GB 10734-2008Primary chemical - Ethylenediamine tetraacetic acid disodium salt (English PDF)

5.3 Content

5.3.1 Principle of the method Coulomb analysis is performed by measuring a quantitative analysis of material from one electrode reaction, or a substance to be analyzed and the electrode reaction Charge (coulombs) chemical reaction product was quantitatively consumed to quantitative analysis. Coulometry principle is based on the law Where. Molar mass M

--- material in units of grams per mole (g/mol);

--- Like the number of electron transfer; F

--- Faraday constant ampere seconds per mole of (A · s/mol); I

--- the current solution by electrolysis, in amperes (A); Constant current precision coulometric titration method is based on a constant current through the electrolytic cell, so that the working electrode electrolysis to produce a titrant with cell The test substance quantitative reaction, electrochemical method to indicate the end of the reaction, the consumption of electricity by electrolysis calculated according to Faraday's law The amount of titrant to calculate the content of the test substance. This method is at a constant current to the amalgamated zinc electrode as an anode, electrolysis divalent zinc ion cell solution to be tested H2Y2 reaction Determination of edetate disodium.

5.3.2 instruments and devices

5.3.2.1 pH meter. meet JJG119-2005 Chapter 4 "0.001" requirements.

5.3.2.2 Weight. meet JJG99 verification requirements. G group, the annual variation of less than 10µg; mg group, the annual variation of less than 4µg.

5.3.2.3 heated fuel tank. temperature control accuracy of ± 0.01 °C.

5.3.2.4 Coulomb constant current device diagram (see Figure 1). 1

--- high precision timing constant current source; 2

--- electrolytic cell; 4

--- end indicator (pH meter); 5

--- dummy load resistor; 6

--- Standard resistance; 7

--- galvanometer; 8

--- temperature standard battery pack; . 9

--- step switch; 10

--- heated fuel tank. Figure

5.3.3 Determination

5.3.3.1 Preparation of formulations Amount of sulfuric acid 111mL, 700mL slowly into the water, cooled and diluted to 1000mL. Weigh 37.22g edetate disodium, is dissolved in water and diluted to 1000mL. Weigh 53.49g of ammonium chloride, dissolved in water and diluted to 1000mL.

5.3.3.2 Test preparation 5.3.3.2.1 cell cleaning The new cell before use lotion soak a while, repeatedly washed with water and pumped to wash the sand core colorless, washed several times with water repeatedly pumping. With ammonium chloride solution (with added disodium edetate about 0.5g) filled with an electrolytic cell, soaked for several days in order to remove the glass from the inner wall of soluble Child (such as calcium, magnesium, etc.), and then repeatedly washed with water until prior to use alternate. Good cleaning electrolytic cell can be used repeatedly, simply removing the experiment was repeatedly washed with water to pumping. 5.3.3.2.2 formulated silicone gel plug Weigh 12.5g of sodium silicate, placed in 150mL beaker, add 50mL water dissolved, add 20mL sulfuric acid solution (2mol/L), were stirred And uniform boiling, After cooling the solution was poured into the cathode compartment of the electrolytic cell (right side), in the sulfuric acid solution was gradually added slowly with stirring (2mol/L) to dissolve Become muddy liquid, gel. Formulated silicone gel stuffed add a little sulfuric acid solution (2mol/L) kept moist. 5.3.3.2.3 amalgamated zinc produced a working electrode On a diameter of about 5mm, 60mm long high-purity zinc bar at one end to make a hole, insert a diameter of about 1mm ~ 1.5mm of copper, zinc bar End copper and are coated with insulating paint drying at low temperature and set aside. Before using zinc rod immersed in a solution of hydrochloric acid (1 + 1) in a moment, remove surface contaminants, thoroughly rinsed with water, after immersion in high-purity mercury sheet Carved to amalgamation. After the manufacture of the electrode, if not should be stored in the ammonium chloride solution, and then the best high purity nitrogen protection. Before use repeatedly use Wash water.

5.3.3.3 said sample The sample was placed in a saturated solution of magnesium nitrate (with excess magnesium nitrate crystals) humidistat the humidity for 2 weeks. Small sample is placed in a polyethylene cup, weighing alternative method to the nearest 0.00001g. The quality of the sample shall be corrected for buoyancy correction See Appendix A.

5.3.3.4 Pre-titration Anode chamber was added 4g of ammonium chloride (excellent pure) and 150mL of water, the solution was adjusted to pH

7.0 with sodium hydroxide solution (10g/L), Stirring from the manifold through the solution into high purity nitrogen to remove dissolved oxygen. Open the piston to the intermediate chamber to introduce about 2mm deep electrolyte solution Was added a few drops of disodium edetate solution (0.1mol/L). Sulfuric acid solution was added to the cathode chamber (1mol/L) 40mL, and the same When added 0.3g of potassium hydroxide (excellent pure) adjusting the pH to 7.0, 10.186mA current pre-titration curve for incremental method (See FIG. 4). After the completion of pre-pressurization and depressurization of the titration method with intermediate washing chamber several times, and the solution was washed with an anode compartment electrolytic cell wall, and finally The electrolyte solution is returned to the intermediate chamber 2mm. The final current value recorded over the titration part of the amount of charge in the calculation of the total charge Amount.

5.3.3.5 titration end point and seek Open the piston, so that the middle chamber filled with electrolyte solution, close the piston, to blow through nitrogen inlet above the surface of the anode chamber is maintained positive Pressure to prevent entry of air. By loading the sample into the hole (with cups) and 0.5g of potassium hydroxide (excellent pure), and stirred until dissolved sample. Slow Under stirring 101.86mA current, the electrolysis of zinc ion titration solution H2Y2-, 99.9% of the sample to be titrated, remove power Source, note the time and calculate the amount of charge consumed. Washed thoroughly with electrolyte solution in the anode chamber and the intermediate chamber wall, and the pH of the solution adjusted Section 7.0, to the middle of the room to introduce 2mm deep electrolyte solution after use 10.186mA current incremental method the painted end curve. The intermediate compartment is washed again several times, until the current value became unchanged, indicating the recording current value. The recording of the current directions - the number of electrolysis time It is drawn endpoint of the titration curve. Typical end curve shown in Figure 4. Fig. A point represents a current value when the electrolysis was stopped, B point represents completion of washing Two straight portion of the current value of the curve to extend the line of intersection C is the endpoint of the titration.

4 a schematic diagram of the end of the curve

Calculate the amount of charge consumed before it reaches the end of the intermediate chamber and the amount of charge consumed by the diffusion of ions H2Y2- to Figure 4, i.e., A, B The amount of charge between two points.

5.3.4 Calculation

5.3.4.1 disodium edetate mass fraction calculation Disodium edetate mass fraction, the value in the "%" means, according to equation (2). = QPQT × 100 = I (2) Where. I

--- the current solution by electrolysis, in amperes (A);

--- The M value disodium edetate molar mass of the units of grams per mole (g/mol);

--- Like the number of electron transfer; F

--- Faraday constant ampere seconds per mole of (A · s/mol); E

--- standard electromotive force in volts (V); R

--- standard resistor in ohms (Omega). (2) In the formula. Where. I1

--- large current electrolysis current value in units of milliamperes (mA); I2

--- pre-titration end point and seek current value, in milliamperes (mA); Uncertainty and assay results of calculation

5.3.4.2 Expanded uncertainty assay results should generally be less than 0.02% (k = 2), the calculation method, see Appendix B. Determined according to the provisions of GB/T 9724's.

5.5.1 Preparation of test solution and preparation

5.5.1.1 sample solution Weigh 0.327g sample is dissolved in hot water, cooled and transferred to 100mL volumetric flask, dilute to the mark.

5.5.1.2 sodium carbonate solution Weigh 0.100g previously dried at 200 °C 2h calcium carbonate, placed in 100mL flask, add 10mL water and 0.4mL hydrochloric acid Solution (20%), was dissolved with aqueous ammonia solution (10%) and diluted to the mark.

5.5.1.3 copper sulphate solution Weigh 0.250g copper sulfate pentahydrate, placed in 100mL volumetric flask, dissolved in water, dilute to the mark.

5.5.2 Determination 5.00mL amount of the sample solution, add 3 drops of ammonia solution (10%) and 2.5mL ammonium oxalate solution (40g/L), shaking continuously, Plus 5.00mL sodium carbonate solution, the solution should be transparent. If, after shaking 1min, the solution is still cloudy, plus 0.2mL sample solution, shake After moving 1min, transparent solution strain. Amount of sample solution 5.00mL, 0.5mL add ammonia solution (1%) and 0.5mL hexacyanoferrate (II) solution of potassium (100g/L), Constantly shaking plus 4.8mL copper sulfate solution, the solution should be bluish green, not a red.

5.6 Clarity test Weigh 5g sample was dissolved in 100mL of water. Turbidity is not greater than HG/T 3484 standard stipulated clarity 3.

5.7 Water insoluble matter Weigh 20g sample was dissolved in 300mL boiling water, measured according to the provisions of GB/T 9738's.

5.8 Chloride Weigh 0.5g sample was dissolved in 10mL water, add 2mL solution of nitric acid (25%), and shaken until complete precipitation of the precipitation, filtration, water Washed three times, the combined filtrate and washings were diluted to 20mL, determined according to the provisions of GB/T 9729's. The turbidity of the solution was not greater than the standard ratio Turbid solution. Standard preparation turbid solution is to take the ratio of 0.02mg containing chloride (Cl) standard solution was diluted to 20mL, and at the same time with the same volume of test solution Sample processing.

5.9.1 Preparation of test solution I Weigh 3g sample placed in a platinum dish, slowly heating carbonization burning to white at 600 °C. If necessary, add 5mL water, evaporated to dryness, and then at 600 °C burning, iterative process until the residue completely white. Add water 20mL, 6mL solution of nitric acid solution (25%), evaporated on a water bath. Disabled Residue dissolved in hot water, cooled, diluted to 30mL (filtered if necessary).

5.9.2 Determination Amount of test solution 5mL I, diluted to 20mL, after adding 0.5mL hydrochloric acid solution (20%) acidification, according to GB/T 9728 regulations Determination. The turbidity of the solution was not greater than the standard turbidity solution. Standard preparation turbid solution is to take the ratio of 0.05mg containing sulfate (SO4) standard solution was diluted to 20mL, at the same time with the same volume of test solution The same treatment.

5.10 nitrilotriacetic acid

5.10.1 Instruments Pulse or oscilloscope pole spectrometer.

5.10.2 Test conditions Working electrode. dropping mercury electrode; Reference electrode. silver - silver chloride or saturated calomel electrode; Electrode. platinum electrode; Sensitivity. properly selected; Way oxygen. nitrogen 5min above; Scanning potential range. -0.6V ~ -1.1V.

5.10.3 Determination Weigh 1g sample was added 30mL of hot water to dissolve, cooled, the pH of the solution was adjusted with sodium hydroxide solution (100g/L) to

10.5 to 10.7 (Control with pH meter). Solution of cadmium chloride solution (50g/L) to a solution of trace precipitation [dropping the pH value should be maintained Between

5.11 Iron

5.11.1 Preparation of the test solution II Weigh 3g sample placed in a platinum dish, slowly heating carbonization burning to white at 600 °C. If necessary, add 5mL water, evaporated to dryness, and then at 600 °C burning, iterative process until the residue completely white. Add 10mL of water to dissolve the residue, was added dropwise a solution of hydrochloric acid (20%) and the excess 1mL, For 10min in a water bath, diluted to 30mL.

5.11.2 Determination II amount of 10mL of the test solution, the solution was adjusted with ammonia solution (10%) to pH 2, was diluted to 15mL, press The provisions of GB/T 9739 Determination. The red solution should not be deeper than the standard colorimetric solution. Preparation of the standard developing solution containing 0.005mg is to take the ratio of iron (Fe) standard solution was diluted to 15mL, and at the same time with the same volume of test solution deal with. Copper

5.12 The amount of 10mL of the test solution II (5.11.1), add 5mL ammonium citrate solution (200g/L), the solution was adjusted with ammonia to pH 9, and the excess 1mL, diluted to 25mL. Add 1mL diethyl dithiocarbamate solution (1g/L), shake, add 5mL isoamyl alcohol Extraction, shaking 1min, the yellow organic phase can not be deeper than the standard colorimetric solution. Preparation of standard color solution is to take the ratio of 0.0025mg containing copper (Cu) standard solution was diluted to 10mL, and at the same time with the same volume of test solution Sample processing.

5.13 Heavy Metal After the amount of 20mL test solution I (5.9.1), the solution was adjusted with ammonia solution (10%) to pH 4, according to GB/T 9735 of Regulation Fixed determination. The solution was dark can not be deeper than the standard colorimetric solution. Preparation of the standard developing solution containing 0.02mg ratio is taken of lead (Pb) standard solution was diluted to 25mL, and at the same time with the same volume of test solution deal with.