ISO 22590:2020 pdf download

ISO 22590:2020 pdf download.Traditional Chinese medicine — Determination of sulfur dioxide in natural products by titration
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 and add 80 ml of dilute hydrochloric acid to the funnel.
f) Open the tap of the funnel to allow the hydrochloric acid solution to flow into the flask, making sure that no sulfur dioxide escapes into the funnel by closing the tap before the last few millilitres of hydrochloric acid solution drain out.
g) Boil for 1 h. Open the tap of the funnel and stop the flow of carbon dioxide as well as the heating and the cooling of the water.
h) Transfer the contents of the test tube with the aid of a little water to a 200 ml wide-necked,conical flask.
i) Heat on a water-bath for 15 min and allow to cool.
j) Add 0,1 ml of a 1 g/l solution of bromophenol blue in ethanol (20 % volume fraction) and titrate with 0,1 M sodium hydroxide until the colour changes from yellow to violet-blue (V 1 ml).
k) Carry out a blank titration (V 2 ml).
NOTE 1 An alternative test method which is validated to be the same as this method can be used (see Table C.1).
NOTE 2 Annex B describes the method of gas chromatography to determine sulfur dioxide in natural products.
NOTE 3 Annex C provides an analysis of the similarities and differences of acid-base titration in different countries.
Different countries, regions and organizations give their own limits of sulfur dioxide in food and natural products of traditional Chinese medicine. Table A.1 shows these limits in various types of food and herbal products. Also, some health authorities provide risk assessment methods [United States Environmental Protection Agency (USEPA)] and recommended sulfur dioxide intake per week [World Health Organization (WHO)]. According to this information and traditional Chinese medicine characteristics, the calculated limits using target hazard quotients (THQ) are listed with the summarized maximum limits from previous references in Table A.1.