When photochemistry data drifts day to day, the chemistry is usually innocent, the hardware is guilty. This FAQ organizes the highest-frequency workstation issues by symptom, cause and fix.
Symptom: rates falling across weeks at identical settings. Cause: lamp aging, the most common drift source in any photolab. Fix: re-measure intensity at the working position now, not at the last calibration, compare with the lamp-hour log, and replace or recalibrate. LEDs age too, and their spectra shift with junction temperature.
Symptom: selectivity changing between morning and afternoon runs. Cause: bath or ambient temperature drift, or a cooling fan filter clogging slowly. Fix: log internal reaction temperature every run, not just bath setpoint, and service filters on schedule. Fixing the symptom means fixing the loop, not re-running the experiment.
Symptom: oxygen-sensitive chemistry suddenly failing. Cause: a seal that has aged, often a vial cap septum or a fitting O-ring. Fix: leak-test with pressure hold or soap solution, replace seals on a calendar schedule rather than a failure schedule, and purge verified volumes before irradiation.
Symptom: replicate vials disagreeing. Cause: magnetic coupling varying across positions, or vials sitting at slightly different heights. Fix: verify stirring visually at every position, standardize vessel seating, and re-run the channel consistency check.
Weekly: intensity spot-check, seal inspection. Monthly: filter cleaning, full uniformity map. Logged always: lamp hours, seal replacements, every calibration. The calendar is short, the alternative is unexplained data.
See instrument maintenance guides for Perfectlight's photochemistry platforms.
