Abstract: A given volume of a test substance is provided into a monitoring line which is filled with a test medium (e.g. air). The line extends along a path for determining concentration profiles of certain substances along the path. For the purpose of transporting a column of test medium through the monitoring line, the pressure in the monitoring line is increased by switching on a pressure pump or, for the same purpose--in an alternative embodiment--the pressure is reduced by switching on a suction pump. A given metering volume of the test substance is automatically released in the monitoring line when the pressure goes beyond a given pressure threshold. The release of the given metering volume of the test substance, after it has been carried along the monitoring line by the column of test medium, results in a test peak for reference reading calibration in a sensor which responds to the test substance and which is connected to the monitoring line.

Abstract: The apparatus enables accurate determination of concentration profiles of liquid or gaseous substances along a given path. A partially permeable line segment is laid along the route and the substances to be detected are allowed to penetrate into its interior. The line is filled with a test medium, and the column of the test medium is forced through the line at chronological intervals and moved past a sensor that is sensitive to the substances. A first closure is incorporated between the sensor and the line, and one or more closures are incorporated into the line to maintain the column of test medium substantially stationary in a position of repose of the system.