(594c) Stability of Oxime Based Microsensor for Organo-Phosphate Vapor Detection

Accurate, rapid detection of volatile toxic organo-phosphates at levels in ppm or less is of great importance for industrial, commercial and military sectors [1]. A micro gas sensor has been previously developed by our group for the detection of organo-phosphate vapors using an aqueous solution of the oxime PBO (1-Phenyl-1,2,3,-butanetrione 2-oxime). The analyte diffuses from the gas stream through a porous membrane to the aqueous oxime solution. It then reacts with the oxime to produce cyanide ions, which are detected electrochemically by the change in solution potential [2]. A basic environment is needed for the oxime anion to form and the detection reaction to take place [3]. Previous work on this oxime electrochemistry indicated that the optimal buffer pH for the aqueous solution which maximized the potential response was approximately 10 [4]. However, sensor response slowly decreases as the aqueous oxime solution ages, by approximately 80% in first 24 hours.

The purpose of this research was to develop a liquid medium in which the oxime would remain stable, while still being able to function as intented in the microsensor. Solutions in pure organic solvents do not show any noticable degradation, however, the reaction between oxime and organo-phosphate requires hydroxide ions in order to take place [3]. As a result, pure organic solvents will not be compatible with the microsensor electrochemistry. To solve both problems, a concentrated organic oxime solution was combined with the basic aqueous buffer just prior to being used in the detection process. Microsensor performance using these solution pre-mixed had no appreciable difference from the original aqueous oxime solution. Additionally, a small serpentine channel component was fabricated with the same dimensions and material as the original microsensor. This allowed for the mixing of the two solutions within the device. Studies show that the sensor response utilizing the integrated micromixer was nearly identical to the response when the solutions were premixed and fed at the same rate.

REFERENCES:

[1] Y. Sun, and K.Y. Ong, Detection technologies for chemical warfare agents and toxic vapors, CRC Press, Boca Raton (2005).

[2] I. Oh et al, IEEE Sensors, In Press.

[3] B. W. Ford, and P. Watts, J. Chem. Soc., Perkin Trans. 2, 1009 ? 1013 (1974).

[4] I. Oh, and R. Masel, Electrochem. Solid-State Lett., 10, J19 ? J22 (2007).