Development of a Sensitive Lazer Spctrophotometric Environmental Monitoring Device Using Droplet Method

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We developed and used the passive sampling device to measure NOx in SOx in air pollution. In the present work we have changed the passive sampler method to the droplet method. Because the passive sampler is, however, not fit to the high sensitivity and precise analysis and, therefore, unable to monitor micro-amounts of variable toxic substances in long period exposure.To meet the solution of disadvantage, we adopted the Dasgupta's droplet method. We use the light-emitting diode and the optical fiber to analyze the droplet which used in the experiment is the cylindrical chamber. In the center of the chamber there is a stainless steel tube. It is used to deliver the solution. And the tip of a stainless tube always keeps the droplet dripping. The gas stream is introduced into the cylindrical chamber at the top, from two oppositely located gas inlets, to achieve more symmetric flow profile around the droplet. Then the droplet collects the gas and is changed the color. The light from a high brightness LED illuminates the droplet. On the diametrically opposite side, the transmitted light is conducted by a plastic optical fiber to a photodiode equipped with an interface filter. A reference photodiode is placed at the back plane of the LED to provide a dual-beam referenced detection arrangement. Absorbance is computed as -log[ (Id-Id')/(Ir-lr') ] +Ko where Id and Ir are the respective photocurrents generated by the detector and the reference photodiode, Id' and Ir' are the corresponding dark currents, and Ko is an offset constant that compensates for the inequality between the intensities of the reference beam and the probe beam directed to the drop.Our purpose and goal are the application of the recent micromachining techniques to the droplet method. A microchip of several centimeter square can collect and analyze the gas sample. Also, microfabrication of the droplet method will give the smallest analysis device which can be applicable to various environmental samples.