TRACE ANALYSIS OF WATER POLLUTANTS BY PHOTOTHERMAL PHASE-SHIFT SPECTROSCOPY WITH AN INTEGRATED OPTICAL MICROINTERFEROMETER

Photothermal phase shift spectroscopy measures the changes of the refr active index, induced by a modulated excitation light beam, by a doubl e microinterferometer, consisting of a 7.5 x 7.5 mm integrated optics silica chip. A laser diode that is integrated at the chip is used as t he probe laser. The flowthrough cell containing the analyte is mounted in one of the two arms of the Michelson interferometer between the mi crochip and the reflecting mirror. The great potential of this phototh ermal microinterferometer as a routine method for process control or e nvironmental surveillance lies in the miniaturization of the system fo r the following reasons. No adjustment is needed because only fixed co mponents are used. The quality of the light beams is significantly imp roved by shortening the light paths and very small sample cell volumes in the range of nano- or microliters are needed. This has at least tw o distinct advantages. On the one hand, a small, compact analytical ap paratus enables direct real time and on site measurements. On the othe r hand, it is possible to build a robust and reliable device, without any movable parts, that is unaffected by external influences. (C) 1996 Society of Photo-Optical Instrumentation Engineers.