HI 



pyridine is added to combine with the acids formed and the reagents are dissolved 

 in anhydrous methyl alcohol. Excess of the Fischer reagent is generally added to the 

 liquid which contains water and the excess of reagent is back titrated with a standard 

 solution of water. The end point can be determined potentiometrically (Carter and 

 Williamson, 1945). Two bright platinum electrodes are immersed in the liquid and a 

 small potential difference is applied. The small current flowing between the elec- 

 trodes remains constant during the titration whilst there is any moisture present, but 

 rises suddenly directly there is excess of reagent. In the alternative method involving 



