The first miniaturized chip was fabricated on a Si wafer for gas chromatography (GC; see Figure 6.1).1 Isotropic etch on a 200 μm thick Si <100> wafer (5 cm diameter) produced a spiral GC channel (200 μm wide, 30 μm deep, 1.5 m long). A relatively short capillary length (1.5 m) with an OV-101 stationary phase was used for GC analysis of hydrocarbons. An etched Si miniature valve with a Ni diaphragm (activated by a solenoid plunger) was used for injections. The separation was completed in less than 10 s. However, the plate numbers only range from 385 to 2,300, and n-hexane and chloroform were not resolved. The GC chip was incorporated with a thermal conductivity detector (TCD), which was separately fabricated on another Si chip. It consisted of an etched cavity in order to reduce thermal mass and to shorten the thermal time constant to about 1 ms. The cavity was insulated by thermal SiO2 (100 nm), sputtered with Pyrex glass (1.5 μm), and patterned with a Ni thin-film (100 nm) resistor.1