# Progressive Cellular Architecture in Microscale Gas Chromatography for Broad Chemical Analyses
## 4 Experimental Evaluation
Each analytical run of the PCA3 mv consisted of three steps: purging, sampling, and separation. The purging step was used to remove any contaminants within the preconcentrators remaining from the preceding run. During purging, Pump2 was actuated, whereas Valve1, Valve2, and Valve3 were switched to connect all the preconcentrators in series. Then the preconcentrators were heated to 150-200 \({}^{\circ}\)C for 30 s to desorb the residue, which was purged out of the sample inlet. At the beginning of sampling, the carrier gas filter heated by a 58 s, 150 \({}^{\circ}\)C thermal pulse, which removed any ambient contaminants trapped in the filter during the preceding run and regenerated the filter for the ongoing run. The PCA3 mv was operated to collect the vapor sample for 30 min using \(\approx\)5 sccm flow rate. For the separation in each cell, the air flow rate was maintained at \(\approx\)0.9 sccm. The preconcentrator was heated from room temperature to 170-180 \({}^{\circ}\)C in 2 s and maintained for 8 s to perform desorption (Figure 7). Column1 provided temperature programmed separation ramping from room temperature to 100 \({}^{\circ}\)C using \(\approx\)0.5 \({}^{\circ}\)C/s ramp rate. Column2 provided temperature programmed separation ramping from room temperature to 100 \({}^{\circ}\)C using \(\approx\)1.3 \({}^{\circ}\)C/s ramp rate. Column3 provided temperature programmed separation ramping from room temperature to 100 \({}^{\circ}\)C using \(\approx\)0.6 \({}^{\circ}\)C/s ramp rate. Valve Module C2 was maintained at 80 \({}^{\circ}\)C during Cell 2 and Cell 3 separation. The guard columns in the separation paths of Cell 2 and Cell 3 were maintained at 60-70 \({}^{\circ}\)C. The guard column of Cell 1 was maintained at room temperature, because the analytes in Cell 1 were sufficiently volatile. Figure 6: Chromatograms of the separation of (**a**) IPA and phosphonate esters, and (**b**) alkanes C\({}_{5}\)–C\({}_{12}\) in Column2. (**c**) The _HETP_ of Column2 calculated using C\({}_{10}\) at 80 \({}^{\circ}\)C at 0.2–1.2 sccm. Column3 showed similar _HETP_ results. Initial tests were directed at the collection and separation of alkanes C\({}_{5}\)-C\({}_{15}\) with a concentration of 100 ppb; typical results are presented in Figure 8. The alkanes C\({}_{5}\)-C\({}_{7}\) were retained and separated in Cell 2, and alkanes C\({}_{8}\)-C\({}_{15}\) were separated in Cell 3. Other tests were directed at alcohols, in particular, methanol, ethanol, IPA, and butanol; and phosphonate esters, in particular, dimethyl methylphosphonate (DMMP) and diethyl methylphosphonate (DEMP)--all at a concentration of 1 ppm. Typical results are presented in Figure 9. Methanol, ethanol, and IPA were separated in Cell 1; 1-butanol and DMMP were separated in Cell 2; 1-butanol and DEMP were separated in Cell 3. Yet other tests were directed at ketones (acetone and butanone) and aromatics (benzene, toluene, ethylbenzene, o-xylene, and mestilbene)--all at a concentration of 200 ppb; typical results are presented in Figure 10. Acetone was separated in Cell 1; 2-butanone, benzene, toluene, and ethylbenzene were separated in Cell 2; toluene, ethylbenzene, o-xylene, and mestilbene were separated in Cell 3. The volatility of each of the tested analytes is represented by its Kovats retention index (RI), which is an indicator of the analyte retention time relative to \(n\)-alkanes [31]. The RI for the tested analytes ranged from 370 to 1500. The PCA3 mv provided \(R_{s}\approx 4.7\) for the first two eluting analytes (methanol and ethanol) with a RI of 370 and 443, respectively. The PCA3 mv also provided \(R_{s}\approx 2.3\) for the two analytes with lowest vapor pressure (C\({}_{14}\) and C\({}_{15}\)) with a RI of 1400 and 1500, respectively. All the separations were performed with \(\Delta T_{avg}\) of 41.7 \({}^{\circ}\)C over 12 min using  
Figure 8: The PCA3 mv chromatogram of 30 min sampling of 100 ppb of alkanes C\({}_{5}\)–C\({}_{15}\).