Dissolved organic carbon contamination induced by filters and storage bottles

Abstract

To optimize experimental protocol for marine dissolved organic carbon (DOC) studies in laboratory conditions, we examined the potential DOC releases from filters of different qualities as well as those from different types of bottles during 10 day-storage of Milli-Q water and 0.2 μm-filtered seawater. The results showed that utilization of 47-mm circle filters including polycarbonate (0.2 and 1 μm-pore size), polytetrafluoroethylene (PTFE: 0.5 μm-pore size) and aluminum oxide (0.2 and 0.02 μm-pore size) may induce significant DOC contamination ranging from 12 to 42 μM C for the first hundred milliliters of the filtrated solutions. However, filtrations of 2 to 4 l of Milli-Q water decreased the DOC blank of the filters to 2–5 μM C. As expected, precombusted (450°C, 6 h) glass fiber filters rinsed with 0.5–3 l of Milli-Q water produced very low blanks (1–4 μM C). We found that 10 day-storage (15°C, in the dark) of Milli-Q water and 0.2 μm-filtered seawater (250 ml) into 1 l-polyethylene, polycarbonate and perfluoalkoxy (PFA)-Teflon bottles, initially cleaned with HCl 1% and abondantly rinsed with copious amounts of Milli-Q water as well as in precombusted glass bottles (450°C, 6 h) induced very low DOC contamination of the solutions (0–5 μM C). Although complete DOC-free contamination experiment is difficult to reach particularly in shipboard conditions, these results strongly suggest that appropriate cleaning procedure of the material is essential to reach blank level compatible with DOC studies in marine environments.