Tools Available for Real-Time Exposure Assessment Phil Smith, PhD, CIH CDR MSC, USN
Objectives Describe the range of field chemical detection systems now available Describe trends in real-time detection and identification tools towards the ideals of “faster,” “cheaper,” and “easier-to-use”
Types of Real-Time Exposure Assessment Tools Transportable Handheld Quantitative Detectors Small Colorimetric Single-use Detectors Man-portable (Derived from Level 4) Increasing cost, expertise, complexity
M8 Paper (simple) M256 Kit (complicated) Military Capabilities without Instrumentation
Length-of-Stain Indicator Tubes Color change produced through chemical rection Length of stain corresponds to concentration when a given volume of air is sampled
Simple Handheld Instruments Capable of Quantitative Detection Photoionization detector as an example… A simple and rugged instrument that uses relatively little power Relies on atmospheric pressure photoionization of target analytes Selectivity is based on ionization potential
Combined PID/Electrochemical Sensors Electrochemical Sensors
Basis for Photoionization UV light energy removes electron from neutral target molecules, creates ions The resulting electrical current from these ions is proportional to contaminant concentration The UV energy emitted must be sufficient to ionize that particular substance, or PID will not detect that analyte
PID Operation ppm Gas enters the instrument UV lamp Ions flow to charged Plates, producing current Current is measured and concentration is displayed on meter Non-ionized gas exits the instrument intact Courtesy of Bob Henderson, GFG Inc.
Courtesy of Bob Henderson, GFG Inc. What does a PID Measure? Some Ionization Potentials (IPs) for Common Chemicals Benzene MEK Vinyl Chloride IPA Ethylene Acetic Acid Methylene chloride Carbon Tet. Carbon Monoxide Styrene Oxygen Ionization Potential (eV) 11.7 eV Lamp 10.6 eV Lamp 9.8 eV Lamp 10.5 Not Ionizable by PID
Sarin Detection and Cleardown, PID
How does Ion Mobility Spectrometry work?
How does Ion Mobility Spectrometry work?
IMS analysis of VX Reactant Ion (H 2 O) Peaks SPME Fiber (with VX) Introduced Reduced Mobility (cm 2 V -1 s -1 )
Person-Portable IR
When a molecular bond vibrates at the same frequency as IR light the bond and the light are resonant The bond is “excited” as the IR light is absorbed by the molecule H – C – C – C – C – C – C – H H|H| H|H| H|H| H|H| H|H| H|H| |H|H |H|H |H|H |H|H |H|H |H|H n-hexane
Field-Portable GC-MS
Existing Level-1 and Level-2 Real-Time Information Capabilities Detection systems found in Level-1 (single use colorimetric) and Level-2 (handheld) have an important role now in exposure assessment (1)New technologies (e.g., field-portable GC-MS) will provide even better qualitative data for increased clarity with immediate feedback (2) Current systems provide actionable real-time data to both hygienist (exposure assessment) AND workers (safety); as systems are further refined for precision and reliability this will grow in importance