Abstract: A method for in situ sampling and monitoring of a fluid flowing in a flow path, whereby the fluid is to be directed to a chamber a first valve may provide a connection between an inlet to the chamber and the flow path and a second valve may provide a connection between flow path, comprising the following steps: a) opening the first valve and the second valve to let the incoming fluid flow through the inlet to the chamber outlet into the continuation of the fluid path, thereby allowing fluid to circulate through the chamber for a certain time, b) trapping the fluid in the chamber by closing the second valve and thereafter closing the first valve, c) opening a valve 9 pressure in the chamber suitable for monitoring the fluid, d) opening an access valve 11 and leading the fluid trapped in the chamber into a monitor system wherein the fluid is analyzed, and thereby providing the data representing the fluid characteristics, e) providing exit for the fluid analyzed through a further fluid path possibly to a low pre