A CRITICAL-EVALUATION OF THE ANALYTICAL BLANK ASSOCIATED WITH DOC MEASUREMENTS BY HIGH-TEMPERATURE CATALYTIC-OXIDATION

The sources, magnitudes and variability of analytical blanks produced during dissolved organic carbon (DOC) measurements by high-temperature catalytic oxidation (HTCO) were investigated using a Shimadzu TOC analyzer and several types of catalysts. The major source of carbon contamination contribution to the blank was derived from the catalyst during the combustion process. Platinized-alumina catalysts from Shimadzu, Aldrich and Sumitomo produced substantial blanks that decreased to fairly constant levels (10-50 muM C) with increasing usage of the catalyst. A platinized quartz catalyst from Shimadzu produced a lower blank (approximately 6 muM C) with relatively little conditioning, whereas combusted (850-degrees-C) quartz chips produced a higher blank (approximately 19 muM C). In light of these findings, it is apparent that the blank should be monitored on a regular basis and accounted for during the analysis of samples.