ADVANCED FLOW-THROUGH EXTERNAL PRESSURE-BALANCED REFERENCE ELECTRODE FOR POTENTIOMETRIC AND PH STUDIES IN HIGH-TEMPERATURE AQUEOUS-SOLUTIONS

A new flow-through external pressure-balanced reference electrode (FTE PBRE) has been developed for potentiometric and pH measurements in hig h temperature aqueous solutions. The unique feature of this advanced F TEPBRE is that the reference solution flows through the electrode so t hat the concentration of solution across the thermal liquid junction i s well defined. Because the electrolyte concentration profile in the r eference electrode is maintained constant, uncertainty in the thermal liquid junction potential (TLJP) can be eliminated at a given temperat ure and pressure. We have employed the silver/silver chloride/platinum /hydrogen non-isothermal electrochemical system for potentiometric mea surements of potentials between HCl(aq) solutions of 0.01 and 0.001 mo l kg(-1) at temperatures up to 633 K and at pressures of 275 and 338 b ar. The results of the measurements have been compared with calculatio ns made using the available thermodynamic data, and good agreement, wi thin +/-3 to 10 mV, between the calculated and the measured potentials is obtained. We concluded that the advanced reference electrode can b e sed to make accurate potentiometric measurements (within a few mV) i n aqueous systems over wide ranges of temperatures and pressures. Also we demonstrated an ability of the thermocell to measure pH with high accuracy of +/- 0.04 to 0.09 over wide ranges of temperature and press ure. (C) 1998 Elsevier Science S.A. All rights reserved.