A NITRITE MICROSENSOR FOR PROFILING ENVIRONMENTAL BIOFILMS

A highly selective liquid membrane nitrite microsensor based on the hy drophobic ion-carrier aquocyano-cobalt(III) -hepta(2-phenylethyl)-cobr ynate is described, The sensor has a tip diameter of 10 to 15 mu m. Th e response is log-linear in freshwater down to 1 mu M NO2- and in seaw ater to 10 mu M NO2-. A method is described for preparation of relativ ely large polyvinyl chloride (PVC)-gelled liquid membrane microsensors with a tip diameter of 5 to 15 mu m, having a hydrophilic coating on the tip, The coating and increased tip diameter resulted in more sturd y sensors, with a lower detection limit and a more stable signal than uncoated nitrite sensors with a tip diameter of 1 to 3 mu m. The coati ng protects the sensor membrane from detrimental direct contact with b iomass and can be used for all PVC-gelled liquid membrane sensors mean t for profiling microbial mats, biofilms, and sediments. Thanks to the se improvements, liquid membrane sensors can now be used in complex en vironmental samples and in situ, e.g., in operating bioreactors. Examp les of measurements in denitrifying, nitrifying, and nitrifying/denitr ifying biofilms from wastewater treatment plants are shown. In all of these biofilms high nitrite concentrations were found in narrow zones of less than 1 mm.