A measuring device for a container having a process connection for determining the concentration of a constituent in an essentially liquid container content, comprising a concentration sensor, wherein the measuring device comprises a filter, an extraction line and a pump, wherein the filter is arranged within the container and the concentration sensor is arranged outside of the container, and the extraction line runs, starting from the filter, through the process connection to the concentration sensor, with the concentration sensor being connected to the pump, and the pump conveys the container content from the container through the filter across the extraction line to the concentration sensor, with the extraction line having at least one bend located between the filter and the process connection.