ISI 10-2e Determination of Carboxyl Groups in Starch

ISI 10-2e Determination of Carboxyl Groups in Starch


1. ScopeThe method is applicable to oxidised starchLT 18. Dec. 1964
Rev. LT 15. marts 1998
2. PrincipleCarboxyl groups are titrated by the Paste Titration Method

 

3. Apparatus3.1 Analytical balance weighing to the nearest 0.1 mg.
3.2 Shaking boiling water bath.
3.3 Büchner funnel 55 mm
4. Reagents4.1 Hydrochloric acid 0.1 N
4.2 Sodium hydroxide 0.1 N
4.3 Phenolphthalein: 1 g in 1 litre ethanol 90%
4.4 Silver nitrate, 0.1%

 

5. ProcedureWeigh 5 g (w) sample to the nearest 0.1 mg in a 100 ml beaker

 Conversion

Add 25 ml hydrochloric acid (4.1) and stir for 1/2 hour.Use magnetic stirrer

 Washing

Filter on filter (3.3) or glass crucible. Flush beaker and filter with water until filtrate is free of chloride - test with silver nitrate (4.4)Increase hydrolysis parameters if flux too low

 Gelatinising

Slurry filter cake with 300 ml distilled water in beaker. Place beaker in boiling water bath (3.2) for 15 min. Stir

Titration

Titrate with (4.2) and (4.3) while still hot.

V = ml (4.2). N = normality of (4.2)

 

 To pH 8.3
6. CalculationCalculate carboxyl content of sample by averaging results of two samples with two decimals.

COOH % = (100 N V M ) / (1000 w) - c

Degree of Substitution (DS) = 0.036 x COOH%

Molecular weight of COOH = M = 45

c corrects for lipids and P - see notes

Eventually correct to value on sample dry matter.

 

7. Notesc = approx. 0.1% on dry basis for maize and wheat starch.
c = 0 for wheat and maize starch defatted by Soxhlet extraction		Correction for lipids
c = 3p for potato starch, where p = phosphorous as P %

 

p ~ 0.03 - 0.09%
8. ReferenceISO 11214

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