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GB 5009.123-2014 PDF in English


GB 5009.123-2014 (GB5009.123-2014) PDF English
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GB 5009.123-2014: PDF in English

GB 5009.123-2014
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National Food Safety Standard - Determination of
chromium in foods
ISSUED ON: JANUARY 28, 2015
IMPLEMENTED ON: JULY 28, 2015
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 Instruments and apparatuses ... 5 
5 Analysis steps ... 6 
6 Description of the analysis result ... 7 
7 Precision ... 8 
8 Others ... 8 
Appendix A Reference conditions of sample determination ... 9 
National Food Safety Standard - Determination of
chromium in foods
1 Scope
This Standard specifies the graphite furnace atomic absorption spectrometry
method for the determination of chromium in foods.
This Standard applies to the determination of chromium in various foods.
2 Principle
After the sample is digested, use the graphite furnace atomic absorption
spectrometry to measure the absorption value at 357.9 nm; compare the
absorption value with the standard series solution within a certain concentration
range.
3 Reagents and materials
Note: Unless otherwise specified, the reagents which are used in this method
are all guaranteed reagents; the water is grade-II water that is specified
in GB/T 6682.
3.1 Reagents
3.1.1 Nitric acid (HNO3).
3.1.2 Perchloric acid (HClO4).
3.1.3 Ammonium dihydrogen phosphate (NH4H2PO4).
3.2 Preparation of reagents
3.2.1 Nitric acid solution (5+95): Measure 50 mL of nitric acid and slowly pour it
into 950 mL of water; mix well.
3.2.2 Nitric acid solution (1+1): Measure 250 mL of nitric acid and slowly pour it
into 250 mL of water; mix well.
3.2.3 Ammonium dihydrogen phosphate solution (20 g/L): Weigh 2.0 g of
ammonium dihydrogen phosphate; dissolve in water; dilute to 100 mL; mix well.
5 Analysis steps
5.1 Pretreatment of the sample
5.1.1 For grains, beans, after removing the impurities, crush them and put them
into clean containers as samples. Seal and mark; the samples shall be stored
at room temperature.
5.1.2 For fresh samples of high moisture content, such as vegetables, fruits,
fish, meat and eggs, directly stir them into homogenate and put them into clean
containers as samples. Seal and mark. The samples shall be kept in the
refrigerator freezer.
5.2 Sample digestion
5.2.1 Microwave digestion
Accurately weigh 0.2 g ~ 0.6 g (accurate to 0.001 g) of the sample in the
microwave digestion tank; add 5 mL of nitric acid; digest the sample according
to the microwave digestion steps (see A.1 for digestion conditions). After cooling,
take out the digestion tank; reduce the acid to 0.5 mL ~ 1.0 mL at 140 °C ~
160 °C on the electric heating plate. After the digestion tank is left cold, transfer
the digestion solution to a 10 mL volumetric flask; use a small amount of water
to wash the digestion tank 2 ~ 3 times; combine the washing solution; use water
to dilute to the mark. Do a reagent blank test at the same time.
5.2.2 Wet digestion
Accurately weigh 0.5 g ~ 3 g of the sample (accurate to 0.001 g) into the
digestion tube; add 10 mL of nitric acid, 0.5 mL of perchloric acid; digest on an
adjustable electric furnace (reference conditions: keep at 120 °C for 0.5 h ~ 1
h; heat up to 180 °C for 2 h ~ 4 h; heat up to 200 °C ~ 220 °C). If the digestive
juice is brown, add more nitric acid to dissolve until white smoke appears; when
the digestive juice is colorless, transparent or slightly yellow, take out the
digestive tube and use water to dilute to 10 mL after cooling. Do a reagent blank
test at the same time.
5.2.3 High pressure digestion
Accurately weigh 0.3 g ~ 1 g of sample (accurate to 0.001 g) into the digestion
inner tank; add 5 mL of nitric acid. Close the inner cover; screw the stainless-
steel jacket tightly; put it in a constant-temperature drying oven; keep it at
140 °C ~ 160 °C for 4 h ~ 5 h. Naturally cool in the box to room temperature;
slowly unscrew the outer tank; take out the digestion inner tank; place it on the
adjustable electric heating plate at 140 °C ~ 160 °C to reduce the acid to 0.5
mL ~ 1.0 mL. After cooling, transfer the digestion solution to a 10 mL volumetric
Where:
X -- content of chromium in the sample, in milligrams per kilogram (mg/kg);
c -- content of chromium in the working sample solution, in nanograms per
milliliter (ng/mL);
c0 -- content of chromium in the blank solution, in nanograms per milliliter
(ng/mL);
V -- total volume of the sample digestion solution at a constant volume, in
milliliters (mL);
m -- sample weighing amount, in grams (g);
1 000 -- conversion coefficient.
When the analysis result is ≥1 mg/kg, retain three significant digits; when the
analysis result is <1 mg/kg, retain two significant digits.
7 Precision
The absolute difference of two independent test results under repeatability
cannot exceed 20% of the arithmetic mean value.
8 Others
Calculate by the weighing amount of 0.5 g and the constant volume of 10 mL;
the detection-limit of the method is 0.01 mg/kg; the quantitation-limit is 0.03
mg/kg.
......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.