**3. Micro dryer and purifier**

Environmental samples do not only have a very low concentration but also contain vapor and various particles, which will make GC column and detector inactive or even fail. Therefore, the proposed mini GC system was integrated with a micro dryer and purifier which can clear up the vapor and micro pollutants in the samples.

GC system based on mini PID was integrated with the micro GC column and the micro pre-

A mini (portable) GC system usually includes an injection unit, a micro pre-concentrator, a micro GC column, and a mini PID. Figure 1 shows schematic of the mini GC system for

The injection unit supplies sample to the pre-concentrator or the GC separation column. The pre-concentrator is a sampling and concentrating device that can significantly improve detection limit of mini GC system with 1~3 orders. The GC separation column separates the complicated mixtures on the basis of their affinity with the stationary phase distributed all along the column length. The detector acquires the signals provided by the separated compo‐

The mini GC system is characterized by a series of innovations. 1) The micro dryer and purifier can remove vapor and particulates in environmental sample. 2) The integrated pre-concen‐ trator can make the system easy to deploy trace gas and suitable for in-field use. 3) A micro GC column instead of a conventional column was used to separate mixtures, which can greatly

Environmental samples do not only have a very low concentration but also contain vapor and various particles, which will make GC column and detector inactive or even fail. Therefore,

**2. Schematic representation of the mini GC system**

**Figure 1.** A schematic representation of the mini GC system architecture

nents at the GC column outlet.

reduce volume of the system.

**3. Micro dryer and purifier**

environmental monitoring and analysis.

concentrator.

130 Current Air Quality Issues

In order to rapidly and effectively eliminate the vapor from the environmental samples, two kinds of micro-pillars were fabricated in micro flow channel of the dryer. The shape of the former pillar is shown in Figure 2(b) (refer to the І pillar), which can break and rapidly atomize the water droplets in the samples. The second pillar (refer to the II pillar in Figure 2(b)) has a relatively large surface area, which can completely come into contact with the micro droplets and then quickly vaporize them.

Fabrication of the chip used silicon wafer and Pyrex 7740 glass wafer as the substrates. The patterns of the dryer and purifier were formed by lithography and fabricated through a series of lithography, etching, and bonding process, where the channels and pillars were fabricated using a deep reactive-ion etching technology. For details on the fabrication process of the micro dryer and purifier, refer to the work in [4]. The length of the chip is 10 mm and the depth and width of the dryer channel were 400 µm and 500 µm, respectively. In order to clear up the vapor, molecular sieve 5A (60–80 mesh) was used as adsorption material and filled in the channel of the micro purifier. In order for the dryer to have a fast self-heating capacity, a micro heater was integrated on the backside of the dryer. The heater with resistance of 8 Ω was fabricated as a 20 nm/250 nm Cr/Pt stack deposited by a magnetron sputtering technology and patterned by a lift-off technology, which can increase the temperature at a speed of 10℃ per second and the highest temperature can be raised up to 200℃in less than 30 s. Figure 2 shows the proposed micro dryer and purifier.

**Figure 2.** The fabricated micro dryer and purifier (a) and micro-pillars in channel (b)

In order to evaluate the performance, one end of the device is connected to a sampling pump, and the other end is connected to a transparent pipe filled with anhydrous CuSO4. Firstly, an environmental sample containing a certain amount of water vapor was passed through the device which is in working state. After being processed by the device, the anhydrous CuSO4 in the pipe did not change in color, which verifies that vapor was completely absorbed by the device.
