Abstract: The disclosure relates to a process for making titanium dioxide, comprising: reacting titanium tetrachloride with oxygen by contacting the titanium tetrachloride with the oxygen in a vapor phase reactor under mixing conditions and at an elevated temperature to form a gaseous product stream containing titanium dioxide; separating the titanium dioxide from the gaseous product stream to form a process stream; analyzing the process stream to detect a concentration of titanium tetrachloride in the process stream; comparing the concentration of titanium tetrachloride detected in the process stream to an aim point concentration; and modifying the oxidation conditions to restore or maintain the concentration of titanium tetrachloride in the process stream at the aim point.