Field Detection of Chlorinated Alkenes in Well Water using the FROG-4000 Portable GC - Case Study

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Courtesy of Northern ANI Solutions Ltd.

Introduction
Defiant’s FROG 4000, a portable GCPID system, was used to identify and determine the concentration of chlorinated alkenes in several extraction wells located in Tacoma Washington. Split samples were taken at each well and sent to an offsite lab for analysis. This case study examines the field exercise and highlights the high degree of agreement between the offsite lab and the FROG-4000 shown in Figure 1.

Site History
Well 12A was a municipal water supply well located in Tacoma Washington approximately 4 miles southwest of the southernmost tip of Commencement Bay. The well is now a superfund site contaminated with chlorinated alkenes. Around 1923, a paint and lacquer thinner manufacturer and an oil recovery facility began operations at this location. The solvents used by this manufacturer were stored in drums and may have leaked. In addition, filter cake from oil recovery efforts were landfilled at this site. In 1981, solvents, particularly chlorinated alkenes, were detected in the water at this site and the well was removed from service. Well 12A was officially added to the national priorities list or NPL in 1983 labeling it a superfund site. [1] There has been a consistent and concerted effort to clean up the site since that time.

The FROG-4000 Portable GC System
Weighing less than 5 pounds, the FROG- 4000 is the smallest portable GC system on the market today. The FROG uses a MEMS preconcentrator which is coated with a novel designer nanomaterial and micro fabricated GC column-technology that cannot be found in even the most advanced bench top GC systems. These leading edge micro-fabricated components enable the FROG to achieve the same detection limits that a traditional bench top GC system achieves but at a fraction of the cost and size. A traditional GC analysis would require the GC itself, a purge-and-trap system, a compressed gas cylinder, a computer, and a generator to operate it in the field. All of that equipment may weigh hundreds of pounds and require up to an hour for every analysis. The FROG-4000, however, has the purge and trap built in, is battery operated, and uses ambient air as the carrier gas yet weighs only 4.8 pounds. In about 5 minutes, the FROG-4000 can analyze water for VOCs and report the results to its display. The FROG’s rechargeable battery will give up to 8 hours of usage in the field. The battery can be swapped in the field for extended use. A small pump on the inside of the FROG scrubs ambient air for the carrier gas. The scrubber material is inexpensive and easy to exchange for fresh material. There is no compressed gas cylinder, which minimizes the cost of ownership of the FROG.

Calibration
A 6 point calibration was prepared in water for vinyl chloride, trans-1, 2-dichloroethene, cis-1, 2-dichloroethene, trichloroethene, and tetrachloroethene. The calibration curve included concentrations of 4, 8, 20, 80, 200, and 400µg/L. Each standard was stored in a VOA vial with zero head space and refrigerated during shipping. (A professionally prepared calibration kit is available on Defiant’s website -www.defiant-tech.com.) The standards were shipped with the FROG to Tacoma. The evening prior to the field test, we calibrated the FROG-4000 using our pre-made standards. Calibrating with 6 calibration standards took approximately 35 minutes and each response curve resulted in an R2 correlation greater than 0.995. While a computer is required for calibrating the FROG, it is not required for use in the field. The calibration can be downloaded to the FROG-4000and when this is done, it will report analyte name and concentration to its display. FROG also has an integrated microSD card which will store every chromatogram from every analysis. This feature allows the user the ability to examine and archive each chromatogram at their leisure after the sampling event.

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