U.S. patent application number 12/232359 was filed with the patent office on 2012-08-09 for chemical sample collection and detection system.
Invention is credited to Kenneth J. Ewing, Paul G. Kahl, JR., Fred Whiton, JR..
Application Number | 20120198912 12/232359 |
Document ID | / |
Family ID | 46599740 |
Filed Date | 2012-08-09 |
United States Patent
Application |
20120198912 |
Kind Code |
A1 |
Ewing; Kenneth J. ; et
al. |
August 9, 2012 |
CHEMICAL SAMPLE COLLECTION AND DETECTION SYSTEM
Abstract
A system for remote detection of a chemical is disclosed. The
system includes a sample collection module that collects a sample
and produces a sample vapor at a first location; a sample delivery
module that delivers the sample vapor from the first location to a
second location; a sample storage and concentration module that
collects the sample vapor at the second location; and a sample
analysis module that analyzes the sample collected in the sample
storage and concentration module.
Inventors: |
Ewing; Kenneth J.;
(Elkridge, MD) ; Whiton, JR.; Fred; (Towson,
MD) ; Kahl, JR.; Paul G.; (Perry Hall, MD) |
Family ID: |
46599740 |
Appl. No.: |
12/232359 |
Filed: |
September 16, 2008 |
Current U.S.
Class: |
73/23.35 ;
73/23.2 |
Current CPC
Class: |
G01N 1/22 20130101; G01N
1/2214 20130101 |
Class at
Publication: |
73/23.35 ;
73/23.2 |
International
Class: |
G01N 30/02 20060101
G01N030/02; G01N 7/00 20060101 G01N007/00 |
Claims
1. A system for remote detection of a chemical, comprising: a
sample collection module that collects a sample and produces a
sample vapor at a first location; a sample delivery module that
delivers said sample vapor from said first location to a second
location; a sample storage and concentration module that collects
said sample vapor at the second location; and a sample analysis
module that analyzes the sample collected in the sample storage and
concentration module.
2. The system of claim 1, wherein said sample delivery module
delivers said sample vapor through a first heated sample transfer
line (HSTL).
3. The system of claim 1, wherein said sample collection module
comprises an aerosol/particle collector and a heater.
4. The system of claim 3, wherein said sample vapor is produced by
heating the aerosols and particles collected by the
aerosol/particle collector.
5. The system of claim 3, wherein said sample collection module
further comprises an ambient vapor collector that collects an
ambient vapor at the first location.
6. The system of claim 3, wherein said sample delivery module also
delivers the ambient vapor collected at the first location to the
sample storage and concentration module.
7. The system of claim 1, wherein said sample concentration module
comprises at least one sorbent tube that collects the sample vapor
delivered from said sample delivery module.
8. The system of claim 7, wherein said sample concentration module
comprises two sorbent tubes.
9. The system of claim 7, wherein said sample concentration module
comprises three sorbent tubes.
10. The system of claim 1, wherein said a sample analysis module
comprises a chemical detector that detect said chemical of interest
using a technology selected from the group consisting of mass
spectrometry (MS), ion mobility spectrometry (IMS) and surface
acoustic wave (SAW) sensors, Raman spectroscopy, infrared
spectroscopy (IRS), gas chromatography (GC), Fourier transform
infrared spectrometry (FTIRS), photoacoustic infrared spectroscopy
(PAIRS), in-flame photometry (IFP), photo ionization detectors
(PIDs), electrochemical sensors, and thermoelectric conductivity
sensors.
11. The system of claim 1, further comprising a command and control
module.
12. The system of claim 11, wherein said command and control module
comprises a memory, a controller, and a external port.
13. The system of claim 1, further comprising a power module.
14. The system of claim 1, further comprising a communication
module.
15. A method for detecting a chemical at a remote site, comprising:
collecting aerosols and particles from a fluid sample at said
remote site; heating the collected aerosols and particles to
produce a sample vapor; transporting the sample vapor over a
distance to a sample storage and concentrating device; absorbing
the transported sample vapor in an absorbent in the sample storage
and concentrating device; desorbing the absorbed sample vapor, and
analyzing the desorbed sample vapor for the presence of said
chemical.
16. The method of claim 15, further comprising: producing an alarm
when said chemical is detected in said desorbed sample vapor.
17. The method of claim 15, wherein said sample vapor is
transported via a heated sample transfer line (HSTL).
18. The method of claim 15, further comprising: collecting an
ambient vapor sample at said remote site, and transport the
collected ambient vapor to said sample storage and concentrating
device.
19. The method of claim 18, wherein said sample vapor and said
ambient vapor are transported to said sample storage and
concentrating device via different heated sample transfer
lines.
20. The method of claim 15, wherein said sample storage and
concentrating device comprises at least two absorbent tubes to
allow parallel processing of multiple vapor samples.
Description
TECHNICAL FIELD
[0001] The invention relates generally to detection systems, and
more particularly, to a system capable of remote detection of
chemicals.
BACKGROUND
[0002] In recent years, there has been a demand for devices capable
of detecting dangerous chemicals, such as chemical warfare agents,
explosives, and toxic industrial chemicals, from a safe distance.
Ideally, such devices should be able to collect both solid and
liquid aerosols, as well as vapors, from a remote site and analyze
the collected materials for the presence of the chemicals of
interest. Since the chemicals of interest may be present at a very
low concentration (e.g., on the order of parts per billion (ppb) or
less), such devices need to be highly sensitive with low false
positive and false negative rates.
SUMMARY
[0003] A system for remote detection of a chemical and aerosol is
disclosed. The system includes a sample collection module that
collects a vapor and aerosol sample and produces a sample vapor at
a first location; a sample delivery module that delivers the sample
vapor from the first location to a second location; a sample
storage and concentration module that collects the sample vapor at
the second location; and a sample analysis module that analyzes the
sample collected in the sample storage and concentration
module.
[0004] Also disclosed is a method for detecting a chemical at a
remote site. The method includes the steps of collecting vapors,
aerosols, and particles from a fluid sample at a remote site;
heating the collected vapors, aerosols and particles to produce a
sample vapor; transporting the sample vapor over a distance to a
sample storage and concentrating device; absorbing the transported
sample vapor in an absorbent in the sample storage and
concentrating device; desorbing the absorbed sample vapor, and
analyzing the desorbed sample vapor for the presence of said
chemical.
DETAILED DESCRIPTION OF DRAWINGS
[0005] FIG. 1 is a schematic of an embodiment of a chemical sample
collection and detection system.
[0006] FIG. 2 is a diagram showing working cycles of the sorbent
tubes in a storage and concentration module.
[0007] FIG. 3 is a flow chart showing a method for detecting
chemicals.
[0008] FIG. 4 is a diagram showing two configurations used for
CSCDS testing.
[0009] FIG. 5 is a diagram showing LoVac signal for 10 ng of
dimethoate.
[0010] FIG. 6 is a diagram showing LoVac signal for 3,880 ng of
methamidophos.
[0011] FIG. 7 is a diagram showing LoVac signal for 1,000 ng of
acephate.
[0012] FIG. 8 is a diagram showing sample introduction setup for
testing the CSCDS capability to detect simulant aerosol.
[0013] FIG. 9 is a diagram showing LoVac response to
dimethoate/Celite sample.
[0014] FIG. 10 is a diagram showing LoVac response to
acephate/Celite sample.
[0015] FIG. 11 is a diagram showing CSCDS response to 250 ng of
dimethoate through the 3 foot long silcosteel HSTL. The
concentration of dimethoate is 11 ppb.
[0016] FIG. 12 is a diagram showing CSCDS response to 1.83 ug of
dimethoate through the 10 foot long silcosteel HSTL. The
concentration of dimethoate is 195 ppb.
[0017] FIG. 13 is a diagram showing CSCDS response to 6 ug of
acephate through the 10 foot long silcosteel HSTL. The
concentration of acephate is 800 ppb.
[0018] FIG. 14 is a diagram showing CSCDS response to 46 ug of
methamidophos through the 10 foot long silcosteel HSTL. The
concentration of acephate is 800 ppb.
DETAILED DESCRIPTION
[0019] FIG. 1 schematically shows an embodiment of a system for
remote detection of a chemical of interest. As shown in FIG. 1, the
chemical sample collection and detection system 100 includes four
primary modules: a sample collection module 110, a sample transport
module 120, a sample storage and concentration module 130, and a
sample detection module 140. These primary modules are combined
with additional supporting modules such as command and control
module 150, communications module 160 and power module 170 to form
a complete system. The chemical sample collection and detection
system 100 can be used to detect trace amount of the chemicals of
interest.
[0020] The "chemicals of interest" can be any chemicals. Examples
include, but not limited to, chemical warfare agents (CWA),
non-traditional agents (NTAs), dusty agents (DAs), toxic industrial
chemical (TIC) vapors, low vapor pressure chemicals (LVPCs),
explosives, explosives and their related compounds, and residues
thereof.
[0021] Examples of CWA includes, but are not limited to, nerve
agents such as GA (Tabun, ethyl
N,N-dimethylphosphoramidocyanidate), GB (Sarin,
isopropyl-methylphosphorofluoridate), GD (Soman,
Trimethylpropylmethylphosphorofluoridate), GF
(cyclohexyl-methylphosphorofluoridate) and VX (o-ethyl
S42-(diiospropylamino)ethyl]methylphosphorofluoridate); vesicants
such as HD (mustard, bis-2-chlorethyl sulfide), CX (Phosgene oxime,
dichloroformoxime), and L (Lewisite, J-chlorovinyldichloroarsine);
cyanides such as AC (Hydrocyanic acid) and CK (Cyanogen chloride);
pulmonary agents such as CG (phosgene, carbonyl chloride) and DP
(Diphosgene, trichloromethylchlorformate).
[0022] NTAs and DAs are CWAs dispersed as either a liquid or
particulate aerosol. For example, dusty mustard is composed of
mustard agent (liquid) dispersed onto fine particulates of
silica.
[0023] Examples of TIC can be found on U.S. Environmental
Protection Agency's reference list of toxic compounds (Alphabetical
Order List of Extremely Hazardous Substances" Section 302 of
EPCRA).
[0024] The term "LVPCs" refers to those chemicals that, at
atmospheric temperature and pressure, only an intangible level, if
any, of the sample exists in the gaseous and/or vapor phase and as
such the sample has, at atmospheric temperature and pressure, a
vapor pressure significantly less than water.
[0025] Examples of LVPCs include, but are not limited to, Novichock
agents, dusty agents, pesticides, and other toxic chemicals with
vapor pressures less than 10.sup.-4 torr.
[0026] Examples of explosives include, but are not limited to,
nitroglycerin-based powders, ammonium nitrate/fuel oil mixtures
(ANFO), Trinitrotoluene (TNT),
[0027] Pentaerythritoltetranitrate (PETN),
Cyclotrimethylenetrinitramine (RDX), and
Cyclotetramethylene-tetranitramine (HMX). Explosive related
compounds include, but are not limited to, residual raw materials,
manufacturing byproducts and degradation products.
[0028] For the purposes of this disclosure, a residue is considered
to be a small amount of a substance, or a material associated with
that substance. A residue may not directly be the substance whose
detection is desired, but may be a substance indicative of the
presence of the first substance. For instance, a residue of a
chemical agent may be a degradation product of the chemical agent,
a chemical binder used to particulate a gaseous CWA, or a substrate
on which a CWA is placed.
[0029] As used herein, the term "remote detection" shall be taken
to mean that the sample of the chemical of interest is taken at a
location that is different from the location of the sample
detection module 140 or the location of the operator of the
detection system.
[0030] As used herein, the term "vaporize" shall be taken to mean
that at least some of the sample has been converted to a vapor.
Sample Collection Module
[0031] With continued reference to FIG. 1, the sample collection
module 110 collects aerosols, particles and vapors from a sample
fluid and prepares the collected materials for transport. As used
in embodiments described herein, the term "aerosol" refers to a
suspension of fine solid or liquid droplets in a gas, such as
ambient air. The term "vapor" on the other hand, refers to the gas
phase of a liquid or solid material. The aerosols are collected
through the use of an aerosol collector 111. The term "fluid," as
used in the embodiments described herein after, refers to a
substance that continually deforms (flows) under an applied shear
stress regardless of how small the applied stress. Fluids are a
subset of the phases of matter and include liquids, gases, aerosols
(particles in a gas stream), plasmas and, to some extent,
solids.
[0032] In one embodiment, the aerosol collector 111 is designed to
capture aerosols in the respirable size range (1 to 10 .mu.m).
[0033] The aerosol collector 111 can be a commercial off-the-shelf
particle/aerosol collector or a collector specifically designed for
the chemical agent detection system 100. Examples of the aerosol
collector 111 include, but are not limited to, electrostatic
collectors, virtual impactors, regular plate impactors, cyclone
separators and filter-based collectors.
[0034] In one embodiment, the aerosol collector 111 is an
electrostatic collector. The electrostatic collector removes
particles from an air sample by using electrostatics to direct the
particles or aerosols onto a metal grid or into a liquid, creating
a highly concentrated particle/aerosol sample.
[0035] In another embodiment, the aerosol collector 111 is a
virtual impactor with a desired threshold size. Briefly, a jet of
particle-laden air is accelerated toward a collection probe
positioned downstream so that a small gap exists between the
acceleration nozzle and the probe. A vacuum is applied to deflect a
major portion of the airstream through the small gap. Particles
larger than a preset threshold size, known as the cutpoint, have
sufficient momentum so that they cross the deflected streamlines
and enter the collection probe, whereas smaller particles follow
the deflected airstream. Larger particles are removed from the
collection probe by the minor portion of the airstream according to
the magnitude of the vacuum applied to the minor portion.
[0036] In another embodiment, the aerosol collector 111 is a
regular impactor. The particles are accelerated through a nozzle
towards an impactor plate maintained at a fixed distance from the
nozzle. The plate deflects the flow creating fluid streamlines
around itself. Due to inertia, the larger particles are impacted
(and collected) on a collector plate while the smaller particles
follow the deflected streamlines.
[0037] In another embodiment, the aerosol collector 111 is a
cyclone separator. Cyclone separators separate particle/aerosol
from gas streams using centrifugal force. In a typical cyclone, the
sample gas stream enters at an angle and is spun rapidly. The
centrifugal force created by the circular flow throws the particles
in the gas stream toward the wall of the cyclone. After striking
the wall, these particles fall into a hopper located
underneath.
[0038] In another embodiment, the aerosol collector 111 is a
filter-based collector that collects the explosives or chemical
agents on a filter. The filter can be a porous material that traps
particles/aerosols.
[0039] The sample can be ambient air collected from a region of
interest, such as a region with a suspected chemical agent plant or
the vicinity of a luggage that may contain an explosive. The sample
may also be a liquid sample. The collection conditions, such as the
sample flow rate and collecting temperature, may be optimized for
the chemical agent of interest.
[0040] With continued reference to FIG. 1, the collected aerosols
are then converted to a vapor through the controlled heating of the
collected material by a heater 112. As the collected material is
heated, vapors are given off. In one embodiment, the aerosol
collector 111 also possess the capability to "flash" off the
aerosol (i.e., evaporate the sample by a rapid increase of
temperature), thus delivering a highly concentrated "puff" of vapor
to the storage and concentration module 130 or directly to the
sample detection system 140. In another embodiment, the aerosol
collector 111 is capable of performing self cleaning operation. In
one embodiment, the aerosol collection surface of the aerosol
collector 111 is heated to the pyrolysis temperature of any
collected sample, effectively reducing any remaining sample or
contaminants into ashes. The pyrolysis temperature of an organic
material is the temperature at which the organic material
decomposes, i.e., break down into simpler molecules.
[0041] In one embodiment, the ambient vapor collector 113 is
capable of collecting chemical vapors. For example, the ambient
vapor collector 113 may use a porous sorbent material that is
capable of absorbing chemical vapors and aerosols in the ambient
air as the ambient air passes through the porous sorbent material.
In one embodiment, the sorbent material is coated on a
polytetrafluoroethylene or stainless steel mesh. In another
embodiment, the sorbent material is coated on the blades of a fan.
In yet another embodiment, the sorbent is used in a packed bed
design. After the sampling period, collected vapors are removed
from the ambient vapor collector 113 by thermal desorption. In one
embodiment, the collected vapors are re-vaporized by heating the
ambient vapor collector 113 to a vaporizing temperature with the
heater 112. The newly generated, concentrated vapor is then
combined with the vapor generated from the other collected
materials, and sent to the sample storage and concentration module
130 through the sample transfer module 120.
Sample Transport Module
[0042] With continued reference to FIG. 1, once in vapor form
(which includes vapor from the aerosol collector 111, the vapor
collector 113 or both), the sample collected by the sample
collection module 110 is transported by the sample transport module
120 to the sample storage and concentration module 130. In one
embodiment, the sample transport module 120 uses the heated sample
transfer line (HSTL) technology, where the vapors are transported
through Teflon.RTM. tubing that is maintained at an elevated
temperature ranging from 100.degree. F. to 160.degree. F., and
preferably at about 130.degree. F. Other types of HSTLs that can be
used as the sample transport module include, but are not limited
to, HSTLs made of stainless steel, silcosteel, sulfinert stainless
steel, and other polymeric or metallic materials. HSTL technology
has been demonstrated to efficiently transfer various chemical
vapors, such as the chemical warfare agent HD (mustard), over
distances up to 60 m. There are a number of possible configurations
of sample transport lines. In one embodiment, a single transfer
line is used to transfer vapors generated from both the aerosol
collector 111 and ambient vapor collector 113. In another
embodiment, two entirely separate transfer lines are used. One line
is dedicated to the transport of aerosol vapors and the other line
is dedicated to ambient vapors.
Sample Storage and Concentration Module
[0043] With continued reference to FIG. 1, after the vapors are
transported by the sample transfer module 120, the vapors are
collected and concentrated by the sample storage and concentration
module 130 using sorbent tube technology. The sorbent tubes collect
the vapor over a period of time, and then thermally desorbs the
vapor for introduction into the sample detection module 140. The
collection and concentration of chemical agent vapors, such as the
explosive, LVPC, and NTA vapors, will be performed at temperatures
where the target vapors are efficiently collected, while vapors of
the lighter, more volatile species, such as water, volatile organic
compounds (VOCs), and many TICs are deliberately excluded. Thermal
desorption of the target vapors is accomplished by controlling the
thermal desorption temperature to remove any background
interferents prior to thermal desorption of the target vapors into
the detector. In one embodiment, two or more parallel sorbent paths
are used to allow continuous operation of the chemical agent
detector 100 and parallel processing of multiple vapor samples. For
example, while a first sorbent tube is undergoing the desorption
process, a second sorbent tube is collecting vapor samples from the
sample collection module 110. When the second sorbent tube goes
into to the desorption process, the first sorbent tube will collect
vapor samples from the sample collection module 110. In another
embodiment, three sorbent tubes are employed. While a first sorbent
tube is collecting vapor samples from the sample collection module
110, the second sorbent tube undergoes the desorption/analysis
process, and a third sorbent tube is being cleaned after the
desorption/analysis process.
[0044] In another embodiment, the chemical agent detector 100
includes multiple sample collection modules 110 located at multiple
sites. Vapor and aerosol samples collected by each sample
collection modules 110 are sent to the sample storage and
concentration module 130 where the samples may be pooled or stored
individually for analysis by the detection module 140. In one
embodiment, multiple sorbent tubes are used to collect samples from
different locations. In another embodiment, vapor samples from
different locations are analyzed sequentially with 2 or 3 sorbent
tubes. In one embodiment, two sorbent tubes are used in the sample
storage and concentration module 130. While a first sorbent tube
containing samples from a first site is undergoing the
desorption/analysis process, a second sorbent tube is collecting
vapor samples from the second site. When the second sorbent tube
goes into to the desorption/analysis process, the first sorbent
tube will collect vapor samples from another site. The three-tube
setting described above may also apply to the analysis of multiple
samples from multiple sites.
[0045] Alternatively, samples from multiple sites may be pooled
first and subjected to a single analysis. If a chemical of interest
is detected in the pooled sample, aliquots of the individual
samples will be screened to decide the source of the chemical.
Sample Detection Module
[0046] With continued reference to FIG. 1, after the vapors have
been collected and concentrated by the sorbent tubes, they are
thermally desorbed into the detection module 140. The detection
module 140 analyzes the sample, and determines if any chemical
agent is present. In one embodiment, the detection module 140
includes a chemical detector 141. The capability of the detection
module 140 to detect explosives and/or LVPCs is dependent on the
concentration of the chemical agent delivered to the detector 141,
and the detection limit of the chemical detector 141. The chemical
detector 141 may use a variety of technologies or combinations
thereof for the detection and identification of chemical agent.
[0047] Examples of the detection technologies include, but are not
limited to, mass spectrometry (MS), ion mobility spectrometry (IMS)
and surface acoustic wave (SAW) sensors, Raman spectroscopy,
infrared spectroscopy (IRS), gas chromatography (GC), Fourier
transform infrared spectrometry (FTIRS), photoacoustic infrared
spectroscopy (PAIRS), in-flame photometry (IFP), photo ionization
detectors (PIDs), electrochemical sensors, and thermoelectric
conductivity sensors.
[0048] A mass spectrometer detects and identifies chemicals by
measuring the mass-to-charge ratio of charged particles. A typical
mass spectrometer is comprised of three parts: an ion source, a
mass analyzer, and a detector. The ion source subjects a sample of
material with an electrical charge that causes the material to emit
ionized particles. These particles are then moved as a gas to the
separator or mass analyzer. Types of ion sources include
electrospray ionization and matrix-assisted laser desorption
ionization. The mass analyzer is the most flexible part of the mass
spectrometer. Since an electric field will deflect charged
particles, and the energy potential can be converted to inertial
movement based on the mass and the potential, the mass analyzer
uses these facts to steer certain ions to the detector based on
their mass-over-charge ratios (m/z) by varying the electrical field
potentials. It can be used to stabilize a narrow range of m/z or to
scan through a range of m/z to catalog the ions present. The
detector simply records the charge induced when an ion passes by or
hits a surface. If a scan is conducted in the mass analyzer, the
charge induced in the detector during the course of the scan will
produce a mass spectrum, a record of the m/z's at which ions are
present.
[0049] An ion mobility spectrometer (IMS) detects and identifies
chemicals based upon the differential migration of gas phase ions
through a homogeneous electric field. Specifically, an IMS system
measures how fast a given ion moves in a uniform electric field
through a given atmosphere. The molecules of the sample need to be
ionized, usually by corona discharge, atmospheric pressure
photoionization (APPI), electrospray ionization (ESI), or a
radioactive source, e.g. a small piece of .sup.63Ni or .sup.241Am.
In specified intervals, a sample of the ions is let into a drift
chamber; the gating mechanism is based on a charged electrode
working in a similar way as the control grid in triodes works for
electrons. For precise control of the ion pulse width admitted to
the drift tube, more complex gating systems such as a
Bradbury-Nielsen design are employed. Once in the drift tube, ions
are subjected to a homogeneous electric field ranging from a few
volts per centimeter up to many hundreds of volts per centimeter.
The electric field drives the ions through the drift tube where the
ions interact with the neutral drift molecules contained within the
system. Ions are recorded at the detector in order from the fastest
to the slowest, generating a response signal characteristic for the
chemical composition of the measured sample. IMS may be coupled
with MS where both size and mass information may be obtained
simultaneously.
[0050] Surface Acoustic Wave (SAW) sensors detect changes in the
properties of acoustic waves as the waves travel at ultrasonic
frequencies in piezoelectric materials. The piezoelectric materials
are coated with materials capable of selectively adsorb chemical
vapors. The acoustic waves interact with the absorbed chemicals and
give characteristic responses that can be used to identify the
chemicals. SAW sensors are typically used in arrays with multiple
coatings. Pattern recognition algorithms are used to provide the
means to identify agent classes and reject interferant responses
that could cause false alarms.
[0051] GC can be used to detect a variety of chemical agents.
Vaporized sample is swept onto a chromatographic column by the
inert carrier gas and serves as the mobile phase. After passing
through the column the solutes of interest generate a signal for a
recording device to read. Like MS, GC also offers high sensitivity
and specificity in detecting chemical agent in many sample forms.
Samples separated by GC may be further analyzed by MS in a GC/MS
detection system. GC may also be coupled with FTIRS. FTIRS is a
technique that can identify compounds that are separated by gas
chromatography. After the separation of the compounds, the sample
passes through a light pipe where an infrared (IR) beam is passed
through it. The adsorption of the IR energy is monitored as the
signal is continuously scanned. Scans are collected on each peak
and the signals are then manipulated with a Fourier transform that
enhances the signal to noise ratio of the spectra taken.
[0052] Raman spectroscopy is based upon the interaction between
optical radiation and various chemical species present in a sample.
When the sample is irradiated with optical radiation a fraction of
the optical radiation is scattered by the molecules in the sample.
The scattered radiation differs from the wavelength of the initial
radiation by an amount proportional to the vibrational modes within
the target molecules. The difference between the scattered
radiation and incident beam, termed the Raman shift, corresponds to
molecular vibrations in the target molecule. The degree of Raman
shift is dependent upon the chemical structure of the molecules
causing the scattering. During irradiation, the spectrum of the
scattered radiation is measured with a spectrometer. In a preferred
embodiment, the detection method is fiber optic Raman spectroscopy.
In another embodiment, the spectroscopic interrogation unit 130 is
an Ahura hand held Raman FirstDefender system (Ahura Corporation,
Wilmington, Mass.).
[0053] IRS identifies chemical agent based on its adsorption
spectrum in the intrared (IR) region of the electromagnetic
spectrum. Characteristic vibrational wavelengths of most CWAs occur
in the IR region. When infrared radiation passes through a gas or
vapor, or is reflected off a surface (diffuse reflection),
adsorption of radiation occurs at specific wavelengths that are
characteristic of the vibrational structure of the gas molecules.
Routine IR instruments measure the amount of light absorbed at a
specific wavelength to look for a characteristic chemical group,
such as the phosphorus-oxygen bond of nerve agents. More
sophisticated instruments scan regions of the IR spectrum to
generate a "fingerprint" pattern for individual chemicals.
[0054] As in IRS, PAIRS uses selective adsorption of infrared
radiation by the target agent vapors to identify and quantify the
agent present. A specific wavelength of infrared light is pulsated
into a sample through an optical filter. The light transmitted by
the optical filter is selectively adsorbed by the gas being
monitored, which increases the temperature of the gas as well as
the pressure of the gas. Because the light entering the cell is
pulsating, the pressure in the cell will also fluctuate, creating
an acoustic wave in the cell that is directly proportional to the
concentration of the gas in the cell. Two microphones mounted
inside the cell monitor the acoustic signal produced and send
results to the control station.
[0055] FID operates by burning an sample in a hydrogen-rich flame.
The compounds present emit light of specific wavelengths in the
flame. An optical filter is used to let a specific wavelength of
light pass through it. A photosensitive detector produces a
representative response signal. Since most elements will emit a
unique and characteristic wavelength of light when burned in this
flame, this device allows for the detection of specific
elements.
[0056] PID operates by passing the air sample between two charged
metal electrodes in a vacuum that are irradiated with ultraviolet
radiation, thus producing ions and electrons. The negatively
charged electrode collects the positive ions, thus generating a
current that is measured using an electrometer-type electronic
circuit. The measured current can then be related to the
concentration of the molecular species present.
[0057] Electrochemical sensors function by quantifying the
interaction between an analyte's molecular chemistry and the
properties of an electrical circuit. Fundamentally,
electrochemistry is based on a chemical reaction that occurs when
the target agent enters the detection region and produces some
change in the electrical potential. This change is normally
monitored through an electrode. A threshold concentration of agent
is required, which corresponds to a change in the monitored
electrical potential. This sensor technology provides a wide
variety of possible configurations.
[0058] Thermoelectric conductivity sensors identify chemical agents
by measuring the electrical conductivity of a surface material that
absorbs the chemical agents. The electrical conductivity of certain
materials can be strongly modulated following surface adsorption of
various chemicals. Heated metal oxide semiconductors and
room-temperature conductive polymers are two such materials that
have been used commercially. The change in sensor conductivity can
be measured using a simple electronic circuit, and the
quantification of this resistance change forms the basis of sensor
technology.
[0059] In one embodiment, the chemical detector 141 is a mass
spectrometer. Mass spectrometers generally have a lower false
positive rate than IMS and SAW detectors.
Command and Control Module
[0060] With continued reference to FIG. 1, the command and control
module 150 provides coordination and control of the components in
the chemical agent detection system 100. The command and control
module 150 is designed to: (a) provide a single user interface to
the entire chemical agent detection system 100; (b) allow a user to
quickly determine the status of all components associated with the
system; and (c) accept input to change parameters which allow for
the configuration changes. At its most basic level, the command and
control module 150 provides an alarm when a target chemical agent
is identified by the detection module 140.
[0061] In one embodiment, the command and control module 150
comprise a memory 152, a controller 154 and an external port 156.
The memory 152 may be used to store libraries of spectrometry
finger prints of chemical agents and operation software. In one
embodiment, the memory 152 is a flash memory. The controller 154
monitors and controls the operation of the chemical agent detection
system 100 and provides an interface to the user about the status
of the overall system. For example, the controller 154 may stage
the timing, temperature and air flow rate of the sample collection
module 110, and compare the results from the detection module 140
with the libraries of spectrometry finger print of chemical agents
in the memory 152 to identify the target agent and reduce false
positives.
[0062] In one embodiment, the controller 154 is a small,
lightweight and available as a standard commercial off-the-shelf
(COTS) product. In another embodiment, the controller 154 is a COTS
offering and is packaged as a microbox PC with a passive PCI bus
backplane. This configuration allows the component modularity for
easy upgrades as computer hardware technologies improve. In another
embodiment, the controller 154 is reside on a single board computer
(SBC) that already have its peripheral interfaces built in: PCI
bus, Ethernet, and RS-232 serial. Flash memory and DRAM can be
sized to the control system requirements with removable memory
sockets on the SBC. Communication from the controller 154 to the
other components of the chemical agent detection system 100 is
handled by COTS data acquisition, digital input/output, and analog
input/output circuit cards that are PCI bus compatible.
[0063] In another embodiment, field-programmable gate array (FPGA)
technology is used for monitors and control circuits in order to
keep the weight, size, and especially power consumption at a
minimum. The FPGA technology also affords minimum hardware redesign
impact when implementing system upgrade.
[0064] The external port 156 is used for downloading software
upgrades to the memory 152 and performing external
trouble-shooting/diagnostics.
Communication Module
[0065] With continued reference to FIG. 1, the communication module
160 maintains the communication between the chemical agent
detection system 100, the other chemical detection systems, the
regional command and control center that monitors all the chemical
detection systems, and/or the local/state/federal authorities
through cable or wireless connection.
Power Module
[0066] With continued reference to FIG. 1, the power module 170
provides power to the chemical agent detection system 100. In one
embodiment, the power module 170 includes a long-life battery or
batteries that can be recharged and reused. Preferably, the
batteries are interchangeable with batteries from other Northrop
Grumman portable systems. In another embodiment, the power module
170 includes an emergency generator. In another embodiment, the
power module 170 includes a solar panel.
[0067] In one embodiment, the chemical agent detection system 100
is designed to autonomously collect both ambient vapor and aerosol
samples, analyze, and report the results in 60 seconds. An
exemplary timing of the collection and analysis cycles are outlined
in FIG. 2. Aerosol sampling/vaporization and vapor collection occur
in parallel for the first 30 seconds of the sampling/analysis
cycle. Once the aerosols and vapors have been collected, they are
desorbed and analyzed by the detector. This process takes an
additional 30 seconds. The total time to result for the system is
60 seconds. In parallel with the desorption and detection of the
first sample, a second sample is taken using the aerosol collector
and the second sorbent tube. This overlap in system processing
allows the unit to produce results every 30 seconds during normal
operation, providing a near real-time monitoring capability.
[0068] Also disclosed is a method for detecting a chemical of
interest at a remote site. An embodiment of the method is shown in
FIG. 3. The method 200 includes collecting (210) vapors, aerosols
and particles from a fluid sample at a remote site, heating (220)
the collected sample to produce a sample vapor, transporting (230)
the sample vapor over a distance to a sample storage and
concentrating device, absorbing (240) the transported sample vapor
in an absorbent in the sample storage and concentrating device,
desorbing (250) the absorbed sample vapor to produce a concentrated
sample vapor, and analyzing (260) the desorbed sample vapor for the
presence of the chemical of interest, and producing (270) an alarm
if the chemical of interest is detected in the desorbed sample
vapor sample. The method 200 may be performed using the system 100
as described above.
[0069] In one embodiment, the method 200 further includes
collecting an ambient vapor and transporting the ambient vapor to
the sample storage and concentrating device.
[0070] In another embodiment, the sample storage and concentrating
device contains multiple sorbent tubes to allow parallel processing
of multiple sample vapors.
EXAMPLES
[0071] The following specific examples are intended to illustrate
the collection and detection of representative chemicals using
methods and devices described in the embodiments. The examples
should not be construed as limiting the scope of the claims.
Example 1
Detection of the Low Vapor Pressure Simulants (Vapor
Pressure=10.sup.-4 Torr) Using the Chemical Sample Collection and
Detection System (CSCDS)
[0072] A. Experimental setting
[0073] Testing of the CSCDS was done using two different sample
introduction configurations that are shown in FIG. 4. In both
configurations the sample transfer/preconcentration/analysis
portion of the system are the same, only the sample introduction
method is different. In configuration #1, a glass tube with a glass
frit is used for sample introduction. Configuration #1, shown in
the top panel of FIG. 4 allows the controlled introduction of
different masses of simulant into the CSCDS. The sample, dissolved
in a solvent (methanol for dimethoate and methamidophos or acetone
for acephate), is placed onto the glass frit using a microliter
syringe. This enables placement of a precise volume of a known
concentration of simulant onto the glass flit so that the mass of
simulant is known and the simulant concentration can be calculated.
The glass tube/frit is placed onto the end of the HSTL using a
standard Swagelok fitting with a Teflon ferrule. A heating sleeve,
which is part of a commercial sorbent tube conditioner, is then
placed over the glass tube/frit. A Dynatherm sampling pump is
started, then the sorbent tube conditioner is turned on and the
temperature of the glass tube/frit increased to 300.degree. C. The
sample is transferred through the HSTL and collected onto a
Dynatherm sorbent tube and then the glass tube/frit is cooled.
Background samples are run after each sample run using the same
procedures except no sample is loaded onto the glass frit. The
sample collected in the Dynatherm sorbent tube is re-vaporized and
transferred to the READ (Reverse Electron Attachment Detector)
through a heated transfer line for the detection of simulants.
[0074] The second CSCDS configuration (#2) replaces the glass
tube/frit sample introduction setup with an compact electrostatic
compactor (CEC) (Sceptor Industries, Inc. Kansas City, Mo.). This
setup tests the capability of the CEC to vaporize the sample and
transfer it through the CSCDS for detection. In the second
configuration, a microliter syringe is used to place a known mass
of simulant (in solvent) onto the Solid Radial Collector Surface
(SRCS) in the CEC. Once the sample is placed into the SRCS the
Dynatherm sampling pump is started and the SRCS is heated to
300.degree. C. The vaporized sample transferred through the HSTL
and collected by the Dynatherm. A background sample is run using no
simulant after the CEC is cooled to be sure the CSCDS is clear of
sample and ready for another run. The sample collected in the
Dynatherm sorbent tube is re-vaporized and transferred to the READ
through a heated transfer line for the detection of simulants.
B. Results
(1) Detection of Simulants Through HSTL--Sample Introduction
Configuration #1
[0075] The first series of experiments on the CSCDS demonstrated
successful detection of the three simulants dimethoate,
methamidophos, and acephate. A 3-ft HSTL was used for dimethoate
and methamidophos, and a 10-ft HSTL was used for acephate. FIG. 5
shows the signal for dimethoate through the 3-ft HSTL. The
dimethoate vapor was generated using experimental configuration #1
where a solution of known concentration was injected onto the glass
frit. Based on the sampling flow rate of the CSCDS this signal
corresponds to 0.43 parts-per-billion (ppb), or 430
parts-per-trillion (ppt), of dimethoate vapor. This result clearly
demonstrates that the CSCDS is capable of detection of ppb levels
of low vapor pressure chemicals. FIG. 6 shows the CSCDS response
for methamidophos. The CSCDS signal is produced from 3,880 ng of
methamidophos, which corresponds to a concentration of 286 ppb.
This result once again demonstrates the CSCDS capability to detect
ppb levels of low vapor pressure chemicals. FIG. 7 shows the CSCDS
signal for acephate transferred through 10 feet of HSTL. This
figure shows the signal produced by introduction of 1000 ng of
acephate, which corresponds to a concentration of 134 ppb of
acephate. The signals for both mass 137 and mass 178 of acephate at
ppb levels demonstrate the capability of the CSCDS for detection of
a third low vapor pressure chemical at ppb levels through a 10 ft
long HSTL.
[0076] As summarized in Table 1, the CSCDS is capable of detecting
dimethoate at a concentration of 9 ppl (particles-per-liter),
methamidophos at a concentration of 3529 ppl, and acephate at a
concentration of 909 ppl.
TABLE-US-00001 TABLE 1 Mass Simulant Detected and the Number of
Particles Corresponding to the Detected Mass Mass Simulant Number
of Threat Concentration Detected (ng) Particles Detected (ppl)
Dimethoate 10 218 9 Methamidophos 3880 84689 3529 Acephate 1000
21827 909
(2) Probability of False Alarm for Dimethoate and Acephate
[0077] The CSCDS will preferably exhibit false alarm rates of
<1%. All false alarm testing was performed using CSCDS
configuration #1 and a 3 ft silcosteel HSTL at a temperature of
180.degree. C. The testing schedule, shown in Table 2, includes
background testing, sample testing and cleaning of the system.
Background testing consists of the tests run without any sample
placed into the glass tube/frit. Sample testing consists of placing
sample onto the glass frit and running the CSCDS to acquire a
signal from the sample. The cleaning protocol removes residual
sample that can result in background signal. A cleaning protocol
that consists of a 10 minute sampling time through the HSTL onto
the sorbent tube, and a 10 minute transfer time from sorbent tube
to focusing trap was determined through experimentation. This
protocol removes all residual LVPC in the CSCDS and provides a
clean background.
TABLE-US-00002 TABLE 2 False Alarm Testing Schedule Day 1 Day 2 Day
3 Day 4 Background Background Clean Clean Background Background
Sample Background Background Sample Background Background Sample
Clean Background Background Clean Background Background Background
Background Sample Background Sample Background Clean Background
Clean sample Background Background Sample Clean Background Sample
Clean Background Background Clean Background Background Background
Background Background Background Sample Sample Background
Background Clean Clean Sample Background Backgound Background Clean
sample Backgound Background Background Clean Backgound Background
Background Background Sample Sample Background Sample Clean Clean
Background Clean Sample Sample Background Background Clean Clean
Sample Background Background Background Clean Background Background
Background Background Background Background Background Background
Sample Sample Sample Background clean Clean Clean Background
[0078] Table 3 shows the results of the testing for the probability
of false alarm for both dimethoate and acephate. Testing was
performed using laboratory air with no special precautions to keep
out any environmental background that might contain interferents.
Therefore, this test does reflect one proposed concept of
operations where the CSCDS operates in a building protection mode
drawing in conditioned room air. The results for dimethoate show a
0% probability of false alarm at a concentration of 0.92 ppb (920
ppt) and for acephate a probability of false alarm of 0% at a
concentration of 61 ppb.
TABLE-US-00003 TABLE 3 Probability of False Alarm Results for
Dimethoate and Acephate Simulant Concentration, ppb P.sub.FA (%)
Test runs Dimethoate 0.55 1.6 62 0.94 0.0 Acephate 61 0.0 42 122
0.0
Example 2
CSCDS Detection of Aerosolized Simulants
[0079] To demonstrate the CSCDS capability to detect aerosols,
configuration #1 was used with a 10-ft HSTL (silcosteel tube). The
sample introduction setup is shown in FIG. 8 with the aerosol
simulant placed on the opposite side of the glass frit from the
HSTL. As in previous experiments, a heating sleeve is placed over
the glass tube/frit containing the simulant/Celite and heated to
300.degree. C. while the Dynatherm draws air through the sample.
The heating and sampling times are the same as previous
experiments. The aerosol simulants used in this test were prepared
to contain 100 ppm (w/w) of each LVPC simulant supported on silica
particulates.
[0080] The response of the CSCDS to dimethoate aerosol and acephate
aerosol through a 10-ft HSTL are shown in FIGS. 9 and 10. The data
demonstrates that the simulants supported on Celite can be
thermally vaporized in air and carried down the 10-ft HSTL in air
and detected by the CSCDS. This proves that the original concept of
the CSCDS to capture aerosols, vaporize them, and transfer them
down an HSTL is feasible. Comparison of the two different plots
also demonstrates the selectivity of the system. In the dimethoate
case two masses, 136 amu and 153 amu, are monitored. Mass 136 amu
does not exhibit a response to dimethoate as expected, however the
acephate plot shows that mass 136 amu and mass 178 amu both show a
strong response, which is expected based on early studies of the
simulant properties when ionized and detected by the READ
detector.
Example 3
CSCDS Full System Testing
[0081] This series of tests demonstrates that the full CSCDS
operates as predicted with all sub-components integrated into the
system. The complete CSCDS includes a CEC, a HSTL, a
preconcentrator (Dynatherm) and a READ detector. The CEC was tested
for its ability to vaporize sample into a 3-ft silcosteel HSTL. The
HSTL is connected to a Dynatherm vacuum line, a mass spectrometer
turbo and roughing pumps. A heated transfer line, covered in
aluminum foil, connects the Dynatherm to the mass spectrometer. The
heat transfer line is heated using heat tape and insulated with
glass wool to keep the line temperature uniform. The glass wool is
covered with aluminum foil to protect the insulation. The heat
transfer line temperature was constant at 200.degree. C. over the
course of all experiments. The READ sample introduction module was
also covered with glass wool insulation and kept at 200.degree.
C.
A Experimental Setting
[0082] The operating parameters of the individual components of the
CSCDS were optimized by adjusting the temperature and flow rates
for each component to maximize the signal strength. A significant
level of effort was devoted to the determination of the best
temperature settings and flow rates used throughout the system to
generate the maximum signal. The CEC temperature was set such that
the temperature at the midpoint of the solid radial collector
surface (SRCS) was 350.degree. C. This temperature setting was a
result of numerous experiments using configuration #1 (glass
tube/frit) to determine the best thermal desorption temperature of
the simulants. A series of experiments reveals that the optimum
location for sample placement on the SRCS was on the tip. The
silcosteel HSTLs operated at 200.degree. C., the Teflon HSTLs
operated at 80.degree. C. The silcosteel lines are adjustable to
different temperatures; however, the manufacturer recommended
keeping the temperature at or below 200.degree. C. The Dynatherm
thermal desorption temperatures for both sorbent tube and focusing
trap desorption temperatures was 300.degree. C. The internal
silcosteel tubing in the Dynatherm was operated at the maximum
allowable temperature, 200.degree. C.
B. Results
1. Detection of Dimethoate Through a 3-ft HSTL
[0083] The 3 ft silcosteel HSTL was used first to determine the
capability of the CSCDS to detect the dimethoate through the
minimum length of HSTL available. A known volume of a standard
solution of dimethoate was spotted onto the tip of the SRCS (250
ng) and the SRCS heated to 350.degree. C. At the same time, the
Dynatherm sampling pump started so that the Dynatherm was sampling
throughout the heating schedule of the SRCS. During this time the
Dynatherm collected the sample, the SRCS was ramped to a
temperature of 350.degree. C. and held there for 2 minutes.
Dynatherm sampling was stopped at 2 minutes and the SRCS
temperature ramped down to ambient. The response of the CSCDS,
shown in FIG. 11, clearly shows good signal strength for
dimethoate. It is important to note that the concentration of
dimethoate in the experiment, based on sample flow rates through
the CSCDS is 11 ppb. Therefore the experiment demonstrates that the
CSCDS is capable of detecting ppb levels of the simulant dimethoate
through a 3 ft HSTL.
2. Detection of Dimethoate, Methamidophos, and Acephate Through a
10-ft HSTL
[0084] Once the CSCDS demonstrated its capability to detect
dimethoate through a 3-ft HSTL the same experiment was performed
through the 10 foot long silcosteel HSTL for all three simulants.
Results for dimethoate are shown in FIG. 12 with the 10-ft HSTL
operating at 200.degree. C. The concentration of dimethoate in the
experiment is 195 ppb and the signal strength is good. This data
clearly shows that the LVPCDS is capable of detecting ppb levels of
dimethoate through 10-ft of HSTL meeting the DHS requirements for
ppb level detection at a distance from the detector.
[0085] FIG. 13 shows the CSCDS response to 800 ppb of acephate
through the 10-ft silcosteel HSTL. As in the case of dimethoate,
the signal strength is strong and the LVPCDS demonstrates the
capability to detect ppb levels of acephate through 10 ft of HSTL.
It is worthwhile noting that the system detects two signals
corresponding to two different mass peaks for acephate at 137 amu
and 178 amu demonstrating the selective nature of the system.
[0086] FIG. 14 shows the response of CSCDS to methamidophos. The
experiment was run using the same parameters as dimethoate and
acephate. The concentration of methamidophos in this example is 8
ppm and the signal strength is good. This concentration does not
represent the detection limit of the CSCDS for methamidophos,
however, based on experience it is likely that the detection limit
is in the high ppb level.
[0087] The Examples above demonstrate that the CSCDS is capable of
detecting ppb levels for 2 of the three LVPC simulants through 3-ft
and 10-ft HSTLs. Data shows the CSCDS capable of detecting ppb to
ppm levels of dimethoate, acephate, and methamidophos over 10 ft of
HSTL. Calculations suggest that at operational threat levels the
system could detect the release of an LVPC at a distance of 60
feet. False alarm data demonstrated that the CSCDS exhibits a
P.sub.FA<1.0% for ppb concentrations of dimethoate and acephate.
A summary of the experimental results showing the detection
capabilities of the LVPCDS and the detection subsystem are
presented in Table 4.
TABLE-US-00004 TABLE 4 Summary of experimental results for the
NGC-LVPCDS CSCDS Detector CSCDS - CEC Demonstrated HSTL Detection
Detection Detection Length, Simulant Limit, ppb Limit Limit, ppb ft
Dimethoate 0.33 0 0.43 3 11** 3 195** 10 Methamidophos 146 0 268 3
8000** 10 Acephate 19 0 134** 800** 10 **Actual measurement
concentration not detection limit
[0088] The CSCDS also detects the simulants dimethoate and acephate
supported on a silica substrate, the combination being a dusty
agent simulant. Data in Table 5 show that the simulants on Celite
were successfully detected over an HSTL distance of 10 feet with
good signal to noise.
TABLE-US-00005 TABLE 5 CSCDS Detection of the Simulants Supported
on the Substrate Material Celite Over a ten-feet Distance Mass HSTL
Celite/Simulant Length, Simulant (mg) Signal Max. SNR (ft)
Dimethoate/Celite 12.1 151 35 10 Methamidophos/Celite -- ND -- 10
Acephate/Celite 7.4 53 12 10
[0089] The foregoing discussion discloses and describes many
exemplary methods and embodiments of the present invention. As will
be understood by those familiar with the art, the invention may be
embodied in other specific forms without departing from the spirit
or essential characteristics thereof. Accordingly, the disclosure
of the present invention is intended to be illustrative, but not
limiting, of the scope of the invention, which is set forth in the
following claims.
* * * * *