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GB 5009.244-2016 PDF in English


GB 5009.244-2016 (GB5009.244-2016) PDF English
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GB 5009.244-2016: PDF in English

GB 5009.244-2016
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National food safety standard -
Determination of chlorine dioxide in food
ISSUED ON. AUGUST 31, 2016
IMPLEMENTED ON. MARCH 1, 2017
Issued by. National Health and Family Planning Commission
of the People’s Republic of China
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Principle ... 4
3 Reagents and materials ... 4
4 Apparatus ... 8
5 Analytical procedures ... 8
6 Expression of analytical results ... 10
7 Precision ... 10
8 Others ... 10
Annex A Standard curve of chlorine dioxide ... 11
Foreword
This Standard replaces SN/T 1954-2007, Determination of chlorine dioxide residues in
iced meat for import and export – Spectrophotometric method.
Compared with SN/T 1954-2007, the major technical changes of this Standard are as
follows.
-- it changes test methods and their applicable scope;
-- it adds classification of samples;
-- it changes sample processing conditions;
-- it changes detection limit and adds quantitative limit.
National food safety standard -
Determination of chlorine dioxide in food
1 Scope
This Standard specifies the spectrophotometric method for the determination of
chlorine dioxide in vegetables, fruits, livestock and poultry meat and aquatic products.
This Standard applies to the determination of chlorine dioxide in vegetables, fruits,
livestock and poultry meat and aquatic products.
2 Principle
Use phosphate buffer to extract chlorine dioxide in sample; after refrigerated
centrifugation, use fibre filter paper for filtration; use glycine as the masking agent to
eliminate the false positive interferences of the substances such as Cl2 and ClO-; add
N, N-diethyl-p-phenylenediamine (DPD) colour developing agent for developing with
chlorine dioxide; use the spectrophotometric method to measure the maximum
absorbance at 552 nm to determine the content of chlorine dioxide in food.
3 Reagents and materials
Unless specified otherwise, all reagents used are analytically pure and the water is
grade two water as specified in GB/T 6682.
3.1 Reagents
3.1.1 Glycine (C2H5NO2).
3.1.2 Ethylenediaminetetraacetic acid disodium (EDTA) (C10H14N2Na2O8).
3.1.3 Potassium iodide (KI). purity 99.5%.
3.1.4 Sodium chlorite (NaClO2).
3.1.5 Acetic acid (CH3COOH).
3.1.6 Sulfuric acid (H2SO4).
3.1.7 Anhydrous sodium sulfate (Na2SO4).
3.1.8 Sodium hydroxide (NaOH).
3.1.9 Potassium dihydrogen phosphate (KH2PO4).
3.1.10 N, N-diethyl-p-phenylenediamine (DPD).
3.1.11 Sodium thiosulfate (Na2S2O3).
3.1.12 Soluble starch.
3.1.13 Potassium dichromate (Cr2K2O7).
3.1.14 High-purity nitrogen.
3.2 Preparation of reagents
3.2.1 DPD colour developing agent (1 g/L). weigh 1 g of DPD (3.1.10) to dissolve in
chloride-free grade two water (3.2.2) containing 8 mL of sulfuric acid solution (1 + 3)
and 200 mg of EDTA; use chloride-free grade two water to dilute to 1,000 mL; store in
a brown glass bottle with stopper; store in a dark place.
3.2.2 Oxidizing chloride-free grade two water. add sodium sulfite (3.1.4) in grade two
water; reduce oxidizing chloride to chloride ion (no colour develops when checked
using DPD); carry out distillation. The water obtained is oxidizing chloride-free grade
two water.
3.2.3 Glycine solution (10%). take 10 g of glycine (3.1.1); use water to dissolve; make
up to 100 mL.
3.2.4 Sodium hydroxide solution (2 mol/L). weigh 80 g of sodium hydroxide; use water
to dissolve; make up to 1 L.
3.2.5 Sodium hydroxide solution (0.1 mol/L). weigh 4 g of sodium hydroxide; use water
to dissolve; make up to 1 L.
3.2.6 Sulfuric acid solution (1 mol/L). measure 54 mL of 98.4% sulfuric acid (3.1.6);
slowly add into about 300 mL of distilled water; after cooling, transfer to a volumetric
flask; use about 20 mL of distilled water to wash the container for 3 times; also transfer
the washings to the volumetric flask; use water to make up to 1 L.
3.2.7 Potassium dihydrogen phosphate [c(KH2PO4) = 0.1 mol/L]. use water to dissolve
13.61 g of potassium dihydrogen phosphate solution (3.1.9); make up to 1 L.
3.2.8 Phosphate buffer solution (pH = 6.5). take 500 mL of 0.1 mol/L KH2PO4 and 81
mL of 0.1 mol/L NaOH; use water to dilute to 1 L.
3.2.9 Sodium chlorite saturated solution. take an appropriate amount of sodium chlorite
(3.1.4) to place in a beaker; add a small amount of water; stir to make a saturated
solution (the solubility of sodium chlorite is quite high, so it shall be prepared in
accordance with the amount required).
3.2.10 Preparation of sodium thiosulfate standard solution [c(Na2S2O3) = 0.1000 mol/L].
weigh 16 g of anhydrous sodium sulfate (3.1.7); dissolve in 1 L of water; heat to boil
for 10 min; allow to cool; filter to use after two weeks’ storage in dark.
3.2.11 Calibration of sodium thiosulfate standard solution [c(Na2S2O3) = 0.1000 mol/L].
weigh 0.15 g of benchmark potassium dichromate (3.1.13) dried to constant weight at
120°C, accurate to 0.000 1 g; place into an iodine flask; add 25 mL of water; after
dissolving, add 2 g of potassium iodide and 20 mL of 20% sulfuric acid solution; shake
up; store in dark for 10 min. Add 150 mL of water; use prepared sodium thiosulfate
standard solution (3.2.10) for titration; add 3 mL of starch indicating liquid (5 g/L)
(3.1.12) near the end; continue titration until the solution changes from blue into bright
green. Meanwhile, carry out blank test.
3.2.12 Starch indicator (5 g/L). weigh 5.0 g of starch to place into a beaker of 50 mL;
measure 1 L of distilled water; use several drops to make starch into a paste; then take
about 900 mL of water to heat to slightly boiling when pour the pasty starch in; use the
residual distilled water to wash the beaker of 50 mL for 3 times; pour the washings into
the beaker; then add 1 drop of 10% hydrochloric acid; slightly boil for 3 min.
3.2.13 Starch solution (1%). weigh 1 g of soluble starch; use a small amount of water
to make a paste; use 100 mL of boiling water to dissolve it; heat to boil until clarified.
3.3 Standard substances
3.3.1 Preparation of chlorine dioxide standard stock solution
Add 300 mL of pure water into bottle A; connect the glass at one end of bottle A to air
compressor and another glass tube to bottle B. Bottle B is a high-strength borosilicate
glass bottle with three glass tubes at the opening; the first one is inserted to 5 mm to
the bottom to introduce air; the second is connected with a graduated cylindrical
separating funnel with its lower end stretching to below the liquid level; the lower end
of the third is apart from the liquid level and the upper end is connected with bottle C.
Dissolve 10 g of sodium chlorite in 750 mL of pure water and pour into bottle B; load
20 mL of sulfuric acid solution in the separating funnel. Bottle C is loaded with the
scrubber tower of sodium chlorite saturated solution. Bottle D is a borosilicate glass
receiving flask of 2 L, which contains 1,500 mL of pure water used to absorb the
chlorine dioxide generated; the residual gas is discharged through exhaust pipes. The
whole apparatus is placed in a fuming cupboard. For the generation and absorption
apparatus of chlorine dioxide see Figure 1.
Figure 1 – Generation-absorption apparatus of chlorine dioxide
Start air compressor to make the air pass through the whole apparatus evenly. Add 5
mL of sulfuric acid solution through separating funnel every 5 min. After adding sulfuric
acid solution for the last time, the air flow shall be maintained for 30 min.
Pour the yellow chlorine dioxide stock solution obtained into a brown bottle and store
it in a refrigerator with its stopper on for storage. Its mass concentration is about 250
mg/L ~ 600 mg/L, which is equivalent to 500 mg/L ~ 1,200 mg/L active chlorine (Cl2).
3.3.2 Calibration of chlorine dioxide standard stock solution
Add 100 mL of pure water, 1 g of potassium iodide and 5 mL of acetic acid into an
iodine flask of 250 mL; shake the iodine flask to make potassium iodide fully dissolve.
Add 10.00 mL of chlorine dioxide standard solution before storing in dark for 5 min.
Use sodium thiosulfate standard solution of 0.1 mol/L (3.2.10) for titration until the
solution appears faint yellow; add 1 mL of starch solution; continue titration to the end.
Add the same amount of reagents in accordance with the above-mentioned
procedures (but only chlorine dioxide is not added); use sodium thiosulfate standard
solution for titration until blue disappears; record the amount of blank used.
The concentration of chlorine dioxide standard stock solution is calculated in
accordance with Equation (1).
where.
ρ(ClO2) – the concentration of chlorine dioxide standard stock solution, in mg/mL;
c – the concentration of sodium thiosulfate standard solution, in mol/L;
V1 – the volume of sodium thiosulfate standard solution used for titration of chlorine
dioxide, in mL;
Separating funnel
V0 – the volume of sodium thiosulfate standard solution used for titration of blank, in
mL;
V2 – the volume of chlorine dioxide, in mL;
13.49 – the mass of chlorine dioxide, expressed in mg, which is equivalent to 1.00 mL
of sodium thiosulfate standard solution [c(Na2S2O3) = 0.1000 mol/L] (3.2.10).
3.4 Preparation of chlorine dioxide standard solution
1 mL of the solution contains 0.25 mg of chlorine dioxide (ClO2); in accordance with
the concentration of chlorine dioxide stock solution to be determined, absorb a certain
amount of chlorine dioxide standard stock solution and use chloride-free grade two
water (3.2.2) to dilute. The solution is prepared immediately before use.
4 Apparatus
4.1 Ultraviolet-visible spectrophotometer.
4.2 Homogenizer. ≥ 8,000 r/min.
4.3 Centrifugal machine. ≥ 10,000 r/min.
4.4 Conical flasks with stopper. 100 mL.
4.5 Filter membranes. 0.22 μm.
4.6 Pipettes. 1.0 mL, 2.0 mL, 5.0 mL and 10.0 mL.
4.7 Analytical balance.
5 Analytical procedures
5.1 Sample preparation
Take about 1 kg of representative sample from all sample product; use a masher to
mash sample completely and uniformly; divide sample into two equal parts; load them
in clean containers as test sample. Seal and label.
5.2 Sample preservation
Sample is preserved at below - 18°C. During the operating process of sampling and
preparation, prevent sample from being polluted or residue content changing.
5.3 Extraction
5.3.1 Fruits and vegetables
Weigh 1.00 g (accurate to 0.01 g) of sample to place into a centrifuge tube of 50 mL;
add 20 mL of phosphate buffer solution (pH 6.5) (3.2.8); carry out homogeneous
extraction for 3 min at 8,000 r/min; carry out refrigerated centrifugation in a high-speed
centrifugal machine for 10 min at 10,000 r/min; take out; use fibre filter paper to filter
into a colourimetric tube with stopper of 10 mL for the determination on a
spectrophotometer.
5.3.2 Livestock-Poultry Products and aquatic products
Weigh 1.00 g (accurate to 0.01 g) of sample to place into a centrifugal tube of 100 mL;
add 50 mL of phosphate buffer solution (pH 6.5) (3.2.8); carry out homogeneous
extraction for 3 min at 8,000 r/min; carry out refrigerated centrifugation in a high-speed
centrifugal machine for 10 min at 10,000 r/min; take out; use fibre filter paper to filter
into a colourimetric tube with stopper of 10 mL for the determination on a
spectrophotometer.
5.4 Determination
5.4.1 Plotting of standard curve
Add a certain amount of chlorine dioxide standard using solution to a series of 10 mL
stoppered colourimetric tubes to make the concentrations of all tubes equal to chlorine
dioxide standard solutions of 0.00 mg/L, 0.05 mg/L, 0.10 mg/L, 0.50 mg/L, 1.00 mg/L,
2.00 mg/L and 5.00 mg/L.
Add respectively 1.0 mL of phosphate buffer solution (3.2.8), 1.0 mL of DPD solution
(3.2.1) and 1.0 mL of glycine solution; make up to scale and shake up; within 60 s, use
cuvettes of 1 cm to measure the absorbance at 552 nm; plot standard curve using the
concentration of standard working solution as the abscissa and the response value
(absorbance value) as the ordinate. See Annex A.
5.4.2 Determination of chlorine dioxide in sample
Take 5 mL of filtrate to pour into a stoppered colourimetric tube of 10 mL; add 1 mL of
glycine solution (3.2.3) to the filtrate to mix up; add 1 mL of phosphate buffer solution
(3.2.8) and 1.0 mL of DPD solution (3.2.1); use water to make up to 10 mL and shake
up. Immediately within 60 s, use cuvettes of 1 cm to measure the absorbance at 552
nm; obtain the concentration of chlorine dioxide in accordance with the standard curve.
NOTE. The whole process shall be carried out in dark.
6 Expression of analytical results
The content of chlorine dioxide in sample is calculated in accordance with Equation
(2).
where.
X – the content of ClO2 in sample, in mg/kg;
c – the concentration of ClO2 in sample solution, in mg/L;
c0 – the concentration of ClO2 in reagent blank, in mg/L;
V – the final making-up volume of sample solution, in mL;
m – the mass of sample represented by final sample solution, in g.
The result of calculation is rounded off to the second decimal place.
7 Precision
The absolute difference between two results measured independently under
repeatable conditions shall not be greater than 10% of their arithmetic mean value.
8 Others
The detection limit of the method is 0.65 mg/kg; the quantitative limit of fruits and
vegetables is 2.00 mg/kg; the quantitative limit of meat and aquatic products is 5.00
mg/kg.
Annex A
Standard curve of chlorine dioxide
For the standard curve of chlorine dioxide see Figure A.1.
Figure A.1 – Standard curve of chlorine dioxide
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.