Real-time analysis of small volume samples with micro ion-selective electrodes

Microelectrode and micro ion-selective electrode (ISE) technologies were applied to obtain real-time analysis of pH, Eh, and major ions (Cl-, Na+, Ca2+ and K+) in pore water samples. The precision and accuracy of micro ISEs were significantly improved by standardizing the solution matrix, accounting for electrode drift and implementing an iterative calibration procedure with analyses of selected samples by conventional techniques. Reliable results were obtained for a chemically complex pore water effluent which ranged in concentration from < 5 to 500 mmol/L. Although labor intensive, this procedure enabled real-time analysis of samples from a column test of very low permeability clay-rich till, which produced effluent sample volumes of only 0.2 to 0.5 mL/d.