SHIPBOARD INVESTIGATION OF DOC IN THE NE ATLANTIC USING PLATINUM-BASED CATALYSTS IN A SHIMADZU TOC-500 HTCO ANALYZER

A shipboard evaluation of the high-temperature catalytic oxidation (HTCO) efficiencies of various Pt-based catalysts, for the conversion of dissolved organic carbon (DOC) to CO2, was carried out using a Shimadzu TOC-500 system on replicate samples from the upper 300 m of the NE Atlantic Ocean. In some cases, catalysts were used in conjunction with scrubbers for removal of interfering gaseous by-products (Cl2, S and CO). Rigorous consideration of blanks, calibration and standards highlighted several uncertainties in the performance of some catalysts. It is postulated that a high and randomly fluctuating instrument blank, most probably arising from the catalysts, may be responsible, The inclusion of chemical scrubbers in combustion columns appears to have only minor effects on the integrity of analyses. The 100% Pt catalyst generally oxidised the greatest proportion of oceanic DOC, although all catalysts used here have produced DOC concentration (90-210 muM C); consistently higher than previous reliable wet oxidation data (50-60 muM C) for this region.