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GB/T 20373-2021 (GB/T20373-2021)

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GB/T 20373-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 67.180.20
CCS X 11
GB/T 20373-2021
Replacing GB/T 20373-2006
Determination of Acetyl Content in Modified Starch -
Titrimetric Method
ISSUED ON: MAY 21, 2021
IMPLEMENTED ON: DECEMBER 1, 2021
Issued by: State Administration for Market Regulation;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative References ... 4 
3 Terms and Definitions ... 4 
4 Principle ... 4 
5 Reagents and Materials ... 4 
6 Instruments ... 5 
7 Methods of Operation ... 5 
8 Result Calculation ... 6 
9 Precision ... 7 
Determination of Acetyl Content in Modified Starch -
Titrimetric Method
1 Scope
This Standard specifies the determination of acetyl content in modified starch through
the titrimetric method.
This Standard is applicable to modified starch that contains acetyl.
2 Normative References
The content of the following documents constitutes indispensable clauses of this
document through normative references in the text. In terms of references with a
specified date, only versions with a specified date are applicable to this document. In
terms of references without a specified date, the latest version (including all the
modifications) is applicable to this document.
GB/T 601 Chemical Reagent - Preparations of Standard Volumetric Solutions
GB/T 603 Chemical Reagent - Preparations of Reagent Solutions for Use in Test
Methods
GB/T 6682 Water for Analytical Laboratory Use - Specification and Test Methods
3 Terms and Definitions
There are no terms and definitions that need to be defined in this document.
4 Principle
Under alkaline conditions (pH 8.5 or higher), modified starch containing acetyl is
saponified by excess alkali. Use a standard hydrochloric acid titration solution to titrate
the remaining alkali. Through conversion, calculate the acetyl content.
5 Reagents and Materials
Unless it is otherwise specified, the used reagents shall be analytically pure. The water
used for tests shall comply with the requirements of Grade-2 water specified in GB/T
6682.
Use 0.10 mol/L sodium hydroxide solution (5.4) to titrate the specimen solution (7.1.1
or 7.1.2) to slightly red, then, add 25.0 mL of 0.45 mol/L sodium hydroxide solution
(5.5); thoroughly shake it and put on the stopper. Under room-temperature conditions,
on a mechanical oscillator, oscillate it for 30 min, or on a magnetic stirrer (6.2), stir it
for 60 min to perform saponification.
7.3 Sample Titration
After the saponification is completed, remove the stopper; use a washing bottle to rinse
the stopper and the wall of the conical flask. Inject 0.20 mol/L standard hydrochloric
acid titration solution (5.6) into the acid burette (6.3); use it to titrate the specimen, until
the pink color vanishes. Record the volume of the consumed standard hydrochloric
acid titration solution as V1.
7.4 Blank Test
7.4.1 Non-pregelatinized modified starch: take 25.0 mL sodium hydroxide solution (5.5)
as a blank; add 50.0 mL of water and 3 drops of phenolphthalein indicator solution
(5.7); shake it well. Inject 0.20 mol/L standard hydrochloric acid titration solution (5.6)
into the acid burette (6.3); use it to titrate the blank, until the pink color vanishes.
Record the volume of the consumed standard hydrochloric acid titration solution as V0.
7.4.2 Pregelatinized modified starch: take 25.0 mL sodium hydroxide solution (5.5) as
a blank; add 5.0 mL of absolute ethanol (5.3), 100.0 mL of water and 3 drops of
phenolphthalein indicator solution (5.7); shake it well. Inject 0.20 mol/L standard
hydrochloric acid titration solution (5.6) into the acid burette (6.3); use it to titrate the
blank, until the pink color vanishes. Record the volume of the consumed standard
hydrochloric acid titration solution as V0.
8 Result Calculation
The mass fraction w0 of acetyl shall be calculated in accordance with Formula (1):
Where,
V0---the volume of the standard hydrochloric acid titration solution consumed by the
blank, expressed in (mL);
V1---the volume of the standard hydrochloric acid titration solution consumed by the
sample, expressed in (mL);
c---the accurate concentration of the standard hydrochloric acid titration solution,
expressed in (mol/L);
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.