Abstract
An instrument for measuring dissolved oxygen in seawater is described. The device uses a conventional polarographic electrode in connection with chronoamperometry to overcome many of the problems limiting the performance of oxygen electrodes. The polarizing potential is applied as a pulse and the resulting current transient is sampled after a 1.5- to 3-s delay. Current during the first few seconds is 4 to 8 times the steady-state current and is unaffected by flow rate past the membrane provided a recovery time of 3 min or more is allowed between pulses. Secondary benefits include reproducibility typically better than ±0.8
μM and essentially drift-free operation for several weeks. At a pulsing rate of 120 h
−1 analysis time is 2 to 4 min per bottle. A microcomputer controls all phases of the measuring process: pulse generation, data acquisition, reduction, and storage. Software is used to correct sensor output for temperature dependence exactly using the activation energy of permeation and the Arrhenius equation. An activity coefficient, a function of temperature and salinity, is computed to correct for salinity. Results of an intercomparison with Winkler determinations are presented and an example is given of the instrument's use to measure the respiration of copepods in an unstirred solution.
