Estimation of Reducing Sugar by Somogyi’s Method
Reagents Required
- Copper reagent: Dissolve the following substance in water and make up 1 liter with distilled water and filter.
(i) Anhydrous sodium phosphate or disodium hydrogen phosphate 28 gms (or) 71 gms, respectively.
(ii) Sodium potassium tartrate-40 gm.
(iii) 1N KOH–5.6 gms in 100 mL.
(iv) 8% CuSO4–8 gms of CuSO4 in 100 mL.
(v) Anhydrous sodium sulfate 180 mg.
(vi) KI-8 gms.
(vii) 1N KIO3-0.892 gm in 50 mL. - In H2SO4—27.8 mL of H2SO4 in 1 liter.
- Standard glucose solution, dissolve 100 mg in 100 mL of water.
- 0.01 N K2Cr2O7 solution—dissolve 490 mg of K2Cr2O7 in 100 mL of water.
- 1% starch indicator: Make paste from 1 gm soluble starch and 5 mL distilled water, pour the suspension into 100 mL boiling water boil for 1 minute. Cool and pressure by adding a drop of chloroform.
Procedure
Standardization of sodium thiosulfate solution: take 10 mL of 0.01 N K2Cr2O7 in a conical flask to this add 1 gm of KI and half a test tube of dilute H2SO4. One to two drops of starch indicator is then titrated against 0.01 N sodium thiosulfate solution. The end point is blue to colorless. From this 0.005 N sodium thiosulfate is prepared.
Pipette out 0.2 to 1 mL of standard glucose solution into a different test tube until the volume is 2 mL with distilled water. Add 2 mL of Cu-reagent to each and add 2 mL of 1 N H2SO4 to each test tube. Keep it aside for 2–3 minutes and then titrate the liberated iodine against sodium thiosulfate sodium using 1% starch as an indicator. Carry out a blank under the same condition using 2 mL distilled water instead of sugar sodium.
Result:
The given unknown sample contains ................ mg / % of sugar.