HTCO METHOD FOR DISSOLVED ORGANIC-CARBON ANALYSIS IN SEAWATER - INFLUENCE OF CATALYST ON BLANK ESTIMATION

Ever since a controversy developed around the measurement of dissolved organic carbon in seawater, it has been important to understand the reasons for the discrepancies among various analysts and methods. In this work we have compared the results obtained with a wet oxidation method (UV-Persulphate) and an HTCO method (Shimadzu TOC 5000 analyzer). It appeared that when significant differences were obtained between the different methods, it was because of a poor estimation of the blank. During HTCO analyses, blanks as high as 80 muM can be measured. Blanks appear to originate mainly from the catalyst. Different catalysts were checked and those made of platinum coated alumina produced very high blanks, probably due to a high capacity to adsorb and desorb CO2. Catalysts made of silica produced much lower blanks. If the blanks are well estimated and a correction is made, the difference between the two wet and HTCO methods represents no more than 10-15% of the total concentration, and is sometimes within the variability of data.