Hand-Held Photoionization Instruments for Quantitative Detection of Sarin Vapor and for Rapid Qualitative Screening of Contaminated Objects

Abstract

Suitable detectors are needed to support survey needs of incident responders and health care personnel who may receive patients from an incident with exposures to hazardous chemicals. In the health care setting, such a detector would avoid cross-contamination to workers, patients, and to the treatment facility and associated equipment. An ideal survey detector would be sensitive, hand-held, capable of extended battery operation, and would provide a nearly immediate detector response on exposure to a broad range of high-concern chemicals. For responders, important capabilities would include quantitative measurement of gas/vapor contamination, and for both response and health care settings, qualitative detection of contaminated people and objects. In this study, the operating characteristics of photoionization detector (PID) instruments were examined using O-isopropyl methylphosphonofluoridate (sarin) in a laboratory setting. Instrument response factors were calculated for quantitation of airborne sarin, and speed of detector response and recovery were examined with point-contaminated cloth material. By sampling a range of sarin-contaminated air, calculated isobutylene unit response factors for high-and moderate-sensitivity commercial PID instrument types were 11.3 and 14.0 (dry air) and 20.1 and 44.4 (50% relative humidity), respectively. Response of the PID systems was highly correlated to concentration sampled, with R² values greater than or equal to 0.997 for all combinations of PID detector type and humidity. While not sensitive enough to warn the unprotected public against a chemical with an extremely low “safe” exposure concentration, quantitation with available PID instruments could be useful to quickly prioritize corrective measures for a PID-detectable chemical. Qualitative survey characteristics were examined for the more sensitive PID tested using a piece of cloth material contaminated by a 1.0 μ L droplet of liquid sarin. Rapid response and recovery times (seconds) were observed when the sampling inlet was moved close to and away from the point of contamination. Within the health care setting, hand-held PID instruments could fill an important and currently unmet need as a point source detector for liquid contamination from extremely dangerous chemicals to help identify contaminated surfaces and limit secondary contamination and exposures.

Keywords:

• photoionization
• sarin
• screening

Notes

^A 16,300 ng sarin spiked to either Tenax sorbent material or directly to solvent, 5.0 μ L injection of sarin dissolved in hexanes (3.26 mg sarin/mL hexanes).

^A Verified sarin concentration stated as ppm (v/v), by active sampling, solvent desorbtion of sarin from sampling tube media, and quantitative GC-MS analysis.

^B ND = not detectable above background PID reading, 0 to 0.003 ppm for ppbRAE and 0 for MultiRAE plus instruments during sampling events.

^C For airborne sarin samples created with 50% humidity, 4-point curves were sought but neither type of PID instrument gave a reading above background when sampling the lowest concentration created from dilution of the PTFE bag containing 0.33 ppm sarin, and the concentration of sarin in this nondetectable sample was not confirmed by active sampling and GC-MS analysis.