GB/T 15555.11-1995 Determination of fluoride in solid waste - Ion selective electrode method
Some standard content:
National Standard of the People's Republic of China
Determination of fluoride in solid waste
Ion selective electrode method
Solid waste-Determination of fluoride-lon selective electrode method1 Subject content and scope of application
GB/T 15555.11--1995
1.1 This standard specifies the fluoride ion selective electrode method for determining fluoride in solid waste leachate. 1.2 This standard method is applicable to the determination of fluoride in solid waste leachate. 1.2.1 The detection limit of this method is 0.05 mg/L (in terms of F-), and the upper limit of determination is 1900 mg/L. 1.2.2 Sensitivity (i.e. the slope of the electrode). When the solution temperature is between 20 and 25°C, the electrode potential changes by 56 ± 2 mV for every 10-fold change in the fluoride ion concentration. At 25°C, the electrode slope should not be less than 55 mV. 1.3 Interference
This method measures the concentration of free fluoride ions. When Ca2+, Mg2+, Al3+, Fe3+, Si(V) and hydrogen ions are present in the leachate, they can form insoluble compounds or complex with fluoride ions and cause interference. The degree of interference depends on the type and concentration of the ions present, the concentration of fluoride and the pH value of the solution. In alkaline solutions, if the concentration of hydroxide ions is greater than 10-'mol/L, hydroxide ions will interfere with the response of the electrode. The pH of the measured solution should be between 5 and 7. The fluoride electrode does not respond to fluoroborate ions (BF). If the sample contains fluoroborate or is seriously contaminated, it should be distilled first. Usually, a total ionic strength regulator is added to maintain the total ionic strength in the solution, complex the interfering ions, and maintain the appropriate pH of the solution. 2 Principle
When the fluoride electrode is in contact with a fluoride-containing test solution, the electromotive force E of the cell changes with the activity of fluoride ions in the solution (obeying the Nernst equation). When the total ionic strength of the solution is constant and sufficient, it obeys the relationship: 2.303RTlogaz
E and logar- are in a linear relationship. 2. 303RT is the slope of the straight line, which is also the slope of the electrode. F
The working cell can be expressed as follows:
Ag|AgCl,Cl-(0.3mol/L),F-(0.001mol/L)ILaF,ltest solutionilexternal reference electrodeNote: When the fluoride ion concentration to be measured cz-<10\\mol/L, the activity coefficient is 1, and cr- can be used to replace its activity ar-3Reagents
Unless otherwise specified, reagents that meet national or professional standards are used, deionized water or water of equivalent purity. 3. 1 Hydrochloric acid (HCI), 2 mol/L.
3.2 Sulfuric acid (HzSO.)0=1.84g/mL.
3.3 Total ionic strength adjusted buffer solution (TISAB) National Environmental Protection Agency, approved on March 28, 1995, State Bureau of Technical Supervision
Implementation on January 1, 1996
GB/T15555.11-—1995
3.3.10.2 mol/L sodium citrate-1 mol/L sodium nitrate solution (TISABI) Weigh 58.8 g of sodium citrate dihydrate and 85 g of sodium nitrate, dissolve them in water, adjust the pH to 5-6 with hydrochloric acid, transfer to a 1000 mL volumetric flask, dilute to the mark, and shake well.
3.3.2 Total Ionic Strength Adjustment Buffer Solution (TISAB) Measure about 500 mL of water into a 1L beaker, add 57 mL of glacial acetic acid, 58 g of sodium fluoride and 4.0 g of cyclohexane diaminetetraacetic acid (CDTA), or 1,2-diaminocyclohexane N,N,N-tetraacetic acid, or 1,2-diaminocyclohexane N,N,N-tetraacetic acid, and stir to dissolve. Place the beaker in a cold water bath, slowly add 6 mol/L NaOH (about 125 mL) while stirring continuously to make the pH between 5.0 and 5.5, transfer to a 1000 mL volumetric flask, dilute to the mark, and shake well. 3.3.3 1mol/L hexamethylenetetramine-1mol/L potassium nitrate-0.03mol/L titanium iron solution reagent (TISAB): Weigh 142g of hexamethylenetetramine [(CH2)N] and 85g of potassium nitrate (KNO,), 9.97g of titanium iron reagent (CH,Na2O.S,H,O), dissolve in water, adjust pH to 5~~6, transfer to a 1000mL volumetric flask, dilute to the mark with water, and shake well. 3.4 Fluoride standard stock solution 100μg/mL: Weigh 0.2210g of standard sodium fluoride (NaF) (pre-dried at 105~110℃ for 2h, or dried at 500~650℃ for 40min, cooled in a dryer), dissolve in water, transfer to a 1000mL volumetric flask, dilute to the mark, shake well, and store in a polyethylene bottle.
3.5 Fluoride standard solution 10.0 μg/mL: Use a non-divided pipette to draw 10.00 mL of sodium fluoride standard stock solution (3.4), inject it into a 100 mL volumetric flask, dilute to the mark, and shake well. 3.6 Sodium acetate (CH.COONa), 15% m/V: Weigh 15 g of sodium acetate and dissolve it in water, dilute to 100 mL. 3.7 Perchloric acid (HCIO,): 70%~72%.
4 Instruments and devices
4.1 Fluoride ion selective electrode.
4.2 Saturated calomel electrode or silver chloride electrode. 4.3 Ion activity meter, millivoltmeter or pH meter, accurate to 0.1 mV. 4.4 Magnetic stirrer with a stirring bar covered with polyethylene or polytetrafluoroethylene. 4.5 Polyethylene cup, 100 mL; 150 mL.
4.6 Fluoride steam distillation apparatus See Figure: Fluoride steam distillation apparatus diagram
1—Thermometer; 2--Condenser; 3—Receiver: 4-Heating jacket 5 Sample storage and treatment
5.1 Sample storage: The overflowing liquid should be collected and stored in a polyethylene bottle. If the sample is neutral, it can be stored for several months. 566
GB/T 15555.11—1995
5.2 Sample treatment: When the leaching solution is not too complicated, the test solution can be taken out directly. If it contains fluoroborate or the composition is complex, it should be distilled first.
In an acid solution with a high boiling point, fluoride can form volatile hydrofluoric acid and fluorosilicic acid to separate from the interfering components. The commonly used method of water vapor distillation is as follows:
Accurately take an appropriate amount (e.g. 25.00mL) of test solution and place it in a distillation flask. Slowly add 15mL of perchloric acid (3.7) while shaking continuously. Connect the device according to the diagram and heat it. When the temperature of the solution in the distillation flask is about 130℃, start to pass steam and maintain the temperature at 140±5℃. Control the distillation rate to about 5-6mL/min. When the volume of the distillate in the receiving flask is about 150mL, stop distillation and dilute the distillate with water to 200mL for determination.
6 Determination steps
6.1 Preparation of the instrument, according to the instruction manual of the measuring instrument and electrode. Determine the actual slope of the electrode before analysis. 6.2 Before determination, the sample should reach room temperature and the temperature of the sample and the standard solution should be the same (the temperature difference should not exceed ±1C). 6.3 Determination of samples
Use a non-divided pipette to draw an appropriate amount of sample and place it in a 50mL volumetric flask. Adjust to near neutrality with sodium acetate (3.6) or hydrochloric acid (3.1), add 10mL of total ionic strength adjustment buffer solution (3.3.1) and dilute with water to the mark, shake the hook, inject it into a 100mL polyethylene cup, put in a plastic stirring rod, insert the electrode, and stir the solution continuously. After the potential stabilizes (the potential change is no more than 0.5mV in 5min), read the potential value E while continuing to stir. Before each measurement, rinse the electrode thoroughly with water and dry it with filter paper. According to the measured millivolts, the fluoride content can be checked from the calibration curve. 6.4 Blank test
Replace the sample with water and carry out a blank test according to the conditions and steps of 6.3. 6.5 Calibration curve method
Use a non-divided pipette to take 1.00, 3.00, 5.00, 10.0, and 20.0 mL of fluoride standard solution (3.5) respectively, and place them in a 50 mL volumetric flask. Add 10 mL of total ionic strength adjustment buffer solution (3.3.1) and dilute with water to the mark. Shake the hook and inject them into 100 mL polyethylene cups respectively. Put a plastic stirring rod in each cup. Insert the electrodes in order from low to high concentration, stir the solution continuously, and wait until the potential stabilizes (the potential change is no more than 0.5mV), read the potential value E while continuing to stir. Before each measurement, rinse the electrode with water and dry it with filter paper. Draw the E (mV)-logCr (mg/L) calibration curve on the semi-logarithmic coordinate paper, with the concentration marked on the logarithmic grid and the lowest concentration marked at the starting point of the horizontal axis.
6.6 Single standard addition methodWww.bzxZ.net
When the sample composition is complex or the composition is unknown, it is advisable to use the single standard addition method to reduce the influence of the matrix. First determine the potential value E of the test solution as described in 6.3, then add a certain amount of fluoride standard solution (3.4 or 3.5) (similar to the fluorine content in the test solution) to the test solution, and read the equilibrium potential value E2 under continuous stirring. The millivolt value of E2 and E should differ by 30~40mV. The result is calculated as follows:
Where: C—concentration of the added standard solution, mg/L; C—concentration of the test solution, mg/L;
V.一一The volume of the standard solution added, mL; 10(E2-E,)/S —
V—The volume of the test solution taken during the determination, mL, E,-The potential value of the test solution measured, mV,
E, The potential value measured after the test solution is added with the standard, mV; S—The measured slope of the electrode.
（2）
AE=E2-E
GB/T15555.11-1995
If Q(AE) is expressed as (,v)
/104E/S
then: C = c, Q(AE)
When V is fixed. The ratio of V, can be calculated by Q(AE) in advance with a calculator and made into a table for reference. In actual analysis, the corresponding Q(△E) can be found in the table (see attached table) according to the measured AE value. 6.7 Storage of electrodes
After use, the electrodes should be fully rinsed with water and the water should be absorbed with filter paper. They should be placed in the air or in a dilute fluoride standard solution. If they are not to be used for a short period of time, they should be cleaned, the water should be absorbed, and the protective cap should be put on to protect the sensitive parts of the electrodes. The electrodes should be fully rinsed and the water should be removed before use.
Representation of results
The fluoride concentration of the leaching solution is calculated according to the following formula: c (mg/L) = c ×
Where: c——fluoride ion concentration in the tested material, mg/L; V is the volume of the test material, mL, and
is the volume of the sample during preparation, mL.
8 Precision and accuracy
（3）
For samples containing 1.0 μg/mL F-, 10 times the amount of Al () as F-, 200 times the amount of Fe () as F- and Si (V) as F-, the relative standard deviation of nine parallel determinations was 0.3%, and the recovery rate of spiked samples was 99.4%. For the analysis of 17 kinds of leachates such as chemical sludge, acid sludge, and steel slag, the recovery rates of spiked samples were between 90% and 110%.
GB/T15555.11-1995
Appendix A
Notes
(reference)
A1 The formulation of the total ionic strength adjustment buffer solution is not limited to 3.3.1, 3.3.2, and 3.3.3. The addition of sodium citrate or CDTA can preferentially complex aluminum with a concentration of 5.0 mg/L, and titanium iron reagent can preferentially complex aluminum below 10 mg/L and release fluoride ions. When the sample composition is complex, acidic (about pH 2) or alkaline (about pH 12), TISABⅢ (3.3.3) can be used without adjusting the pH value of the test solution. Using TISAB (1), when the concentration of F is 1μg/mL, A13+, 15 times Zr1+, and 50 times Ce++ greater than 10 times F- can cause significant interference. Fe3+, 100 times Mg2+, 400 times SiO-, and 200 times B,0% greater than 500 times F- can also cause interference. A2 Do not touch the membrane surface of the electrode with your fingers. In order to protect the electrode, the measured concentration of fluorine in the test solution should not exceed 40mg/L. A3 The depth of electrode insertion should be consistent, and the solution should not be stirred before insertion to avoid bubbles adhering to the electrode surface and affecting the accuracy of the measurement. A4 The stirring speed should be moderate and stable, and no vortex should be formed. Stirring should be continued during the measurement. The stirring speed is about 180/min. When the potential change is no more than 0.5mV in 5min, the stirring can be stopped and the potential value is recorded after 15s. A5 If the membrane surface of the electrode is contaminated by organic matter, it must be cleaned before use. Cleaning can be done with organic reagents such as methanol and acetone, or detergents. For example, the electrode can be immersed in warm dilute detergent (1 part detergent plus 9 parts water) for 3 to 5 minutes. If necessary, it can be placed in another part of detergent, then rinsed with water, and then immersed in 1+1 hydrochloric acid for 0.5 minutes. Finally, rinsed with water and the water was absorbed with filter paper.
A6 According to the results of the complex stability constant and interference experimental research of fluoride, it has been shown that A13+ has the most serious interference, followed by Zr1+, Sc3+, Th+, Cea+, etc., and high concentrations of Fe3+, Ti4+, Ca2+, and Mg2+ also interfere. Adding appropriate complexing agents can eliminate their interference. A7 The concentration (c.) of the standard solution added in the single standard addition method should be 10 to 100 times higher than the concentration of the test solution (cx), and the added volume should be 1/10 to 1/100 of the test solution, so that the TISAB concentration of the system does not change much. A8 The attached table shows the corresponding values of Q and △E when the volume of the test solution changes by 10% at 25℃ after adding the standard. A9 Steam distillation is safer than direct distillation. When the test solution contains organic matter, sulfuric acid should be used instead of perchloric acid to prevent explosion. A10 When determining a series of samples, the low concentration should be determined first and then the high concentration. Before determining the next sample, the stirring bar and electrode can be rinsed with the next test solution. If a low concentration test solution is to be measured after a high concentration test solution has been measured, the electrode and stirring bar should be rinsed well to eliminate the memory effect before the low concentration test solution can be measured.
Note: For the preparation method of the overflow solution, refer to Appendix B of GB/T15555.1-1995 "Determination of Total Mercury in Solid Waste by Cold Atomic Absorption Spectrophotometry". Appendix B
The corresponding values of Q and AE when the volume of the measured solution changes by 10% (25℃) (Supplement)
GB/T15555.11—1995
Appendix A
Notes
(Reference)
A1 The formulation of the total ionic strength adjustment buffer solution is not limited to 3.3.1, 3.3.2, and 3.3.3. The addition of sodium citrate or CDTA can preferentially complex aluminum with a concentration of 5.0 mg/L, and titanium iron reagent can preferentially complex aluminum below 10 mg/L and release fluoride ions. When the sample composition is complex, acidic (about pH 2) or alkaline (about pH 12), TISABI (3.3.3) can be used without adjusting the pH value of the test solution. Using TISAB (I), when the concentration of F is 1μg/mL, A13+ greater than 10 times F-, Zr4+ greater than 15 times, and Ce4+ greater than 50 times F- can cause significant interference. Fe3+ greater than 500 times F-, Mg2+ greater than 100 times, Si0- greater than 400 times, and B,O- greater than 200 times F- can also interfere. A2 Do not touch the membrane surface of the electrode with your fingers. In order to protect the electrode, the measured concentration of fluorine in the test solution should not exceed 40mg/L. A3 The depth of electrode insertion should be consistent, and the solution should not be stirred before insertion to avoid bubbles adhering to the electrode surface and affecting the accuracy of the measurement. A4 The stirring speed should be moderate and stable, and no vortex should be formed. Stirring should be continued during the measurement. The stirring speed is about 180/min. When the potential changes by no more than 0.5mV in 5min, the stirring can be stopped, and the potential value is recorded after 15s. A5 If the membrane surface of the electrode is contaminated by organic matter, it must be cleaned before use. Cleaning can be done with organic reagents such as methanol and acetone, or with detergents. For example, the electrode can be immersed in warm diluted detergent (1 part detergent plus 9 parts water) for 3 to 5 minutes. If necessary, it can be placed in another part of detergent, then rinsed with water, and then immersed in 1+1 hydrochloric acid for 0.5min, finally rinse with water and absorb the water with filter paper.
A6 According to the results of the complex stability constant and interference experiment of fluoride, it has been shown that: A13+ has the most serious interference, followed by Zr4+, Sc3+Th4+, Ce++, etc., and high concentrations of Fe3+, Ti4+, Ca2+, and Mg2+ also interfere. Adding appropriate complexing agents can eliminate their interference. A7 The concentration of the standard solution added by the single standard addition method (c.) should be 10 to 100 times higher than the concentration of the test solution (c×), and the added volume should be 1/10 to 1/100 of the test solution, so that the TISAB concentration of the system does not change much. A8 The attached table is 25C, and the corresponding values of Q and △E when the volume of the test solution changes by 10% after the addition of the standard. A9 Steam distillation is safer than direct distillation. When the test solution contains organic matter, sulfuric acid should be used instead of perchloric acid to prevent explosion. A10 When predicting a series of samples, the low concentration should be measured first and then the high concentration. Before measuring the next sample, the next test solution can be used to rinse the stirrer and electrode. If a low-concentration test solution is to be measured after a high-concentration test solution has been measured, the electrode and stirrer should be rinsed thoroughly to eliminate the memory effect before measuring the low-concentration test solution.
Note: For the preparation method of the leaching solution, refer to Appendix B of GB/T15555.1-1995 "Determination of Total Mercury in Solid Waste by Cold Atomic Absorption Spectrophotometry". Appendix B
Corresponding values of Q and AE (25°C) when the volume of the measured solution changes by 10% (supplement)
Additional notes:
GB/T 15555.11—1995
This standard was proposed by the Science and Technology Standards Department of the State Environmental Protection Administration. This standard was drafted by the China National Environmental Monitoring Center. The main drafter of this standard is Wang Sufang.
This standard is entrusted to the China National Environmental Monitoring Center for interpretation. 571
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