Instrument and method for measurement of the organic carbon content of

Abstract

Apparatus and methods for measurement of total organic carbon content of water, particularly of low relative organic content, are described, featuring a single sample cell for exposure of a static sample to ultraviolet radiation and comprising electrodes for measuring the conductivity of the water. The conductivity is monitored as a function of time and the second time derivative of the conductivity signal is monitored to indicate when the oxidation reaction has been completed. Compensation for the contribution to conductivity of the water sample made by the instrument is achieved by subtracting a quantity proportional to the first time derivative of the conductivity at a time when the second time derivative reaches zero, indicating that the oxidation reaction is complete, from the change in the total conductivity measurement, the remainder being equal to the contribution to conductivity made by oxidation of the organic content of the water. The electrodes may have surfaces of a material which when irradiated by the ultraviolet radiation catalyzes the oxidation reaction. Electrophoresis may also be employed to speed the reaction. In appropriate cases, the pH of the water sample is additionally measured and used together with the temperature of the sample to derive a series of values for the carbon dioxide content of the sample from the measured values of the conductivity. For further accuracy, the actual carbon dioxide content values may be employed in the analysis in lieu of the conductivity values.