HG/T 3812-2006Sodium thiocyanate for industrial use (English PDF)

4.1 Safety tips

Some reagents used in this test method are toxic or corrosive; operators must exercise extreme caution! If splashed on skin, rinse immediately with water; for severe cases, seek immediate medical attention. When using flammable materials, never use an open flame for heating.

4.2 General provisions

Unless otherwise specified, the reagents and water used in this standard refer to analytical grade reagents and grade III water as specified in GB/T 6682-1992.

Unless otherwise specified, the standard solutions, impurity standard solutions, preparations and products required for the test shall be prepared in accordance with the provisions of HG/T 3696.1, HG/T 3696.2 and HG/T 3696.3.

4.3 Determination of sodium thiocyanate content

4.3.1 Method summary

Excess silver nitrate is added to an acidic solution to produce silver thiocyanate, which is then back-titrated with a standard ammonium thiocyanate titration solution using ammonium ferric sulfate as an indicator.

4.3.2 Reagents

4.3.2.1 95% ethanol.

4.3.2.2 Nitric acid solution. 1+9.

4.3.2.3 Ammonium ferric sulfate solution. 50 g/L.

4.3.2.4 Silver nitrate standard titration solution. c(AgNO3)~0.1 mol/L.

4.3.2.5 Ammonium thiocyanate standard titration solution. c(NH4SCN)~0.1 mol/L.

4.3.3 Analysis steps

Weigh approximately 3 g of a crystalline sample dried to constant weight at (105±2) °C, or approximately 6 g of a liquid sample, accurate to 0.0002 g, and place it in a 250 mL beaker. Dissolve the sample in water and transfer the entire amount to a 500 mL volumetric flask. Dilute to the mark and mix well. Pipette 50 mL of the solution into a 250 mL Erlenmeyer flask, add 10 mL of 95% ethanol and 5 mL of nitric acid solution, and then pipette 50 mL of silver nitrate standard titration solution and shake well. Add 2 mL of ammonium ferric sulfate solution and titrate with ammonium thiocyanate standard titration solution. When nearing the endpoint, shake vigorously with each additional drop. The endpoint is reached when the solution turns a light brownish-red color and remains so for 30 seconds.

4.3.4 Result calculation

The sodium thiocyanate content is expressed as the mass fraction w1 of sodium thiocyanate (NaSCN), and the value is expressed as a percentage (%). It is calculated according to formula (1). where V1 -- the volume of silver nitrate standard titration solution (4.3.2.4) added, in milliliters (mL);

V2 -- the volume of ammonium thiocyanate standard titration solution (4.3.2.5) consumed in the titration, in milliliters (mL). c1 -- the accurate concentration of silver nitrate standard titration solution, in moles per liter (mol/L); c2 -- the accurate concentration of ammonium thiocyanate standard titration solution, in moles per liter (mol/L); m -- the mass of the sample, in grams (g).

M -- the molar mass of sodium thiocyanate (NaSCN), in grams per mole (g/mol) (M=81.08).

The arithmetic mean of the parallel measurement results is taken as the measurement result, and the absolute difference between the two parallel measurement results shall not be greater than 0.2%.

4.4 Determination of iron content

4.4.1 Method summary

It is the same as Chapter 2 of GB/T 3049-1986.

4.4.2 Reagents

It is the same as Chapter 3 of GB/T 3049-1986.

4.4.3 Instruments

Spectrophotometer. It is equipped with an absorption cell with a thickness of 3 cm.

4.4.4 Analysis steps

4.4.4.1 Plotting the working curve

Follow the procedure in 5.3 of GB/T 3049-1986, select a 3 cm absorption cell and the corresponding amount of iron standard solution, and plot the working curve.

4.4.4.2 Analysis steps

Weigh a certain mass of sample (if crystal, superior product. 15 g, first-class product/qualified product. 7 g; if liquid product. 15 g), accurate to 0.01 g, place it in a 100 mL beaker, and dissolve the crystalline product in 50 mL of water. Add 10 mL of hydrochloric acid and stir until homogeneous. Heat in a water bath for 30 minutes. In another beaker, add 50 mL of water and 10 mL of hydrochloric acid, and use it as the blank test solution. Transfer the test solution and the blank test solution, respectively, to 100 mL volumetric flasks and then proceed with the operation according to steps in 5.4.1 of GB/T 3049-1986, starting with "use the ammonia solution...".

4.4.5 Result calculation

The iron content is expressed as the mass fraction w2 of iron (Fe), and the value is expressed as a percentage (%). It is calculated according to formula (2). where m1 -- the mass of iron obtained from the working curve based on the measured absorbance of the test solution, in milligrams (mg); m2 -- the mass of iron obtained from the working curve based on the measured absorbance of the blank test solution, in milligrams (mg). m -- the mass of the sample, in grams (g).

The arithmetic mean of the parallel measurement results is taken as the measurement result, and the absolute difference between two parallel measurement results shall not be greater than 0.0001%.

4.5 Determination of water-insoluble matter content

4.5.1 Method summary

The mass fraction of water-insoluble matter in a sample is determined by the gravimetric method.

4.5.2 Instruments and equipment

Sintered-glass filter crucible. with a pore size of 5 µm~15 µm.

4.5.3 Analysis steps

Weigh approximately 25 g of the crystalline sample or 100 g of the liquid sample, […]