SINGLE OPTICAL FIBER, POSITION-SENSITIVE DETECTOR-BASED MULTIWAVELENGTH ABSORBENCY SPECTROPHOTOMETER

A relatively simple, yet stable and versatile, multiwavelength absorbance spectrophotometer Is described. A broad-band mercury-xenon source was coupled Into a single UV-vis transmitting optical fiber, through a detection cell, and dispersed by a monochromator onto the face of a continuous position-sensitive detector (PSD). Two wavelength regions illuminated opposite ends of the PSD while the remainder of the dispersed light was masked. Photocurrent contributions by the two wavelength regions were readily balanced to achieve a stable electronic null condition. The resulting optical configuration provided absorbance measurements simultaneously at two wavelengths, while also correcting for light source Intensity fluctuations and refractive Index aberrations. The absorbance detector was applied In microbore liquid chromatography with a 6 mm path length z-configuration flow cell (12 μL volume). A 1.1 ✕ 10 au (3 ✕ root mean square noise level, 60-s intervals) was routinely achieved, which constitutes over a factor of 10 reduction in noise due to light source fluctuations. Aldehyde derivatives with 2, 4-dirtttrophenylhyrazine were chromatographlcally analyzed as a test system. The mass detection limit of injected formaldehyde was 4 pg. Since two wavelength regions are simultaneously measured, molar absorptivity ratios of the aldehyde derivatives were obtained and compared to absorbance spectra obtained from a commercial Instrument. Results suggest that molar absorptivity measurements can be obtained more simply than with the typical photodiode array based Instruments. The new detection system should be advantageous In remote-sensing applications, including flow injection analysis, high-temperature liquid chromatography, biological monitoring, and environmental monitoring. © 1990, American Chemical Society. All rights reserved.