BS 6068-2 41-1993 Water quality - Physical chemical and biochemical methods - Determination of fluoride electrochemical probe method for potable and lightly polluted water《水质 第2部分 .pdf

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1、BRITISH STANDARD BS 6068-2.41: 1993 ISO 10359-1: 1992 Water quality Part 2: Physical, chemical and biochemical methods Section 2.41 Determination of fluoride: electrochemical probe method for potable and lightly polluted waterBS6068-2.41:1993 This British Standard, having been prepared under the dir

2、ectionof the Environment andPollution Standards Policy Committee, was published underthe authority of the Standards Board and comes into effect on 15March 1993 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference EPC/44 Draft for comment 91/54580 DC ISBN

3、0 580 21643 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Environment and Pollution Standards Policy Committee (EPC/-) to Technical Committee EPC/44, upon which the following bodies were represented: Association of Consulting Scienti

4、sts British Association for Chemical Specialities British Gas plc Chemical Industries Association Convention of Scottish Local Authorities Department of the Environment (Water Directorate) Department of the Environment for Northern Ireland Department of Trade and Industry (Laboratory of the Governme

5、nt Chemist) Electricity Association Industrial Water Society Institute of Gas Engineers Institution of Water Officers Institution of Water and Environmental Management National Rivers Authority Royal Institute of Public Health and Hygiene Royal Society of Chemistry Scottish Association of Directors

6、of Water and Sewerage Services Soap and Detergent Industry Association Water Companies Association Water Research Centre Water Services Association of England and Wales The following bodies were also represented in the drafting of the standard, through subcommittees and panels: British Agrochemicals

7、 Association Ltd. British Ceramic Research Ltd. British Laboratory Ware Association British Soft Drinks Association Ltd. Department of Trade and Industry (Warren Spring Laboratory) GAMBICA (BEAMA Ltd.) Institute of Terrestrial Ecology Ministry of Defence Society of Chemical Industry South West Polyt

8、echnic Swimming Pool and Allied Trades Association Ltd. Amendments issued since publication Amd. No. Date CommentsBS6068-2.41:1993 BSI 07-1999 i Contents Page Committees responsible Inside front cover National foreword ii 1 Scope 1 2 Normative reference 1 3 Principle 1 4 Reagents 1 5 Apparatus 2 6 S

9、ampling and sample preservation 2 7 Procedure 2 8 Calculation and expression of results 3 9 Precision 3 10 Test report 4 Annex A (informative) Bibliography 5 Table 1 Preparation of reference solutions 3 Table 2 Precision data 4 List of references Inside back coverBS6068-2.41:1993 ii BSI 07-1999 Nati

10、onal foreword This Section of BS 6068, which has been prepared under the direction of the Environment and Pollution Standards Policy Committee, is identical with ISO10359-1:1992 Water quality Determination of fluoride Part 1: Electrochemical probe method for potable and lightly polluted water. The i

11、nternational standard was prepared by Technical Committee 147, Water quality, of the International Organization for Standardization (ISO) with the active participation and approval of the UK. BS 6068 is being published in a series of Parts subdivided into Sections that will generally correspond to p

12、articular international standards. Sections are being, or will be, published in Parts 1 to 7, which together with Part 0, are listed below. Part 0: Introduction; Part 1: Glossary; Part 2: Physical, chemical and biochemical methods; Part 3: Radiological methods; Part 4: Microbiological methods; Part

13、5: Biological methods; Part 6: Sampling; Part 7: Precision and accuracy. Fluoride ions occur in almost all ground and surface waters. Their concentration depends primarily on the hydrogeological conditions and is generally below1mg/l. Certain industrial waste waters may contain fluoride ions in high

14、er concentrations. The fluoride value is also dependent on the type and concentration of cations present at the same time in water, such as Ca 2+ , Mg 2+ , Al 3+or Fe 3+ , which may form sparingly soluble compounds with fluoride ions or complexes of low dissociation constant. Apart from these compou

15、nds, stable boron-fluoride complexes exist. Several different methods are available for determining fluoride and the choice of method depends on the type of problem posed as follows. a) Direct measurement using fluoride ion selective electrodes. This method is suitable for the determination of fluor

16、ide in potable and surface water. It is specified in this Section of BS6068. b) Determination of the total inorganically bound fluoride using decomposition, distillation and potentiometric measurement. This method will be specified in another Section of BS6068. Cross-reference International standard

17、 Corresponding British Standard ISO 5667-3:1985 BS 6068 Water quality Section 6.3:1986 Guidance on the preservation, and handling of samples (Identical)BS6068-2.41:1993 BSI 07-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standar

18、ds are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi to iv, pages1 to6, an inside back cover and a back cover. This standar

19、d has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankISO 10359-1:1992(E) BSI 07-1999 1 1 Scope 1.1 Field of application This part of ISO 10359 specifies a method for the determination of diss

20、olved fluoride in fresh, potable and low contaminated water, and some surface waters, using an electrochemical technique. The method is directly suitable for measuring fluoride concentrations from0,2mg/l to2,0g/l. After the addition of a known amount of fluoride, concentrations as low as0,02mg/l can

21、 be detected (see7.3). The method is not suitable for waste waters and industrial effluents; this determination will be the subject of ISO10359-2. 1.2 Interferences The electrode will respond directly to hydroxide ions. The formation of HF under acidic conditions will reduce the measured fluoride co

22、ncentration. Therefore, buffer all test aliquots to a pH between5 and7 to prevent such interference. Cations such as calcium, magnesium, iron and aluminium form complexes with fluoride or precipitates to which the electrode does not respond. Therefore the buffer solution also contains trans-1,2- dia

23、minocyclohexane-N,N,N,N-tetraacetic acid (CDTA) as a decomplexing agent to free bound fluoride. The boron tetrafluoride anion, , is not decomplexed by the addition of buffer. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions

24、 of this part of ISO 10359. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this part of ISO 10359 are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below.

25、 Members of IEC and ISO maintain registers of currently valid International Standards. ISO 5667-3:, Water quality Sampling Part3:Guidance on the preservation and handling of samples 1) . 3 Principle When a fluoride ion-selective electrode comes into contact with an aqueous solution containing fluori

26、de ions, a potential difference develops between the measuring electrode and the reference electrode. The value of this potential difference is proportional to the logarithm of the value of the fluoride ion activity in accordance with the Nernst equation. Temperature and ionic strength may influence

27、 the potential difference. Accordingly, these parameters shall be the same during calibration and measurement and shall be kept constant throughout the procedure. The activity of the fluoride ions is also pH-dependant. Values of pH between5 and7 have proved favorable for measurement. Special buffer

28、solutions are used to fix the pH and the activity coefficient. On these assumptions, this method will no longer refer to activities, but to fluoride ion concentrations. Fluoride ion-selective electrodes operate between0,2mg/l and2000mg/l, and show a linear relationship between the potential and the

29、logarithm of the numerical value of the fluoride activity. 4 Reagents During the analysis, use only reagents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Sodium hydroxide, c(NaOH) = 5 mol/l. Dissolve cautiously 100g 0,5g of sodium hydroxide in water, coo

30、l and dilute to500ml. 4.2 Total ionic strength adjustment buffer (TISAB) Add 58 g of sodium chloride (NaCl) and57ml of glacial acetic acid (CH 3 COOH) = 1,05g/ml to500ml of water in a1litre beaker. Stir until dissolved. Add150ml of the sodium hydroxide solution (4.1) and4g of CDTA (trans-1,2- diamin

31、ocyclohexane-N,N,N,N-tetraacetic acid). Continue stirring until all the solids have dissolved and adjust the solution to pH 5,2 with sodium hydroxide solution using a pH meter. Transfer to a1000ml one-mark volumetric flask, make up to the mark with water and mix. The solution is stable for about6 mo

32、nths, but do not use it if a precipitate forms. NOTE 1This solution is commercially available. 1) To be published. (Revision of ISO 5667-3:1985) BF 4ISO 10359-1:1992(E) 2 BSI 07-1999 4.3 Fluoride, stock solution, 1000mg/l. Dry a portion of sodium fluoride (NaF) at150C for4h and cool in a desiccator.

33、 Dissolve 2,210g 0,001g of the dried material in water contained in a1000ml one-mark volumetric flask. Make up to the mark with water and mix. Store the solution in a screw-capped polyethylene container. 4.3.1 Fluoride, working standard solution I, 10mg/l. Pipette 10ml of the fluoride stock solution

34、 (4.3) into a1000ml one-mark volumetric flask. Make up to the mark with water and mix. All standard solutions should be stored in plastic bottles and are usable for one month. 4.3.2 Fluoride, working standard solution II, 5 mg/l. Pipette 5ml of the fluoride stock solution (4.3) into a1000ml one-mark

35、 volumetric flask and make up to the mark with water. 4.3.3 Fluoride, working standard solution III, 1 mg/l. Pipette 100ml of the working standard solutionI(4.3.1) into a1000ml one-mark volumetric flask and make up to the mark with water. 4.3.4 Fluoride, working standard solutionIV,0,5mg/l. Pipette

36、100ml of the working standard solutionII(4.3.2) into a1000ml one-mark volumetric flask and make up to the mark with water. 4.3.5 Fluoride, working standard solution V, 0,2 mg/l. Pipette 20ml of the working standard solutionI(4.3.1) into a1000ml one-mark volumetric flask and make up to the mark with

37、water. 5 Apparatus Usual laboratory apparatus and 5.1 Meter, a millivolt meter with an impedance of not less than10 127, capable of resolving potential differences of0,1mV or better. 5.2 Fluoride ion-selective electrode, which shall give stable readings. The e.m.f response, using standard solutions,

38、 shall not be less than55mV per decade change in fluoride concentration at25C. 5.3 Reference electrode, either a calomel electrode, filled with saturated potassium chloride (KCl) solution, or a silver/silver chloride electrode shall be used. NOTE 2Single junction, sleeve-type electrodes which reduce

39、 the liquid-liquid junction potential are preferable. 5.4 Measuring cells, of capacity 100ml, made of polypropylene and fitted with a thermostatted jacket. 5.5 Water bath, capable of supplying water to the jacket of the measuring cell (5.4) at a temperature of25C 0,2C. 5.6 Magnetic stirrer, with a p

40、olytetrafluoroethylene (PTFE)-coated stirring bar. 5.7 Polyethylene beaker, of capacity 100ml. 5.8 Membrane filtration device, with membrane filters of pore size0,454m. 6 Sampling and sample preservation Samples shall be taken in polyethylene bottles which have been washed thoroughly and rinsed with

41、 fluoride-free water. No preservative is normally necessary, but the analysis should be performed as soon as possible, preferably within3days. (See also ISO 5667-3.) 7 Procedure 7.1 Preparation for measurement Since the electrode characteristics of a fluoride ion-selective electrode generally vary w

42、ith time, check the calibration curve on the day of use. To accelerate the establishment of the equilibrium potential, condition the electrode prior to measurement in the following way. Prior to measurement, immerse the electrode for1h in the cell (5.4) which contains the reference solution5 (seeTab

43、le 1). After rinsing with the first solution to be measured, the electrode is ready for use. 7.2 Measurement Filter the solution through a membrane filter (5.8). NOTE 3Measurement without filtration is also possible, however this should be stated with the result. Pipette25ml of the buffer solution (

44、4.2), followed by25ml of the water sample, into a measuring cell (5.4). Ensure that the pH is5,2 0,2; if necessary, adjust the pH with hydrochloric acid or sodium hydroxide solution, using as little as possible. NOTE 4If a precipitate is formed, perform the analysis with a diluted sample. NOTE 5Any

45、dilution of the sample should be taken into account during the calculation of the results. For a series of determinations, start the measurement with the lowest concentration and finish with the highest following the anticipated concentration of the samples.ISO 10359-1:1992(E) BSI 07-1999 3 After me

46、asuring the high concentrations, recondition the electrode before measuring the low concentrations (see7.1). Measure all the solutions according to the following procedure. Wait until constant temperature (e.g.25C 0,5C) is reached and carry out all the measurements at this temperature. Put a stirrin

47、g bar into the measuring cell (5.4) and place it on the magnetic stirrer (5.6). Insert the electrodes (5.2) into the solution and fix them in place. Adjust the stirring rate to about180min 1to200min 1 . When the potential does not change by more than0,5mV in5min, switch off the stirrer. After at lea

48、st15s, record the value obtained. Rinse the stirring bar and the electrodes with the next solution to be measured, before starting the next measurement. 7.3 Measurement after concentration enhancement If a water sample contains less than0,2mg/l F, proceed as follows: to 25ml of the sample, add 500 4

49、l of the fluoride standard solution I (4.3.1) using a piston pipette, and25ml of the buffer solution (4.2) with a volumetric pipette; continue as described in7.2; when calculating the result, subtract the amount of fluoride ions added from the total result. 7.4 Calibration Establish a calibration function using the five reference solutions in the corresponding concentration range. For the range0,2mg/l to10mg/l, proceed as follows: pipette 25,0ml of the buffer solution (4.2) into each of five measuring cells (5.4);