(ii) Measurement during irradiation (e.g. for 1 hour) -during this phase, a change in oxygen concentration due to action of the photocatalyst is expected (iii) Measurement of post-reaction baseline after irradiation (typically 15-30 min) -if a change in oxygen concentration occurred during irradiation, the oxygen concentration will equilibrate again during this time Data collected during phases (i) and (iii) can be used for baseline correction during data analysis (see Section 6), allowing for a more precise quantification of changes of O2 concentration during irradiation.