ABSTRACT
Chromatographic Systems ...................................................... 324 9.2.2 Commercial Instrumentation Based on
Micromachining ...................................................................... 326 9.3 Prototype Microanalytical GC Systems ............................................. 327 9.4 Sample Handling and Injection for Micro-GC .................................. 327
9.4.1 Sample Valves and Loops ...................................................... 327 9.4.2 Solid-Phase Microextraction................................................... 328 9.4.3 Other Technologies ................................................................. 329
9.5 Microfabricated GC Columns ............................................................ 330 9.6 Theory of Microfabricated GC Columns........................................... 330
9.6.1 Transport Model...................................................................... 330 9.6.2 Separation Model .................................................................... 334 9.6.3 Is Smaller Better? ................................................................... 337 9.6.4 Theory Discussion................................................................... 338
9.7 GC Column Fabrication and Coating ................................................ 338 9.8 Micro-GC Detectors ........................................................................... 341
9.8.1 Thermal Conductivity ............................................................. 342 9.8.2 Surface Acoustic Wave........................................................... 344 9.8.3 Chemiresistors......................................................................... 344 9.8.4 Flame Ionization and Flame Atomic
Emission Detector ................................................................... 345 9.8.5 Photoionization ....................................................................... 346 9.8.6 Glow Discharge and Molecular Emission.............................. 346 9.8.7 Photoacoustic Detector ........................................................... 347 9.8.8 Miniature Mass Analysis ........................................................ 347
9.9 Improvements and Future Directions................................................. 350 9.9.1 Column Coating ...................................................................... 350 9.9.2 Microfluidics, Pumps and Valves, Transfer
Tubes ....................................................................................... 350
9.9.3 Detectors ................................................................................. 351 9.9.4 Power....................................................................................... 351 9.9.5 Materials Deposition and Fabrication .................................... 351 9.9.6 Integration ............................................................................... 352 9.9.7 New Technologies .................................................................. 354
References.................................................................................................... 354
The analysis of gases and vapors is of major importance in manufactur-
ing, environmental monitoring, and public safety. The introduction of inte-
grated circuit technology and the more recent micromachining technology
has pushed gas-phase chemical sensing to smaller and more elaborate analysis
tools. This chapter provides a review of developments in microanalytical
separation systems that operate in the gas phase. Specifically, we will review
the modern history of gas sensing and examine the evolution from discrete
sensors to sensor array systems to microanalytical systems with miniaturized
sampling, separation, and detection components.
