1、BRITISH STANDARD BS ISO 11271:2002 BS 7755.3.14:2002 Soil quality Determination of redox potential Field method ICS 13.080.20 BS ISO 11271:2002 This British Standard, having been prepared under the direction of the Health and Environment Sector Policy and Strategy Committee, was published under the
2、authority of the Standards Policy and Strategy Committee on 4 November 2002 BSI 4 November 2002 ISBN 0 580 40677 6 National foreword This British Standard reproduces verbatim ISO 11271:2002 and implements it as the UK national standard. The UK participation in its preparation was entrusted by Techni
3、cal Committee EH/4, Soil quality, to Subcommittee EH/4/3, Chemical methods and soil characteristics, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implement internati
4、onal publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include a
5、ll the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries
6、on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to v, a blank page, p
7、ages 1 to 12, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsINTERNATIONAL STANDARD ISO 11271 First edition 2002-10-01 Reference number ISO 11271:2002(E) S
8、oil quality Determination of redox potential Field method Qualit du sol Dtermination du potentiel doxydorduction Mthode de terrainBSISO11271:2002BSISO11271:2002iiISO 72112002:1)E( ISO 2002 r llAithgs reservde iii Contents Page 1 Scope . 1 2 Normative reference . 1 3 Term and definition . 1 4 Princip
9、le 1 5 Apparatus . 2 6 Reagents 3 7 Site selection and sampling 3 8 Procedure . 3 9 Evaluation . 4 10 Expression of results 4 11 Test report 4 Annexes A Description of the construction of redox electrodes, of the salt bridge, and their arrangement during measurement 5 B Potentials of platinum electr
10、odes in different solutions . 9 C Potentials of reference electrodes. 10 D Soil moisture status. 11 Bibliography. 12 BSISO11271:2002iiiISO :17211(2002)E vi ISO 2002 Ar llithgr seresvde Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards b
11、odies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizati
12、ons, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the
13、 ISO/IEC Directives, Part 3. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that s
14、ome of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. International Standard ISO 11271 was prepared by Technical Committee ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical methods
15、and soil characteristics. Annexes A, B, C and D of this International Standard are for information only. BSISO11271:2002ivISO 72112002:1)E( ISO 2002 r llAithgs reservde v Introduction The redox potential is a physicochemical parameter used to characterize soil aeration status in a global way. Under
16、field conditions, it gives information on the condition of oxidation or reduction of those compounds which, depending on the case, play an important part in plant nutrition, can induce toxicity phenomena or intervene in gas transfer to the atmosphere (greenhouse effect). It can also be used to a cer
17、tain extent to follow soil performances in case of sludge disposal or composting, and to adjust applications accordingly. Under laboratory conditions, it can be used in order to study oxygen diffusion phenomena to aggregate level. BSISO11271:2002vANRETNIITOTS LANDNADRA ISO 72112002:1)E( ISO 2002 r l
18、lAithgs reservde 1 Soil quality Determination of redox potential Field method 1 Scope This International Standard specifies a field method for the determination of soil redox potential ( ). NOTE The electrochemical measurement of redox potential described here is possible only if the relevant soil h
19、orizon has a moisture status defined as fresh or wetter according to the classes presented in annex D. 2 Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequ
20、ent amendments to, or revisions of, this publication do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest editi
21、on of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 3696:1987, Water for analytical laboratory use Specification and test methods 3 Term and definition For the purposes of this International Standard, the followi
22、ng term and definition apply. 3.1 redox potential electrochemical potential reflecting the oxidation-reduction status of a liquid chemical system (in this case of the soil solution) 4 Principle Redox potential is an electrochemical equivalent of the free energy of redox reactions, and for an equilib
23、riated single redox system of the general form: (1) is given by the Nernst equation: (2) whereand are the activities of the oxidized and reduced forms of the element, respectively; refers to the electron(s) involved in the reaction; refers to the proton(s) involved in the reaction; E h E h A ox +ne
24、+mH + A red E h =E 0 + RT nF ln A ox A red 2,303mRT nF pH A ox A red e H + BSISO11271:20021ISO :17211(2002)E 2 ISO 2002 Ar llithgr seresvdeand are the numbers of electrons and protons involved in the reaction, respectively; is the standard value of the potential, i.e. when and ; is the universal gas
25、 constant ( ); is the absolute temperature; is the Faraday constant ( ); is the natural log of 10. Redox potential is related to electron activity ( ) in the system as follows: (3) NOTE Users of this International Standard unfamiliar with these electrochemical concepts should consult appropriate tex
26、ts, or seek professional advice. The electrometric determination of redox potential is analogous to the determination of pH. The determination of follows the principle of measuring potential differences between an inert measuring electrode (usually a platinum electrode), i.e. an electrode not reacti
27、ng with the solution per se, with respect to the standard hydrogen electrode used as the reference electrode. Many redox systems are involved in the soil solution, and the resulting potential is a mixed potential depending on the existing electroactive redox couples. For practical reasons, a silver-
28、silver chloride electrode is usually used as the reference electrode, the potential of which is added to the measured potential difference (see annex C) in order to obtain the values expressed on the basis of the standard hydrogen electrode. 5 Apparatus 5.1 Millivoltmeter, with an input resistance n
29、ot less than and sensitivity of . 5.2 A set of redox-electrodes, constructed as in A.1. All electrodes should be sufficiently robust for field use. 5.3 Reference electrode: silver/silver chloride reference electrode in or potassium chloride solution. Other reference electrodes such as the calomel el
30、ectrode can also be used, but are not recommended because of the health hazard connected with the use of mercury. The potential of such reference electrodes with respect to the standard hydrogen electrode is given in annex B. Reference electrodes should be stored in a potassium chloride solution (6.
31、4) of the same concentration as that present in the electrode, or directly in the salt bridge (5.5) containing the same concentration of potassium chloride. It should be noted that lower concentrations of potassium chloride will reduce contamination of the soil with this salt. 5.4 Rigid rod, (stainl
32、ess steel has been found suitable), to in length, with a diameter greater than that of the redox electrodes (5.2). The rod shall have a length which allows the redox electrodes to be inserted to the desired depth in the soil. 5.5 Salt bridge, to connect the reference electrode with the soil (see A.2
33、). 5.6 Hand auger, with a diameter to greater than that of the salt bridge. 5.7 Electrode cleaning materials: finest grade of steel wool, scouring powder and some cotton cloth have been found suitable. nm E 0 A ox =A red pH= 0 R 8,314 1 J mol 1 K 1 T F 96 500 C mol 1 2,303 e E h = RT F ln e E h 10 G
34、 1mV 1 mol/l 3 mol/l 20 cm 100 cm 2 mm 3mm 5mm BSISO11271:20022ISO 72112002:1)E( ISO 2002 r llAithgs reservde 3 5.8 Thermometer, to measure the temperature at the location of the reference electrode (see clause 8) with an accuracy of . 6R e a g e n t s 6.1 Redox buffer solution, to calibrate the red
35、ox electrodes. Use either buffered quinhydrone solution (prepared by adding quinhydrone to a pH buffer to obtain a suspension), or an equimolar solution of potassium hexacyanoferrate(III) and potassium hexacyanoferrate(II) (see annex B). 6.2 Water, conforming to grade 2 of ISO 3696. 6.3 Agar, , in a
36、 potassium chloride solution of the same concentration as that in the reference electrode. 6.4 Potassium chloride solution, of the same concentration as that chosen in 5.3. NOTE This solution is used to store the reference electrode and to add to the salt bridge, as needed. 7 Site selection and samp
37、ling The selection and description of the place of measurement, and of samples for laboratory measurement, should follow the guidelines given in ISO 10381-1: and ISO 11464. 8 Procedure 8.1 Care, cleaning and testing of the redox electrode system The platinum electrodes shall be stored in air and kep
38、t clean. They shall be inspected for damage and/or contamination at intervals of not more than one year, and every time they are used. Oils, fats and waxes, and other chemicals likely to adhere are particularly damaging to electrode performance. If contaminated with soil material they shall be clean
39、ed gently with a cotton cloth, and rinsed with distilled water. In cases of severe contamination, e.g. with oils, etc. (above), an appropriate solvent followed by scouring material (5.7) shall be used (see Note below). The reference electrode(s) shall also be inspected at the same time as the platin
40、um electrode(s). Any visible change in the colour or transparency of the potassium chloride electrolyte solution indicates probable trouble. In such cases the reference electrode shall not be used. Crystals of potassium chloride are, however, a normal feature of saturated potassium chloride solution
41、s, and are no reason to reject the electrode in question. The electrodes shall be checked prior to each series of measurements, by determining their response in the redox buffer solution (6.1). The measured redox potential values shall be as given in annex B. Any electrode differing by more than fro
42、m the required value shall be cleaned and tested again, and discarded if cleaning fails to correct the problem. NOTE Experience has shown that the use of strong oxidizing agents, e.g. nitric acid or hydrogen peroxide solution, as cleaning agents for platinum electrodes can result in high redox poten
43、tials. The use of such agents is therefore not recommended. In practical terms, the reference electrode potentials can be checked against each other. An electrode which gives a reading differing by more than from the other(s) is likely to be faulty, and should be discarded. This check procedure requ
44、ires a minimum of three reference electrodes, connected in turn. Reference electrodes can be checked in absolute terms only against a standard hydrogen electrode. This can be done only in specialist laboratories. It is usually more convenient to buy electrodes only from a reputable source. 1 C = 0,5
45、 % 10 mV 10 mV BSISO11271:20023ISO :17211(2002)E 4 ISO 2002 Ar llithgr seresvde 8.2 Preparation of site and measurement of redox potential At the place of measurement, drive a hole into the soil using the rigid rod (5.4) to a depth to less than the desired measurement depth. Immediately insert the r
46、edox electrode into the hole to a depth deeper by to than that of the hole. At least two electrodes should be installed for each measurement depth. Leave the platinum electrodes in the soil for at least following installation before connecting them to the millivoltmeter. At a distance of to from the
47、 redox electrode, auger a hole down to a fresh (or wetter) soil layer (see annex D), and install the salt bridge so as to obtain good contact between the ceramic cup of the salt bridge and the soil. Measure the potential difference, , in millivolts between the platinum electrode and the reference el
48、ectrode after , using the millivoltmeter (5.1). The measurement period can be shorter (but not ) only if the difference between successive measurements at intervals is . Measure the temperature (5.8) at the location of the reference electrode at the time of measurement of the potential difference, .
49、 It is recommended that the platinum electrode be disconnected from the millivoltmeter between readings. Potassium chloride can leak from the salt bridge and reach significant amounts after about . If this is undesirable, then the salt bridge should be removed from the soil and re-installed prior to each set of measurements. Protect the reference electrode from direct heating by the sun. Keep in mind that the temperature
