Tools Available for Real-Time
Exposure Assessment
Phil Smith, PhD, CIH
CDR MSC, USN
psmith@usuhs.mil
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
Man-portable
(Derived from Level 4)
Handheld Quantitative Detectors
Small Colorimetric Single-use Detectors
Military Capabilities without Instrumentation
S
Cl
M8 Paper
(simple)
O
H3C
P
CH3
O
CH3
M256 Kit
(complicated)
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
100.0 ppm
+
-
+
-
Current is measured
and concentration is
displayed on meter
+
-
-
+
Gas enters the
instrument
Ions flow to charged
Plates, producing
current
Non-ionized gas exits the
instrument intact
UV lamp
Courtesy of Bob Henderson, GFG Inc.
What does a PID Measure?
Some Ionization Potentials (IPs) for Common Chemicals
9.8 eV
Lamp
10.6 eV
Lamp
15
11.7 eV
Lamp
Not Ionizable by
PID
14.01
14
Ionization
Potential 13
(eV)
12
12.1
11
10.5
9.99 10.1
10
11.3211.47
10.66
9.24 9.54
9 8.4
8
Carbon
Monoxide
Oxygen
Carbon Tet.
Methylene
chloride
Acetic Acid
Ethylene
IPA
Vinyl Chloride
MEK
Benzene
Styrene
Courtesy of Bob Henderson, GFG Inc.
Sarin Detection and Cleardown, PID
How does Ion Mobility
Spectrometry work?
How does
Ion Mobility
Spectrometry work?
IMS analysis of VX
O
O P
S
CH3
Reactant Ion (H2O) Peaks
SPME Fiber (with VX)
Introduced
Reduced Mobility (cm2V-1s-1)
N
Person-Portable
IR
H H H H H H
|
|
|
|
|
|
H–C–C–C–C–C–C–H
|
|
|
| |
|
H
H
H
H
H
H
n-hexane
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
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