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GB/T 5009.18-2003 (GB/T5009.18-2003)

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GB/T 5009.18-2003: PDF in English (GBT 5009.18-2003)

GB/T 5009.18-2003
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 67.040
C 53
Replacing GB/T 5009.18-1996
Determination of fluorine in foods
ISSUED ON: AUGUST 11, 2003
IMPLEMENTED ON: JANUARY 01, 2004
Issued by: Ministry of Health of PRC;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Principle ... 4 
3 Reagents ... 4 
4 Instruments ... 5 
5 Analytical procedures ... 6 
6 Principle ... 8 
7 Reagent ... 9 
8 Instruments ... 9 
9 Analytical procedures ... 10 
10 Principle ... 12 
11 Reagent ... 12 
12 Instruments ... 13 
13 Analytical procedures ... 13 
Determination of fluorine in foods
1 Scope
This standard specifies the method for determination of fluorine in foods such
as grains, vegetables, fruits, beans and their products, meat, fish, eggs.
This standard applies to the determination of fluorine in foods. The fluoride ion
selective electrode method is not suitable for the specimens which have higher
fat content but are not ashed (such as peanuts, fat meat, etc.).
The detection limit of this method is 0.10 mg/kg for the method 1 and 1.25 mg/kg
for the method 2.
Method 1 -- Diffusion-fluorine reagent colorimetry
2 Principle
In the food, the fluoride reacts with the acid in the diffusion box, to generate
hydrogen fluoride gas, which is diffused and absorbed by the sodium hydroxide.
Fluoride ion and lanthanum (III), fluorine reagent (alizarin complexone) form a
blue ternary complex at a suitable pH. The color deepens with the increase of
fluoride ion’s concentration. It is extracted by the amine-containing organic
solvent or not; then compared to the standard series for quantification.
3 Reagents
The water used in this method is deionized water which contains no fluorine.
The reagents are of analytical grade. All reagents are stored in polyethylene
plastic bottles.
3.1 Acetone.
3.2 Silver sulfate-sulfuric acid solution (20 g/L): Weigh 2 g of silver sulfate.
Dissolve it in 100 mL of sulfuric acid (3 + 1).
3.3 Sodium hydroxide-anhydrous ethanol solution (40 g/L): Take 4 g of sodium
hydroxide. Dissolve it in absolute ethanol and dilute it to 100 mL.
3.4 Acetic acid solution (1 mol/L): Take 3 mL of glacial acetic acid. Add water to
4.3 Visible spectrophotometer.
4.4 Acidity meter.
4.5 Muffle furnace.
5 Analytical procedures
5.1 Diffusion monochromatic method
5.1.1 Processing of specimen
5.1.1.1 Cereal specimen: Remove the shell of rice. Remove visible impurities
from other grains. Take 50 g ~ 100 g of representative specimen. Crush it. Make
it pass through a 40 mesh sieve.
5.1.1.2 Vegetables and fruits: Take the edible part. Wash it. Dry it naturally.
Chop it. Mix it uniformly. Weigh 100 g ~ 200 g of specimen. Use blower to dry it
at 80 °C. Crush it. Make it pass 40 mesh sieve. The results are expressed in
terms of fresh weight. Meanwhile it shall determine the moisture.
5.1.1.3 Special specimens (specimens which contain high fat, are not easy to
crush and sieve, such as peanuts, fat meat, fruits with high sugar content, etc.):
Weigh 1.00 g ~ 2.00 g of the ground specimen in crucible (nickel, silver,
porcelain, etc.). Add 4 mL of magnesium nitrate solution (100 g/L). Add sodium
hydroxide solution (100 g/L) to make it alkaline. Mix it uniformly. Immerse it for
0.5 h. Fix the fluorine in the specimen. Then put it in water bath to evaporate it
dry. Then heat and carbonize it until it is smokeless. Put it in a muffle furnace to
ash it at 600 °C for 6 h. After ashing is completed, take it out and allow it to cool.
Take the ash for diffusion.
5.1.2 Determination
5.1.2.1 Take a number of plastic boxes. At the center of the box cover,
respectively add 0.2 mL of sodium hydroxide-anhydrous ethanol solution (40
g/L). Apply it evenly in the circle. Dry it in a 55 °C ± 1 °C incubator to form a film.
Take it out to prepare for use. Or otherwise stick the filter paper (3.14) in the
box.
5.1.2.2 Weigh 1.00 g ~ 2.00 g of the treated specimen in a plastic box. Add 4
mL of water, so that the specimen is evenly distributed and not agglomerated.
Add 4 mL of silver sulfate-sulfuric acid solution (20 g/L). Immediately cover it
tightly. Gently shake it uniformly. If the specimen is ashed, first transfer all the
ash into a plastic box. Use 4 mL of water to wash the crucible clean for several
times. Pour the washing solution into the plastic box. Disperse ash evenly. If
the crucible is not completely cleaned, it may add 4 mL of silver sulfate-sulfuric
The absolute difference between two independent determinations as obtained
under repeatability conditions shall not exceed 10% of the arithmetic mean.
5.2 Diffusion complex color method
5.2.1 Processing of specimen
Same as 5.1.1.
5.2.2 Determination
5.2.2.1 Same as 5.1.2.1
5.2.2.2 Same as 5.1.2.2.
5.2.2.3 Same as 5.1.2.3.
5.2.2.4 Take out the box. Remove the cover. Respectively, use 10 mL of water
to dissolve the sodium hydroxide film in the cover for several times. Use a
dropper to carefully transfer all of it in a 25 mL.
5.2.2.5 In the colorimetric tube with stopper, respectively add 2.0 mL of alizarin
complexone solution, 3.0 mL of buffer solution, 6.0 mL of acetone, 2.0 mL of
lanthanum nitrate solution. Then add water to the mark. Mix it uniformly. Place
it for 20 min. Use a 3 cm cuvette (reference wavelength 580 nm) to adjust the
zero point through the zero tube. Determine the absorbance of each tube. Draw
a standard curve for comparison.
5.2.3 Calculation of results
Same as 5.1.3.
5.2.4 Precision
The absolute difference between two independent determinations as obtained
under repeatability conditions shall not exceed 10% of the arithmetic mean.
Method 2 -- Ashing distillation-fluorine reagent
colorimetry
6 Principle
The fluorine in the specimen is fixed by magnesium nitrate. After ashing at high-
temperature, under acidic conditions, it is distilled to separate the fluorine. The
distilled fluorine is absorbed by the sodium hydroxide solution. The fluorine
immerse it for 0.5 h. Place it on a water bath to evaporate it dry. Then carbonize
it at low-temperature, until it is smokeless. Transfer it into the muffle furnace.
Ash it at 600 °C for 6 h. Remove it. Allow it to cool.
9.3 Distillation
9.3.1 In the crucible, add 10 mL of water. Slowly add a few drops of sulfuric acid
(2 + 1). Prevent the solution from splashing. Neutralize it until no bubbles are
formed. Transfer this solution in a 500 mL distillation flask. Use 20 mL of water
to rinse the crucible for several times. Incorporate it into the distillation flask.
9.3.2 In a distillation flask, add 60 mL of sulfuric acid (2 + 1) and several small
fluorine-free beads. Connect to the distillation device. Heat to distill it. The
distillate is absorbed in a 50 mL beaker which contains 5 mL of water, 7 drops
~ 20 drops of sodium hydroxide solution (100 g/L), 1 drop of phenolphthalein
indicator. When the temperature of solution in the distillation flask rises to
190 °C, stop distillation (the entire distillation time is about 15 min ~ 20 min),
9.3.3 Remove the condenser tube. Use the dropper to add water to rinse the
condenser tube for 3 ~ 4 times. Incorporate the washing solution into the beaker.
Transfer the absorbing solution from the beaker to a 50 mL volumetric flask.
Use a small amount of water to rinse the beaker for 2 ~ 3 times. Incorporate it
into the volumetric flask. Use hydrochloric acid (1 + 11) to neutralize it, until red
color is just disappeared. Use water to dilute it to the mark. Mix it uniformly.
9.3.4 Respectively, pipette 0, 1.0, 3.0, 5.0, 7.0, 9.0 mL of fluorine standard use
solution into a distillation flask. Add water to 30 mL. The following steps are
same as in 9.3.2 and 9.3.3. 10 millimeter of this distilled standard solution
corresponds to 0, 1.0, 3.0, 5.0, 7.0, 9.0 µg of fluorine, respectively.
9.4 Determination
9.4.1 Respectively, pipette 10.0 mL of each of the standard series distillate and
specimen distillate into a 25 mL colorimetric tube with stopper.
9.4.2 Same as the operation of 5.2.2.5.
9.4.3 Calculation of results: The content of fluorine in the specimen is calculated
according to formula (2).
Where:
X - The content of fluorine in the specimen, in milligrams per kilogram
(mg/kg);
(Na3C6H5O7 • 2H2O). Dissolve it in 300 mL of water. Add 14 mL of perchloric
acid. Then add water to dilute it to 500 mL.
11.3 Total ionic strength buffer: Mix equivalent amount of sodium acetate
solution (3 mol/L) and sodium citrate solution (0.75 mol/L). Prepare it before
use.
11.4 Hydrochloric acid (1 + 11): The same as 7.2.
11.5 Fluorine standard solution: The same as 3.12.
11.6 Fluorine standard use solution: Pipette 10.0 mL of fluorine standard
solution into a 100 mL volumetric flask. Add water to dilute it to the mark. Repeat
diluting it as such, until each millimeter of this solution is equivalent to 1.0 µg of
fluorine.
12 Instruments
12.1 Fluoride electrode.
12.2 Acidity meter: ±0.01 pH (or ion meter).
12.3 Magnetic stirrer.
12.4 Calomel electrode.
13 Analytical procedures
13.1 Weigh 1.00 g of specimen which has been smashed and passed through
a 40 mesh sieve. Place it in a 50 mL volumetric flask. Add 10 mL of hydrochloric
acid (1 + 11). Seal and immerse to extract it for 1 h (slightly shake it from time
to time). It shall avoid the specimen from attaching to the wall of flask as
practical as possible. After extraction, add 25 mL total ionic strength buffer. Add
water to the mark. Mix it uniformly. Prepare for use.
13.2 Pipette 0, 1.0, 2.0, 5.0, 10.0 mL of fluorine standard solution (equivalent to
0, 1.0, 2.0, 5.0, 10.0 µg of fluorine). Respectively, place it in a 50 mL volumetric
flask. In each volumetric flask, add 25 mL of total ionic strength buffer and 10
mL of hydrochloric acid (1 + 11). Add water to the mark. Mix it uniformly. Prepare
for use.
13.3 Connect the fluorine and calomel electrodes to the negative and positive
ends of the measuring instrument. Insert the electrode into a 25 mL plastic cup
filled with water. There is an iron stir bar which has a polyethylene tube in the
cup. In the electromagnetic stirring, read the equilibrium potential value. After
replacing the water for 2 ~ 3 times and the potential value is balanced, it may
......
 
(Above excerpt was released on 2019-06-18, modified on 2021-06-07, translated/reviewed by: Wayne Zheng et al.)
Source: https://www.chinesestandard.net/PDF.aspx/GBT5009.18-2003