Monitoring cell for performing a measurement of a reaction fluid produced in a reaction vessel in an NMR spectrometer, in particular for monitoring of a chemical reaction by means of NMR spectroscopy, wherein the monitoring cell has the following components: a hollow NMR sample probe for receiving the reaction fluid to be measured in the NMR spectrometer; an inlet transport capillary for receiving the reaction fluid from the reaction vessel and for transport of the reaction fluid from the reaction vessel to the sample probe; an outlet transport capillary for return transport of the reaction fluid from the sample probe to the reaction vessel; a device for conducting the temperature control fluid around the inlet and outlet transport capillaries (112, 123), which comprises a feed line for feeding the temperature control fluid to the monitoring cell and a return line for return of the temperature control fluid from the monitoring cell, the feed line being coaxially guided within the return line; an adapter section, through which the transport capillaries (112, 123) are fed; and an adapter head on the sample side end of the adapter section, which is configured for coupling of the transport capillaries (112, 123) to the sample probe, wherein the inlet transport capillary extends into the sample probe, and wherein the adapter head removably connects the sample probe to the adapter section; characterized in that the transport capillaries (112, 123) are guided within the feed line in parallel next to one another - and not coaxially - and both transport capillaries (112, 123) are attached in a fluid-tight manner to the adapter head; and that the feed and the return lines (306, 358) are configured for the temperature control fluid and attached to the adapter section in such a way that a reversal of the temperature control fluid stream occurs in the adapter section. a hollow NMR sample probe for receiving the reaction fluid to be measured in the NMR spectrometer; an inlet transport capillary for receiving the reaction fluid from the reaction vessel and for transport of the reaction fluid from the reaction vessel to the sample probe; an outlet transport capillary for return transport of the reaction fluid from the sample probe to the reaction vessel; a device for conducting the temperature control fluid around the inlet and outlet transport capillaries (112, 123), which comprises a feed line for feeding the temperature control fluid to the monitoring cell and a return line for return of the temperature control fluid from the monitoring cell, the feed line being coaxially guided within the return line; an adapter section, through which the transport capillaries (112, 123) are fed; and an adapter head on the sample side end of the adapter section, which is configured for coupling of the transport capillaries (112, 123) to the sample probe, wherein the inlet transport capillary extends into the sample probe, and wherein the adapter head removably connects the sample probe to the adapter section; characterized in that the transport capillaries (112, 123) are guided within the feed line in parallel next to one another - and not coaxially - and both transport capillaries (112, 123) are attached in a fluid-tight manner to the adapter head; and that the feed and the return lines (306, 358) are configured for the temperature control fluid and attached to the adapter section in such a way that a reversal of the temperature control fluid stream occurs in the adapter section.