# Progressive Cellular Architecture in Microscale Gas Chromatography for Broad Chemical Analyses
The outputs of the cells are routed to a common detector, which generates the resulting chromatogram. The cells are progressively cascaded in series to cover a broad range of vapors. In each cell, for the specific volatility range of analytes, the tailored separation column can rapidly and efficiently provide the desired separation resolution with modest temperature programming or none at all. Reduced heating requirements also extend the lifetime of the stationary phase coating within the separation columns, particularly when operating in complex environments and ambient air that may degrade these coatings at elevated temperatures [28]. This paper focuses on tailoring cells to the volatility range of targeted groups of analytes, although the polarity of the preconcentrator and separation column in each cell can also be tailored in principle. The PCA uses the concept of multi-bed preconcentrators in an unconventional manner. Conventionally, multi-bed preconcentrators are packed with multiple sorbents arranged  
Figure 1: Progressive cellular architecture functional concept and the resulting chromatogram. sequentially by adsorption strength [29; 30]. During sampling, low-volatility analytes are trapped by the weak sorbent bed located upstream, whereas high-volatility analytes break through the weak bed and are trapped by the stronger sorbent bed located downstream. Although the different beds within a preconcentrator cause a partial separation during the sampling step, this preliminary separation is lost at the start of the separation cycle, when the entire preconcentrator is heated in order to create a single injection peak that is routed into the common separation column. Consequently, the partial separation achieved during sampling is lost in conventional systems. In contrast, within the PCA, each cell contains a single bed preconcentrator that targets a specific range of analytes; the preconcentrator of each cell is individually heated to inject these analytes into the corresponding separation column. Collectively, the sequential arrangement of cells achieves the function of a multi-bed preconcentrator but also preserves the separation that is naturally achieved during sampling (Figure 1). There is an additional benefit to the preconcentrator arrangement used in the PCA. In conventional uGCs, the peaks of high-volatility analytes can be significantly broadened by slow injection, particularly if the separation column is not sufficiently retentive. In the PCA, because each column is tailored to a specific range of analytes, sufficient retention can be provided even for high-volatility analytes. This alleviates the requirement for rapid preconcentrator heating and ultrasharp analyte injection. From an architectural perspective, the PCA is complementary to the uGC \(\times\) uGC. The PCA is intended to provide energy efficient analysis for a wide volatility range of analytes, whereas the uGC \(\times\) uGC is intended to enhance the separation of analytes with similar volatility values by adding a dimension of separation based on polarity. The separation columns in the PCA are arranged \"in parallel\" with each receiving a different volatility range of analytes. In contrast, the two-dimensional separation columns in the uGC \(\times\) uGC are arranged \"in series\" with all columns receiving the entire range of analytes. The preconcentrator in each cell of the PCA only injects the analytes once. In contrast, the uGC \(\times\) uGC uses a modulator to periodically inject the analytes eluting the first dimension column into the second dimension columns [22; 24]. It is worth noting that the PCA can, in principle, be combined with uGC \(\times\) uGC, as each PCA cell can selectively incorporate two-dimensional separation columns that are tailored for this cell. Compared to other uGC architectures under limited energy budgets, the PCA accommodates a superior volatility range of analytes while maintaining moderate or superior separation (Table 1).