Pulsed excitation source multiplexed fluorometry for the simultaneous measurement of multiple analytes. Continuous measurement of atmospheric hydrogen peroxide

Presently, solid-state sources such as light-emitting diodes (LEDs) provide for intense, nearly monochromatic fight They are available over a broad range of emission wavelengths. Unlike incandescent and discharge lamps, LEDs can be turned on and off at high speeds. The resulting light pulses are highly reproducible. This allows the use of a single photomultiplier tube (PMT) often the most expensive component in a high-sensitivity measurement system, as a multiplexed detector with multiple, fiber-optic-coupled, fluorescence-detection cells excited by solid-state sources. A time resolution of 1 min is adequate in many continuous detection schemes. This enables multiple-channel single-detector multiplexed measurement without any loss of S/N. On the basis of this principle, we describe a new automated continuous instrument for the simultaneous measurement of atmospheric hydrogen peroxide and methyl hydroperoxide (MHP). A Nafion membrane diffusion scrubber (DS) is used with hematin-catalyzed oxidation of thiamine to thiochrome for the measurement of H202, and an expanded poly(tetrafluoroethylene) (ePTFE) DS is used with a H202 destruction catalyst and horseradish peroxidasecatalyzed oxidation of thiamine to thiochrome for the measurement of MHP. The respective limits of detection are 25 pptv and 15 pptv. Design, performance details, and illustrative results from a field campaign (Philadelphia NE03PS study, 2001) are presented. [PUBLICATION ABSTRACT]