The measurement of dissolved carbon dioxide (excluding HCO3 - and CO3 2-) in water is one of the most important parameters for water monitoring. AMT GmbH has developed now a new membrane covered optical CO2 sensor with titanium housing and other improved characteristics. So the new AMT-CO2 sensor is designed for depths of up to 1,000 m, has an analogue or digital output, a reduced current uptake and includes an automatic internal temperature compensation. The sensor is designed to be interfaced externally to CTD probe systems, to own measuring systems or as stand alone sensor.