Development of a Simple Monitoring Device for Ultra-Trace Silicate lon in Quality Control High-Purity Water Used in Semiconductor Production.

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The aim of this project is to develop a simple monitoring device for quantitation of ultra-trace (sub-ppb to ppb) silicate ion in high-purity water using flow preconcentration-spectrophotometric detection system. The basic ideas and the underlying chemistry are :1.Silicate ion is converted to molybdosilicate blue which has the absorption maximum in near infrared region, at 830nm. Thus, one can devise a cheap detector based on the optosemiconductors, such as LEDs and photodiodes (PD).2.Anionic molybdosilicate blue is adsorbed on cellulose-type materials as the ion-pair with a large organic cation which is very readily desorbed (eluted) with certain organic solvents. These leads the high-performance flow preconcentration systems.The optimized system consists of two pump units for sampling and elution, respectively, and a short column (4 cm) packed with ashless pulp. Molybdosilicate blue in 30 ml is concentrated on the ashless pulp column as an ion-pair with octyltrimethyl ammonium ion and the ion-pair is eluted with 80 wt% acetonitrile-water mixture down to the LED-PD detector operated at 830nm.In order to ensure the practical capability, the prototype equipment is now under field testing in some semiconductor production manufacturers and electric power plants.