GB/T 2091-2008Phosphoric acid for industry use (English PDF)

6.2 General provisions

The reagents and water that are used in this Standard, when no other

requirements are specified, refer to analytical reagents and grade-III water

which is specified in GB/T 6682-1992. The standard titration solutions, impurity

standard solutions, preparations and products that are used in the test shall be

prepared in accordance with the provisions of HG/T 3696.1, HG/T 3696.2, HG/T

3696.3, when no other requirements are specified.

6.3 Appearance determination

Determine visually under natural light conditions.

6.4 Color determination

Determine according to the method that is specified in GB/T 605.

6.5 Determination of phosphoric acid content

6.5.1 Gravimetric method (arbitration method)

6.5.1.1 Method summary

In the acidic medium, the phosphate radical in the test solution forms a

precipitate with the added precipitating agent, quinoxaline ketone. Calculate the

phosphoric acid content by filtration, drying, and weighing.

6.5.1.2 Reagents

6.5.1.2.1 Hydrochloric acid;

6.5.1.2.2 Quinoxaline ketone solution.

6.5.1.3 Instrument

6.5.1.3.1 Sintered-glass filter crucible: the hole diameter is 5 µm ~ 15 µm;

6.5.1.3.2 Electric oven: the temperature can be controlled at 180 °C ± 5 °C or

6.5.1.4 Analysis steps

6.5.1.4.1 Preparation of test solution

Weigh approximately 1 g of the sample, accurate to 0.0002 g, in a 100 mL

beaker; add 5 mL of hydrochloric acid and a small amount of water; cover the

watch glass; boil for 10 min. After cooling, transfer to a 500 mL volumetric flask;

add 10 mL of hydrochloric acid; use water to dilute to the mark; shake well.

6.5.1.4.2 Preparation of blank solution

Except that no sample is added, the amount of other added reagents is exactly

the same as that of the test solution. The same treatment is carried out

simultaneously with the sample.

6.5.1.4.3 Determination

Pipette 10 mL of the test solution and the blank test solution into the 250 mL

beakers respectively; add water to a total volume of about 100 mL. Add 35 mL

of quinoxaline ketone solution; cover the watch glass; heat in a water bath until

the temperature in the cup reaches 75°C ± 5°C; keep for 30 s (do not use open

flame when heating; do not stir when adding reagent or heating, so as to avoid

clot formation). Cool to room temperature; stir 3 ~ 4 times during cooling. Use

the sintered-glass filter crucible, which has been dried to a constant mass at

180°C ± 5°C or 250 °C ± 10 °C in advance, to suction-filter the supernatant;

take decantation to wash the precipitate for 5 ~ 6 times, each with about 20 mL

of water. Transfer the precipitate to the sintered-glass filter crucible; continue to

use water to wash for 3 ~ 4 times. Place the sintered-glass filter crucible in an

electrically heated drying oven at 180 °C ± 5 °C, to bake for 45 min; or bake at

6.5.1.5 Result calculation

The phosphoric acid content is calculated by the mass fraction w1 of phosphoric

acid (H3PO4); the value is expressed in %; it is calculated according to Formula

(1):

Where:

m1 -- the value of the mass of the quinoline phosphomolybdate precipitate that

is formed in the test solution, in grams (g);

m2 -- the value of the mass of the quinoline phosphomolybdate precipitate that

is formed in the blank solution, in grams (g);

m -- the value of the mass of the sample, in grams (g);

0.044 28 -- the value of quinoline phosphomolybdate that is converted to

phosphoric acid.

6.7.2.1 Ethanol: 95% (volume fraction);

6.7.2.2 Hydrochloric acid solution: 1+3;

6.7.2.3 Barium chloride (BaCl2·2H2O) solution: 250 g/L;

6.7.2.4 Sulfate standard solution: 1 mL of solution contains 0.010 mg of sulfate

(SO4); prepare when needed.

Pipette 1 mL of the sulfate standard solution that is prepared according to HG/T

3696.2; place it in a 100 mL volumetric flask; use water to dilute to the mark;

shake well.

6.7.3 Analysis steps

For superior and first-class products, weigh 1.00 g ± 0.01 g of samples; for

qualified products, weigh 0.50 g ± 0.01 g of samples; put them in 25 mL

colorimetric tubes; add 10 mL of water, 5 mL of ethanol, 1 mL of hydrochloric

acid solution; add 3 mL of barium chloride solution dropwise when shaking

continuously; use water to dilute to the mark; shake well. Let stand for 10 min;

compare with the sulfate standard turbidimetric solution.

Preparation of sulfate standard turbidimetric solution: for the superior products,

transfer 3.0 mL of sulfate standard solution; for the first-class and qualified

products, transfer 5.0 mL of sulfate standard solution; place in a 25 mL

colorimetric tube; treat at the same time as the sample.

6.8 Determination of iron content

6.8.1 Method summary

Same as Chapter 3 of GB/T 3049-2006.

6.8.2 Reagents

Same as Chapter 4 of GB/T 3049-2006.

6.8.3 Instruments

Same as Chapter 5 of GB/T 3049-2006.

6.8.4 Analysis steps

6.8.4.1 Drawing of the working curve

According to 6.3 of GB/T 3049-2006, use a 2 cm absorption cell and the

corresponding iron standard solution to draw the working curve.

6.8.4.2 Preparation of test solution

Weigh about 3 g, to the nearest 0.01 g, of the sample; put it in a 100 mL

volumetric flask; add water to about 60 mL; use hydrochloric acid solution or

ammonia solution to adjust the pH of the solution to approximately 2 (use

precision pH test paper to check). Add 1 mL of ascorbic acid solution, 20 mL of

buffer solution, 10 mL of phenanthroline solution; use water to dilute to the mark;

shake well.

6.8.4.3 Preparation of blank test solution

Except that no sample is added, the amount of other added reagents is exactly

the same as that of the test solution. The same treatment is carried out

simultaneously with the sample.

6.8.4.4 Determination

Take the test solution and the blank test solution; select a 2 cm absorption cell;

measure the absorbance according to 6.3.3 of GB/T 3049-2006.

Subtract the absorbance of the blank test solution from the absorbance of the

test solution; find out the mass of iron in the test solution according to the

working curve.

6.8.5 Result calculation

The iron content is calculated by the mass fraction w2 of iron (Fe); the value is

expressed in %; it is calculated according to Formula (3):

Where:

m1 -- the value of the mass of iron in the test solution, in milligrams (mg);

m -- the value of the mass of the sample, in grams (g).

Take the arithmetic mean of the parallel determinations as the determination

result. The absolute difference between the results of two parallel

measurements shall not be greater than 0.000 2%.

6.9 Determination of arsenic content

6.9.1 Method summary

Same as Chapter 3 of GB/T 610.1-1988.

6.9.2 Reagents

Same as Chapter 4 of GB/T 610.1-1988.

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