Basic Concepts in Clinical Biochemistry-A Practical Guide.7z

the precipitation of cuprous oxide and keeps the cuprous ions in solution. Na 2 CO 3
prevents destruction of sugar by providing the supply of OH ions.

12.4 Reaction

Potassium thiocyanateþCu^2 þ

ðÞblue

!cuprous thiocynate

ðÞwhite ppt

Addition of Na 2 CO 3 also helps to visualize end point, which is the disappearance
of blue color.

12.5 Reagents........................................

1.Benedict’s quantitative reagents:
Sol.A: Dissolve 20 g of sodium citrate, 7.5 g of Na 2 CO 3 , and 1.25 g of potassium
thiocyanate in about 60 ml warm water, and cool the solution.
Sol.B: Dissolve 1.8 g of CuSO 4 in 10 ml of distilled water.

Add solution B to solution A gently with constant mixing. To the resultant solution,
add 5% aqueous solution of potassium ferrocyanide. Make thefinal volume to 1 litre
with distilled water.

2.Na 2 CO 3 anhydrous salt

14.3 Procedure

1. Pipette out 25 ml of Benedict’s quantitative reagent in 100 ml conicalflask. To
   this add 3–4gofNa 2 CO3.


2. Add few glass beads to reduce bumping and bring to a boil.


3. While still in boiling condition, add urine slowly dropwise using the burette, and
   mix the contents by shaking.


4. Add the urine until the blue color changes to white.


5. Note the volume of urine used. Repeat the titration to get concordant values.

12.7 Precautions

1. Add marbles or glass beads to avoid bumping.


2. Sample should be added to boiling reagent slowly with constant shaking.

54 12 Quantitative Analysis of Reducing Sugars in Urine