Life…The life expectancy of Photoionisation Detector (PID) lamps depends on how they are operated. Factors such as detector temperature, current through the lamp, sample type and window cleaning procedures all directly affect useful life.

Operation…Typical useful life for lamps with lithium fluoride window (11.7eV or more) is about 200 hours when the lamp is operated at room temperature. Lamps with these windows should not be operated above room temperature because lithium fluoride is susceptible to degradation by water vapour at elevated temperatures.

During normal operation of the photoionisation detector, the lamp window can become coated with a film of UV absorbing materials which is deposited from the gas stream. This reduces the lamp’s effective light output, results in a loss of sensitivity and shows as a substantial drop in peak height or area on the chromatogram. Removal of the lamp and proper cleaning of the lamp window will usually restore the detector sensitivity.

Maintenance…Since some UV inhibiting deposits are invisible to the eye, regular cleaning of the lamp window is strongly recommended. It is best to clean the lamp frequently, once a week or more depending on the detector usage, to prevent heavy build-up of deposits that may be difficult to remove.

Lamps with lithium fluoride windows can be cleaned by gently polishing the surface of the window with anhydrous alcohol on a cotton swab, followed by an anhydrous methanol or ethanol rinse and then wiping dry with a soft tissue. Do not allow the alcohol to remain on the window surface as it will leave a film.

Use care during the polishing step so that the film is removed without damage to the window surface. Stubborn films may require multiple cleanings for complete removal.

Lamps not in use should be stored in an anhydrous environment to prevent slow degradation of the lithium fluoride window by ambient moisture.