ISI 14-2e Determination of Acetyl Content

1. Scope	The method is applicable to acetylated starch	KM Rev. LT 14 Sep 1999
2. Principle	Bound acetyl reacts with strong alkali and excess alkali is titrated
3. Apparatus	3.1 Burette 3.2 Conical flask, Erlenmeyer 250 ml with stopper
4. Reagents	4.1 Sodium hydroxide 0.1 N 4.2 Sodium hydroxide 0.45 N 4.3 Hydrochloric acid 0.2 N 4.4 Phenolphthalein: 1 g in 1 l ethanol 90%
5. Procedure	Weigh 5 g of sample to the nearest mg. Transfer to conical flask (3.2) and disperse in 50 ml distilled water. Add a few drops of indicator (4.4) and titrate with (4.1) to permanent pink colour.
Bound acetyl reaction	Add 25.0 ml of NaOH 0.45 N (4.2). Stopper and shake vigorously for ½ hour	Use mechanical shaker
Titration	Flush stopper and neck of flask with a little distilled water and titrate excess alkali with 0.2N HCL to disappearance of pink colour.
Blank	25.0 ml 0.45N NaOH (4.2) is titrated as a blank
6. Calculation	Calculate acetyl groups by averaging results of two samples with two significant digits: Acetyl groups % of sample = ((b-s) * N * 0.043 * 100) / w ; where b = ml 0.2 N HCl used to titrate blank s = ml 0.2 N HCl used to titrated sample N = normality of 0.2 N HCL w = weight of sample in g Correct eventually to acetyl groups % of sample dry matter	Molecular weight of CH3CO = M = 43
7. Notes	Alternative determination of acetyl by enzymatic method ISO 11213
8. Reference	JECFA

Methods