title: Toward a microfabricated preconcentrator-focuser for a wearable micro-scale gas chromatograph.
abstract: This article describes work leading to a microfabricated preconcentrator-focuser (μPCF) designed for integration into a wearable microfabricated gas chromatograph (μGC) for monitoring workplace exposures to volatile organic compounds (VOCs) ranging in vapor pressure from ∼0.03 to 13kPa at concentrations near their respective Threshold Limit Values. Testing was performed on both single- and dual-cavity, etched-Si μPCF devices with Pyrex caps and integrated resistive heaters, packed with the graphitized carbons Carbopack X (C-X) and/or Carbopack B (C-B). Performance was assessed by measuring the 10% breakthrough volumes and injection bandwidths of a series of VOCs, individually and in mixtures, as a function of the VOC air concentrations, mixture complexity, sampling and desorption flow rates, adsorbent masses, temperature, and the injection split ratio. A dual-cavity device containing 1.4mg of C-X and 2.0mg of C-B was capable of selectively and quantitatively capturing a mixture of 14 VOCs at low-ppm concentrations in a few minutes from sample volumes sufficiently large to permit detection at relevant concentrations for workplace applications with the μGC detector that we ultimately plan to use. Thermal desorption at 225°C for 40s yielded ≥99% desorption of all analytes, and injected bandwidths as narrow as 0.6s facilitated efficient separation on a downstream 6-m GC column in <3min. A preconcentration factor of 620 was achieved for benzene from a sample of just 31mL. Increasing the mass of C-X to 2.3mg would be required for exhaustive capture of the more volatile target VOCs at high-ppm concentrations.
authors.affiliation: Department of Environmental Health Sciences, University of Michigan, Ann Arbor, MI 48109-2029, United States; Center for Wireless Integrated MicroSensing & Systems, University of Michigan, Ann Arbor, MI, United States.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Bryant-Genevier
authors.affiliation: Department of Environmental Health Sciences, University of Michigan, Ann Arbor, MI 48109-2029, United States; Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-2029, United States; Center for Wireless Integrated MicroSensing & Systems, University of Michigan, Ann Arbor, MI, United States. Electronic address: ezellers@umich.edu.
authors.forename: Edward T
authors.initials: ET
authors.lastname: Zellers
mesh_terms: D002244:Carbon / Q000737:chemistry; D002623:Chemistry Techniques, Analytical / Q000295:instrumentation* / Q000379:methods*; D002849:Chromatography, Gas / Q000295:instrumentation*; D055616:Microtechnology; D016273:Occupational Exposure / Q000032:analysis*; D015203:Reproducibility of Results; D055549:Volatile Organic Compounds / Q000032:analysis*
chemical_list: D055549:Volatile Organic Compounds; D002244:Carbon
keywords: Benzene; Micro gas chromatography; Microfabricated; Preconcentrator; VOC mixture