IEC 60746-2 pdf download

IEC 60746-2 pdf download Expression of performance of electrochemical analyzers – Part 2: pH value
1 scope
This lnternational Standard is intended:
– to specify terminology,definitions and requirements for statements by manufacturers for
analyzers，sensor units and electronic units used for the determination of the pH ofaqueous solutions;
to establish performance tests for such analyzers, sensor units and electronic units;
to provide basic documents to support the applications of quality assurance standards Iso9o01,Iso 9002 and lso 90o3.
2Normative reference
The following referenced documents are indispensable for the application of this document.For dated references,only the edition cited applies. For undated references, the latest editionof the referenced document (including any amendments) applies.
IEC 60746-1:2002,Expression of performance of electrochemical analyzers – Part 1 : GeneralIso 9001,Quality management systems – Requirements
Iso 9002，Quality systems – Model for quality assurance in production,installation andservicing
Iso 9003,Quality systems – Model for quality assurance in final inspection and test
3 Terms, definitions, symbols and abbreviations
3.1 Terms and definitions
For the purposes of this part of lEC 60746, the definitions given in Clause 3 of lEC 60746-1,as well as the following apply.
3.1.1
pH value
A measure of the conventional hydrogen ion activity ag+ (see equation (1)), in an aqueoussolution given by the expression:
pH = -log aH+
lt is measured with respect to pH values assigned to certain reference pH buffer solutions.The measurement is performed by determining the e.m.f.，E， between a pair of electrodesimmersed in the sample to be measured,according to the cell scheme:
Reference electrode l Sample l pH electrode
E
and a measurement with the same electrode pair at the same temperature in a referencebuffer solution of pH(s1) according to
Reference electrode l Buffer (s1)l pH electrodeE(S1)
The e.m.f.s E(S), etc. are defined as the difference of the potential of the right-hand (pH)electrode minus the potential of the left-hand (reference) electrode.
The pH of the sample is then given ideally by:
where k = 2,3026 R.T/F, the theoretical,Nernstian, slope (see 3.1.2) .
Numerical values for k, the theoretical slope factor, at temperatures from 0 °C to 95 °C, aregiven in Annex A.
NOTEMeasurements in non or partially aqueous media are beyond the scope of this document; the reader shouldrefer to specialist texts.
3.1.2
practical slope factor and percentage theoretical slopePTs
performance of the electrode pair may fall below the theoretical slope k exhibiting the practicalslope k which may be determined by replacing the sample with a second reference buffersolution of pH value pH(S2) with an e.m.f.E(S2), then:
E(s2)-E(s,)k= nHS2)-pH(S2)
NOTE The difference in pH value between the two reference buffer solutions should be as large as possible,however, solutions above pH 10 and below pH 3 should not generally be used (see Annex B).
The percentage theoretical slope (PTS) is given by:
PTS = “Uu
Equations (1) and(2) can be combined by substituting k for k in equation (1) where:
pH= pH(s,)_ E-E(S)].[pH(Sz)-pH(sz)E(S2)-E(s,)
and the two reference buffers are usually chosen to bracket the pH of the sample.