PRESIDENT OF THE
COMMITTEE OF SCIENCE AND TECHNOLOGY
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|
SOCIALIST REPUBLIC OF VIETNAM
Independence - Freedom - Happiness
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|
No. 407-QD
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Hanoi, November 20th
1984
|
DECISION
No.
407-QD - ISSUED BY THE COMMITTEE OF SCIENCE AND TECHNOLOGY, PROMULGATING TWO
STANDARDS
THE PRESIDENT OF THE COMMITTEE OF
SCIENCE AND TECHNOLOGY
Pursuant to the Decree No. 141-HĐBT dated
August 24th 1982 of the Minister Council, issuing the Regulation on
standardization;
At the request of the Ministry of Food
Industry in the Official Dispatch No. 194-CNTP/KT dated October 24th
1983.
DECISION
Article 1– Promulgating
two Vietnam’s Standards:
TCVN 3973-84. Edible salt (sodium chloride). Test
methods.
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Article 2 – These
standards come into effect from January 01st 1986, and shall be observed.
Doan Phuong
(Signed)
TCVN 3973-84.
EDIBLE
SALT (SODIUM CHLORIDE) TEST METHODS
- Compiler: The Department of Salt Industry –
The Ministry of Food Industry
- Requester: The Ministry of Food Industry
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- Issuer: The Committee of Science and
Technology
- Promulgated together with the Decision No.
107/QĐ dated November 20th 1984.
This Standard specifies the method of
sampling and determinating organoleptic, chemical, and physical indicators of
edible salt (Sodium Chloride – NaCl).
1. Sampling.
1.1. The quality of a shipment of salt is
determined based on the analysis of the average sample of the shipment.
A shipment of salt is an amount of salt in
the same category, produced from the same technological line, and delivered at
the same time.
The average sample is taken from the initial
samples of the shipment. Before taking an initial sample, the form, impurities,
and packaging conditions should be observed.
1.2. Taking initial samples.
1.2.1. Group all initial samples of the
shipment into a general sample. The amount of initial samples must ensure that
the general samples weigh at least 20 kg.
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Initial samples are taken from at least 03
trenches, 0.5 m deep, 0.5 m wide. Put a shovel to deep into the salt (do not
scratch horizontally) at 9 points evenly distributed along the trench.
For big shipments of at least 1,000 tonnes,
take a sample from every 20 tonnes evenly distributed along the height and the
cross-section of the shipment. Samples shall be taken during the unloading of
salt.
1.2.3. For salt in boats or barges.
Initial samples are taken 3 times while unloading:
at the beginning of the unloading, after one fourth of the shipment is
unloaded, and after three fourth of the shipment is unloaded. 10 samples shall
be taken at various positions of the boat or barge.
For boats of 3-5 tonnes, 3 samples shall be
taken from each boat.
1.2.4. For big bags or small bunches of salt.
Initial samples shall be taken from 3% of the
bags or bunches. At least 3 bags or bunches shall be sampled. Samples shall be
taken from sequential segments. For example: a shipment has 100 bags, the 20th,
50th, and 80th etc. shall be sampled.
1.3. Taking average samples.
Mix the general samples, evenly spread them
over a clean plane to form a square. Divide the square into 4 triangles by its
two diagonals, remove 2 opposite parts, and mix the remaining 2 parts. Repeat
this process until 1.5 kg of sample remains. This is called an average sample.
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The label on the average sample must indicate
the producer, product name, quality class, shipment weight, sampling date and
place, name of the sample taker.
The arbitration analysis agency and the place
where the arbitration sample are selected by the consignor and consignee.
Notes:
1. The general sample is usually divided into
1.5-kg parts (average sample) at the sampling place before being taken to the
laboratory.
2. Where salt is unloaded by conveyor belts
or chutes, initial samples shall be taken when salt leaves the end of conveyor
belt or chute. Use a 0.6 x 0.6 x 0.05 m tray to catch salt from its flowing
stream. The weight of sample is similar to above.
1.4. Sampling tools.
All sampling tools must be dry and clean. Sampling
tools and sample containers include: small knives, 50×50×20cm glaze or plastic
trays (or 80×80×20cm wooden trays with plastic lining), wooden shovels (similar
to a sand shovel), salt shovels, capped jars, 20 x 55 cm 2-layer polyethylene, tools
for seaming and sealing bags, 2-layer jute or sedge bags (the inner layer is
plastic) to contain initial salt samples.
2. Test methods.
In all tests, pure reagents shall be used for
analysis.
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2.2. Determination of taste: Dissolve 5 g of
salt in 100 ml of distilled water at ambient temperature; taste it to determine
the taste.
2.2. Determination of smell: Grind 20 g of
salt in a ceramic mortar at ambient temperature; smell it to determine the
smell.
2.4. Determination of humidity.
2.4.1. Use a capped ceramic bowl and a heater
that could produce a temperature of 140 oC.
2.4.2. Testing: heat the capped ceramic bowl
at 140 oC and cool it down in a desiccator. Weigh the bowl, and keep
heating it until the weight remains unchanged.
Put 10 g of salt (± 0.01 g) in the bowl. Heat
the salt at 140 oC ± 10 oC for 3 hours. Cap the bowl,
cool it in a desiccator, and weigh it. Keep heating it for 30 minutes and weigh
it until the difference between two weighing times does not exceed 0.01 g.
2.4.3. Result calculation. Salt humidity is
expressed as percentage (X1) using the formula below:
m1: weight of the bowl and salt before
heating, expressed as gram; m2: weight of the bowl and salt after heating,
expressed as gram.
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2.5. Determination of water-insoluble
impurity content.
2.5.1. Tools.
- Analysis scale, accuracy of 0.001g.
- Desiccator.
- Filter paper.
2.5.2. Testing process
Put 25 g of dried salt (salt dried until its
weight remains unchanged) in a 400-ml beaker and dissolve it with 100 ml of
distilled water.
Boil the solution for 10 minutes, cap the
glass and keep boiling for 30 minutes; cool it down to ambient temperature. Pass
the solution through a funnel with filter paper (the filter is dried and its
weight is known). Rinsing and washing water is brought to the filter funnel. Rinse
insoluble substances right on the filter paper many times by distilled water until
no white precipitate of silver chloride is seen when making the washing water react
silver nitrate 0.1N. Put the solution in a 500-ml volumetric flask; cool it
down and add more distilled water to reach the mark; shake the cylinder to
analyze ions.
The filter paper and insoluble substances
shall be put on a glass dial, dried at 105 ± 2 oC for 3 hours,
cooled down in a desiccator, and weighed. This process shall be repeated until
the difference between two weighing times does not exceed 0.001 g.
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The content of impurities insoluble in water
is expressed as percentage of dry matter (X2) using the following formula:
m1: Weight of the filter paper and heated insoluble
substances, expressed in gram.
m2: Weight of the filter paper, expressed in
gram.
m: Weight of salt, expressed in gram.
The result is the arithmetic mean of 2 calculations.
2.6. Determination of content of chlorine
ions (Cl-)
2.6.1. Principles: Titrate chlorine ion by
silver nitrate solution (AgNO3) with the potassium
chromate (K2CrO4) as an indicator.
2.6.2. Reagents and tools.
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- Potassium chromate, 10% solution.
- 250-ml volumetric flask.
2.6.3. Testing process: take 25 ml of salt
solution from the 500-ml volumetric flask (Point 2.5) and put it in a 250-ml volumetric
flask; dilute it with distilled water at the mark, and shake the cylinder. Put
25 ml of the salt solution in the 250-ml beaker in a 150-ml conical flask; add
25 ml of distilled water, 5 – 10 drops of 10% potassium chromate solution
(light yellow). Begin the titration by 0.1N silver nitrate solution until the
solution turns to a red-brown color.
2.6.4. Result calculation.
The content of Chlorine ions is expressed as
percentage of dry matter (X3) according to the following formula:
0.00355: Amount of chloride ion corresponding
to 1 ml of AgNO3 solution (0.1N ), expressed in gram.
V: Volume of AgNO3.(0.1N) that is
consumed when titrating, expressed in ml.
200: Dilution factor
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2.7. Determination of sulfate ion content (SO4--)
(Arbitration method).
2.7.1. Principle: This method is based on the
precipitate of SO4-- in the form of barium sulfate by barium
chloride, , thence calculate the content of SO4--.
2.7.2. Reagents and tools.
- Hydrochloric acid, 10% solution (pH= 5 –
6).
- 0.1N Barium chloride solution.
- Furnace capable of producing a temperature
of 650 ± 5 oC.
2.7.3. Testing process.
Take 100 ml of salty water from the 500-ml volumetric
flask to a 200-ml beaker, add 3 ml of HCl 100% and boil them. Heat 10 ml of
BaCl2 close to the boiling point, and put the hot BaCl2
solution into the salt solution. Use a glass rod to stir the solution for 3
minute and let it cool down to ambient temperature (no precipitate is seen when
some drops of BaCl2 is put into the solution)
Filter out precipitate by thick filter paper.
First filter the upper part of precipitate, then add 25 ml of boiled distilled
water to the beaker. Repeat this process 5 times then put all precipitate on
filter paper, rinse the beaker and wash the precipitate 5 times by hot distilled
water until the filtered water does not cause a chlorine reaction with 0.1N AgNo3
.
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2.7.4. Result calculation.
The content of sulfate is expressed as
percentage of dry matter (X4) according to the following formula:
0.445 : Factor of conversion from BaSO4
to SO- -.
m1: Weight of the heated bowl with the
precipitate, expressed in gram.
m2: Weight of the heated bowl without
precipitate, expressed in gram.
m: Weight of salt, expressed in gram.
V: Volume of the volumetric flask, expressed
in ml.
v: Volume of the solution taken from the volumetric
flask, expressed in ml.
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2.8. Determination of sulfate ion content (SO4--)
2.8.1. Principle.
Use amount of barium chloride intended to
form sulfate (SO4--) precipitate of a salt in weak acid (precipitate
of BaSO4).
Use Trilon B to titrate, the indicators are eriochrome
black T and methyl red.
Use Trilon B to titrate the amount of used
BaCl2, Ca++ and Mg++ of salty water, with the same environment and
indicators as above.
The content of SO4-- shall be
found from the third titration.
2.8.2. Reagents and tools.
- 0.025M Trilon B solution.
- Barium chloride, 0.05M solution.
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- Indicator: ET00 0.5%
- Methyl red, (0.2% solution).
- Strong hydrochloric acid.
- Burette.
2.8.3. Testing process.
Take 20 ml of salty water from the 500-ml volumetric
flask (Point 2.5) to a 250-ml conical flask, add 30 ml distilled water and 1
drop of strong HCl. Add 5 ml of BaCl while shaking the solution. When a white precipitate
is seen, allow the solution to stand for 1 – 2 more minutes, then add 2 ml of
NH4OH - NH4Cl, 10 drops of ET100, and 10 drops of methyl
red. Use Trilon B solution to titrate until the solution turns red, then ashy,
then green. Record the amount of used Trilon B (V1).
Take 20 ml of salty water from the 500-ml volumetric
flask (Point 2.5) to a 250-ml conical flask, sequentially add 30 ml distilled and
2 ml of Trilon B until the solution color changes as above. Record the amount
of Trilon B used (V2).
2.8.4. Result calculation.
The content of SO4-- ions is
expressed as percentage of dry matter (X3) according to the following formula:
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96: molecular mass of SO4--
25: Dilution factor
V1: Volume of Trilon B used for the first
titration (titrating Mg+ + , Ca+ + and Ba+ +), expressed in ml.
V2: Volume of Trilon B used for the second
titration (titrating 5 ml of BaCl2 solution) expressed in ml.
M: molecular concentration of trilon B.
m: weigh of salt, expressed in gram.
The result is the arithmetic mean of two
parallel calculations. The difference between two parallel calculations shall
be smaller than 0.5%.
2.9. Determination of Calcium ion content
(Ca++)
2.9.1. Principle.
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2.9.2. Reagents and tools.
- 0.01N Trilon B solution.
- 0.5% calcein indicator
- 1N sodium hydroxide solution.
- Burette.
2.9.3. Testing process.
Take 20 ml of salt solution from the 500-ml volumetric
flask, add 30 ml or distilled water, 5 ml of 1N NaOH, 1 drop of 0.5% Calcein. Begin
the single-color titration to identify the necessary Trilon B.
Prepare a similar specimen to the experiment
above and add 90% of the amount of Trilon B recorded in the specimen above. Then
add 5 ml of NaOH (1N solution) and 4 drops of 0.5% calcein. Use a microburette
to keep titrating by Trilon B until the solution turns red and then bluish-yellow.
Record the total amount of Trilon B after 2 titrations.
2.9.4. Result calculation
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0.0004 : Amount of calcium corresponding to
4ml Trilon B, expressed in gram.
V1: Volume of 0.01N Trilon B solution consumed
during the titration, expressed in ml.
V2: Volume of salt solution taken from the volumetric
flask, expressed in ml.
500: Capacity of the volumetric flask,
expressed in ml.
m: Weight of the salt sample, expressed in
gram.
The result is the arithmetic mean of two
parallel calculations. The difference between two parallel calculations shall
be smaller than 0.05%.
2.10. Determination of magnesium ion content
(Mg++)
2.10.1. Principle.
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2.10.2. Reagents and tools.
- 0.01N Trilon B solution.
- Eriochromee black T crystals.
- Buffer: NH4OH - NH4Cl, pH = 10.
- Burette.
2.10.3. Testing process.
Take 20 ml of salt solution from the 500-ml volumetric
flask and put it in a 250-ml conical flask, then add 30 ml or distilled water, 10
ml of buffer with pH = 10, and some ETOO crystals.
Use 0.01N Trilon B to titrate until the
solution completely turns from red to blue. Record the amount of consumed
Trilon B.
2.10.4. Result calculation
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0. 00024: Amount of magnesium corresponding
to 1 ml of 0.01N Trilon B, expressed in gram.
V2: Volume of 0.01N Trilon B solution that
was used to titrate Mg++, expressed in ml.
V2: Volume of 0.01N Trilon B solution that
was used to titrate Ca++, expressed in ml (Point 2.9 with the same amount as
the determination of Mg++).
V: Volume of salt solution taken from the volumetric
flask, expressed in ml.
m: weigh of salt, expressed in gram.
The result is the arithmetic mean of two
parallel calculations. The difference between two parallel calculations shall
be smaller than 0.5%.
2.11. Determination of potassium ion content
(K+)
2.11.1. Principle.
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2.11.2. Reagents and tools.
- Sodium tetraphenylborate.
Dissolve 3 g of sodium tetraphenylborate NaB(C6H5)4
and 0.5 g of aluminum nitrate Al(NO3)3 in water. Distill
10 ml of the solution and allow it to stand for one night (only mix before
use);
- 1N acetic acid.
Washing solution: use 100 ml of distilled
water mixed with 2ml of 3% sodium tetraphenylborate and 2ml of 1N acetic acid.
- A filter funnel No. 4
2.11.3. Testing process.
Take 20 ml of salt solution from the 500-ml
volumetric flask (Point 2.5) and put it in a 250-ml volumetric flask, then add
water until it reaches the mark.
Take 50 ml of solution from the 250-ml volumetric
flask, put it in a 150-ml beaker. Acidize it by 5 ml of 1N acetic acid. Boil it
at 40 – 50 oC. Slowly add 10 ml of 3% sodium tetraphenylborate. Stir
the solution and cool it down to ambient temperature.
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Repeat the process of heating, cooling and
weighing until the weight remains unchanged.
2.11.4. Result calculation
The potassium ion content is expressed as
percentage of dry matter (X7) according to the following formula:
0.1091: Potassium conversion factor from
NaB(C6H5)4.
125: Dilution factor
M: Weight of the precipitate, expressed in
gram.
m: Weight of the salt sample, expressed in gram.
The result is the arithmetic mean of two
parallel calculations. The difference between two parallel calculations shall
be smaller than 0.5%.
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2.12.1. Principle.
Use potassium antimony K2H2Sb2O7
to form a precipitate if sodium in a neutral environment or weak acid. Dissolve
the precipitate in a mixture of hydrochloride acid and potassium iodide, then
use sodium thiosulfate to , and thence calculate the Na+ content.
First Mg+ + and Ca+ + ions must be removed
from the solution by making it react with oxygen quioline to form a precipitate
of Mg(C9H6NO2)2.4H2O.
To reduce the solubility of Na2H2Sb2O7.4H2O
in water, the precipitate shall be form in Ethanol solution.
2.12.2. Reagents and tools.
- A solution of 8 2% aniolin oxygen in Ethanol.
- Precipitation solution: dissolve 20g potassium
antimony in 1 litre of boiled distilled water. Cool it and add 1g of KOH. Allow
it to stand for one night and filter out the sediment.
- 0.05N sodium thiosulfate solution.
- Anhydrous Ethanol.
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- Potassium iodide crystals.
- Starch, 0.5% ammonium hydroxide solution.
- Heated bath.
2.12.3. Testing process.
Take 100 ml of salty water from the 500-ml volumetric
flask (Point 2.5) to a 150-ml beaker. Slightly boil the solution. Then add 10
ml of 2% 8_ Oxy Aninolin solution and 0.3 ml of 10% NH4OH. Boil the
solution in the heated bath for 1 -2 minutes and let it cool down; filter out
the precipitate on the funnel No. 4. Use 100 ml of distilled water to wash the
precipitate many times (in this way Mg++ and Ca++ have been taken out of the
solution.
Concentrate the solution above until its
volume reaches 25 ml, and add 25 ml of anhydrous ethanol.
Heat this solution in a heated bath and
gradually add 25 ml of K2H2Sb2Os
while stirring it. Speed up this process when a precipitate is formed.
Allow it to stand at ambient temperature for
1 hour then filter out the precipitate on the funnel No. 4 and wash 7 times by ethanol
solution.
Move all precipitate on the funnel to a
150-ml beaker and dissolve the precipitate by 8 ml of strong HCl. Wash the
filter funnel and the beaker with distilled water and add more distilled water
until the volume reaches about 50 ml. Add 1g of KI crystal and allow it to
stand for 5 minutes. Then titrate it against sodium thiosulfate solution until
the solution turns light-yellow. Add 5 ml of 0.5% starch indicator. Shake and
keep titrating until the solution is colorless.
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The sodium ion content is expressed as
percentage of dry matter (X9) according to the following formula:
V: Volume of Na2S2O3
consumed during the titration, expressed in ml.
N: Concentration of Na2S2O3.
v: Amount of salt water taken, expresses in
ml.
m: Weight of the salt sample, expressed in
gram.
: Sodium conversion
factor
500: Capacity of the volumetric flask,
expressed in ml.
The result is the arithmetic mean of two
parallel calculations. The difference between two parallel calculations shall
be smaller than 0.1%.
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After knowing the contents of ions in salt,
the compounds must be demonstrated as follows:
- The combination of Ca++ and SO4-- is
expressed as CaSO4.
- Deduct the amount of SO4-- that
reacts with Ca++ from the total amount of SO4--, and combine the
remainder with MgSO4
- Deduct the amount of Mg+ + that
reacts with SO4—from the total amount of Mg++, and combine the
remainder with Chlorine to form MgCl.
Summary of salt composition demonstration.
Cation
Anion
Ca+ +
Mg+ +
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Na+
SO4- -
Cl-
CaSO4
MgSO4
MgCl2
KCl
NaCl
Note: The sodium content determined by the
method in Point 2.2 may be combined with Chlorine to demonstrate the
composition of NaCl. If the result does not matches the table above, that
figure may be used for reference.