Final Report: Microchip Analytical System for Inexpensive, Real-Time Aerosol Chemical Speciation

EPA Contract Number: EPD15025
Title: Microchip Analytical System for Inexpensive, Real-Time Aerosol Chemical Speciation
Investigators: Dekleva, Philippe
Small Business: MicroChemica, LLC
EPA Contact: Manager, SBIR Program
Phase: I
Project Period: September 1, 2015 through February 29, 2016
Project Amount: $99,999
RFA: Small Business Innovation Research (SBIR) - Phase I (2015) RFA Text |  Recipients Lists
Research Category: Small Business Innovation Research (SBIR) , SBIR - Air and Climate

Description:

Atmospheric aerosols, also known as particulate matter (PM), have significant roles in weather, climate, and human health. Instruments for monitoring the physical characteristics of aerosols,  such  as  total number, size distribution, and mass are well developed but do not address the chemistry  of  the particles. There is a need for improved aerosol chemistry instrumentation in  order  to  better  address impacts on health, climate and source apportionment. MicroChemica, LLC is addressing this need by developing an instrument that will provide real-­‐time, quantitative chemical speciation of bulk aerosols with ~1-­‐min time resolution, µL sample volumes, the ability to monitor multiple species simultaneously, unattended operation for extended periods, and the ability to interface with  existing  steam-­‐based aerosol collectors.  In production this system will cost $20,000-­‐25000 with an annual consumables cost of approximately $2000.

Summary:

MicroChemica has developed a continuous-­‐flow microchip electrophoresis (MCE) device for coupling to steam-­‐based aerosol collectors that is faster, cheaper and less complex than existing chemical speciation instrumentation. This technology provides comparable sensitivity to traditional methods, but cost, analysis time, and reagent consumption are significantly lower for our technology. The most common current technology used today for quantitative monitoring of aerosol chemistry is ion chromatography (IC). MCE requires considerably less complex instrumentation than IC. While IC requires a high-­‐pressure pump, peristaltic pump, and a stationary phase that can foul with  time,  MCE  uses  open  capillaries instead of a stationary phase, and high voltages to drive flows instead of pumps. The temporal resolution is 2-­‐20× faster than IC. Historically, the primary concerns of employing MCE in environmental analysis are online interfacing with sample solutions, detection sensitivity, and the ability  to autonomously operate for extended times (weeks to months). We have addressed each of these in our Phase-­‐I R&D. A new online MCE interface was developed that is compatible with both continuous-­flow and batch sample solutions. Contact conductivity detection with MCE provided detection limits below 1.1 micrograms per cubic meter each of the most important inorganic species: nitrate, sulfate, chloride, oxalate, ammonium, potassium, calcium, sodium, and magnesium. Lower detection limits could be achieved through larger injection volumes, multi-­‐injection averaging, or larger injection volumes. The MCE interface also permits theoretical operation times of at  least  two  months  without  buffer replacement. Thus, we have demonstrated the proof of concept that MCE can be coupled to a PILS or similar aerosol collector, and we are now working to eliminate some of the artifacts and system faults.

Conclusions:

The results of the Phase I project are the following:

  1. MicroChemica has developed separation chemistry to detect both a suite of anions and cations commonly found in particulate matter. Anions are  chloride,  sulfate,  nitrate,  and  oxalate. Cations are ammonium, potassium, calcium, sodium, and magnesium. Analysis times are ~1 min, and detection limits when connected to a standard PILS collector are in the 20-­‐90 ng per cubic meter range. Additional analysis time or operational modifications can lower this detection limit substantially.
  2. The company developed a new microchip electrophoresis interface that permits online sampling from either continuous flows or batch processes. Unattended operation times are theoretically expected to be at least two months.
  3. The new chemistry and microchip interface were tested with long operation using a constant sample; both peak signal times and quantified concentrations had relative standard deviations near 0.5%, thus demonstrating extremely high precision and reproducibility.
  4. Software was developed to both operate the microchip and perform real-­‐time, automated data analysis.