High-accuracy oxygen polarograph for photosynthetic systems

A new system is presented here, whose design is based on the electrochemical phenomena occurring on the platinum electrode that we examined before [P. Meunier and R. Popovic (unpublished)]. The architecture of the system is articulated around an IBM-PC computer which controls the polarization of the electrodes, the triggering of the flash lamp, and the acquisition of data. The potentiostat circuit and new electrode design improve the response of the electrode to a rise time of 4 ms and a decay time constant of 21 ms, without the signal being distorted by filters and without using the first derivative of the signal. This polarograph shows a 50-dB signal-to-noise ratio (0.3% error) during experiments with the motile algae Dunaliella tertiolecta. The determination of amplitudes of oxygen production is performed with third-order cubic spline interpolations, after subtraction of the current base line. The resulting accuracy and reproducibility will enable researchers to attain a higher degree of refinement in the quantification of properties of the oxygen evolving complex.