ISO 11216 pdf download.Modified starch — Determination of content of carboxymethyl groups in carboxymethyl starch
1 Scope
This International Standard specifies a method for the determination of the content of carboxymethyl groups in carboxymethyl starch. The method is suitable for determining carboxymethyl group contents between 1 ,6 % ( m / m ) and 1 0,0 % ( m / m ).
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of the publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on the International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 1 666:1 996, Starch — Determination of moisture content — Oven-drying method. ISO 3696:1 987, Water for analytical laboratory use — Specification and test methods.
3 Definition
For the purposes of this International Standard, the following definition applies. 3.1 carboxymethyl group content mass of carboxymethyl groups in the acid form divided by the mass of the test portion of carboxymethyl starch in the acid form NOTE The carboxymethyl group content is expressed as a percentage by mass.
4 Principle
The carboxymethyl groups are converted into the acid form by acidifying a solution or a suspension of the starch with hydrochloric acid. After the starch is precipitated with methanol, it is allowed to settle before being filtered off on a sintered glass crucible. The excess acid is completely removed by washing with methanol. The starch is dried and a weighed portion is treated with a measured excess of sodium hydroxide solution. The sodium hydroxide not used by the sample is back-titrated with hydrochloric acid.
5 Reagents and materials
Use only reagents of recognized analytical grade. 5.1 Water, complying with at least grade 3 in accordance with ISO 3696. The water shall be free from carbon dioxide. 5.2 Methanol, 1 00 %. 5.3 Hydrochloric acid, c (HCl) = 4 mol/l. 5.4 Sodium hydroxide solution, c (NaOH) = 0,1 mol/l, free from carbon dioxide. 5.5 Phenolphthalein solution, in ethanol 90 % ( V/V ), r(phenolphthalein) = 1 0 g/l. 5.6 Dilute hydrochloric acid, c (HCl) = 0,1 mol/l. 5.7 Sodium chloride.
6 Apparatus
Usual laboratory apparatus and, in particular, the following. 6.1 Beakers, of capacity 1 50 ml. 6.2 pH meter. 6.3 Mechanical stirrer, capable of high shear, and being explosion proof. 6.4 Beakers, of capacity 500 ml. 6.5 Crucibles, sintered glass, 40 ml volume, porosity P40 (pore size index 1 6 µm to 40 µm). 6.6 Drying oven, capable of being maintained at a temperature of 40 °C ± 2 °C, provided with air ventilation and being explosion proof. 6.7 Pestle and mortar. 6.8 Sieve, 800 µm. 6.9 Blade mill. 6.10 Magnetic stirrer.
7 Sampling
It is important that the laboratory receive a sample which is truly representative and has not been damaged or changed during transport or storage. Sampling is not part of the method specified in this International Standard.
8 Preparation of test sample
Sieve the laboratory sample through the 800 µm sieve (6.8). If the material does not pass through the sieve, then grind the sample with a blade mill (6.9) until it passes completely through the 800 µm sieve. Homogenize the sample.
9 Procedure
WARNING — Methanol is a key material in this analysis and is used in quite large quantities. Take all necessary safety precautions because of the toxicity and flammability of methanol. Carry out all work in an explosion-proof fume cupboard. All mechanical and electrical equipment used shall be explosion proof. In addition, disposal of waste methanol shall be in accordance with legal requirements. 9.1 Test portion Weigh, to the nearest 1 mg, about 3 g of the prepared test sample into a 1 50 ml beaker (6.1 ). 9.2 Conversion of the carboxymethyl salts Wet the test portion with 3 ml of methanol (5.2) and stir with a spatula until homogeneous. Add 75 ml of water (5.1 ) and stir until fully dispersed. NOTE For highly viscous starch, 6 ml of methanol and 1 00 ml of water can be used to give a solution which can be easily stirred. Acidify this solution with hydrochloric acid (5.3) to pH = 1 using the pH meter (6.2). Stir for 30 min with the stirrer (6.3). 9.3 Precipitation of the acid form Add 300 ml of methanol (5.2) into a 500 ml beaker (6.4). Pour the dissolved test portion solution dropwise into the methanol, while stirring vigorously. NOTE If the test portion is dispersed in 1 00 ml of water (see note in 9.2), then 400 ml of methanol has to be used to precipitate the starch. When addition is complete, continue stirring for one further minute. Cover the beaker and allow to stand for 2 h.