Date of Award

Summer 2002

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Chemistry - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Kenneth Rudolph Farmer

Third Advisor

Dentcho V. Ivanov

Fourth Advisor

Barbara B. Kebbekus

Fifth Advisor

Durgamadhab Misra

Sixth Advisor

Nicholas Harrer Snow

Abstract

The detection and quantitative measurement of trace components is a challenging task. The key component in such an instrument is the concentration step where the analytes are accumulated before the analysis. In this research, simple and inexpensive processes for the microfabrication of microconcentrator that can be used with sensors and as an injector in GC were developed. Analytes are selectively concentrated in the microconcentrator. Rapid electrical heating of the microconcentrator releases the adsorbed species as a 66 concentration pulse", which serves as an injection for the detection system. The relatively small size of the microconcentrator allows it to be heated and cooled rapidly. The microconcentrator serves the dual purposes of sample concentration and injection.

The devices were fabricated on 6-inch silicon substrate using standard photolithographic processes. First, a microheater embedded in silicon wafer was fabricated. The channels were lined with a conductive layer by sputtering metal film through which an electric current could be passed causing Ohmic heating. The preconcentration was done on thin-film polymeric layer deposited in the channel. Rapid heating of the conductive layer caused the "desorption pulse" to be injected into the sensor/detector. Several channel configurations were fabricated with a width between 50 to 456 μ-m depth between 35 and 350 μ-m and length between 6 and 19 cm. The separation distance between the channels was varied such that the entire microheater fitted in a 1cm 2 area. Due to their small size, the microconcentrators could be fabricated more than 50 at a time on a 6-inch silicon wafer.

In the first part of this research, the heating characteristics of the microheaters are studied. Deposition of metals to form a resistive heating element in microchannels was demonstrated. It was found that temperature as high as 360°C could be attained in a ten seconds. The microconcentrator was effective as a concentrator plus injector. It exhibited high signal enhancement and precision.

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