A reactor assembly for analysing the effluent stream from at least one flow-through reactor, The reactor includes a flow-through reactor for performing at least one chemical reaction. The flow-through reactor includes a reaction chamber including a reaction zone, the reaction chamber being connected to a reactor inlet for a reactant, upstream of the reaction zone and a reactor outlet for the effluent stream from the reaction zone, downstream of the reaction zone; and an analyser for subjecting the effluent stream to an analysing procedure, each reactor outlet being connected to an analyser by an effluent conduit. The reactor assembly further includes a dilution fluid supply member for adding a dilution fluid to the effluent stream, downstream of the reaction zone.