Abstract: Monitoring acidity at the ppm level in phenol-acetone-cumene process streams on a continuous basis is accomplished with a standard hydrogen electrode and a double-junction reference electrode with an external body solution comprising phenol, acetone, water, and a tetraalkyl- or tetraarylammonium salt, which provide a time invariant voltage without the necessity of adding any external solvent to the process stream. Phenol/acetone ratios can be varied from 1:10 to 10:1 which encompass the 1:1 ratio produced by the phenol-acetone process. A direct correlation of the electrode potential with the acidity of the medium is obtained. With the aqueous mixture isolated by a low flow ceramic junction from the process stream, no contamination of the process stream occurs.

Abstract: A microprocessor-controlled pH and ion concentration meter is disclosed with improved calibration and testing procedures. For calibration (standardization), the meter stores number pairs (pX.sub.a, E.sub.a), (pX.sup.b, E.sub.b) where the pX values may be pH values (e.g., 4.00 and 7.00) and the E values are expressed in mV/deg K. When multiple standard values are stored, remeasuring one (e.g., replacing E.sub.a1 by E.sub.a2) can be used to update the others (e.g., E.sub.b1 to E.sub.b2) without remeasurement by applying the formula:E.sub.b2 =E.sub.b1 +(E.sub.a2 -E.sub.a1).Additionally, the meter can be tested for excessive internal bias current by measuring the potential (V1) when the meter is connected to a circuit of low impedance and the potential (V2) when the meter is connected to a circuit of the same voltage source but of known high impedance and having the meter compare (V2-V1) to a preset limit value.

Abstract: A combination pH/reference electrode is provided with the two electrochemical references being symetrically thermally insulated from the sensing membrane and being thermally adjacent each other. The portion of the pH fill buffer in contact with the inner surface of the sensing membrane is thermally insulated, as by KCl crystals, to rapidly equilibrate in temperatures with the sample solution.

Abstract: A double junction reference electrode which includes an inner body enclosing an inner chamber, a reference element disposed within and extending through the inner body, an outer body disposed around the inner body and enclosing an outer chamber between the inner body and the outer body, an inner ion path through the inner body and providing for the flow of ions between the inner and outer chambers, an outer ion path through the outer body and providing for the flow of ions between the outer chamber and the area exterior of the outer body, a means for introducing an electrolyte into the inner and outer chambers, and a means for releasably joining the inner and outer bodies together to form a unitary electrode structure.