Device in a gas flow cell and a method of analyzing chemical substances by means of the gas flow cell

Device in a gas flow cell (1) for the analysis of chemical substances by spectrophotometry, the gas flow cell (1) having an elongated, preferably cylindrical body (2), which comprises two longitudinal ducts (3,4), connected to one another by an essentially radial connection (5) so that a first flow is permitted through the ducts (3,4) and the connection (5), where the first duct (3) in the direction of flow has a separation column and the second duct (4) is a light guide duct, characterised in that in the connection (5) there is a coupling, which is connected via a communicating duct (11) with the outlet from an external separation unit, designed to separate the chemical substances, and which is designed to receive a second flow comprising the substances separated in the external separation unit together with a first carrier gas, so that the second flow is added to the first flow in the connection (5), the device being able to switch over to either of two operating positions, where in the first position the first flow comprises the chemical substances and a second carrier gas and the other flow is stopped, and where in the second position the first flow comprises the second carrier gas and the second flow is connected up.