GB/T 40998-2021 English PDF (GBT40998-2021)

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GB/T 40998-2021: Determination of hydroxypropyl content in modified starch -- Spectrophotometric method
GB/T 40998-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 67.180.20
CCS X 11
Determination of hydroxypropyl content in modified starch -
Spectrophotometric method
ISSUED ON: NOVEMBER 26, 2021
IMPLEMENTED ON: JUNE 01, 2022
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 Principle ... 4 
4 Reagents and materials ... 4 
5 Instruments ... 5 
6 Operating methods ... 5 
7 Interpretation of results ... 7 
8 Precision ... 7 
Determination of hydroxypropyl content in modified starch -
Spectrophotometric method
1 Scope
This document specifies a spectrophotometric method for the determination of
hydroxypropyl content in modified starch.
This document applies to modified starches containing hydroxypropyl.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this
document and are indispensable for its application. For dated references, only the
edition corresponding to that date is applicable to this document; for undated references,
the latest version (including all amendments) is applicable to this document.
GB/T 601, Chemical reagent - Preparations of reference titration solutions
GB/T 6682, Water for analytical laboratory use - Specification and test methods
3 Principle
The modified starch containing hydroxypropyl is oxidized to form propylene glycol in
concentrated sulfuric acid medium, and propylene glycol is further dehydrated to form
propionaldehyde and propenol. Propionaldehyde and propenol form a purple complex
with ninhydrin in concentrated sulfuric acid medium. By measuring the absorbance of
the complex at 590 nm, obtain hydroxypropyl content through calculation.
4 Reagents and materials
Unless otherwise specified, the reagents used shall be analytical reagents. The water
used for the test shall meet the requirements for class-II water specified in GB/T 6682.
4.1 Sulfuric acid (H2SO4): guaranteed reagent, purity ≥98%, well sealed.
4.2 Ninhydrin hydrate (C9H6O4).
4.3 Sodium hydrogensulfite (NaHSO3).
Weigh 0.05 g ~ 0.10 g of sample, accurate to 0.000 1 g, in a 100 mL volumetric flask;
add 25 mL of sulfuric acid solution (4.7). Heat in a boiling water bath until the sample
dissolves; after cooling, use water to dilute to 100 mL. If necessary, further dilute it, to
ensure that the hydroxypropyl contained in each 100 mL of the sample solution does
not exceed 4 mg; then, dilute the blank starch in the same proportion.
Note 1: When the sample is in a boiling water bath, be careful to prevent the cap of the
volumetric flask from popping out. After the sample is dissolved, it will be a
clear and transparent solution. If there is turbidity or there is starch on the wall
of the volumetric flask, shake the liquid gently and then dissolve it in a boiling
water bath.
Note 2: Blank starch refers to the starch that is extracted by physical methods and not
modified. Preference is given to selecting the unmodified starch corresponding
to the sample by physical extraction.
6.3 Determination
6.3.1 Take 1 mL of each of the standard series working solutions (6.1.2); transfer them
into 25 mL graduated test tubes with stoppers respectively; place the test tubes in an
ice-water bath; add 8 mL of sulfuric acid (4.1) dropwise accurately and slowly. After
mixing, accurately heat in a boiling water bath for 3 min; then, immediately move the
test tube into an ice-water bath to cool down. Carefully add 0.60 mL of ninhydrin
hydrate solution (4.5) along the wall of the test tube; shake it up immediately; keep it
in a water bath at 25 °C for 100 min. Use sulfuric acid (4.1) to dilute the volume to 25
mL in each test tube; invert the test tube several times to mix (do not shake); after
standing for 5 minutes, immediately transfer part of the solution into a 1 cm colorimetric
cell of the spectrophotometer; measure the absorbance value at 590 nm; draw a standard
curve according to the absorbance value.
Note 1: Add 8 mL of sulfuric acid dropwise; accurately measure the volume and add
slowly. The function of adding 8 mL of sulfuric acid for the first time is to
dehydrate propylene glycol to form propionaldehyde and propenyl alcohol;
control the rate of addition; mix from time to time to prevent side reactions.
Note 2: Use sulfuric acid to fix the volume in each test tube to 25 mL; at this time, add
sulfuric acid along the wall of the tube; invert the test tube to mix, to prevent
damage to the complex formed by propionaldehyde, propenyl alcohol and
ninhydrin.
Note 3: Sulfuric acid should be sealed in time after use to prevent changes in purity
from affecting the measured value.
Note 4: "Accurate heat in the boiling water bath for 3 minutes", the boiling water bath
time is strictly controlled to ensure uniform heating; if there are multiple
samples or parallel, ensure that the boiling water bath time for each test tube