1：Experimental Design and Method Selection:

The study employs heart-cutting 2-dimensional gas chromatography (GC) with miniaturized components for portable formaldehyde detection. It uses a micro-Deans switch for flow routing, preconcentrators for sample trapping, and photoionization detectors (μPID and μHDBD-PID) for detection. The design focuses on miniaturization, automation via LabView?, and accurate temperature control.

2：Sample Selection and Data Sources:

Formaldehyde vapor samples were generated from aqueous solutions at concentrations ranging from 0.5 to 100 ppb (V/V), as listed in Table 1. Samples were prepared using a purge setup with purified air flow, and vapors were trapped using preconcentrators.

3：5 to 100 ppb (V/V), as listed in Table Samples were prepared using a purge setup with purified air flow, and vapors were trapped using preconcentrators. List of Experimental Equipment and Materials:

3. List of Experimental Equipment and Materials: Key equipment includes GC columns (Rtx?-VMS and Rt? Q-BOND), preconcentrators with adsorption materials (Carbopack? B, Carbopack? X, Carboxen? 1000), detectors (μPID and μHDBD-PID), micro-Deans switch, valves, pumps, data acquisition card (USB-6003 OEM), and various wires and connectors. Materials were sourced from Sigma-Aldrich, Supelco, Lee Company, Omega Engineering, Restek, National Instruments, Parker Hannifin, and others.

4：Experimental Procedures and Operational Workflow:

Air samples are collected at 40 mL/min flow rate for adjustable sampling times (e.g., 6 min), trapped in preconcentrators, injected into the 1st-dimensional GC column. Formaldehyde is heart-cut using a micro-Deans switch and re-injected into the 2nd-dimensional column for separation, detected by μHDBD-PID. Other VOCs are detected by μPID. The process is automated with temperature control and data acquisition.

5：Data Analysis Methods:

Data were acquired using a USB-6003 OEM card with LabView? software. Formaldehyde peak areas were integrated from chromatograms, and linearity, sensitivity, and detection limits were calculated using statistical methods (e.g., LOD = 3σ/S).