# Progressive Cellular Architecture in Microscale Gas Chromatography for Broad Chemical Analyses
## 3 Design and Implementation
### Microfabricated Components  
A variety of \(\upmu\)GC components have been reported, typically as standalone elements: preconcentrators [35], valves [36; 37], separation columns [38; 39; 40], detectors [41; 42; 43; 44; 45; 46], and pumps [47; 48; 49]. In the PCA3 mv, Cell 2 and Cell 3 each used a monolithic chip that integrated a preconcentrator, a separation column, and a T-connector (Figure 3a); Cell 1 did not use a monolithic chip as the coating method for the Column1 stationary phase has not been developed. The microfabricated Column2 and Column3 were designed as serpentine channels with 0.6 m total length, 500 \(\upmu\)m width, and 160-180 \(\upmu\)m height. As noted previously, Column2 incorporated a 5.0 \(\upmu\)m thick PDMS stationary phase, whereas Column3 incorporated a 0.3 \(\upmu\)m thick PDMS stationary phase. Precon2 and Precon3 were designed as 3.5 \(\upmu\)L U-shaped chambers for accommodating sorbent particles. Each chamber incorporated two arrays of micropillars for confining the sorbent particles and a loading port for loading the sorbent particles. Precon2 was packed with an estimated 1.4 mg of Carbopack(tm) X. Precon3 was packed with an estimated 2.4 mg of Carbograph(tm) 2.  
The Cell 2 monolithic chip, the Cell 3 monolithic chip, and the carrier gas filter each consisted of two glass dies bonded together. The top glass die included gas flow channels created by sandblasting (provided by Bullen Ultrasonics Inc., Eaton, OH, USA, and Ikonics(r) Corporation, Duluth, MN, USA). The bottom glass die included thin-film metal heaters and thermistors to allow servo-controlled heating. The die bonding used an epoxy (#377, Epoxy Technology, Billerica, MA, USA). The packed sorbent masses were estimated based on the sorbent chamber volumes and the sorbent densities. After sorbent packing, the loading ports were sealed with epoxy.  
Precon1 was a standalone preconcentrator (Figure 3b) with an inner volume of 2.4 \(\upmu\)L, and was packed with an estimated 1.2 mg of Carboxen(tm) 1000. The connector T1 (Figure 3c) was a stand-alone microfabricated T-connector for connecting Precon1, Valve1, and Column1. The carrier gas filter (Figure 3d) was designed as a chamber with an inner volume of 12.5 \(\upmu\)L and was packed with an estimated 2.1 mg of Carboxen(tm) 1000, 1.7 mg of Carbox(tm) X, and 2.9 mg of Carboxen(tm) 2. Precon1, T1, and the carrier gas filter were also microfabricated and assembled in a manner similar to Cell 2 and Cell 3 monolithic chips.  
The microvakes contained in Valve Module C1 and Valve Module C2 included gas flow channels, valve seats, and embedded thin-film metal heaters and thermistors (Figure 3e,f). These were monolithically fabricated and assembled in a manner similar to Cell 2 and Cell 3 monolithic chips as well. Each microvake incorporated a prefabricated polyimide valve membrane which was actuated by a latching solenoid actuator (#151082-234, Ledex, CA, USA). Each valve module was housed within a custom housing 3D-printed from Ultem 1010 [50].  
All the microfabricated chips were supported by glass spacers and mounted on a common printed circuit board (PCB). The spacers were 1 mm thick and custom-sized to support certain portions of these chips while cantilevering the sorbent chambers in the preconcentrators and the carrier gas filter above the PCB. Cantilevering provided thermal isolation of preconcentrators and the carrier gas filter from the PCB.  
The microfabricated chips were fluidically interconnected with 250 \(\upmu\)m ID guard columns (#10010, Restek, PA, USA), which were uncoated capillary tubes with surface treatment to minimize adsorption. To prevent surface adsorption of highly adsorptive analytes in the guard columns, resistive heating was provided by externally wrapped copper wires. The temperature of the guard columns was monitored by a commercial thermistor (#490-4801-1-ND, Digi-key Electronics, Thief River Falls, MN, USA).