食物中二氧化硫分析簡介 - uri=govtlab.gov

Briefing Session on Analysis 

of Sulphur Dioxide in Food 

Dr. Jasmine LAU Po-kwan 

Chemist 

Food Safety B Section 

Government Laboratory, HKSAR

Background 

Contents 

Testing Methods 

Findings in 2007 

Proficiency Tests

Cap 132BD 

Background 

Preservatives in Food Regulations 

食物內防腐劑規例 

Preservatives: any substance which is capable of 

inhibiting, retarding or arresting the process of 

fermentation, acidification or other deterioration of food of 

masking any of the putrefaction. 

防腐劑: 指任何能抑制、減慢或遏止食物的發酵、發酸或其 

他變壞過程或能掩蓋食物腐爛徵狀的物質。

FOOD WHICH MAY CONTAIN PRESERVATIVE AND THE NATURE 

AND PROPORTION OF PRESERVATIVE IN EACH CASE 

可含防腐劑的食品及每種食品可含防腐劑的性質及分量 

Specified food 指明食物 Permitted preservatives 

Fruit juice, sweetened or unsweetened 

whether concentrated not 

加糖或不加糖的果汁(不論是否濃縮) 

Pickles, other than pickled olives 

醃製食品,醃製橄 

欖除外 

Dessert, fruit based milk and cream 

甜品及以水果拌製的奶類及忌廉 

准許防腐劑 

Sulphur dioxide 二氧化硫 350 



Parts per million not 

exceeding 

含量不得超逾的百萬分率

Cap 132W 

Background 

Food and Drugs (Composition and Labelling) 

Regulations 

食物及藥物(成分組合及標籤)規例 

If a food consists of or contains sulphite in a concentration 

of 10 parts per million or more, the functional class of the 

sulphite and its name shall be specified in the list of 

ingredients. (L.N. 85 of 2004) 

如食物由濃度達到或超過百萬分之十的亞硫酸鹽組成或含有 

上述濃度的亞硫酸鹽,有關的亞硫酸鹽的作用類別及其名稱 

須在配料表中指明。 (2004年第85號法律公告)

Background – Food categories 

for the analysis of Sulphur Dioxide 

Range of food samples 

Beverage (soft drinks, juices, 

coffee…) 

Pickles or preserved 

food( prune, plum..) 

Fruits (orange, snow pear, 

lemon, watermelon….) 

Sauce (oyster sauces, soya 

sauce, salad dressing…) 

Meat (beef, lamp chop, pork…) 

Etc……

Testing Method: International Standard Methods 

AOAC 975.32 Sulphurous acid in Food Qualitative Test 

AOAC 961.09 Sulphites in Meats Qualitative Test 

AOAC 990.28 Sulphites in Food Optimized Monier- 

Williams Method 

AOAC 990.29 Sulphite (Total) in Foods and 

Beverages 

ISO 5522:1981 Sulphur dioxide in Fruits, 

Vegetables and derived products 

ISO 5523:1981 Sulphur dioxide in Liquid fruit and 

vegetable products 

Flow Injection 

Analysis Method 

Titration Method 

Iodometric titration

Testing Method: 

Methods used by the Government Laboratory 

i) Qualitative Test for Sulphurous Acid in Food using 

AOAC method 975.32 

ii) Qualitative Test for Sulphurous Acid in Meat using 

AOAC method 961.09 

iii) Determination of Sulphur Dioxide by Optimized 

Monier-Williams Method similar to AOAC 990.28 

iv) Determination of Sulphur Dioxide by Flow Injection 

Analysis similar to AOAC 990.29

Qualitative Test for Sulphurous Acid in Food 

Comminute and homogenise the samples 

Place ~25g well blended sample in a 200 mL Erlenmeyer flask. 

Add a small amount of zinc dust and about 3 mL conc. HCl. 

Place a moisten lead acetate paper on the mouth of the flask. 

Positive results are indicated by 

blackening of the lead acetate paper

Standards at diff. conc. level 

Screening results of the Qualitative Test 

0 ppm 

8 ppm 

50 ppm 

Blank samples spiked at diff. conc. level 

0 ppm 

8 ppm 

50 ppm 

Examples of blank samples spiked at diff. conc. level

Qualitative Test for Sulphurous Acid in Meat 


Transfer ~3.5 g ground meat to an impervious white surface 

Add 0.5 mL malachite green solution to the sample and mix vigorously 

with a spatula 

Observe the colour after a few mins 

Malachite green solution: Dissolve 200 mg 

malachite green in water and dilute to 1 L

Screening results of the Qualitative Test 

Standards at diff. conc. level 

50 ppm 

8 ppm 

0 ppm 

Blank samples spiked with diff. conc. level 

50 ppm 

8 ppm 

0 ppm 

Malachite green is 

decolourised in the 

presence of sulphites 

Normal meat becomes 

blue-green

Determination of Sulphur Dioxide 

by Optimized Monier-Williams Method 

Homogenise the whole submitted sample thoroughly 

Weigh accurately 25g sample into a three necked 1L round 

bottomed flask 

Add about 400 mL water-ethanol mixture (95:5 v/v) to the flask 

with further addition of 2 drops of anti-foaming agent for carrying 

out the distillation 

For dried herbal or dehydrated sample, 

soak the homogenised sample with the 

ethanol-water for 1 hour prior the 

analysis

Connect a gas inlet tube for the introduction of N 2 

Add 30 mL 3% H 2 O 2 solution to a collection vessel and add a few drop of 

methyl red to the solution for trapping the distillate (SO 2 ) 

Add HCl into flask and start heating the solution for about 100 minutes 

Collect the distillate for titration analysis 

The introduction of a steady N 2 flow is 

important!

Determination of Sulphur Dioxide by Titration 

Titrate the distillate with pre-standardised 0.01M NaOH solution to the 

yellow point of methyl red 

Record the volume of NaOH used

Determination of Sulphur Dioxide content by 

barium sulphate gravimetric method 

Add 5 mL 10% BaCl 2 solution to the titrated content of the vessel 

Filter the white precipitate 

Dry the filter at 105 to 110°C and weight the resulted barium 

sulphate

Determination of Sulphur Dioxide 

in Food by Flow Injection Analysis 


Weigh 10g sample in 50 mL centrifuge tube 

Add 30-50 mL TCM extraction solution 

~ 2 mL Carrez solutions to the centrifuge tube 

(solid and semi-solid sample only) 

• Shake and sonicate for ~10 mins respectively 

Sodium tetrachloromercurate (TCM) extraction solution, 0.04M Hg: 

Dissolve 4.70g NaCl, 10.90 HgCl 2 and 6.80g KH 2 PO 4 in 1L Milli-Q water 

Carrez Solution 1: 10.6 g potassium ferrocyanide (II) (K 4 [Fe(CN) 6 ].3H 2 O) in 100 mL 

distilled water 

Carrez Solution 2: 22.0 g zinc acetate and 3 mL glacial acetic acid in distilled water 

and dilute to 100 mL

Centrifuge the sample at 2000 r.p.m. for 10 mins 

Filter the extract of the test sample 

Repeat the extraction process twice 

Centrifuge the solution at 2000 r.p.m. for 10 mins before injecting the 

solution into the flow inject analyser (FIA) 

•Sample size may be deducted according to the 

nature of the food type 

•Dilution of the extract may be needed for samples 

with suspected high concentration 

•The method is not applicable to any dehydrated 

samples

• Pump speed: 25 s 

• Cycle period: 200 s 

Setup of the Flow Injection Analysis 

• Injection of sulphuric acid is suggested 

between samples injections

FIA spectrum of sulphur dioxide 

•The degree of decoloration of the malchite 

green is ∝ the amount of sulphite in the 

sample solution

Reporting Limits 

Quantitation of SO 2: 

8 mg/kg 

PCB

Total samples: 2,075 

No. of positive samples: 180 

Findings in 2007 

Types of samples No. of 

Positive samples 

Concentration range found 

Cakes, bread 2 21 ppm to 150 ppm 

Meat products, fresh, frozen 45 10 ppm to 5,500 ppm 

Preserved fruits and 

vegetables 

125 10 ppm to 9,500 ppm 

Sauces 1 52 ppm 

Seeds, nuts and their 

products 

1 15 ppm 

Sugar confectionery 6 10 ppm to 1,000 ppm

• Identification and assay 

determination 

• Reference Procedures 

can be obtained from 

Food Chemcials Codex 

JECFA specification 

Standards Validation 

http://www.fao.org/ag/agn/jecfa-additives/search.html?lang=en

FAPAS 

Proficiency Test 

http://www.fapas.com 

Proficiency Test Start Date Matrix Analytes 

T2740 31/10/2008 Jam -sulphites 

T2055 07/08/2008 Meat -sulphur dioxide

Proficiency Test 

LGC Standards Proficiency Testing Group 

http://www.lgcpt.com/ 

QBS 

QUALITY IN BEVERAGES SCHEME Scheme 

•Next Dispatch Date will be on 02 Sept 2008 

QFCS 

QUALITY IN FOOD CHEMISTRY SCHEME 

•3 distributions per annum 

•Next Dispatch Date will be on 29 July 2008 

SODAS 

SOFT DRINKS PROFICIENCY TESTING SCHEME 

•Scheme operates from October to September each year and test materials are 

distributed quarterly . 

•Next Dispatch Date will be on 07 Apr 2008

THANK YOU

食物中二氧化硫分析簡介 - uri=govtlab.gov

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