IEC 60746-2-2003 pdf – Expression of performance of electrochemical analyzers – Part 2: pH value

IEC 60746-2-2003 pdf – Expression of performance of electrochemical analyzers – Part 2: pH value.
3.1.5 temperature compensator electrical sensor in thermal contact with the sample providing the means for temperature compensation 3.1.6 sensor unit insertion or flow-through housing into which pH and reference sensors, as well as usually, a temperature compensator (see 4.3.4) and possibly auxiliary devices (see 4.3.5) are fitted. 3.1.7 zero point pH pH value at which the e.m.f. of the electrode pair (sensor unit) is 0 V at a given temperature, unless otherwise stated, understood to be 25 °C. 3.1.8 isopotential pH, pH i , of the electrode pair (sensor unit) pH, pH i , at which the e.m.f., E i , of the electrode pair is temperature invariant. It is a function of the temperature coefficients of the individual electrodes and provides temperature compensation for the electrode pair zero shift with appropriate instrumentation. 3.1.9 alkaline (or sodium) error of the glass electrode error of the e.m.f. caused by sensitivity of pH glass electrodes to alkali ions at high pH resulting in apparent low pH values. Major interferences are Na + > Li + > K + > Ba 2+. Errors increase with increasing alkali concentration, pH and temperature. The magnitude is dependent on the glass membrane composition. 3.1.10 reference buffer solution aqueous solution prepared according to a specific formula using recognized analytical grade chemicals and water having a conductivity no greater than 2 µ⋅cm –1 at 25 °C (see Annex B) 3.1.11 solution ground (earth) electrode inert metal electrode required for differential input instrumentation as a comparison point against which glass and reference electrode potentials are determined. For other applications, it establishes the sample potential at instrument ground (earth) 3.1.12 simulator simulator providing Nernstian values of e.m.f.s (see 3.1.1 and Table A.1), representing pH values at selected temperatures through a high value series resistor representative of pH sensors. The simulator comprises a stepped voltage source followed by a selectable series resistor.
5 Recommended standard values and ranges of influence quantities affecting the performance of electronic units See Annex A of IEC 60746-1. 6 Verification of values See Clause 6 of IEC 6046-1, plus the following: 6.1 General aspects 6.1.1 Glass electrodes shall be conditioned according to the manufacturer’s instructions. At least 12 h hydration in a neutral or mildly acidic buffer solution shall be allowed for initial equilibration of new electrodes. 6.1.2 Reference pH buffer solutions shall be used for all tests unless otherwise agreed upon with the manufacturer (see 3.5 of IEC 60746-1 and Annex B) . NOTE IUPAC recommended reference buffer solutions are tabulated in Annex B. Other reference pH buffer solutions may be used . 6.1.3 Test solutions shall be applied in a manner suited to the sensor unit. 6.1.3.1 Flow-through sensor units Solutions shall be applied at a flow rate within the manufacturer’s rated range. 6.1.3.2 Insertion sensor units For measurements with more than one solution, unless otherwise indicated, the electrode pair (sensor unit) shall be rinsed with deionized water, thereafter pre-rinsing with the new solution prior to immersion. It is recommended that measurements shall be made in continuously stirred solutions to ensure homogeneity. 6.2 Test procedures for electronic units Prior to testing the analyzer, the electronic unit shall be separately tested with a simulator such as that described in 3.1.12 and using either manual temperature control or a suitable resistor connected to the temperature compensator input.
6.2.1 pH scaling If adjustable, set the isopotential control to the zero point pH, usually both are pH 7, and, if provided, cancel or adjust the sample pH temperature compensation to zero. If manually adjustable, set the percentage slope control to 100%. Adjust the manual or simulated temperature to 25°C or other reference temperature. Connect a simulator and check the scaling throughout pH 0 to pH 14 or the test pH range. At the scale length extremes, switch-in the series high resistance simulating that of the glass electrode as a check of the instrument’s input impedance, an immediate transient should rapidly dissipate. Repeat the procedure for other temperatures within the test range (see Table A.1). With the simulator, impose a lower percentage slope output (for example, at 25 °C for 90 % slope, 53,24 mV per pH unit) at 25 °C or other reference temperature to assess the percentage slope facility.