ISO 22590:2020

INTERNATIONAL ISO
STANDARD 22590
First edition
2020-11
Traditional Chinese medicine —
Determination of sulfur dioxide in
natural products by titration
Médecine traditionnelle chinoise — Dosage du dioxyde de soufre dans
les produits naturels par titrage
Reference number
©
ISO 2020
© ISO 2020
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ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Apparatus . 2
5 Reagents . 2
6 Sampling and preservation of samples . 2
6.1 Sampling . 2
6.1.1 Laboratory samples . 2
6.1.2 Sample identification . 2
6.2 Sample preparation and preservation . 3
6.2.1 Sample preparation . 3
6.2.2 Sample preservation . 3
7 Test method . 3
7.1 T est procedure . 3
7.2 Calculation . 4
Annex A (informative) Reference of national, regional and organizational limits of
sulfur dioxide in food and natural products of traditional Chinese medicine and
calculated limits using target hazard quotients based on USEPA and WHO .6
Annex B (informative) Gas chromatography — Determination of sulfur dioxide in natural
traditional Chinese medicine materials . 9
Annex C (informative) Analysis of the similarities and differences of acid-base titration
in different countries .10
Bibliography .13
Foreword
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This document was prepared by Technical Committee ISO/TC 249, Traditional Chinese medicine.
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iv © ISO 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 22590:2020(E)
Traditional Chinese medicine — Determination of sulfur
dioxide in natural products by titration
1 Scope
This document specifies the determination method of sulfur dioxide in natural products used in
traditional Chinese medicine, which includes the requirements of the device, chemicals, operational
procedures and formula.
It is applicable to natural products of traditional Chinese medicine, including Chinese materia medica
(whole medicinal materials) and decoction pieces derived from plants or animals.
It is not applicable to minerals used in traditional Chinese medicine.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
sulfur dioxide
toxic gas with a pungent, irritating odour, the chemical compound with the formula SO
3.2
sulfur dioxide residue
sulfur dioxide that remains in or on a natural product
Note 1 to entry: Sulfur dioxide residue is expressed as mg/kg.
3.3
maximum residue limit
MRL
highest level of sulfur dioxide that is permitted in or on a natural product
Note 1 to entry: Maximum residue limit is expressed as mg/kg.
3.4
acceptable daily intake
ADI
estimate of the amount of sulfur dioxide in natural products that can be safely consumed daily over a
lifetime without adverse health effects
Note 1 to entry: ADI is expressed in milligrams of the sulfur dioxide, as it appears in the natural products, per
kilograms of body mass per day (mg/kg/day).
3.5
acid-base titration
determination of the concentration of an acid or base by exactly neutralizing the acid or base with a
base or acid of known concentration
4 Apparatus
4.1 Glass sample, cleaned thoroughly before use.
4.2 Electronic balance, with a minimum reading of 0,1 mg.
4.3 Separatory funnel, with a capacity of 50 ml or 100 ml.
4.4 Round-bottom flask, with a capacity of 500 ml or 1 000 ml.
5 Reagents
All reagents shall be of recognized chromatographic grade or analytical purity. Distilled water or water
of equivalent purity or above, recently boiled, shall be used.
5.1 Distilled water.
5.2 Bromophenol blue, 1 g/l solution of bromophenol blue in ethanol (20 % volume fraction).
5.3 Hydrochloric acid, 6 mol/l solution of diluted hydrochloric acid. Dilute one volume of concentrated
hydrochloric acid.
5.4 Hydrogen peroxide, 3 % volume fraction solution of diluted hydrogen peroxide, free from
sulfate ions.
5.5 Sodium hydroxide, 0,1 mol/l solution of sodium hydroxide (standard volumetric solution).
6 Sampling and preservation of samples
6.1 Sampling
6.1.1 Laboratory samples
Raw material samples received by the laboratory shall be accompanied with complete information such
as the source and time of collection of the samples. The samples for testing can include Chinese materia
medica (whole medicinal materials) and decoction pieces derived from plants or animals.
6.1.2 Sample identification
When a sample is received, it shall be immediately assigned a unique label which will accompany it
through all stages of the analysis to the reporting of the results. Samples shall be subject to the
appropriate disposal review system and all records shall be accurately kept.
2 © ISO 2020 – All rights reserved

6.2 Sample preparation and preservation
6.2.1 Sample preparation
Before testing, the sample shall be dried and powdered. Samples shall be pre-treated as soon as possible
and stored in a cool and dry place – if possible, in a refrigerator.
6.2.2 Sample preservation
If samples cannot be analysed immediately, they shall be stored in a cool and dry place, away from the
direct sunlight, and analysed within a few days.
7 Test method
7.1 Test procedure
a) Introduce 150 ml of water into the flask (see Figure 1, key 1), open the condenser pipe (key 3) and
pass carbon dioxide through the whole system for 15 min at a rate of 100 ± 5 ml/min. To 10 ml of
diluted hydrogen peroxide solution add 0,15 ml of a 1 g/l solution of bromophenol blue in ethanol
(20 % volume fraction).
b) Add 0,1 M sodium hydroxide until a violet-blue colour is obtained, without exceeding the end point.
c) Place the solution in the test tube (key 4). Without interrupting the stream of carbon dioxide,
remove the funnel (key 2) and introduce through the opening into the flask 25,0 g of the prepared
sample, with the aid of 100 ml of water.
d) Replace the funnel.
e) Close the tap of the funnel
...