Growth Tube Microchip Electrophoresis System for Monitoring of Aerosol Compositions
At A Glance
Researchers at Colorado State University have patented a microchip capillary electrophoresis method and apparatus for the semicontinuous measurement and separation of inorganic anions in atmospheric aerosol extracts. Protocols provide limits of detection below 300nM and sub-minute time resolution. Additionally, the separation scheme allows for immediate subsequent injections, ideal for such analyses.
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Particulates suspended in the atmosphere originate from a wide variety of biogenic and anthropogenic sources. Water-soluble species include inorganic cations (ammonium, potassium, calcium, sodium, and magnesium), inorganic anions (sulfate, nitrate, nitrite, chloride), some heavy metals, and water-soluble organic carbon species such as oxalate, other organic acids, carbohydrates, and organic amines.
Most often these constituents are measured by in-field collection on a filter, followed by offline, laboratory-based sample extraction and analysis. Generally, the time resolution is poor, and results are not known for several weeks after the collection. Inorganic ions in atmospheric particles can also be measured in-situ by coupling a steam injection particle collector to an ion chromatography analyzer.
Microchip capillary electrophoresis is an inherently less expensive and less bulky method than ion chromatography. It is more sensitive, with much lower detection limits on a mass basis. It is much faster, with separation times of the order of one minute as compared to several minutes or longer for ion chromatography. “Lab on a chip” is an established approach for the chemical analysis of solutions wherein many of the components required for the analysis are incorporated onto a microchip. Generally speaking, these microchips contain a sample reservoir that holds the solution to be analyzed, a separation channel for separating the analytes of interest from other constituents, and a means of detecting those constituents after separation. Through the application of electrical voltages or hydrodynamic forces, a small amount of solution is moved from the sample reservoir to the beginning of the separation channel. The analytes travel down the separation channel with a characteristic migration time dependent on the analyte and are detected when they arrive at the end of the channel. The separation can be done by electrophoresis, where ions move under the influence of an electric potential difference applied across the channel. Detection can be done by measuring the change of electrical conductivity of the solution.
- One-minute time resolution at very low concentration levels (micrograms of analyte species per cubic meter of air)
- Aerosol composition monitoring that is smaller, faster, and portable
- Assay of sulfates, nitrates, chlorides and organic acids contained in fine and submicrometer atmospheric particles
- Extension to other analytes is possible
Scott D. Noblitt, Gregory S. Lewis, Yan Liu, Susanne V. Hering, Jeffrey L. Collett, Jr., and Charles S. Henry. “Interfacing Microchip Electrophoresis to a Growth Tube Particle Collector for Semicontinuous Monitoring of Aerosol Composition.” Analytical Chemistry 2009 81 (24), 10029-10037 DOI: 10.1021/ac901903m
Last updated: May 2020
Chuck Henry, Charles Henry, Chuck S. Henry, Chuck S Henry