A disposable cartridge (10) for use in making electrochemical analytical determinations in the form of a plug-in test cartridge for one-time use with an associated analytical instrument such as a portable blood gas analyzer has a relatively flat base member (16), a handle (12) toward one end, designed to fit a plug-in port in the associated instrument. A raised housing (28) is fixed to the base member (16) that with the base member (16) defines internal flow through measurement chamber (30), a waste storage chamber (32) and connecting passage (36). A sample inlet port (38) in the housing accesses the measurement chamber (30). A sensor substrate (50) carrying an array of electrochemical sensors (40-48) and integral heater is fixed in the measurement chamber (36) and an electrical interface including a plurality of conductors (25) providing input/output connection to the electrochemical sensor array (40-48) and heater is provided. An amount of calibration medium is carried in the measurememt chamber (30) to calibrate one or more of the electrochemical sensors (40-48).
