1、BRITISH STANDARD BS 7310:1990 Specification for Ion-selective electrodes, reference electrodes, combination electrodes and ion-selective electrode meters for determination of ions in solutionBS7310:1990 This British Standard, having been prepared under the direction of the Laboratory Apparatus Stand
2、ards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 30 September 1990 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference LBC/16 Draft for comment 89/51788 DC ISBN 0 580 18452 8 Committees responsible for
3、 this British Standard The preparation of this British Standard was entrusted by the Laboratory Apparatus Standards Policy Committee (LBC/-) to Technical Committee LBC/16, upon which the following bodies were represented: British Kinematograph, Sound and Television Society British Pharmacopoeia Comm
4、ission Chemical Industries Association Electricity Supply Industry in England and Wales GAMBICA (BEAMA Ltd.) Institute of Medical Laboratory Sciences Royal Society of Chemistry Sira Ltd. Society for Applied Bacteriology Society of Chemical Industry University of Newcastle upon Tyne Amendments issued
5、 since publication Amd. No. Date CommentsBS7310:1990 BSI 10-1999 i Contents Page Committees responsible Inside front cover Foreword ii Section 1. General 1.1 Scope 1 1.2 Definitions 1 Section 2. Ion-selective electrodes 2.1 Performance 6 2.2 Information to be supplied by the manufacturer 6 Section 3
6、. Reference electrodes 3.1 Performance 7 3.2 Information to be supplied by the manufacturer 7 Section 4. Combination electrodes 4.1 Performance 8 4.2 Information to be supplied by the manufacturer 8 Section 5. ISE meters 5.1 Performance and design 9 5.2 Information to be supplied by the manufacturer
7、 11 Appendix A Outline of procedures for using ion-selective electrodes 12 Appendix B Check tests on electrodes 13 Appendix C Instrument check tests 16 Appendix D Standard reference solutions for direct potentiometry 17 Appendix E Bibliographical references 18 Figure 1 Calibration curve and determin
8、ation of practical limit of detection 4 Table 1 Values of the slope factor k at temperatures from 0 C to 95 C 12 Table 2 Applied voltages for calibrating pX scales 17 Table 3 Applied voltages for calibrating temperature-compensating devices 17 Publications referred to Inside back coverBS7310:1990 ii
9、 BSI 10-1999 Foreword This British Standard has been prepared under the direction of the Laboratory Apparatus Standards Policy Committee. The most practised method of potentiometry is the determination of hydrogen ions, i.e. pH measurement, but because of its importance this is dealt with separately
10、 in BS1647, BS2586 and BS3145. Potentiometric determination of ion concentrations/activities received a fillip in the early 1970s with the commercial availability of a new range of ion-selective membrane electrodes 1, 2, 3 related to the familiar pH glass electrode, but responsive to a variety of ot
11、her cations, for example K +and Ca 2+ , and anions, for example F and , some of which could not previously be determined potentiometrically. This British Standard covers this new range of ion-selective (membrane) electrodes and reference electrodes and an outline of procedures for using ion-selectiv
12、e electrodes is given inAppendix A. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. NO 3
13、Summary of pages This document comprises a front cover, an inside front cover, pagesi and ii, pages1 to 18, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside
14、 front cover.BS7310:1990 BSI 10-1999 1 Section 1. General 1.1 Scope This British Standard specifies performance requirements and other requirements for ion-selective electrodes, reference electrodes and combination (dual) ion-selective electrodes in general laboratory use, and for ion-selective elec
15、trode meters for laboratory use. NOTE 1An outline of procedures used for determining ionic species (except hydrogen ion), and neutral species indirectly, using ion-selective electrodes, is given inAppendix A. NOTE 2Recommended tests of performance of electrodes are described inAppendix B. NOTE 3Inst
16、rument check tests are described inAppendix C. NOTE 4Appendix D covers standard reference solutions for direct potentiometry. NOTE 5The titles of the publications referred to in this standard are listed on the inside back cover. The numbers in square brackets represent the bibliographical references
17、 given inAppendix E. 1.2 Definitions For the purposes of this British Standard the following definitions apply. 1.2.1 General 1.2.1.1 pX the quantity defined by analogy with pH as pX = pa X= log a X , where a Xis the single ion activity of the species X, or alternatively as pX = pc X=logc X , where
18、c Xis the species concentration of X in mol/L 1.2.1.2 reference standards aqueous solutions which are the basis for standardizing the ISE cell (see 1.2.1.12) NOTEValues may be assigned as described inAppendix D. 1.2.1.3 practical response time the length of time that elapses between the instant at w
19、hich an ion-selective electrode and a reference electrode are brought into contact with a sample solution (or instant at which the concentration of the ion of interest is changed) and the first instant when the potential change of the cell has reached90% of the final value NOTEThe experimental condi
20、tions used should be stated, i.e. the stirring rate, the ionic concentration and composition of solution of which the response time is measured, the ionic concentration and composition of the solution to which the electrode was exposed prior to this measurement, the history and preconditioning of th
21、e electrode, and the temperature. 1.2.1.4 liquid junction any junction between two electrolyte solutions of different composition. Across such a junction there arises a potential difference, called the liquid junction potential NOTEIn the ISE cell, the junction is between the test, or standard, solu
22、tion and the filling solutions, or the bridge solution (see 1.2.3.3), of the reference electrode. 1.2.1.5 residual liquid junction (potential) error an error arising from breakdown in the assumption that the liquid junction potential remains constant on change of solution 1.2.1.6 slope factor, k the
23、 temperature-dependent proportionality factor between potential difference and pX for monovalent ions NOTEValues of k are given inTable 1. 1.2.1.7 test solution the solution of which the ionic activity, or ionic concentration, is required 1.2.1.8 drift this is the slow, non-random change with time i
24、n the potential difference of an ion-selective reference electrode cell maintained in a solution of constant composition and temperature 1.2.1.9 hysteresis (electrode memory) the occurrence of a different value in the potential difference after the concentration has been changed and then restored to
25、 its original value. The reproducibility of the electrode is consequently poor. The systematic error is generally in the direction of the concentration of the solution in which the electrode was previously immersed. Hysteresis may occur as a result of temperature change 1.2.1.10 membrane a continuou
26、s layer covering a structure or separating two electrolytic solutions. The membrane of an ion-selective electrode is responsible for the potential response and selectivity of the electrode 1.2.1.11 interfering substance any species, other than the ion being measured, whose presence in the sample sol
27、ution affects the measured potential difference of a cellBS7310:1990 2 BSI 10-1999 1.2.1.12 ISE cell electrochemical cell, which is the basis of practical measurements, consisting of an ion-selective electrode (ISE) (see1.2.2.1) responding to the species X and a reference electrode (see1.2.3.1) dipp
28、ing in the test solution 1.2.1.13 ionic-strength adjustment buffer a pH-buffered solution of high ionic strength added to both sample and calibration solutions before measurement in order to achieve identical strength and hydrogen ion activity. Complexing agents and other components are often added
29、to minimize the effects of certain interferences 1.2.1.14 standard addition method (or known addition method) a procedure for the determination of the activity or concentration of a particular species in a sample by adding known amounts of that species to the sample solution and recording the change
30、 in potential difference of the ion-selective cell 1.2.1.15 standard subtraction method (or known subtraction method) a variation of the standard addition method (see1.2.1.14). In this procedure changes in the potential resulting from the addition of a known amount of a species which reacts stoichio
31、metrically with the ion of interest (e.g. a complexing agent) are employed to determine the original activity or concentration of the ion 1.2.1.16 ionic strength of a solution the ionic strength of a solution I (in mol/L) is defined by the following equation: where c iis the concentration of the ion
32、, i (in mol/L); z iis the change of the ion, i. 1.2.1.17 gran plot a means of evaluating titration, or standard addition, results in which a suitable function of the potential difference of the measuring cell is plotted on the vertical axis against volume increments on the horizontal axis, giving a
33、linear plot allowing the concentration of the sensed species to be obtained from the intercept on the horizontal axis 4 1.2.2 Ion-selective electrodes 1.2.2.1 ion-selective electrode (ISE) 1.2.2.1.1 general electrode responding to ions of species X, usually consisting of a membrane in the form of a
34、disc, or other suitable shape, of special material attached to a stem of plastics or glass complete with internal reference electrode (see1.2.2.2) and, optionally, an internal filling solution system (see1.2.2.3). Other geometrical forms may be appropriate for special applications, e.g. flow electro
35、des for measurement of ionic species in body fluids ion-selective electrodes may be classified as crystalline, non-crystalline and sensitized (see1.2.2.1.2 to 1.2.2.1.4) 1.2.2.1.2 crystalline electrodes these are categorized as follows a) Homogeneous, in which the membrane is a crystalline material
36、prepared from either a single compound or a homogeneous mixture of compounds (e.g. Ag 2 S and AgI+Ag 2 S). b) Heterogeneous, in which an active substance, or mixture of active substances, is mixed with an inert matrix, such as silicone rubber or PVC, or placed on hydrophobized graphite, to form the
37、sensing membrane. 1.2.2.1.3 non-crystalline electrodes these consist of a matrix containing an ion-exchanger which is usually interposed between two aqueous solutions. The matrix may be porous (e.g. cellulose ester) or non-porous e.g. glass or inert polymeric material such as polyvinyl chloride (PVC
38、) typical of this class are glass electrodes in which the sensing membrane is a thin piece of glass. The chemical composition of the glass determines the selectivity of the membrane, e.g. hydrogen ion-selective electrodes (seeBS2586) and monovalent cation-selective electrodes electrodes with a mobil
39、e carrier are categorized as follows a) Positively charged, e.g. those of quaternary ammonium salts or salts of transition metal complexes such as derivatives of1,10-phenanthroline. b) Negatively charged, e.g. bulky anions such as dialkyl phosphate and tetrakis (p-chlorophenyl) borate anions. c) Unc
40、harged or neutral carrier, e.g. antibiotics, macrocyclic compounds or other sequestering agents. (1) I Cc i z 2 i = RO () 2 PO 2 BS7310:1990 BSI 10-1999 3 1.2.2.1.4 sensitized ion-selective electrodes these are categorized as follows a) Gas sensing electrodes. These are sensors composed of an indica
41、tor and a reference electrode and use a gas-permeable membrane or an air-gap to separate the sample solution from a thin film of an intermediate solution that is either held between the gas membrane and the ion-sensing membrane of the electrode or placed on the surface of the electrode using a wetti
42、ng agent (e.g. air-gap electrode). This intermediate solution interacts with the gaseous species in such a way as to produce a change in a measured value (e.g. pH) of the intermediate solution. This change is then sensed by the ion-selective electrode and is proportional to the partial pressure of t
43、he gaseous species in the sample. NOTEGas-sensing electrodes are in fact whole electrochemical cells. b) Enzyme substrate electrodes In these an ion-selective electrode is covered with a coating containing an enzyme which causes the reaction of an organic or inorganic substance (substrate) to produc
44、e a species to which the electrode responds. Alternatively, the sensor could be covered with a layer of substrate that reacts with the enzyme to be assayed. An example is an ammonium ion-selective electrode coated with urease for urea determination. 1.2.2.2 internal reference electrode (of an ion-se
45、lective electrode) electrode, e.g. silver-silver chloride, electrically connected to the screened input cable to the meter, and in contact with the internal filling solution NOTEIn all-solid-state electrodes the material of the reference electrode is deposited directly on to the membrane and the int
46、ernal filling solution is unnecessary. 1.2.2.3 internal filling solution (of an ion-selective electrode) aqueous electrolyte solution, which may be gelled, containing a fixed concentration of ion X and a fixed concentration of the ion to which the inner reference electrode is reversible, e.g. chlori
47、de ion in the case of silver-silver chloride or calomel electrodes 1.2.2.4 screened cable coaxial shielded cable connecting the ion-selective electrode internal reference electrode system to a plug for input to the measuring instrument (ISE meter) NOTESome electrodes may be provided with detachable
48、screened cables. 1.2.2.5 screened ion-selective electrode ion-selective electrode in which the screening is continued down almost the whole length of the stem of the electrode NOTECombination electrodes are screened by the external reference electrode filling solution (see1.2.3.1 and 1.2.3.2). 1.2.2
49、.6 zero point (of an ion-selective electrode) value of the pX of a solution, which in combination with a stated outer reference electrode, gives zero potential difference from the cell 1.2.2.7 electrode error deviation of an ion-selective electrode from the X ion response function 1.2.2.8 calibration curve of an ion-selective electrode a plot of the potential difference of a given ion-selective electrode cell against the logarithm of the ionic activity (or concentration) of species X NOTEA calibration curve usually has the shape shown in Figure 1. An ioni
