GB/T 20373-2021 English PDF (GBT20373-2021)

This Standard specifies the technical requirements, sampling, test methods, inspection rules, marking and quality certificate, packaging, transportation and storage of foliar microelement fertilizer. This Standard applies to foliar fertilizers based on microelements.

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);