Preconcentration and detection of chlorinated organic compounds and benzene

Abstract

Remote and automated detection of organic compounds in subsurface aquifers is crucial to superfund monitoring and environmental remediation. Current monitoring techniques use expensive laboratory instruments and trained personnel. The use of a filled tubular preconcentrator combined with a chemicapacitive detector array presents an attractive option for the unattended monitoring of these compounds. Five preconcentrator materials were exposed to common target compounds of subsurface remediation projects (1,1,2-trichloroethane, trichloroethylene, t-1,2-dichloroethylene, benzene, and perchloroethylene). Rapid heating of the tube caused the collected, concentrated effluent to pass over the surface of a chemicapacitive detector array coated with four different sorbent polymers. A system containing a porous ladder polymer and the sensor array was subsequently used to sample the analytes injected onto sand in a laboratory test, simulating a subsurface environment. With extended collection times, effective detection limits of 5 ± 3 ppbV for 1,1,2-trichloroethane and 145 ± 60 ppbV for benzene were achieved. Effects of the preconcentrator material structure, the collection time, and sensor material on the system performance were observed. The resultant system presents a solution for remote, periodic monitoring of chlorinated organic compounds and other volatile organic compounds in a soil matrix.

Polymers of Intrinsic Microporosity

“…In a related application, PIM-1 has been used as a preconcentrator medium for adsorbing organics from air which can then be desorbed by heating into a conventional sensor [139,140]. For this application, the thermal stability of PIMs is of importance.…”

Developments toward a low-cost approach for long-term, unattended vapor intrusion monitoring

“…The stainless steel tube was inserted into a ceramic outer tube, soldered to threaded brass ends, and then filled with absorbent media. 20 The difference between this preconcentrator and our previous device was the replacement of the press-fit connections with threaded tube-end fittings for gas-tight connections. The preconcentrator is resistively heated by applying a controlled voltage between the brass electrodes for short durations.…”

“…The polymer-filled microcapacitors, or chemicapacitors, were fabricated by Seacoast Science, and their structure has been extensively reported on. 20,23,26,27 The chemicapacitor array chips used in the VIM were 2 × 5 mm and contained 10 capacitors, 8 of which were filled with polymer and measured. † Each chemicapacitor was filled with a different polymer.…”

“…However, earlier work 20 demonstrated that a polymer with intrinsic microporosity 31,32 (PIM-1) provides a higher sorption capacity for the chlorinated hydrocarbons than does Tenax TA, which is commonly used in GC preconcentrators. 33 PIM-1, a yellow powder, was synthesized in-house, and sieved with mesh screens to collect a 60 to 80 mesh fraction.…”

“…This vapor intrusion monitor (VIM) work builds on earlier developments of sorbent traps (preconcentrators) 20 and oven-less gas chromatographs for education 21 and industry 22 . The VIM system consists of a packed-tube preconcentrator, a resistively heated commercial chromatography column, and a detector array.…”