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GB/T 5009.123-2003 PDF in English


GB/T 5009.123-2003 (GB/T5009.123-2003, GBT 5009.123-2003, GBT5009.123-2003)
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GB/T 5009.123-2003: PDF in English (GBT 5009.123-2003)

GB/T 5009.123-2003
GB/T5009.123-2003
GB
ICS 67.040
C 53
NATIONAL STANDARD
OF THE PEOPLE’S REPUBLIC OF CHINA
Replacing GB/T 14962-1994
Determination of chromium in foods
ISSUED ON. AUGUST 11, 2003
IMPLEMENTED ON. JANUARY 01, 2004
Issued by.
Ministry of Health of the People’s Republic of China;
Standardization Administration of the People’s Republic of
China.
Table of Contents
Foreword ... 3 
1  Scope ... 4 
2  Principle ... 4 
3  Reagents ... 4 
4  Instruments ... 4 
5  Analysis Procedures ... 5 
6  Result calculation ... 6 
7  Precision ... 6 
8  Principle ... 7 
9  Reagents ... 7 
10  Instruments ... 8 
11  Analysis procedure ... 8 
12  Result calculation ... 9 
13  Precision ... 9 
Foreword
This Standard replaces GB/T 14962-1994 Method for determination of chromium in foods.
Compared with GB/T 14962-1994, main changes of this Standard are as follows.
— Change the Chinese name of standard to Determination of chromium in foods;
— Revise the structure of previous standard according to GB/T 20001.4-2001 Rules
for drafting standards - Part 4. Methods of chemical analysis.
This Standard was proposed by and shall be under the jurisdiction of Ministry of Health of
the People’s Republic of China.
The responsible drafting organizations of method I of this Standard. Hebei Sanitation and
Anti-epidemic Station, Henan Food Hygiene Supervision and Inspection Institute, West
China Medical University, and Nanjing Railway Medical College.
The responsible drafting organizations of method II of this Standard. West China Medical
University and Institute of Nutrition and Food Hygiene, and Chinese Academy of
Preventive Medicine.
The chief drafting staffs of method I of this Standard. Zhang Xinmian, Wang Huaizhou, Li
Fasheng, Tian Yongbi, and Jiang Zhaokun.
The chief drafting staffs of method II of this Standard. Wang Guangjian, Tian Yongbi, and
Wang Huaizhou.
Previous standard was issued in 1994. This version is the first revision.
Determination of chromium in foods
1 Scope
This Standard specifies the content of chromium in foods which is determined by graphite
furnace atomic absorption spectrometry (GFAAS) and oscilloscope polarography method.
This Standard is applicable to the determination of total chromium in all kinds of foods.
Detection limit of this Standard. GFAAS is 0.2ng/mL; oscilloscope polarography method is
1ng/mL.
First method Graphite Furnace Atomic Absorption Spectrometry (GFAAS)
2 Principle
After digestion, the sample is dissolved by deionized water and diluted to certain volume.
Absorb appropriate amount of liquid sample into graphite furnace atomizer to atomize.
Under the parameters of selected instrument, chromium absorbs the resonance line with
wavelength of 357.9nm; the absorbance is in proportion to content of chromium.
3 Reagents
3.1 Nitrate.
3.2 Perchloric acid.
3.3 Hydrogen peroxide.
3.4 1.0mol/L nitrate solution.
3.5 Chromium standard solution. Dissolve 1.4135g of guaranteed reagent dichromate
(baked at 110 °C for 2 h) in water. Dilute with water to 500mL. This solution contains
1.0mg/mL chromium and is the standard stock solution. When using, dilute it with 1.0mol/L
nitrate into standard solution with 100ng/mL chromium.
4 Instruments
Soak the glassware and teflon inner-barrel of high-pressure digestion tank in hot
hydrochloric acid (1+1) for 1h. Use hot nitrate (1+1) to soak for 1h. Then use water to rinse
thoroughly before each use.
4.1 Atomic absorption spectrophotometer
refrigerator for long-term storage.
9.7.2 1×10-3 mol/L α,α’-bipyridine solution.
Absorb 10.0mL of 1×10-2 mol/L α,α’-bipyridine solution. Add water to dilute to 100mL. Mix
well.
9.8 6 mol/L sodium nitrite solution.
Weigh 41.4g of sodium nitrite (AR) to dissolve in water. Add water to dilute to 100mL. Mix
well. Store in refrigerator.
10 Instruments
10.1 Oscillographic polarograph.
10.2 Voltage-regulated and temperature-control electric hot plate.
11 Analysis procedure
11.1 Accurately weigh 1g~2g of representative sample into a 150mL conical flask. Add
3.0mL of sulfuric acid and 20mL~30mL of hydrogen peroxide. Place on the electric hot
plate. Heat and digest them at 160°C~200°C until they are in colorless and transparent
solution (if necessary, it may add hydrogen peroxide). Continue to heat until hydrogen
peroxide is completely decomposed and sulfur trioxide (SO3) smoke appears in flask.
Take down to cool. Add 10mL of water and 2 drops of thymol blue indicator. Neutralize it
with 1mol/L sodium hydroxide until the solution just turns to blue. Additionally add 20
drops. Add 2mL of hydrogen peroxide. Heat to dissolve on hot plate at 160°C~200°C.
After most of hydrogen peroxide is decomposed, add 10 drops of 0.5% potassium iodide
solution. Continue to heat until hydrogen peroxide is completely decomposed. Take down
to cool. Use water to transfer into a 50mL volumetric flask. Dilute to scale. Take 5.0 mL of
this solution and place into a 25mL colorimetric tube for analysis. Meanwhile, make
digestion blank.
11.2 Standard curve
Respectively add 0.00, 0.20, 0.50, 1.00, 2.00, 3.00 and 4.00 mL of standard application
solution (equivalent to 0.00, 0.02, 0.05, 0.10, 0.20, 0.30 and 0.40 µgCr) into 25mL
colorimetric tubes. Respectively add 1.0mL of 5.4mol/L sulfuric acid, 1 drop of thymol blue
indicator. Neutralize them with 10 mol/L sodium hydroxide until the solution just turns to
blue. Additionally add 2 drops. Mix well.
11.3 Determination
In sample and standard series tubes, respectively add 2.5mL of ammonia-ammonium
chloride buffer solution, 1.0mL of 1×10-3 mol/L α,α’-bipyridine solution, and 1.0mL of 6
mol/L sodium nitrite solution. Dilute to 25mL. Mix well. On oscillographic polarograph, use
three-electrode, cathodic, original potential -1.2V to read the peak height of second
derivative peak of chromium polarographic peak.
12 Result calculation
The result shall be calculated according to Formula (2).
Where.
X — The content of chromium in sample. Unit is [mg/kg(mg/L)];
A — The content of chromium in sample digestive liquid. Unit is µg;
V1 — The total volume of sample digestive liquid. Unit is mL;
V — The volume of sample digestive liquid for determination. Unit is mL;
m — The mass or volume of sample. Unit is [g(mL)].
13 Precision
Under the repeatability condition, the absolute difference of two independent determined
results shall not be over 15% of arithmetic mean.
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Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.