1、May 1984 UDC 628.u.3: 001.4:620.1: 543.3: 541.138 DEUTSCHE NORM German standard methods for the examination of water, waste water and sludge Physical and physico-chemical parameters (Group C) I 38404 Determination of the oxidation reduction (redox) potential (C 6) Part 6 Deutsche Einheitsverfahren z
2、ur Wasser-, Abwasser- und Schlammuntersuchung; physikalische und physikalisch-chemische Kenngrssen (Gruppe C); Bestimmung der Redox-Spannung (C 6) ln keeping with current practice in standards published by the International Organization for Standardization IlSol, a comma has been used throughout as
3、the decimal marker. This standard has been prepared jointly with the Study Group Wasserchemie of the Gesellschaft Deutscher Chemiker (Society of German Chemists) (see Explanatory notes). For analyses in compliance with this standard, the services of specialists and specialized laboratories shall be
4、sought. 1 Field of application This method is applicable to all aquatic environments which satisfy the conditions specified in subclause 8.2. 2 Scope The redox voltage serves as an indication of the condi- tions and processes in an aquatic environment in connec- tion with which oxidizing and reducin
5、g substances become active 11. Note. The redox voltage was formerly known as the redox potential (see Gesetz ber Einheiten im Messwesen (Law on units in metrology) and DIN 1323). 3 Concept The redox voltage is generated by oxidizing or reducing substances dissolved in the water, in so far as these s
6、ub- stances become active at the surface of the electrode. It is specified as the voltage between an inert electron con- ductor and the standard hydrogen electrode. 4 Principle of the method For practical reasons, the measurement is carried out with platinum or gold electrodes against, for example,
7、a siIver/siIver chloride reference electrode, and the meas- ured voltage is recalculated in relation to the standard hydrogen electrode (see clause 9) 2 3. Changes in the redox voltage in the positive direction are an indication of a more pronounced influence of oxidizing substances. The same applie
8、s vice versa. In many cases, more than one redox pairs are present in aquatic environments, but they are not necessarily in a state of redox equilibrium 4. Consequently, the pos- sibility shall be ruled out of using the measured value to draw inferences on the concentration of individual redox pairs
9、 or of individual components. The redox voltage is temperature-dependent to an unforeseeable degree; it can also very with the pH value. 5 Interference The measurement is liable to suffer severe interference from deposits on the surfaces of the redox electrodes (see subclause 7.11, e.g. deposits of
10、grease or reaction products of substances contained in the water. Therefore the bare metal surfaces of the electrodes must be kept bright and free of these deposits. For example, Mn2+ ions are liable under certain condi- tions to promote manganese oxide deposits on the platinum electrode. The diaphr
11、agm of the reference electrode shall not become clogged (see DIN 38 404 Part 5). Figure 1. Continuous flow vessel as specified in subclause 7.4 6 Designation The method for the electrometric determination of the redox voltage (C 6) shall be designated as follows: Method DIN 38 404 - C 6 Continued on
12、 pages 2 to 5 euth Verlag GmnH. Berlin 30, has exclusive sale lights for German Standards (fllN-Normen) DIN 38 404 Part 6 Engl. Price group 5 Sales No. 0105 06.85 Page 2 DIN 38 404 Part 6 _ c (KCU Temperature 1 mol/l 3 mol/l 3,5mol/l Satu rated Measured voltage U, 0 “C mV 10 218 245 247 251 15 208 2
13、35 239 243 20 199 228 231 236 25 191 220 224 230 30 173 204 209 217 40 164 195 200 210 45 155 187 192 203 50 146 178 184 196 Table 1. Redox voltages of the Ag/AgCL/KCL/redox buffer (as in subclause 7.9) measuring chain 1, to be measured using a platinum electrode Redox vol tage UH*) pH-value rnV 462
14、 7,06 450 7,04 439 7 ,O2 427 7.00 404 6,96 391 6,95 379 6,95 366 6,95 7 Apparatus and reagents 7.1 Redox electrode as measuring electrode (platinum or e.g. with DIN 12 242 - KNS 14/23 ground joint. 7.2 Reference electrode with DIN 12 242 - KNS 14/23 ground joint; silver/silver chloride reference sys
15、tem. Reference electrodes should be stored in a potassium chloride solution of the same concentration as that present in the electrode (see also DIN 38 404 - C 5 method). 7.3 pH electrode2), e.g. as specified in DIN 19 261, with DIN 12 242 - KNS 14/23 ground joint. 7.4 Continuous flow vessel, e.g. a
16、s shown in figure 1. 7.5 Thermometer, e.g. DIN 12 775 - E 0,1/0/50 thermometer. 7.6 Millioltmeter), with an input resistance not less than 1012Q. 7.7 Cleaning agent for the metal electrode, e.g. mildly abrasive household detergent or cleanser. All reagents used shall be of analytical quality, and on
17、ly distilled water or water of the same degree of purity shall be used. 7.8 Hydrochloric acid, g = 1,12g/ml. 7.9 Test solution (redox buffer) The following shall be dissolved in 1 of water: - potassium hexacyanoferrate (II), - potassium hexacyanoferrate (III), - potassium dihydrogen phosphate, KH,P0
18、4, 1.8 g; - disodium hydrogen phosphate, (See table 1 for the redox voltages.) The test solution will remain well preserved for approxi- mately one month if stored in a dark coloured bottle. K4 FdCN),. 3 H,O, 5,28 9; K3 Fe(CN)6, 4,11 9; NaZHP04. 2 H20, 39 9. 8 Procedure 8.1 Pretreatment of redox ele
19、ctrodes The electrodes shall be cleaned at regular intervals, preferably prior to each series of measurements in the 1 Intermediate values shall be interpolated linearly. 2, Also used as singlerod measuring chain with the 3, Laboratory pH meters are equipped with a switch- reference electrode. over
20、facility for voltage measurement. All measuring instruments shall be suitable for measurements in earthed solutions (see DIN 38 404 Part 5, subclause 6.1, January 1984 edition). DIN 38 404 Part 6 Page 3 case of laboratory measurements. The cleaning proce- dure shall involve the following steps: - de
21、greasing and cleaning using cleaning agents (as specified in subclause 7.7); - rinsing with water; - treatment with hydrochloric acid (as specified in subclause 7.8); - rinsing with water. Any further pretreatment will depend on the anti- cipated redox voltage level and on the type of metal electrod
22、e used. No further pretreatment will be neces- sary if gold electrodes are used. Platinum electrodes shall undergo further pretreatment, as follows: a) when measurements are taken in an oxidizing medium, - rinse with an ammonia solution, w(NH3) = 25%; b) when measurements are taken in a reducing med
23、ium, - rinse with iron(I1)sulfate solution or with an iron(II1)citrate solution; - rinse with water in both cases. The measuring system shall be checked with the aid of the test solution (as specified in subclause 7.9). After cleaning, the electrode shall be immersed imme- diately in the solution to
24、 be measured. 8.2 Measurement of redox voltage Note. Platinum electrodes generally exhibit a higher setting speed, provided that they have been pretreated as specified in subclause 8.1. Gold electrodes are less suitable in an oxidizing medium in the presence of sequestering agents, catalytic poisons
25、 (such as dihydrogen sulfide (H2S), for example), and in the case of higher chloride concentrations, in the simultaneous presence of atmospheric oxygen. The measurement shall be carried out in a closed con- tinuous flow vessel (e.g. as specified in subclause 7.4) in order to avoid any interference f
26、rom atmospheric oxygen for example. The spot where the sample is taken and the measuring vessel shall be connected to one another by a length of hose which should be kept as short as possible. After insertion of electrodes and thermometer and the subsequent connection of the electrodes4) to the mill
27、ivoltmeter (see subclause 7.6). the water to be investigated is fed through the measuring appliance at a uniform rate. The volume flow rate shall be approximately 10ml/s. Before the reading is taken, the water shall be allowed to flow through the appliance for as long as is necessary to ensure that
28、the temperature remains constant and that the measured value does not vary by more than 1 mV within one minute. A constant measured value may in certain cases only be attained after a considerable lapse of time (from approximately 5 to 30 minutes). In addition, the pH value and the water temperature
29、 shall be measured. 9 Evaluation The measured voltage U, shall be related to the voltage of the standard hydrogen electrode (zero point of the electrochemical series) as the reference electrode, using equation (1 ); the voltage UH obtained in this way is designated the redox voltage. (1) where U, is
30、 the redox voltage; U, is the measured voltage; UB is the standard voltage of the reference electrode used for the test. The standard voltages U, of some reference electrodes are given in table 2 as a function of the temperature. The redox voltage may be either positive or negative. 10 Expression of
31、 result The values of the redox voltage shall be quoted rounded to the nearest 1 O mV. Together with the figure quoted, the pH value and the temperature of the water shall also be stated. Example of calculation Measurement: +500 mV, measured with a platinum electrode against a silver/silver chloride
32、 reference electrode, c (KCL) = 3 rnol/l. Calculation: UH = (+500+ 2175) mV = + 717mV, rounded to +720 mV. Example of presentation of result: Redox voltage VH (in accordance with the DIN 38 404 - C6 method) = + 720 mV Water temperature 8= 10,3C. pH value of water = 7,3. 11 Analysis report The report
33、 shall make reference to this method and shall incorporate the following details: precise identification of the sample of water; expression of result in accordance with clause IO; pretreatment of sample, if such a treatment has been carried out; any deviation from the specifications of this standard
34、, and a statement of all factors which may possibly have had an influence on the results. 4, The measuring electrode (see subclause 7.1) is the metal electrode which is always to be connected to the high impedance input. 5, Value taken from table 2 for 8= IOC. Page 4 DIN 38 404 Part 6 Tempe- rature
35、8 Table 2. Standard voltages U, of a number of reference electrodes, rounded to the nearest 1 mV 3, 4 u, u, Hg/Hg terminology DIN 12 242 Part 1 Laboratory glassware; conical ground joints for interchangeable connections; dimensions, tolerances DIN 12775 Laboratory glassware; laboratory thermometers
36、with 0,l OC, 0,2 OC and 0.5“C scale divisions DIN 19261 pH measurement; terms and definitions relating to methods of measurement using galvanic cells DIN 38 404 Part 5 German standard methods for the examination of water, waste water and sludge; physical and physico-chemical parameters (Group C); de
37、termination of pH value (C 5) I Hsselbarth, Ulrich. Bestimmung des Redoxpotentials (Determination of the redox potential), Handbuch der Lebensmittelchemie (Handbook of foodstuffs chemistry), vol. 8, parts 1 and 2 (Wasser und Luft), Springer-Verlag, Berl in ( 1970). Galster, Helmut. Natur, Messung un
38、d Anwendung der Redox-Spannung (Nature, measurement and utilization of the redox voltage), Chemie fr Labor und Betrieb 30 (19791, pp. 330-335 and 377-380. Baucke, Friedrich G. K. Standardpotentiale der Silber/Silberchlorid-Elektrode in 3,5 molarer und in gesttigter Kaliumchloridlsung un ter Verwendu
39、ng entsprechender Membranelektroden (Standard potent ia1 s of th e si Ive r /s i I ve r chloride electrode in a 3.5 molar and in a saturated potassium chloride solution, using corresponding membrane electrodes), Chemie Ing. Tech. 47 ( 1975), pp. 565-566. Clark, W. M. Oxidation reduction potentials o
40、f organic systems, The Williams & Wilkins Company, Baltimore (1 960). 2 3 4 DIN 38 404 Part 6 Page 5 Explanatory notes This standard incorporates the German standard method “Determination of the redox voltage (C 6)“ prepared jointly by the Normenausschuss Wasserwesen (Water Practice Standards Commit
41、tee) of DIN and by the Study Group Wasserchemie of the Gesellschaft Deutscher Chemiker. In addition, all standard methods contained up to now in the loose-leaf publication Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung (German standard methods for the examination of water,
42、 waste water and sludge) will be successively incorporated in the body of German standards so that, after a transition period, all standard methods will be available as DIN Standards. Standard methods published as DIN Standards can be obtained from Beuth Verlag GmbH either individually or grouped in
43、 volumes. The above-mentioned loose-leaf publication of Verlag Chemie GmbH incorporating the standard methods will continue to be published separately. Standards or draft standards bearing the group title “German standard methods for the examination of water, waste water and sludge“ are classified u
44、nder the following categories (main titles) : General data (Group A) (DIN 38 402) Physical and physico-chemical characteristics (Group C) (DIN 38 404) Anions (Group D) (DIN 38 405) Cations (Group E) . (DIN 38 406) Jointly determinable substances (Group F) Gaseous constituents (Group G) (DIN 38 408)
45、Summary indices of actions and substances (Group H) (DIN 38 409) Microbiological methods (Group KI (DIN 38 41 1) Test methods using water organisms (Group L) (DIN 38 412) Individual components (Group Pl (DIN 38 413) Sludge and sediments (Group S) (DIN 38 414) Information on the parts of these standards, which have already been published, can be obtained from the office of the Normenausschuss Wasserwesen (NAW) of DIN, telephone (030) 26 01-423, or from Beuth Verlag GrnbH. Postfach 11 07, D-1000 Berlin 30. International Patent Classification G O1 N 33-18
