Tools Available for Real-Time Exposure Assessment
Phil Smith, PhD, CIH
CDR MSC, USN
ObjectivesDescribe the range of field chemical Describe the range of field chemical detection systems now availabledetection systems now available
Describe trends in real-time detection Describe trends in real-time detection and identification tools towards the and identification tools towards the ideals of “faster,” “cheaper,” and ideals of “faster,” “cheaper,” and “easier-to-use”“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 PaperM8 Paper(simple)(simple)
M256 KitM256 Kit(complicated)(complicated)
P
O
O
CH3
H3C CH3S Cl
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/ElectrochemicalSensors
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
Gas enters theinstrument
UV lamp
Ions flow to charged Plates, producing current
Current is measured and concentration is displayed on meter
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--Non-ionized gas exits theinstrument intact
Courtesy of Bob Henderson, GFG Inc.
9.999.54
Courtesy of Bob Henderson, GFG Inc.
What does a PID Measure?
8
9
10
11
12
13
14
15
8.4
9.24
10.110.66
11.3211.4712.1
14.01
Some Ionization Potentials (IPs) for Common Chemicals
Ben
zene
ME
K
Vin
yl C
hlo
ride
IPA
Eth
ylene
Acetic A
cid
Meth
yle
ne
chlo
ride
Carb
on
Te
t.
Carb
on
M
on
ox
ide
Styren
e
Oxy
gen
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?
400B IMS Operation Smiths.exe
How does Ion Mobility Spectrometry work?
IMS analysis of VX
Reactant Ion (H2O) Peaks
SPME Fiber (with VX)Introduced
Reduced Mobility (cm2V-1s-1)
SN
P
O
CH3
O
Person-PortableIR
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
n-hexane
Field-Portable GC-MS
Existing Level-1 and Level-2 Real-Time Information
CapabilitiesDetection systems found in Level-1 (single usecolorimetric) and Level-2 (handheld) have an importantrole now in exposure assessment
(1)New technologies (e.g., field-portable GC-MS)will provide even better qualitative data for increasedclarity with immediate feedback
(2) Current systems provide actionable real-time datato both hygienist (exposure assessment) AND workers(safety); as systems are further refined for precision andreliability this will grow in importance
