Hybrid preconcentrator/focuser module for determinations of explosive marker compounds with a micro-scale gas chromatograph

• Published in: Journal of Chromatography A Vol. 1279; pp. 76 - 85
• Main Authors: Serrano, Gustavo, Sukaew, Thitiporn, Zellers, Edward T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2013; Elsevier
• Subjects: adsorbents; air; Analytical chemistry; Applied sciences; Butanes - analysis; Chemical industry and chemicals; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, Gas - instrumentation; Chromatography, Gas - methods; desorption; Dinitrobenzenes - analysis; Exact sciences and technology; Explosive Agents - analysis; Explosives; Gas chromatographic methods; Gas chromatography; heat; heaters; Industrial chemicals; Microfabrication; Powders, propellants, explosives; Preconcentration; silicon; stainless steel; temperature; trinitrotoluene; Trinitrotoluene - analysis; Preconcentration; Gas chromatography; Explosives; Microfabrication; Trace analysis; Chemical analysis; Microequipment; Portable equipment; Chemical enrichment
• ISSN: 0021-9673; 1873-3778
• DOI: 10.1016/j.chroma.2013.01.009

► This module combines microfabricated and non-microfabricated components. ► It was optimized for two vapor-phase markers of TNT. ► Markers are selectively trapped, focused, and injected with 86% transfer efficiency. ► Preconcentration factors of 1800–4500 are achieved from a 1-L air sample. This article describes the development and characterization of a partially selective preconcentrator/focuser (PCF) module for a field-portable micro-scale gas chromatograph (μGC) designed to rapidly determine trace levels of two vapor-phase markers of the explosive trinitrotoluene (TNT): 2,3-dimethyl-2,3-dinitrobutane (DMNB) and 2,4-dinitrotoluene (2,4-DNT). The PCF module has three primary components. The first is a high-volume sampler, comprising a resistively-heated 6-cm long stainless steel tube packed with tandem beds of the graphitized carbons Carbopack B (C-B, 30mg) and Carbopack Y (C-Y, 15mg), which traps the markers but permits more volatile interferences to pass through largely unretained. The second component is a microfocuser (μF), comprising a 4.2×9.8mm Si chip containing a deep-reactive-ion-etched (DRIE) cavity packed with 2mg of C-B, a Pyrex cap, integrated heaters, and etched fluidic channels. The third component is a commercial polymer-membrane filter used as a pre-trap to remove particles and adsorbed low volatility interferences. Markers captured in the sampler are thermally desorbed and transferred to the μF, and then thermally desorbed/injected from the μF into a downstream separation (micro)column and detected. Scrubbed ambient air is used as carrier gas. The adsorbent capacities, baseline temperatures, sampling and desorption flow rates, and heating profiles were optimized for each PCF module component while minimizing the analysis time. An overall transfer efficiency of 86% was achieved at marker concentrations of ∼0.2–2.6ppb. In the final configuration the PCF module requires just 60s to collect a 1-L sample (3L/min), focus (40mL/min), and inject the markers (3mL/min), producing half-maximum injection peak widths of ∼2 and 5s, and preconcentration factors of 4500 and 1800, for DMNB and 2,4-DNT, respectively.