Tunable ultraviolet visible photoacoustic detection - Analysis of the sensitivity and selectivity provided by a xenon flash lamp

A fundamental understanding of the physical and chemical properties that di ctate the absorption of pulsed light and subsequent release of heat to gene rate a transient pressure wave was used to test the concept of a multi-wave length photoacoustic detector. Analysis of the wave equation predicts that with long-pulse excitation, i.e. microseconds FWHM, absorption by the solve nt, and not electrostriction determines the limit of detection. Calculation of the mechanical to electrical conversion efficiencies of piezoelectric t ransducers shows that absorbed pulse energies of microjoules, typical of pu lsed flash lamps, are sufficient to provide measurable photoacoustic signal s. A pulsed xenon Rash (amp 12 mus FWHM) which emits a broad spectrum over the UV and visible region is used as an excitation source to detect trace q uantities of metals in aqueous solution using pulsed photoacoustic detectio n. In this work, dielectric mirrors were used to detect two analytes, CrO42 - (monitored at 355 nm) and Co2+ (monitored at 532 nm), simultaneously. Thi s approach increases both the flexibility and selectivity of pulsed photoac oustic methods. We obtained a detection limit of 2.6 x 10(-4) absorbance un its per centimeter in aqueous samples. This work shows that pulsed lasers a re not a necessity for ultra-sensitive photoacoustic spectroscopy. (C) 2001 Elsevier Science B.V. All rights reserved.