Comparison of self-referencing techniques for photothermal detection of trace compounds in water

self-referencing techniques are compared for a closed-cell photothermal det ector that uses a water meniscus as a pressure sensor. Deflection of the me niscus was measured using an optical fibre Fabry-Perot interferometer. For long measurement integration times, interference fringe drift was a serious limitation on the detection repeatability for non self-referenced measurem ents. Two self-referencing techniques were compared for measurements of opt ical absorption. The first technique used a simultaneous reference absorpti on signal at a second wavelength, and the second used a simultaneous volume tric modulation within the cell. Both methods have been evaluated with phot othermal excitation by a 658-nm LED, a 478-nm LED and a UV discharge lamp. For the detection of absorption in aqueous solutions, the two methods had s imilar performance. However, the volumetric method could be used for detect ion of any absorbing compound, regardless of its absorption spectrum and wa s more convenient to use. (C) 2000 Elsevier Science S.A. All rights reserve d.