An automated photochemical method for the determination of dissolved organic carbon in sea and estuarine waters

Abstract

An improved version of Ehrhardt's (1969) method for the analysis of dissolved organic carbon is described. The method, which is automated, determines the carbon dioxide with a non-dispersive infra-red analyser. The conditions of photo-oxidation have been examined in order to achieve maximum performance. It was found that careful attention needed to be paid to U-V source, “oxygen source”, pH and time or irradiation. The completeness of the method was examined by three independent procedures. We concluded that in all cases the extent of oxidation of organic material was in excess of 98%. Typical performance figures were: precision ±2.5% above 2.0 mg C l −1, approaching 0.03 mg C l −1 below 1.0 mg Cl −1; blank, equivalent to 0.3 mg C l −1; sampling frequency, 10 samples per hour. The lower limit of sensitivity is mainly governed by the blank. The upper limit of the method is greater than 40 mg C l −1. A wholly continuous modification of the method has been devised which permits on line analyses. An attentuated version of the method has been used for the analysis of total carbonate. The present and other published methods for the analysis of dissolved organic carbon in natural waters are discussed in relation to one another.