An analytical device for determining a parameter of a liquid sample, especially a digestion parameter, such as chemical oxygen demand, total carbon content or total nitrogen content, comprising a reactor, and measuring system for ascertaining the parameter of the liquid sample. A container system for storing samples, reagents and waste products in containers, a transport and dosing system for metering and transporting the sample and reagents from the containers into a metering container and for disposal of waste products from the metering container into a waste container, and a measuring transducer for registering a measured parameter correlating, measured value of the liquid sample mixed in the reactor, and measuring, system, in given cases, with one or more reagents is provided. The transport and dosing system is embodied at least of a metering container, a piston pump and an additional sample taking apparatus at least for removal from a sample taking location of a predetermined volume of a liquid as a liquid sample.