Membrane introduction mass spectrometry (MIMS) has been applied to monitor and compare in real time the extent by which three photocatalytic remediation processes-Fenton＇s reagent/ UV, ferrioxalate/H2O2/UV, and TiO2/UV-destroy two common water pollutants-phenol and trichloroethylene (TCE). Continuous MIMS and selected ion monitoring (MIMS-SIM) of both phenol and TCE degradation and CO2 production show first-order kinetics for the three processes. Phenol half-life times indicate that Fenton＇s reagent/UV and ferrioxalate/H2O2/UV destroys phenol 10 times faster than TiO2/UV, that is, Fenton＇s reagent/UV approximate to ferrioxalate/H2O2/UV >> TiO2/UV. For TCE, half-life times for the three remediation processes are ordered as follows: ferrioxalate/H2O2/UV >> Fenton＇s reagent/UV > TiO2/UV. For phenol, the extent of mineralization measured via total organic carbon analysis was lower than the extent of degradation measured by MIMS-SIM; hence, for the three processes, the intermediate products of phenol photocatalytic degradation are slowly destroyed. For Fenton＇s reagent/UV and ferrioxalate/H2O2/UV GC/MS analysis detected pyrocatechol as the main intermediate of phenol degradation and p-benzoquinone for TiO2/UV.