REDUCING SUGARS 297 



0.5% Soluble Starch. 



0.02 N Sodium Thiosulfate. 



PROCEDURE 



1. Pipette 7 lA. of the 0-1.5% sugar soln. into the bottom of a 

 paraffined reaction vessel (page 169). 



2. Add a stirring "fiea" and pipette 10 jul. carbonate buffer into 

 the tube. 



3. Mix the buffer and sugar soln. and add 6 /xl. iodine soln. from 

 the automatic pipette, whose tip is below the surface of the liquid 

 in the tube to prevent evaporation of iodine. 



4. Directly afterward pipette 10 fxl. 1.2 M sulfuric acid into the 

 tube to form a seal across the narrow neck of the tube, and then 

 place another seal of about 10 lA. starch soln. above the acid seal 

 (Fig. 38, page 167). These seals prevent loss of iodine. 



5. Stir the reaction mixture and let stand for 20 min. 



6. Cap the tube and centrifuge for 1 min. at about 1500 R.P.M. 

 to collapse the seals and cause them to mix with the reaction liquid. 



7. Titrate the iodine with 0.02 A^ thiosulfate, using a micro- 

 burette in which mercury is not in contact with the thiosulfate. 



8. Run a control in which water is substituted for sugar soln. 



Heck, Brown, and Kirk Cerimetric Method for Reducing Sugars 



SPECIAL REAGENTS 



14% Sodium Carbonate. Prepare from anhydrous salt. 



1.5% Potassium Ferricyanide. 



10% (by vol.) Suljuric Acid. 



0.01 N Ceric Sulfate. 



0.01 N Ferrous Ammonium Sulfate in 0.1 N Sulfuric Acid. Store 



as directed on page 275. 

 0.0025 M Phenanthroline Ferrous Sulfate. Prepare as described 



on page 275. 



PROCEDURE 



1. Measure soln. of sample containing 1-12 [xg. glucose, or that 

 quantity of other sugar with equivalent reducing power, into a tube 

 (3 mm. inside diameter, 35 mm. long) calibrated at 200 ix\.* 

 * It would be well to simplify this step as indicated on page 165. 



