Rapid, high-precision potentiometric titration of alkalinity in ocean and sediment pore waters

A system for rapid, high precision potentiometric determination of alkalinity in sea water and sediment pore water is presented. Two titration units were used: a 40 ml unit for seawater and a small volume unit for sediment pore water. Titration time was normally less than 10 minutes per sample, including sample exchange. With a 40 ml sample volume, the relative standard deviation of the alkalinity obtained in the laboratory was 0.05% and at sea 0.1%. The small-volume system (0.5-1.5 ml) gave a precision of 0.07%. Five titration points, in two groups after the second equivalence point; were used to evaluate the equivalence volume. Results from equilibrium calculations and computer simulated alkalinity titrations show that it was possible to use a non-modified Gran function [(V-0 + v)*10((E/Z))] and still achieve good accuracy and precision. (C) 1998 Elsevier Science Ltd. All rights reserved.