# Progressive Cellular Architecture in Microscale Gas Chromatography for Broad Chemical Analyses
## 3 Design and Implementation  
### Subsystem Overview  
The PCA3 mv subsystem contained a number of elements. In particular, it incorporated three \(\upmu\)GC cells as well as a carrier gas filter, two valve modules, a bidirectional pump module, and the controlling electronics (Figure 2). The \(\upmu\)GC cells provided the preconcentration, injection, and separation of analytes. The valve modules and the pump module provided the sampling and separation flow. An external detector was used to evaluate the PCA3 mv operation and performance. Each cell incorporated a T-connector, a preconcentrator, and a separation column. To maximize the analyzable analyte range, the adsorption strength of the preconcentrator and the retentiveness of the separation column in each cell had to be significantly different from those of the other cells. Cell 1, which targeted the volatility range from C3 to C5, incorporated the strongest sorbent in its preconcentrator and the most retentive stationary phase in its separation column. Among the commercially available sorbents, Carboxen(tm) 1000 (#10477-U, Sigma Aldrich, St. Louis, MO, USA) has the highest surface area of 1200 m\({}^{2}\)/g, hence it was selected for the Cell 1 preconcentrator. Similarly, among the common stationary phases, polylotivinylbenzene (pDVB) is a non-polar, porous, and highly retentive material, hence it was selected for the Cell 1 separation column. Cell 2, which targeted C5 to C8, incorporated a moderate sorbent and a less-retentive stationary phase. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Case 4** & **Case 5** & **Case 6** \\ \hline Stationary Phase & & & & \\ Thickness (\(\upmu\)m) & & & & \\ \(\Delta\)Tavg (\({}^{\circ}\)C) & 27.5 & 72.5 \({}^{\circ}\) & & \\ \(\Delta\)Tmax (\({}^{\circ}\)C) & 55 & 145 & & \\ Total Analysis & & & & \\ Time (s) \({}^{\text{b}}\) & 108 & 277.8 & & \\  & & & & Overall: 231 \\ \(E_{\text{diss}}\) (J) & 41.6 & 282.0 & & \\  & & & & \\ \(E_{\text{mass}}\) (J) & 38.5 & 101.5 & & \\  & & & & Overall: 84 \\ \(E_{\text{total}}\) (J) & 80.1 & 383.5 & & \\  & & & & Overall: 184.3 \\ \hline \hline \end{tabular}  
* All cases computed the separation of alkanes C3–C11 using a 3 m long, 250 \(\upmu\)m ID separation column. All cases used a 30 \({}^{\circ}\)C/min ramp rate starting at 25 \({}^{\circ}\)C. \({}^{\text{b}}\) Total analysis time is based on the retention times of alkanes in Table 3. \({}^{\text{c}}\) Red font indicates undesirable outcomes compared to other cases.  
\end{table} 
Table 4: Computed \({}^{\text{a}}\) values of energy consumption for temperature programmed Cases 4–6. Figure 2: Structural arrangement of the three-cell (PCA3 mv) subsystem. Carbopack(tm) X (#10437-U, Sigma Aldrich, MO, USA) has a surface area of 240 m\({}^{2}\)/g, which is typically used for this volatility range; hence, it was selected for the Cell 2 preconcentrator. A relatively thick layer of PDMS (5 \(\upmu\)m) was selected for the Cell 2 separation column. Cell 3, which targeted C\({}_{8}\) to C\({}_{15}\), incorporated the weakest sorbent and least-retentive stationary phase. Carbograph(tm) 2 (#1728, Grace Davison Discovery Science, IL, USA) has a surface area of 10 m\({}^{2}\)/g; hence, it was selected for the Cell 3 preconcentrator. A relatively thin layer of PDMS (0.3 \(\upmu\)m) was selected for the Cell 3 separation column. The gas flow was controlled by two valve modules; Valve Module C1 incorporated three 2-way valves (Valve1, Valve2, and Valve3) and Valve Module C2 incorporated two 2-way valves (Valve4 and Valve5). Valve Module C1 was connected to the preconcentrators, whereas Valve Module C2 was connected to the separation columns. The gas flow was provided by a bi-directional pump module, which included Pump1 for providing sampling flow, Pump2 for providing separation flow, and a 3-way valve (Valve6) for selecting between these two options. A stand-alone microfabricated carrier gas filter was connected between Precon1 and Valve6 to capture chemicals and moisture that may be present in the carrier gas used in separation.