588 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Estimation of Glucose in Blood. 



The exact determination of glucose in small quantities of blood (1-2 c.c. 

 and less) is a problem of some difficulty ; numerous adaptations of the methods 

 of estimating glucose after removal of the protein have been tried. The various 

 processes have been tested by A. D. Gardner and H. Maclean l who recom- 

 mend the removal of protein by precipitation with colloidal iron solution and 

 the estimation of the glucose by a modified Bertrand procedure. 



Maclean 2 has improved the method of removing protein from blood by 

 means of colloidal iron and has adopted a simpler and more convenient method 

 of estimating the glucose. This method depends on the formation of cuprous 

 iodide on acidifying an alkaline solution containing copper sulphate, iodide 

 and iodate after being boiled with glucose. This solution is titrated before 

 and after reduction with 'oc^N thiosulphate. The first result gives the total 

 iodine content, the second the amount of iodine not in combination as cuprous 

 iodide : the difference gives the amount of iodine in combination with reduced 

 copper from which the amount of glucose is determined. Maclean has 

 published a table giving the amounts of glucose corresponding to the amount 

 of thiosulphate which is required for the cuprous iodide. 



The reagents and apparatus required are : 



(1) Dialysed iron, free from acid, of sp. gr. not under 1*045. 



(2) s per cent, phosphoric acid solution. 



(3) Saturated aqueous solution of sodium sulphate. 



(4) Alkaline copper iodine solution : 



Potassium bicarbonate 20 gm. 



Potassium carbonate 10 gm. 



Copper sulphate (exactly 5 per cent, aqueous solution) 15 c.c. 



Potassium iodide i gm. 



Potassium iodate exactly OT gm. 

 Distilled water to 100 c.c. 



This is prepared by dissolving the 20 gm. of bicarbonate by gentle heating 

 in 50-60 c.c. of water; the 10 gm. of carbonate are then added. Before 

 the whole of this has dissolved, the 15 c.c. of copper sulphate are gradually 

 added with gentle shaking. After the resulting effervescence has ceased, the 

 volume is nearly made up and any undissolved potassium salt brought into 

 solution by gentle heating, if necessary. The iodide and iodate are added and 

 the volume made up to 100 c.c. 



(5) *oo4N sodium thiosulphate solution : 



This must be prepared fresh daily from -iN solution, which can be kept 

 in the dark for a comparatively long time. The -iN solution is prepared by 

 dissolving 2*4823 gm. of pure sodium thiosulphate Na 2 S 2 O 3 . 5H 2 O in 100 c.c. 

 of water. The thiosulphate crystals are purified by grinding up the pure salt 

 with alcohol, filtering, treating with ether and drying in the air. 



(6) Starch solution : 



i gm. of soluble starch is dissolved in 100 c.c. boiling water and cooled. 



(7) Pure hydrochloric acid of sp. gr. IT 6. 

 Conical flasks of 100 c.c. 



Condenser from which the lower part of projecting inner tube has been 

 cut off, or test tube fitted with glass tubing for the circulation of cold water. 



(8) Filter papers about 1 5 cm. in diameter. 



(9) Pieces of washed and dried calico 6-8 inches square. 



(10) Funnels. 



^iochem. J., 1914, 8, 391. *J. Physiol., 1916, 50, 168. 



