A monitoring cell, used to perform a measurement in an NMR spectrometer of a reaction fluid produced by a reaction vessel, has a body having inlet and outlet transport coaxial capillaries for transporting the reaction fluid between the body and the reaction vessel. Cooling lines are also positioned coaxially with the transport capillaries to transport cooling liquid between the body and the reaction vessel. The cell further has a hollow sample probe for insertion into the NMR spectrometer and a coupler section that removably connects the sample probe to the body so that the inlet transport capillary extends through the body into the interior of the sample probe and the outlet transport capillary is sealed to the sample probe to allow reaction fluid that enters the sample probe via the inlet transport capillary to exit the sample probe via the outlet transport capillary.