Observation and quantitative analysis of curvilinear regions of time-varying oxygen concentrations with an oxygen electrode and a minicomputer

Abstract

A system capable of obtaining estimates of rate of change and acceleration of oxygen concentration over time intervals as short as 12 s can easily be assembled using only commercially available oxygen electrodes, a pH meter with a BCD printer output, and a minicomputer with a standard IEEE parallel port. Most of this 12-s time interval is consumed in conducting a linear regression between the oxygen concentration values and associated values of time supplied by the computer. The interval over which data are actually collected is far shorter, being determined by the number of data points specified for the linear regression and the frequency of data output by the pH meter (10 values · s −1). This system makes it possible to use the standard clerk-type oxygen electrodes in a mode of operation greatly superior to that generally employed. In this alternative procedure the polarizing voltage is applied to the electrode for only 1–2 s during which 10 or more values of time and electrode output must be collected and analysed. This mode of operation has the advantages that the electrode signal is totally independent of stirring rate, the sensitivity of an electrode is 5–10 times greater operated in this manner, electrode response to temperature is greatly reduced and the electrode response does not change even if the membrane properties alter with time. The period over which data are collected is so short relative to the time constants associated with experimentally observed changes in oxygen concentration that each data set is perfectly represented by a straight line approximation. That is, even the most curvilinear regions of time-varying oxygen concentration plots are observed as, and quantitatively assessed as, straight line segments since the data are collected over time intervals which are vanishingly small. Each processed data set yields statistical criteria of the fitting and estimates of intercept and slope. Plots of slope versus time can then be employed to obtain quantitative estimates of acceleration of oxygen production and consumption. Adaptation of the photo-synthetic capacity of the macroalga Ecklonia radiata (C. Ag.) J. Agardh to the frequency of flashing light was observed by being able to rapidly accumulate rate estimates. After 30 min of exposure to a light regime of 1 min L, 1 min D a greater than four-fold enhancement of the P/R ratio was observed.