Shaelah Reidy

An Integrated Micro-Analytical System for Complex Vapor Mixtures

A micro gas chromatograph (muGC) capable of quantitatively analyzing the components of complex vapor mixtures at trace concentrations is described. The muGC features a micro- preconcentrator/focuser (muPCF), dual-column pressure- and temperature-programmed separation module, and an integrated array of nanoparticle-coated chemiresistors. The latest design modifications and performance data are presented. Highlights include a 4-min separation of a 30-component mixture with a 3-m DRIE Si/glass microcolumn, a 14-sec separation of an 11-component mixture on a 25-cm microcolumn, a complete multi-vapor analysis from a hybrid microsystem that combines analytical, rf- wireless, and microcontroller modules, and a rapid analysis driven by a 4-stage peristaltic micropump.

Microfabricated thermal modulator for comprehensive two-dimensional micro gas chromatography: design, thermal modeling, and preliminary testing

In comprehensive two-dimensional gas chromatography (GC x GC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, thereby enhancing the resolution and the selectivity of analytes. As part of an effort to develop a microGC x microGC prototype, in this report we present the design, fabrication, thermal operation, and initial testing of a two-stage microscale thermal modulator (microTM). The microTM contains two sequential serpentine Pyrex-on-Si microchannels (stages) that cryogenically trap analytes eluting from the first-dimension column and thermally inject them into the second-dimension column in a rapid, programmable manner. For each modulation cycle (typically 5 s for cooling with refrigeration work of 200 J and 100 ms for heating at 10 W), the microTM is kept approximately at -50 degrees C by a solid-state thermoelectric cooling unit placed within a few tens of micrometres of the device, and heated to 250 degrees C at 2800 degrees C s(-1) by integrated resistive microheaters and then cooled back to -50 degrees C at 250 degrees C s(-1). Thermal crosstalk between the two stages is less than 9%. A lumped heat transfer model is used to analyze the device design with respect to the rates of heating and cooling, power dissipation, and inter-stage thermal crosstalk as a function of Pyrex-membrane thickness, air-gap depth, and stage separation distance. Experimental results are in agreement with trends predicted by the model. Preliminary tests using a conventional capillary column interfaced to the microTM demonstrate the capability for enhanced sensitivity and resolution as well as the modulation of a mixture of alkanes.

A Micropump-Driven High-Speed MEMS Gas Chromatography System

We report (1) the integration of the first functioning MEMS gas chromatography system ( muGC) featuring a micropump, a micro-column, and a micro-chemiresistor sensor array; and (2) experimental demonstration of the state-of-the-art multi-vapor gas separation and detection. In particular, we report the best GC analysis data from the first micropump-driven muGC system to date: the separation and detection of 11 volatile organic compounds (VOC)s within only 78 seconds while consuming only 15.1 mW of power within a small volume of 0.5 cc. We also report the use of temperature programming (TP) of the separation column for fast analysis, which shortened the analysis time from 78 seconds to 24 seconds while maintaining gas analysis resolution.

A low power, high-speed miniaturized thermal modulator for comprehensive 2D gas chromatography

In comprehensive two-dimensional gas chromatography (GC×GC), a modulator is placed at the juncture between two separation columns to focus and re-inject eluting mixture components, and thereby enhance the selectivity, sensitivity, and analyte capacity. Here, we present the design, fabrication, and testing of a two-stage microscale thermal modulator (µTM). The °™ cryogenically trap analytes eluting from the first column and thermally inject them into the second column. For this operation, each stage is periodically heated to 200 °C for 100 ms and then cooled to −50 °C for a few second. Preliminary results using a conventional capillary column interfaced to the µTM demonstrate successful modulation of a mixture of alkanes with a sensitivity enhancement as high as 24 folds

A low-mass high-speed µGC separation column with built-in fluidic chip-to-chip interconnects

This paper reports a low-mass high-speed separation column with built in fluidic chip-to-chip interconnects for a micro gas chromatograph. The 25cm-long suspended column has been successfully coated, and separations have been obtained. The column can be heated to 100°C with 200mW in air and only 80mW in vacuum. The corresponding thermal time constants are 1.2sec and 2.5sec, respectively. Built-in heated interconnects eliminate cold-spots from long and difficult to heat capillary tubes, and plug directly into the preconcentrator and chemi-resistive detector chips, miniaturizing the fluidic analysis path to a size compatible with eventual use in devices such as cellular phones.