Detector Tubesfor

Chemical Warfare Agents (CWAs)

Presented by:Gretchen B. Manning Product Group ManagerPortable Instruments

© MSA 2002

www.msanet.com

Response to CWA Incident

Federal help (analytical-grade equipment) is ~6 hours away

First responders – typically local FD or Hazmat crew – are in charge at the beginning

Need to(1) assess nature of threat(2) define “hot zone”(3) aid the injured

Chemical Weapons for TerroristsNerve agents (G)

GA (Tabun) IDLH = 0.03ppm (0.2mg/m3)GB (Sarin) IDLH = 0.03ppm (0.2mg/m3)GD (Soman) IDLH = 0.008ppm (0.07mg/m3)VX IDLH = 0.002ppm (0.02mg/m3)

Blister agents (H)HD (Mustard) IDLH = 0.0004ppm (0.003mg/m3)

Choking/Blood agentsAC (cyanide) IDLH = 50ppm (60mg/m3)CK (cyanogen chloride) Phosgene IDLH = 2ppm (10mg/m3)

TICs (easier to access)Ammonia IDLH = 300ppm (230mg/m3)Chlorine IDLH = 10ppm (30mg/m3)

First Responder Detector Needs

Fits the budgets of local fire companies

Easy to use – first responders are not Ph.D. analytical chemists

Extremely low rate of false positives, false negatives

Some idea of nature of hazard

Technologies for CWA Detection

Ion Mobility Spectrometry (IMS)

Portable

Distinguishes among agent families

Detects at IDLH/10

$6 -12K

Pesky radioactive source

Sensitive to some “battlefield interferents”

Technologies for CWA Detection

Chromatography (GC-MS, GC-IMS, etc.)

Transportable (often in dedicated truck)

Best variants detect at below TWA

$25 -100K

Skilled operators with “refresher training”

Nearly no false positives/negatives

Analyses require 30 minutes or more

Technologies for CWA Detection

Detector Tubes

Portable

Detects at IDLH/10 to IDLH

Discriminates among families of agents

$10/tube

Simple to use…go / no-go

Low false positive rate

What are Detector Tubes?

Based on color change when analyte participates in a chemical or enzyme-catalyzed reaction

Indicator compound supported on solid(i.e. silica gel) inside a glass tube

First implementation in the 1910s for carbon monoxide detection

Over 300 target analytes, including CWAs and TICs

Example of Detector Tube Use (H)

Detector tube for

HD

HN

ComponentsChemically treated indication layer

Reagent ampoule

Pump to drawsample throughthe tube

indication layer

reagent ampoule

Example of Detector Tube Use (H)

Break off tube tips on both ends

Attach to pump – 40 strokes (4-10 sec. ea.)

Break reagent ampoule to wet indication layer

White to blue color change indicates presence of agent

indication layer

reagent ampoule

0.01mg/L

0.001mg/L

Detector Tube Chemistry (H)

mustard agent Indicator (colorless)

developer (reagent)

- HCl

Cl CH2 CH2 S CH2 CH2 Cl N CH2 NO2

Cl CH2 CH2 S CH2 CH2 N CH NO2

NaOH

Cl CH2 CH2 S CH2 CH2 N CH NO

O

_

__

+

Na

+OH

-

complex (blue)

Mustard Agent

How does nerve agent really work?

Humans and detector tubes have more in

common than you think!

How does nerve agent work?

Synapse

Close up viewof synapse

The synapse is the electrical switching center throughout the nervous system

Stimulating signals are fired across the synapses by chemicals

A chemical called acetylcholine carries the stimulating signals

An enzyme known as Cholinesterase, specifically acetylcholinesterase, breaks down or inhibits the stimulating signals

Pesticides and nerve agents actually inhibit the Cholinesterase, therefore, preventing the breakdown of the stimulating signal (acetylcholine)

The result jams the nervous system so muscles being directed by nerves to move can’t stop and move uncontrollably!

Rapid twitching, paralyzed breathing, convulsions, and even death can occur

In summary…

Build-up of Cholinesterase inhibitors or nerve agent occurs

Cholinesterase inhibition

Constant firing of electrical messages

Twitching, trembling, paralyzed breathing, convulsions, andeven death

So, how does the human nervoussystem relate to detector tubes?

Detector tubes are based on the same inhibition of

enzyme – the same mechanism that affects

humans

Example of Detector Tube Use (G)

For detection of Phosphoric Esters: nerve agents GA, GB, GD, VX

Based on inhibition of enzyme – the same mechanism that affects humans

Two reagent ampoules and two supported solids

Example of Detector Tube Use (G)

√ Read after 2 minutes

< 0.00005 mg/L

> 0.0005 mg/L

(no reaction = agent is present!)

reagent 1

reagent 2

substrate

enzyme

√ Break off both tube tips

√ Break ampoule 1 to wet white (enzyme) layer

√ Draw sample through tube (30 strokes)

√ Break ampoule 2 to wet yellow (substrate) layer

Detector Tube Chemistry (G)

(CH3)3NCH2CH2SCCH3 + H2O

=O+

(CH3)3NCH2CH2SH + CH3COOH+

substrate (white layer)enzyme (catalyst) in

yellow layer

+ O2N - - S – S - - NO2

HOOC COOH

(CH3)3NCH2CH2S – S - - NO2 +

COOH

S - - NO2 S = =N

COOH

=

O

COOH

nerve agent stops the first reaction…no color change!

X

X

Detector Tube Target Analytes

nerve agents(GA, GB, GD, VX)

blister agent (H), blister agent (L), blister agents (general, including H)

blood/choking agents (CG, DP, AC, CK)

formaldehyde, acetic acid, acetone

trichloroethane, ammonia, aromatics (benzene)

chlorine, ethylene, ethanol, triethylamine, ethylmercaptan

CO2, CS2, hexane, gasoline, mercury, MEK, NO2

…over 300in all!

phenol, phosphene, phosgene, SO2, SF6, vinyl chloride, toluene

Summary

They are an ideal option for local first responders withsmall budgets

Improvements to detector tubes will make them even more convenientto use

Colorimetrictubes provide an inexpensive, accurate, simple-to-use alternative for detection of TICsand CWAs