Tools Available for Real-Time Exposure Assessment

Phil Smith, PhD, CIH

CDR MSC, USN

psmith@usuhs.mil

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

++

--

++

--

++

--++

--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