ASTM D4127-2012 Standard Terminology Used with Ion-Selective Electrodes《离子选择性电极的标准术语》.pdf
《ASTM D4127-2012 Standard Terminology Used with Ion-Selective Electrodes《离子选择性电极的标准术语》.pdf》由会员分享,可在线阅读,更多相关《ASTM D4127-2012 Standard Terminology Used with Ion-Selective Electrodes《离子选择性电极的标准术语》.pdf(7页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: D4127 12Standard Terminology Used withIon-Selective Electrodes1This standard is issued under the fixed designation D4127; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parenthes
2、es indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This terminology covers those terms recommended bythe International Union
3、 of Pure and Applied Chemistry(IUPAC),2and is intended to provide guidance in the use ofion-selective electrodes for analytical measurement of speciesin water, wastewater, and brines.2. Referenced Documents2.1 ASTM Standards:3D1129 Terminology Relating to Water3. Terminology3.1 DefinitionsFor other
4、definitions used in thisterminology, refer to Terminology D1129.3.2 Definitions of Terms Relevant to Ion-Selective ElectrodeTechnology:acid error, nin very acid solutions, the activity of water isreduced (less than unity) causing a non-Nernstian responsein glass electrodes.DISCUSSIONA positive error
5、 in the pH reading results.activity, nthe thermodynamically effective concentration ofa free ion in solution.DISCUSSIONIn dilute solutions, ionic activity, and concentration arepractically identical, but in solutions of high ionic strength, or in thepresence of complexing agents, activity may differ
6、 significantly fromconcentration. Ionic activity, not concentration, determines both therate and the extent of chemical reactions.activity coefficient, na factor, , that relates activity, A,totheconcentration, C of a species in solution:A 5 CDISCUSSIONThe activity coefficient is dependent on the ion
7、icstrength of the solution. Ions of similar size and charge have similaractivity coefficients.alkaline error, nin alkaline solutions, where hydrogen ionactivity becomes very small, some glass electrodes respondto other cations, such as sodium.DISCUSSIONAnegative error in the pH reading results. By c
8、hangingthe composition of the glass, the affinity of the glass for sodium ion canbe reduced. Such electrodes are known as lithium glass, high-pH, orfull-range electrodes.analate, nthe sample being analyzed; used in the terms“analate addition” and “analate subtraction”.DISCUSSIONThis term differs fro
9、m the term “analyte,” whichdescribes the chemical species of interest in an analytical test.asymmetry potential, nthe potential across a glass pHelectrode membrane when the inside and outside of themembrane are in contact with solutions of identical pH.DISCUSSIONThis term has also been used to defin
10、e the observedpotential differences between identical electrode pairs placed in iden-tical solutions.calibration curve, na plot of the potential (emf or E) of agiven ion-selective electrode cell assembly (ion-selectiveelectrode combined with an identified reference electrode)versus the logarithm of
11、the ionic activity (or concentration)of a given species.DISCUSSIONFor uniformity, it is recommended that the potential beplotted on the ordinate (vertical axis) with the more positive potentialsat the top of the graph and that paA(log activity of the speciesmeasured, A)orpcA(log concentration of spe
12、cies measured, A)beplotted on the abscissa (horizontal axis) with increasing activity to theright. See Fig. 1 and Fig. 2. Region I of Fig. 1 represents the segmentof the curve where the potential no longer changes in response tochanges of the measured species activity and the electrode no longerdemo
13、nstrates Nernstian response.IUPACactivity standard, na standardizing solution whose value isreported in terms of ionic activity.DISCUSSION If the electrode is calibrated using activity standards,the activity of the free, unbound ion in the sample is determined.concentration standard, na standardizin
14、g solution whosevalue is reported in terms of total concentration of the ion ofinterest.1This terminology is under the jurisdiction of ASTM Committee D19 on Waterand is the direct responsibility of Subcommittee D19.05 on Inorganic Constituentsin Water.Current edition approved Aug. 1, 2012. Published
15、 January 2007. Originallyapproved in 1982. Last previous edition approved in 2006 as D4127 06. DOI:10.1520/D4127-12.2Recommendations for Nomenclature of Ion-Selective Electrodes, IUPAC Com-mission on Analytical Nomenclature, Pergamon Press, Oxford, 1976.3For referenced ASTM standards, visit the ASTM
16、 website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United
17、States1DISCUSSIONIf the electrode is calibrated using pure-concentrationstandards and measurements made on untreated samples, results mustbe corrected for the sample ionic strength and the presence ofcomplexing agents. More commonly, a reagent is added to all standardsand samples before measurement
18、in order to fix the ionic strength, thusavoiding the need for bination electrode, nan electrochemical apparatus thatincorporates an ion-selective electrode and a referenceelectrode in a single assembly thereby avoiding the need fora separate reference electrode.concentration, nthe actual amount of a
19、 substance in a givenvolume of solution.DISCUSSIONWhen measuring ionic concentrations by electrode, adistinction is made between the concentration of the free, unbound ion,and total concentration that includes ions bound to complexing agents.dissociation constant, na number indicating the extent tow
20、hich a substance dissociates in solution.DISCUSSIONFor a simple two-species complex AB, the constant isgiven by the product of the molar concentrations of A and of B dividedby the molar concentrations of the undissociated species AB. Forexample, with hydrofluoric acid:H1#F2#!/HF#! 5 K 5 6.7 31024at
21、25CThe smaller the value of K, the less the complex is dissociated. Kvaries with temperature, ionic strength, and the nature of the solvent.drift, nthis is the slow nonrandom change with time in thepotential (emf) of an ion-selective electrode cell assemblymaintained in a solution of constant compos
22、ition and tem-perature.electrode life, nthe length of time that an electrode functionsusefully.DISCUSSIONLife-time of solid-state and glass electrodes is limitedby mechanical failure of the electrode body or chemical attack on thesensing membrane, and can range from a few days, if the electrode isus
23、ed continuously in hot or abrasive flowing streams, to several yearsunder normal laboratory conditions. The life-time of liquid membraneelectrodes is limited by loss of ion exchanger with use, and is generally1 to 6 months.electrode pair, na sensing electrode and a reference elec-trode; the referenc
24、e electrode may be separate or combinedin one body with the sensing electrode.electrolyte, na substance that ionizes in aqueous solution;also, a solution containing ions.DISCUSSIONWeak electrolytes are only slightly dissociated into ionsin solution (acetic acid), and strong electrolytes are highly d
- 1.请仔细阅读文档,确保文档完整性,对于不预览、不比对内容而直接下载带来的问题本站不予受理。
- 2.下载的文档,不会出现我们的网址水印。
- 3、该文档所得收入(下载+内容+预览)归上传者、原创作者;如果您是本文档原作者,请点此认领!既往收益都归您。
本资源只提供5页预览,全部文档请下载后查看!喜欢就下载吧,查找使用更方便
10000 积分 0人已下载
下载 | 加入VIP,交流精品资源 |
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- ASTMD41272012STANDARDTERMINOLOGYUSEDWITHIONSELECTIVEELECTRODES 离子 选择性 电极 标准 术语 PDF

链接地址:http://www.mydoc123.com/p-516335.html