Photothermal deflection spectroscopy of an aqueous sample in a narrow bore quartz capillary

Abstract

Articles you may be interested inMid-infrared photothermal heterodyne spectroscopy in a liquid crystal using a quantum cascade laser An apparatus to perform photothermal deflection spectroscopy on liquid samples within a cylindrical capillary is described. A tunable dye laser, modulated by an optical chopper, serves as an excitation source. The resolution of a spectral absorption peak near 575 nm, of a 1ϫ10 Ϫ3 M Nd 3ϩ aqueous solution, demonstrates the effectiveness of the system. The sample is contained within a 75 m internal diameter quartz capillary, typical of those used for capillary electrophoresis. Across the middle of the probed section of the capillary, the magnitude of the resolved peak is 5.2ϫ10 Ϫ5 absorbance units. A helium-neon laser, focused to a 1/e 2 waist diameter of 40 m, provides an optical probe beam across the center of the sample, overlapping the excitation beam at an angle of 3°. Maximum signal-to-noise ratio is achieved with the apparatus when the excitation beam is modulated at a frequency near 205 Hz. The deflection responsivity of the probe beam at this frequency is 650 nrad per W of absorbed excitation radiation, with an internal noise level in the system of 0.6 nrad Hz Ϫ1/2 . The shot noise from probe beam radiation upon the photodiodes in the position sensitive detector exceeds noise from other sources. ͓S0034-6748͑98͒03506-0͔

Time-resolved photothermal methods: accessing time-resolved thermodynamics of photoinduced processes in chemistry and biology

“…Similar approaches based on capillary tubing have been proposed for photothermal beam deflection set-ups. 56 An extremely promising cell for pulsed PAS that uses transmission of light through a pair of dovetail prisms has also been described. 57 The layered prism cell combines the enhanced timeresolution capabilities of the 'layered' front-face irradiation geometry with the zero background and broadband flexibility of the classical cuvette geometry.…”