296 TITRIMETRIC METHODS 



from a pipette fixed vertically, by raising the tube on a mechanical 

 stand so that the tip and shaft of the pipette pass through the two 

 seals without touching the sides of the tube at any point. 



7. After 5 min. the bromination is complete; then use the "flea" 

 to draw the potassium iodide seal down into the liquid in the bottom 

 of the tube and mix them. 



8. Raise the tube on a stand so that the tip of the burette 

 passes through the starch seal and dips into the bottom liquid 

 without touching the sides of the tube. Add thiosulfate from the 

 burette until the yellow color just disappears. Remove the tube, and 

 with a quick snap of the hand throw the starch seal down into the 

 bottom liquid. Replace the tube in the titration position and con- 

 tinue the titration to the end point. Use a previously titrated sample 

 as a colorless control to facilitate judgment of the end point. 



9. Run blank titrations on the bromine without a lipid sample. 



REDUCING SUGARS 



The iodometric method for the estimation of reducing sugars was 

 adapted by Linderstr0m-Lang and Holter (1933a) to the micro 

 scale. Their procedure has a precision of about 0.06 lA. of 0.05 N 

 thiosulfate, which corresponds to 0.25 /xg. glucose. Holter and Doyle 

 ( 1938) introduced a few alterations in concentration and volume of 

 the reagents and employed a reaction tube with a narrow neck 

 (Fig. 38, page 167), which enabled an increase in precision to 

 0.04 lA. of 0.02 N thiosulfate. 



Heck, Brown, and Kirk ( 1937) adapted the cerimetric method 

 to the determination of reducing sugars with an average accuracy 

 of about ±1%. The cerimetric method was also used by Lewy 

 (1946) for the determination of glucuronic acid. For a colorimetric 

 method see page 210. 



Holter and Doyle Modification of Linderstr0ni-Lang 

 and Holter Iodometric Method for Reducing Sugars 



SPECIAL REAGENTS 



04 M Carbonate Buffer (pH 10.2) . 



0.1 M Iodine in Potassium Iodide. Store in a black bottle connected 

 by a siphon arm to a 6 fA. automatic pipette (Fig. 60, page 175). 

 1.2 M Sulfuric Acid. 



