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International Starch Institute
Science Park Aarhus, Denmark
ISI 10-2e Determination of Carboxyl Groups in Starch
|1. Scope||The method is applicable to oxidised starch||LT 18. Dec. 1964
Rev. LT 15. marts 1998
|2. Principle||Carboxyl groups are titrated by the Paste Titration Method
|3. Apparatus||3.1 Analytical balance weighing to the nearest 0.1 mg.
3.2 Shaking boiling water bath.
3.3 Büchner funnel 55 mm
|4. Reagents||4.1 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. Procedure||Weigh 5 g (w) sample to the nearest 0.1 mg in a 100 ml beaker|
|Add 25 ml hydrochloric acid (4.1) and stir for 1/2 hour.||Use magnetic stirrer|
|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|
|Slurry filter cake with 300 ml distilled water in beaker. Place beaker in boiling water bath (3.2) for 15 min.||Stir|
|Titrate with (4.2) and (4.3) while still hot.
V = ml (4.2). N = normality of (4.2)
|To pH 8.3|
|6. Calculation||Calculate 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. Notes||c = 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. Reference||ISO 11214|
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Keywords: laboratory,method,determination,carboxyl,COOH group,oxidised,starch