U.S. patent number RE31,915 [Application Number 06/258,753] was granted by the patent office on 1985-06-18 for gas detecting and measuring device.
This patent grant is currently assigned to Becton Dickinson & Company. Invention is credited to Keith F. Blurton, Harry G. Oswin.
United States Patent |
RE31,915 |
Oswin , et al. |
June 18, 1985 |
Gas detecting and measuring device
Abstract
A device for the detection of and quantitative measurement of a
gas in a given environment, such as alcohol in the breath or carbon
monoxide in the atmosphere, is described. The device comprises
intake and flow control means for the gas sample, and an
electrochemical cell having an anode which provides a site for
electrochemical reaction of the gas being detected, a cathode, a
reference electrode, and an electrolyte in contact with the anode,
cathode, and reference electrode. The anode, to ensure that the
current production is a result of the gas being detected and not
other gases, including oxygen, is maintained at a fixed potential
in relation to the potential of the reference electrode. The device
provides an accurate and inexpensive means of detecting and
quantitatively measuring a gas contained in a given environment,
i.e., alcohol in the breath of the subject being tested or carbon
monoxide in the atmosphere.
Inventors: |
Oswin; Harry G. (Chauncey,
NY), Blurton; Keith F. (Ossining, NY) |
Assignee: |
Becton Dickinson & Company
(Paramus, NJ)
|
Family
ID: |
27375925 |
Appl.
No.: |
06/258,753 |
Filed: |
April 29, 1981 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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88267 |
Nov 10, 1970 |
3776832 |
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Reissue of: |
172486 |
Aug 17, 1871 |
03824167 |
Jul 16, 1974 |
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Current U.S.
Class: |
204/412;
204/432 |
Current CPC
Class: |
G01N
1/34 (20130101); G01N 33/4972 (20130101); G01N
27/4045 (20130101) |
Current International
Class: |
G01N
27/49 (20060101); G01N 1/00 (20060101); G01N
33/483 (20060101); G01N 1/34 (20060101); G01N
33/00 (20060101); G01N 33/497 (20060101); G01N
027/46 () |
Field of
Search: |
;204/1T,1N,1S,1K,195P,195R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1163576 |
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Feb 1964 |
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DE |
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1153551 |
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Mar 1964 |
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DE |
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1202595 |
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Aug 1970 |
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GB |
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Other References
Ives et al., "Reference Electrodes", 1961, pp. 360-378. .
Mayell et al., "A Study of Surface Oxides on Platinum Electrodes",
Journal of the Electro-Chemical Society, Apr. 1964, pp. 438-446.
.
Latimer, "The Oxidation States of the Elements and their Potentials
in Aqueous Solutions", 2nd ed., 1952, pp. 339-348. .
Grubb, "J. of the Electrochemical Society", Apr. 1964, pp. 477-478.
.
Muto et al., "New Methods of Microanalyzing Gases", Analysis &
Instruments, vol. 6, No. 5, (1968), pp. 287-291. .
K. A. Gresch u.a., "Die Coulometrische Analyse", Verlay Chermie,
Weinheim, (1961), Seite 83, Insbe Abb 31. .
W. Vielstick, "Brennstoff Element", Verlay Chermie, Weinheim,
(1965), Seite 41, Insbes. Abs 3. .
Hanar, "Electrode Potential Gradients and Cell Design in Controlled
Potential Electrolysis Experiments", Analytical Chemistry, Aug.
1966, pp. 1148-1156..
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Primary Examiner: Tung; T.
Attorney, Agent or Firm: Larson and Taylor
Parent Case Text
This application is a continuation-in-part of our copending
application U.S. Ser. No. 88,267 filed Nov. 10, 1970, now U.S. Pat.
No. 3,776,832.
Claims
It is claimed:
1. A gas .Iadd.device for continuously, quantitatively
.Iaddend.detecting and measuring .[.unit.]. .Iadd.a noxious gas in
the presence of air .Iaddend. comprising in combination intake
means, an electrochemical cell, means for drawing a gas through
said intake means and into said electrochemical cell at a
controlled flow rate, .[.and read-out means for reading the
quantity of said detected gas,.]. said electrochemical cell
comprising .Iadd.a housing, .Iaddend.an anode .Iadd.comprising
catalyst bonded to a hydrophobic fluorocarbon membrane to provide a
diffusion electrode.Iaddend., a cathode, a reference electrode at
which substantially no current flows, .Iadd.all positioned within
said housing, .Iaddend.and an aqueous electrolyte in an electrolyte
chamber, .[.said electrolyte being in contact with.]. .Iadd.each of
.Iaddend.said anode, cathode, and reference .[.electrode,.].
.Iadd.electrodes having a catalyst surface containing said
electrolyte and said reference electrode contacting air,
.Iaddend.means for exposing said anode to a gas to be detected
.Iadd.in the presence of air.Iaddend., .Iadd.potentiostat
.Iaddend.means .[.for.]. maintaining said anode at a fixed
potential relative to the reference electrode of from about 0.7 to
1.5 volts with respect to a reversible hydrogen electrode potential
in said electrolyte of said cell, within which range oxygen
reduction or oxidation of water to oxygen does not occur, .[.said
anode comprising a catalyst bonded to a hydrophobic fluorocarbon to
provide a diffusion electrode and.]. said catalyst .Iadd.of said
anode catalyst surface .Iaddend.catalyzing an electrochemical
reaction with a gas selected from the group consisting of CO,
hydrocarbons, alcohols, NO, NO.sub.2 and SO.sub.2 at said fixed
potential.Iadd., said anode being arranged in said cell so that one
surface of said anode contacts said gas exposing means and the
opposite surface contacts said electrolyte whereby the noxious gas
to be detected migrates from the surface contacting said exposing
means to the internal surface of said anode to interface with the
electrolyte for electrochemical reaction in the presence of said
catalyst, means for continuously measuring said current flowing
between said anode and cathode of said cell, said measured current
being a measure of the concentration of the gas being detected, and
read-out means for continuously reading said concentration of gas
being detected.Iaddend..
2. The unit of claim 1 adapted for detecting and measuring carbon
monoxide and including scrubber means between said intake means and
electrochemical cell for selectively collecting absorbables while
permitting the gas being detected to pass through.
3. The unit of claim 2 wherein the scrubber means contains
activated carbon.
4. The unit of claim 2 wherein the scrubber means contains
charcoal.
5. The unit of claim 2 wherein the intake means is in communication
with a sump bottle constructed and arranged with said intake means
whereby gas to be detected and measured passes through said sump
bottle prior to entering the electrochemical cell.
6. The unit of claim 1 wherein said means for drawing gas through
said intake means and into said electrochemical cell at a
controlled flow rate includes pump means and flow control
means.
7. The unit of claim 6 wherein the flow control means is a
restricted orifice.
8. The unit of claim 6 wherein said pump means and flow control
means are constructed and arranged behind said electrochemical
cell.
9. The unit of claim 1 adapted for detecting and measuring alcohol
and including a selectively permeable membrane which will
selectively pass alcohol while inhibiting the flow of carbon
monoxide and hydrocarbons.
10. The unit of claim 9 wherein the intake means includes a
multi-position valve and said valve is in controllable
communication with a sample collector and the atmosphere.
11. The unit of claim 10 wherein the multi-position valve is
further in communication with a verification sample collector.
12. The unit of claim 11 wherein the multi-position valve is in
further communication with a calibrating sample.
13. The unit of claim 10 wherein the sample collector is an endless
tube.
14. The unit of claim 1 wherein the electrochemical cell includes a
composite electrode structure comprising a non-conductive base and
on said non-conductive base said cathode and said reference
electrode electrically separated from said cathode.
15. The unit of claim 14 wherein said electrochemical cell has a
reservoir in communication with the electrolyte chamber.
16. The unit of claim 1 wherein the hydrophobic fluorocarbon is
polytetrafluoroethylene.
Description
FIELD OF INVENTION AND BACKGROUND
This invention relates to a device for detecting and quantitatively
measuring the quantity of a select gas in a gaseous medium. More
particularly, the invention relates to a device which is compact,
dependable, easy to operate, and relatively inexpensive for
detecting and quantitatively measuring a gas such as carbon
monoxide, hydrocarbons or an alcohol in an environment. The device
includes intake means, means for pumping the gas being analyzed,
and an electrochemical cell for detecting and quantitatively
measuring a select gas. Although the invention is not limited
thereto, for convenience it will be described with reference to a
device for detecting and measuring the alcoholic content in the
breath of a test subject or for detecting and measuring carbon
monoxide in a given environment. As will be apparent, however, the
device can be modified or adapted for detecting and measuring
hydrocarbons including separation of saturated and unsaturated
hydrocarbons, gases capable of being converted to alcohols, carbon
monoxide, or hydrocarbons, or other gases which can be
electro-chemically consumed, where similar conditions apply.
Alcohol Detection
Although the social problem of the drinking or drunken driver is
not new, the ever-increasing number of cars on the highway and the
increasing horsepower and speed of these cars is greatly enhancing
the problem of the drinking or drunken driver. As a result, in the
past few years insurance companies and safety groups have been
publicizing this social deficiency, emphasizing the uncontestable
fact that alcohol consumption on the part of drivers lead to
impaired driving attitudes and habits. After the consumption of
alcoholic beverages, both judgment and reaction times deteriorate,
resulting in a greater probability that the driver will be involved
in a car accident.
Because of the greater public awareness of the drunken or drinking
driver, some states have adopted legislation aimed at the drunken
driver, sometimes referred to as "driving while drinking laws," and
other states are considering such laws. These laws, to be
enforceable, must set objective standards as to what constitutes
intoxication. Moreover, for the laws to be effective, the level of
intoxication of any driver must be easily and reproducibly
established--preferably at roadside--by a method which is socially
acceptable, i.e., not offensive to the public as a result of the
manner in which the test is conducted.
To date, the blood alcohol level is the only quantitative
measurement known for determining intoxication which can be made
with sufficient accuracy and which is independent of physiological
and psychlogical variations from one individual to the next.
Although direct quantitative tests on the whole blood are the most
accurate, such tests are unsatisfactory in view of the need to take
a blood sample from the test subject and the relatively complex
analytical tests required to determine alcohol levels of whole
blood. Although the alcohol content of urine can be correlated to
the alcohol content of blood in the test subject, it is not easy to
obtain a urine sample for analysis, at least not at roadside; and,
moreover, the correlation of the alcohol content in urine with the
alcohol content of blood requires a relatively complex analysis.
Additionally, a time factor is involved in the alcohol reaching the
urine after consumption of the alcohol. Therefore, most tests being
considered by law enforcement and other concerned agencies are
based on the alcoholic content of the test subject's breath. It is
fully established that not only is alcoholic intoxication directly
related to blood alcohol level, but also that the blood alcohol
level and degree of a person's intoxication can be determined by
the alcohol content of the test subject's breath derived from the
alveolae. The alveolae are the small bulbs in the lung wherein
oxidation of blood impurities take place.
Although breath tests are socially acceptable, to be fully
satisfactory for use by law enforcement personnel, the breath test
method employed must be
(1) sufficiently accurate and reliable to ensure that a high
percentage of drivers above the allowable limit and only a low
percentage of those below the allowable limit will be detected and
subsequently charged with drunken driving;
(2) conducted in a hygienic manner with due regard to the health
and dignity of the individual driver tested;
(3) conducted with portable and easy-to-operate equipment at
roadside by a law enforcement officer of only average intelligence
who has no technical background or special training;
(4) rapidly carried out under all climatic conditions so that
within a few minutes the apprehending officer can decide whether or
not to charge the test subject with drunken driving; and
(5) low-cost, including initial cost of equipment, maintenance and
operation of the equipment, and officer training costs.
Although various methods have been suggested for determining the
blood alcohol level of a test subject's breath, none have met all
of the aforesaid requirements. Most methods utilize chromatographic
or colorimetric determinations based on the oxidation of alcohol.
Such devices having sufficient accuracy, however, are not suitable
for roadside checks and/or are complex and/or are expensive
precluding widespread use. Moreover, presently available methods of
collecting breath samples, and methods of calibrating and verifying
breath samples have various deficiencies.
Carbon Monoxide Detection
The problems associated with carbon monoxide pollution and the need
for carbon monoxide detectors, while being of a somewhat different
nature for carbon monoxide detectors, while being of a somewhat
different nature than the problem associated with the drinking
driver and alcohol detection, are of no less social importance. As
a result of increasing pollution, particularly in the major cities,
with much of the pollution being the result of cars and other
sources giving off carbon monoxide, the need for a simple and rapid
means of determining and monitoring polluting gas levels in the
atmosphere is critical. Although various devices are available,
including infra-red detectors, chromagraphic or colorimetric
devices, such units are expensive and/or slow and difficult to use
as a result of establishing or adjusting to a zero line, the need
to remove any water present to avoid false readings, and the like.
Moreover, such devices are only marginally portable.
OBJECTS AND GENERAL DESCRIPTION OF THE INVENTION
Accordingly, a primary object of the present invention is to
provide a compact, inexpensive, and easy-to-operate device for
accurately and reproducibly detecting and quantitatively
determining the level of a given gas in a specific environment.
Another object of this invention is to provide a compact,
inexpensive, and easy-to-operate device for accurately and
reproducibly detecting and quantitatively determining the blood
alcohol level of a test subject from a breath sample.
It is another object of this invention to provide improved methods
of collecting breath samples from a test subject which do not
permit condensation of moisture in the breath and which permits the
collection of substantially only olveolar breath.
Another object of this invention is to provide a breath sample
collector having low energy surfaces with low heat transfer
properties inhibiting the condensation of water droplets thereby
increasing the accuracy of subsequent tests on the sample.
It is another object of this invention to provide a calibrator for
use with blood alcohol level analyzers which is accurate,
relatively inexpensive, and easy to use.
It is another object of this invention to provide a breath sample
from a test subject for confirmatory analysis at a later time.
It is another object of this invention to provide a device for
electrochemically detecting and quantitatively measuring the
quantity of carbon monoxide in a gaseous medium.
It is another object of this invention to provide a device for
electrochemically detecting and quantitatively measuring the
quantity of hydrocarbon in a gaseous medium.
It is another object of this invention to provide improved
composite electrodes for utilization in an electrochemical device
for detecting gases in a fluid medium.
It is another object of this invention to provide electrodes for
utilization in an electrochemical device which will selectively
diffuse gases from a gaseous medium.
These and other objects of the present invention will be more
readily apparent from the following detailed description with
particular emphasis being directed to the drawings and preferred
embodiments.
The aforesaid objects of the present invention are accomplished by
constructing a gas detecting unit comprising in combination intake
means, an electrochemical cell, means for drawing a gas through
said intake means and into said electrochemical cells at a
controlled flow rate, and read-out means for reading the quantity
of detected gas. The electrochemical cell comprises an anode which
provides a catalytic site for electrochemical reaction with the gas
being detected, i.e., an alcohol, carbon monoxide, etc.; a cathode,
a reference electrode, and an electrolyte in contact with an anode,
cathode, and reference electrode. The anode of the cell is
maintained at a fixed potential relative to the potential of the
reference electrode, which is substantially free of current flow,
to ensure that the current production is a result of the gas being
detected and not other gases including oxygen. The fixed potential
is selected within the range of from about 0.7 to 1.5 volts in
order that only the gas being detected is electrochemically
reacted, precluding the possibility that other gases in the sample,
as well as an oxygen/water redox couple, will influence the current
produced. The means for drawing gas through the intake means into
the cell will effectively pass a predetermined quantity of gas to a
predetermined anode surface area, thus assuring continuous accuracy
in the quantitative measurement. Preferably, the quantity of gas
fed to the anode surface is controlled by a constant flow control
means, as will be developed more fully hereinafter, which feeds the
gas sample to the electrochemical cell at a constant rate with the
balance of the gas sample being vented off. Pumping or suction
means are normally employed to draw the gas sample through the
intake means, the electrochemical cell, and flow control means in
metered amounts. Preferably the anode chamber will define a
labyrinthine path through which the gas sample is passed to the
anode surface. Other designs can be employed, it only being
essential that the geometric anode surface area remains constant,
or substantially constant, and is fed with a predetermined quantity
of gas over a predetermined period of time.
In this regard it is to be noted that insofar as the actual gas
being detected is concerned, it is immaterial whether the flow rate
is high or low. For example, if the sample is fed to a 4 in..sup.2
electrode surface area at a low flow rate, i.e., approximately 50
cc./min., substantially all of the gas in the sample will be
oxidized (greater than 95 percent). In this instance the partial
pressure of the gas will be lowered substantially from the time the
sample gas enters the cell to the time it exits from the cell. If
the flow rate is increased to 500 cc./min., with the surface area
of the electrode being maintained constant, a substantially lower
percentage of the gas will be oxidized (approximately 50 percent).
In this instance the lowering of the partial pressure of the sample
gas between entrance of the sample into the cell and its exit will
be less. If the flow rate is very high, i.e., 1500 cc./min., over
the same electrode surface area, probably only about 10 percent of
the gas in the sample will be oxidized. However, the partial
pressure of the gas will be substantially constant between the
entrance and exit of the sample from the cell. In all cases the
reading obtained from the cell determines the gas content in the
sample. Accordingly, it is only essential to control the flow rate
of the sample and to maintain a substantially constant geometric
anode surface area.
The anode of the electrochemical cell can be any anode upon which
the gas is being detected, i.e., alcohol, carbon monoxide,
unsaturated hydrocarbon, etc.; will electrochemically react.
Preferably, however, the anode will be a lightweight electrode
comprising a catalytic material such as platinum black deposited on
a suitable substrate, such as unsintered polytetrafluoroethylene
(PTFE), or platinum black admixed with a binder such as PTFE. The
support substrate can be a plastic material such as PTFE or carbon
or a metal. As will be apparent to one skilled in the art, the
platinum can be replaced with other catalytic materials such as
rhodium, and the like, which will effectively oxidize the gas which
is being detected. The PTFE binder and/or substrate material can be
replaced with other binder or substrate materials including the
hydrophobic fluorocarbons such as polychlorotrifluoroethylene or
the like, as well as less hydrophobic materials including
polyacrylonitrile, polyvinylchloride, polyvinylalcohol,
carboxymethyl cellulose, or the like. As will be further apparent
to one skill in the art, when the support substrate is a
hydrophobic material such as PTFE, the hydrophobic material must be
oriented in the cell in order that the catalyst is in contact with
the gas sample, with the catalytic layer being in contact with the
electrolyte.
The specific structure of the cathode which is employed in the
electrochemical cell again is not critical. It is only essential
that the cathode provides a site at which oxygen will
electrochemically react and withstand the corrosive environment of
the electrolyte employed in the cell. The lightweight electrodes
defined hereinbefore in considering the anode are preferred in view
of their light weight, compactness, and stability. Their low gas
diffusion resistance provides a rapid response characteristic.
The reference electrode of the electrochemical cell can be a
conductive metal such as nickel, zirconium, or the like, capable of
maintaining a relatively constant potential in the environment of
the electrochemical cell. The third or reference electrode can be
positioned between the anode and cathode, or it can be positioned
behind either the anode or cathode or on the same plane or
substrate as the cathode or anode. Preferably, however, in order to
obtain greater compactness of the cell and due to optimum
ion-transfer characteristics, and the like, the cathode and the
third or reference electrode will be part of a common substrate. It
is only necessary that the anode, cathode, and third electrode be
electrically insulated from each other. Thus, a polymer substrate
such as polytetrafluoroethylene can have two separate and distinct
portions coated with a catalytic material such as platinum black,
or an admixture of platinum black and PTFE particles. The entire
substrate will, therefore, function as both the cathode and
reference electrode. As will be more fully apparent hereinafter,
various designs or lay-outs can be used.
Reference electrode, as the term is used herein, defines an
electrode at which no, or substantially no, current flows.
Accordingly, the reference electrode and anode must be connected
through electronic circuitry, or the like, to preclude or minimize
current flow between the reference electrode and working electrode,
i.e., anode, so as to define and maintain a known reference
potential. Although it is virtually impossible to completely
eliminate current flow, the reference potential cannot show
extensive drift, i.e., more than about .+-.25 mv.; or rapid drift,
i.e., more than .+-.5 mv., over a period of ten seconds. If
extensive or rapid drift occurs, a false reading as to the quantity
of the detected gas may be obtained. As is apparent, the actual
extent of current drift depends upon the accuracy of the
measurement needed. If high accuracy is unnecessary, a greater
current drift can be tolerated. Circuitry for the detector is set
forth in applicants' aforesaid co-pending application U.S. Ser. No.
88,267.
At times it may be desirable to employ non-porous semi-permeable
membranes in the fabrication of the anode in order to restrict the
diffusion of gases other than the select gas being analyzed. The
principle of selecting the membrane is based on
solubility/diffusibility co-efficients of the various gases. For
example, in detecting and quantitatively measuring alcohol, a
membrane such as shellac, polyvinylalcohol, water-soluble
cellulose, i.e., the cellulose ethers, esters, or ether-esters;
oxyethylene, or the like, in which alcohol is soluble will be
chosen. A particularly effective membrane is Edisol M manufactured
and sold by Polymer Films, Inc., Woodside, N.Y., and which is
methylhydroxypropyl cellulose. Another particularly effective
membrane is made from dimethyl silicone polymers. Gases such as
carbon monoxide and the hydrocarbons which are not soluble in the
membrane would be precluded, or substantially precluded, from
passage, enhancing the accuracy of the determination.
Understandably, if a membrane is water-soluble, it must not be
exposed to the electrolyte of the cell. This can be done by using
the membranes in conjunction with hydrophobic membranes such as
PTFE. As will also be understood, the selection of the membrane
depends upon the gas being detected. Furthermore, in the event
carbon monoxide is the gas being detected, it can be desirable to
employ a scrubber, such as a carbon black or activated charcoal
scrubber, between the sample intake and the electrochemical cell to
remove absorbables other than water. Water is not detrimental. The
scrubber can be used alone or in combination with a selective
permeable membrane.
As will be fully apparent to one skilled in the art, the proper
selection of anode, cathode, and reference electrode, the operating
electrolyte, as well as ancillary components such as scrubbers and
selectively permeable membranes will depend upon the gases which
are to be analyzed and the operating conditions which must be met.
The essential feature of the electrochemical cell, as pointed out
hereinbefore, is in having the anode maintained at a fixed
potential of from about 0.7 to 1.5 volts anodic relative to the
hydrogen couple as a zero base with reference to the third or
reference electrode as hereinbefore defined. Furthermore, it is
necessary that the anode have a fixed geometric surface area
available to the gaseous reactant which is fed at a controlled
flow. This is preferably accomplished by using a labyrinthine path
or by utilizing a fan for flowing the reactant gas to the electrode
surface. The latter configuration is described more fully in our
aforesaid co-pending application U.S. Ser. No. 88,267.
The housing of the electrochemical cell can be made of any suitable
material which does not form soluble oxidizable products,
preferably plastics such as the olefinic or methacrylate polymers.
The housing is to be designed to permit the cathode to have an area
exposed to ambient air. In view of the small quantity of air
consumed, however, this can be through the electrolyte chamber or
even from oxygen dissolved in the electrolyte. Moreover, as
developed above, the anode must have a chamber adjacent thereto to
permit controlled sample flow to the anode. The electrolyte which
can be either an aqueous acid or aqueous alkaline solution can be
free-flowing or trapped in a suitable matrix. In the event a matrix
is employed, the matrix material must be sufficiently hydrophilic
to permit continuous wetting of the anode and cathode surfaces as
well as the surface of the third or reference electrode. Materials
such as asbestos, Kraft paper, polyvinylalcohol, polyvinylchloride
which has been treated to render it hydrophilic, or the like, can
be selected.
In addition to the electrochemical cell, it is necessary that the
detecting device include sample intake means and means to control
the flow of the gas sample through the cell. The control of the
flow rate of the sample can be accomplished in various ways. Thus,
the gas sample is received through the intake means of the
detecting device and pulled into the electrochemical cell,
preferably by means of a suitable pump. The flow rate can be
controlled in various ways including a restricted intake orifice
positioned between the pump means and the intake means. In order
that the test sample is received in the electrochemical cell with
the minimum likelihood of water condensation in the sample and the
like, the electrochemical cell is preferably positioned immediately
adjacent to the sample intake with the flow meter being positioned
between the pump and electrochemical cell. The flow meter and pump
can be of various commercial design and form no part of the present
invention. The only criterion is that the pump means have
sufficient capacity to pull the gas sample through the
electrochemical cell and flow meter. The flow meter must have
precision sufficient to control the volume being carried through
the electrochemical cell with reasonable accuracy.
When the device is used to measure the alcohol content of a test
subject's breath, the sampling device, i.e., the means for
collecting the breath sample, which is utilized is of substantial
importance. Thus, the breath sample--for a fully accurate
determination--must reach the electrochemical cell at substantially
the same temperature as the test subject, i.e., approximately body
temperature or 98.degree. F. Moreover, it is important that
moisture in the sample does not condense. Finally, inasmuch as the
blood alcohol level is directly correlated to the breath from the
alveolae, it is desirable that the sample being tested come from
the alveolae and not from the mouth, throat, or trachea of the test
subject. It is preferable, therefore, that the test subject
thoroughly exhaust the breath from his mouth and from the throat
and trachea before collecting a sample for feeding into the
electrochemical cell. While it is possible to accomplish this by
asking the test subject to take one or more quick breaths prior to
blowing into the sample collector, under the conditions of
receiving a sample, i.e., from a test subject at roadside at a time
when the test subject may not be fully cooperative, it is
preferable that the test sample be collected in as simple a manner
as possible. In accordance with an aspect of the present invention,
a sample collector is provided which comprises a long, open-ended
tube having a relatively small diameter. The test subject will
breathe into the sample collector with a relatively deep breath.
The sample will be fed to the electrochemical cell in order that
the last breath into the sample collector is the first breath out.
By utilizing this method for first sample received by the
electrochemical cell will be breath primarily or entirely from the
alveolae providing an accurate reading of the blood alcohol level.
Since the tube is open-ended, continued operation of the pump of
the detecting device will exhaust and flush out the sample system
and the detecting device.
Particularly in cold climates, to ensure that moisture condensation
from the breath sample does not occur, it can be desirable to
utilize a sample collector comprising two concentric tubes. The
first and internal tube will be the open-ended tube described
hereinbefore. However, a substance such as wax, Glaubers salts, or
the like, which is constituted to have a melting or flow point at
substantially the temperature of the test subject's body, i.e.,
110.degree. F., will be placed between the first tube and the inner
walls of the second tube. The sample collector will be maintained
at a temperature of 98.degree. F., or slightly above, in order that
the wax or the like will be in the fluid condition. Due to the
latent heat of solidification, the entire sample
collector--particularly the inner tube--will be maintained at
98.degree. F., precluding any possibility of moisture condensation
during the collection of, and analysis of the sample.
From the standpoint of legality of detection and determination of
alcohol in the test subject, it is desirable that the device be
quickly and accurately calibrated immediately before use. The
detecting and measuring devices of the present invention permit a
convenient and rapid determination of a zero or base line in
contradistinction in infra-red and the like devices where it is
necessary to pass nitrogen gas or some other gas which does not
affect the reading through the machine to establish a zero or base
line followed by feeding a gas into the device of known
concentration to establish millivolts per part per million of gas.
Accordingly, two separate calibrating tanks are necessary. With the
present invention, the flush gas is not needed. Rather, gas flow to
the device is cut off and in this way any detectable gas within the
electrochemical cell is oxidized or burned off to establish its own
base or zero line. Thereafter, a calibrating gas of known
concentration is fed to the device to establish millivolts per part
per million of gas as in infra-red or the like units. The aforesaid
feature of the invention is particularly advantageous in legally
determining the alcohol content in the breath of a test subject.
Thus, after the detector device is operated without gas flow for a
period of time, a calibrating vapor comprising a specific and
predetermined ethanol content mixed with nitrogen or air is fed to
the detector for a predetermined period, about 20 seconds, and the
read-out of the device calibrated by adjusting the flow rate of the
sample through the device or by adjusting a resistance valve in
order that the predetermined reading is obtained. After the
calibration and the electrochemical device is flushed by drawing in
atmospheric air, the test sample will be analyzed. To ensure
accuracy, it is essential that the calibrating sample be of a
predetermined and consistent concentration of ethanol. This is
accomplished by having the ethanol sample in a compressed gas
cylinder containing air or an inert gas such as nitrogen or helium
and ethanol vapor. It is important that no water vapor be in the
sample. The composition of the sample is chosen in order that the
partial pressure of ethanol is always less than that which would
exist over pure ethanol at the lowest required operating
temperature. Provided that this condition is maintained, no liquid
ethanol will condense out and the sample composition will remain
constant. It is essential that the calibrating test sample contain
only ethanol and air or the inert gas. Water will complicate the
calibration due to formation of condensate; and from the standpoint
of temperature stability, i.e., at temperatures below the dew
point, the concentration of the sample would vary.
It is also desirable from the standpoint of providing a legally
acceptable method of determining the blood alcohol level of a test
subject to provide verification means. In accordance with the
present invention, this is accomplished by utilizing a sealed
container having an opening at either end which can be plastic,
metal, or glass, with the intake of the sealed container being in
contact with a long, thin tube. The second end of the long, thin
tube will be in contact with the second opening in the container,
with both the inlet opening and the exit opening having a one-way
valve. The test subject will breath into the verification tube in
the same manner in which he breathed into the original sample
collector. It may be desirable to collect the sample for immediate
testing and the verification sample at the same time by having the
subject breathe into a sample intake having a rotating disk which
splits the breath sample into the two parts, one part being
immediately analyzed and the second part being saved for
verification. As with the original sample, the last breath in will
be the first breath which is received by the electrochemical device
and will be consistent with the original test sample analyzed at
roadside. Within experimental error, the verification sample will
be identical to that originally tested by the operator of the
detecting device.
The final form of the detector and measuring device as hereinbefore
described can vary depending upon the accuracy required in
determining the blood alcohol level. For example, rather than
utilizing the device for an accurate determination of the blood
alcohol level, it may be desirable to merely obtain a rough
indication to verify a law enforcement officer's suspicion that the
test subject is under the influence of alcohol. Accordingly, the
device can be designed as a sniffer-type detection unit whereby the
intake of the device is merely brought within the general vicinity
of the test subject. The exhaled breath of the test breath of the
test subject will be brought into contact with the electrochemical
device as defined hereinbefore with a reading being given of the
alcoholic content of the exhaled breath. Necessarily, this method
cannot be completely accurate and will be used primarily to verify
or negate a police officer's suspicion that the test subject is
under the influence of alcohol and will dictate or preclude
requiring the test subject to undergo more accurate testing. In
view of the environment of the test, i.e., in most instances at
roadside where carbon monoxide is possibly present as a result of
passing cars and the like, it may be desirable to filter the carbon
monoxide from the sample entering the detecting device to avoid
possible false readings. Accordingly, it can be desirable to
include a filtering cartridge between the intake means of the
detecting device and the electrochemical cell to remove carbon
monoxide. The filtering cartridge can be a perm-selective membrane
which will selectively pass alcohol while rejecting carbon
monoxide, hydrocarbons, and the like, as discussed hereinbefore; or
it can be a unit which will selectively absorb carbon monoxide. It
has been found that organo-metallic compounds having the formula
MXR(P(C.sub.2 H.sub.5).sub.3).sub.2 wherein M is palladium,
platinum, nickel, cobalt, or the like; X is a halogen or SO.sub.4
=radical; and R is a lower alkyl radical or an aromatic radical; or
the formula RMn(CO.sub.5) wherein R is aryl or alkyl, are
particularly effective in taking up carbon monoxide. Similarly,
hydrocarbons, saturated and unsaturated, can be filtered by passing
them through heavy oils, waxes, or the like.
The detecting device of the present invention and the nature of the
ancillary components will be more readily apparent from the
accompanying drawing wherein like numerals are employed to
designate like parts. In the drawing:
FIGS. 1 and 2 are diagrammatic views in block form of a preferred
device;
FIG. 3 is a cross-sectional view of an electrochemical cell useful
in the detector unit;
FIG. 4 is an exploded perspective view of a second electrochemical
cell useful in the detector unit;
FIG. 5 is a partial cross-section of a sample collector;
FIG. 6 is a cross-section of a calibrator bottle;
FIG. 7 is a cross-section of a verification sample collector;
FIG. 8 is a scrubber unit for incorporation in the device of FIG.
1;
FIG. 9 is a sump bottle for utilization with the device of FIG. 1;
and
FIG. 10 is a monitoring curve, plotting the concentration of carbon
monoxide in the atmosphere and the effect of the sump bottle of
FIG. 9 in smoothing out the curve.
More specifically, referring to FIGS. 1 and 2, the detecting device
1 is positioned within a housing 10. The device includes a sample
intake means 11 in direct communication with the electrochemical
cell 20 which, in turn, is in communication with pump 30 through
flow meter 40. The electronic circuitry of the device is not shown.
The circuitry, however, as set forth hereinabove, is shown in
applicants' co-pending application U.S. Ser. No. 88,267.
The electrochemical cell, as seen most clearly from FIGS. 3 and 4,
will include a cathode 21, an anode 24, and a third or reference
electrode 26, all positioned within a housing 28. In the embodiment
of FIG. 3, the cathode, anode, and third electrode are in contact
with a free-flowing electrolyte 29. Adjacent anode 24 is reactant
chamber 27 having reactant gas inlet 27.1 which is in direct
communication with intake 11 and outlet 27.2 which is in
communication with flow meter 40. In the embodiment shown, cathode
21 is in direct communication with atmospheric air. Both the anode
and cathode are lightweight electrodes comprising a plastic
substrate 24.1 and 21.1 in direct contact with reactant chamber 27
in the case of the anode, and with the ambient environment in the
case of the cathode, and catalytic layers 24.2 and 21.2 which
comprise a mixture of platinum black and polytetrafluoroethylene
particles. The catalyst layers are in contact with the electrolyte
of the cell. The platinum black is present at a loading of 10
mg./cm..sup.2. The ratio of platinum to PTFE is 10 to 7 on a weight
basis. Reference electrode 26 which is in electrical contact with
anode 24 is a porous, platinum coated nickel structure which is
approximately 7 mils thick. A fixed potential of +1.0 volt with
respect to a reversible hydrogen electrode in the same electrolyte
is maintained on the anode by means of the reference electrode
through a potentiostat. The anode and cathode of the cell are
connected through the electrical circuit, the wiring being shown in
parent application U.S. Ser. No. 88,267.
FIG. 4 shows an alternative cell wherein the housing 28 is
constructed in three pieces, 28a, 28b, and 28c. 28a has a cavity
28d having holes which form gas inlets 27.1 and 27.2. A
labyrinthical path is formed by vertical ribs 28e. An anode 24
comprising a polytetrafluoroethylene substrate 24.1 having a
coating of platinum and PTFE particles applied as a suitable
pattern 24.2 is adjacent to element 28a in order that the PTFE
substrate is in contact with the reactant gas. Section 28b is
adjacent to anode 24 and contains a hole 28f which serves as the
electrolyte cavity. The cavity has an extension which maintains the
hydrostatic head above the elecrolyte constant and serves as a
reservior to accommodate any changes in volume due to environment.
Additionally, air through the electrolyte contacts cathode 21 which
again is on a PTFE substrate 21.1. The substrate 21.1 also serves
as the base for reference electrode 26. In this manner the cell can
be extremely compact. In order to show the pattern of the cathode
and reference electrode, the component 21/26 is reversed. In
actuality, cathode 21 and reference electrode 26 are in contact
with the electrolyte of the cell. Housing element 28c forms the top
of the cell and together with housing element 28a maintains the
elements of the cell in operative association. Electrical leads
from the cell, not shown, are fitted through the cell housing.
As noted hereinbefore, pump 30 and flow meter 40 can be any of
numerous conventional units. In instances where the detector is to
be employed as a portable alcohol sniffer, it may be desirable to
replace the pump with a vacuum chamber which can be repeatedly
evacuated by a hand piston or with an ancillary pump. Accordingly,
when the device is to be used, actuation of the switch turning the
device on will actuate the vacuum chamber drawing sample into the
cell for detection. Furthermore, the flow meter can be replaced
with a suitable restrictive orifice in instances where the accuracy
of the determination is not overly critical.
The device as shown in FIG. 1 is eminently suitable for a sniffer
device for detecting alcohol in the general vicinity, or as a
carbon monoxide detecting unit. In the event the device is to be
used as a carbon monoxide detecting unit, preferably a scrubber
will be placed between the intake 11 and electrochemical cell 20.
The scrubber, as shown in FIG. 8, will comprise a U-tube containing
activating carbon, charcoal, or other material which will remove
condensibles such as alcohols, aldehydes, hydrocarbons, and the
like; but which will not collect carbon monoxide. Accordingly, the
gas entering the electrochemical cell will only be the carbon
monoxide to be detected. In the event the unit is to be employed as
an alcohol detector unit, and if the quantitative measurement is
critical, it can be desirable to utilize a perm selective membrane
in the electrochemical cell to separate the carbon monoxide which
may be in the environment from the alcohol.
As seen in FIG. 2, where the device is used to detect alcohol in
the breath of a test subject intake 11 is in contact with the
electrochemical cell through multi-position valve 12. In a first
position, air from the outside will pass through the valve directly
into the cell. By turning valve 12 to a second position, intake 11
will be in communication with sample collector 50. By turning the
valve to a third position, the sample collector 50 will be in
direct communication with the electrochemical cell 20. By turning
the valve to a fourth position, intake 11 will be in communication
with verification sample collector 70. Sample collector 50 is
placed in fluid communication with calibrating sample 60 by opening
valve 61.
The sample collector, as seen most clearly in FIG. 5, comprises an
open-ended tube 51 which is surrounded with a second tube 53. The
cavity between tubes 51 and 53 contains a composition 55 which is
solid up to temperatures of about 98.degree. F., but which becomes
fluid or molten at about 98.degree. F. Since the tube 51 is
open-ended but of narrow diameter, gas passing into the tube will
remain in the tube unless displaced by additional gas by pressure
or vacuum means. Accordingly, when air is passed into the tube
through first opening 57, it will progressively travel toward
second opening 59.
As seen in FIG. 6, calibrating device 60 is a plastic pressure
bottle having a two-way valve 61 and a button 63. The bottle will
contain a calibrating sample which is a mixture of nitrogen and
ethanol at a predetermined concentration.
As seen from FIG. 7, the verification sample bottle 70 has openings
71 and 73. These openings are connected by a continuous tube 75 of
narrow diameter. As with the sample collector 50, the air passes
into the tube through opening 71 and exits through opening 73.
Since the sample is verification sample, it is essential that the
openings 71 and 73 be closed with a one-way valve 71.1 and
73.1.
In conducting an analysis to detect and measure the blood alcohol
level, the operator after selecting a test subject will actuate the
detecting unit, place multi-position valve 12 in a position such
that air from the environment will pass into inlet 11 and directly
into the electrochemical cell. When valve 12 is in this position,
valve 61 will be positioned in order that sample collector 50 is in
communication with calibrating bottle 60. Actuator button 63 will
be pressed to permit calibrated sample from bottle 60 to flow into
and fill sample collector 50. Thereafter, valve 12 will be
positioned in order that the calibrating sample from sample
collector 50 is fed to cell 20. After the sample is passed into the
cell, and the cell has sufficient time to reach equilibrium, i.e.,
a period of about 20 seconds, the detector unit will be adjusted in
order that the read-out gauge, not shown, will indicate the
predetermined alcohol concentration. The correcting adjustment
preferably will be made by adjusting the flow rate of the sample
through the cell. After the cell is calibrated, air will be drawn
through open-ended sample collector 50 by merely leaving the unit
running to flush the sample collector and the entire system.
Thereafter, valve 12 will be positioned in order that intake 11 is
in direct communication with sample collector 50. The operator will
instruct the test subject to breathe into intake 11 with a breath.
The breath, coming directly from the alveolae, which will be the
last breath into the sample collector will be the first breath out.
Valve 1 is then again positioned in order that sample collector 50
is in direct communication with the electrochemical cell and the
blood alcohol level of the test subject will be read directly from
the read-out gauge. In the event the blood alcohol level of the
test subject is at a predetermined level, a verification sample
will be collected to verify the determination by a future analysis.
This is accomplished by positioning valve 12 in order that intake
11 is in direct communication with verification sample collector
70. The test subject will again be instructed to breathe into
intake 11. Again the last breath in will be the first breath out of
the tube when the verification sample is later analyzed to provide
an accurate duplication.
The entire operation can be accomplished in less than from about
three to five minutes by an operator having a minimum of technical
training. The analysis including the calibration and collection of
the verification sample is inexpensive since the entire unit can be
used repeatedly. In view of the calibration and the collection of a
verification sample, the unit provides the necessary safeguards
against error. In any instance where there is an error, the error
will necessarily be to the advantage of the test subject and,
accordingly, the final determination is not subject to discrediting
in any instances where the blood alcohol level is above the
prescribed amount.
The detecting and measuring device of this invention can include
various ancillary features or modifications to meet particular and
specific conditions. It may be desirable, for example in order to
maintain constant humidity and temperature, to thermostat the cell
by including a small heating coil or the like in the device.
Furthermore, when using the device to continuously monitor carbon
monoxide or other gases in the environment, to avoid sharp and
rapid changes due to the extreme sensitiviy of the detecting
device, it can be desirable to include a sump bottle between the
intake means and electrochemical cell to smooth out the plotting
curve. A suitable sump bottle is shown in FIG. 9. The effect when
using the sump bottle is shown in FIG. 10. In region A, the gas
from the environment is fed directly to the cell. Note the sharp
and quickly changing responses. In region B, the gas sample passes
through the sump bottle providing a more average reading. As will
be apparent, when sharp and quickly changing responses are needed,
the intake means should be in direct communication with the
atmosphere. However, where sharp responses are not necessary and
the average and more level change is desirable, a sump pump can be
useful.
Moreover, when the concentration of the gas being detected is very
high, it may be difficult to obtain linearity due to swamping of
the electrode with the gas sample or due to difficulty of voltage
control. This can be compensated for in any of several ways:
(1) The flow of the gas can be restricted in order that the anode
of the cell only receives a small amount of sample gas.
(2) A restrictive membrane can be employed. An ion-exchange
membrane such as a sulphonated polystyrene ion-exchange membrane
can be inserted between the working and reference electrodes to
remove reactive materials. In the case of alcohol detection and
measuring, this will restrict the flow of alcohols and aldehydes in
the cell providing a more linear reading for the alcohol detection.
Alternatively, any membrane which will restrict the flow of gases
can be positioned on the gas side of the working electrode of the
cell.
(3) The gas stream can be diluted with clean air at a known ratio,
i.e., at a ratio of 1:1, 1:2, 1:4, or the like, in order that the
anode of the electrochemical cell sees a less concentrated gas
stream. This allows one to work in the concentration range which is
more acceptable; for example, when determining alcohol in the blood
stream above 0.12.
(4) The utilization of a reference electrode which will not oxidize
or be poisoned by the gas being detected, i.e. alcohol, such as a
lead oxide/lead sulphate or mercury sulphate/mercury electrode.
More particularly, when a platinum/oxygen reference electrode is
exposed to alcohol, this electrode will start to oxidize the
alcohol and will drift in the negative direction. Therefore, the
working potential will go negative. Platinum/oxygen will be
reduced, causing a local cathodic current which will diminish the
size of the anodic current. If this change of potential reaches the
sensing electrode there will be a cathodic current, giving a lower
reading for the alcohol being detected.
Further, it may be desirable to incorporate a drying capsule 41
immediately adjacent to flow meter 40. This drying capsule will
collect any condensation which, for example, may be in the breath
sample in the case of a BAL analysis, precluding the possibility
that the condensate will interfere with the accuracy of the flow
meter.
Additionally, although the present invention has been described
primarily with reference to the detecting and quantitatively
measuring of alcohol in the breath of a test subject, or as a
carbon monoxide monitoring device, it is possible to selectively
measure unsaturated hydrocarbons which are the primary smog
producing hydrocarbons. Smog, according to the present
understanding, is the photochemical reaction of hydrocarbons and
primarily the unsaturated hydrocarbons which have greater activity
to produce peroxy acids. Smog is formed from unsaturated
hydrocarbons by splitting each --C.dbd.C-- bond of the molecule to
give two molecules of peroxy acid when oxidized. The selective
measuring of unsaturated hydrocarbons can be accomplished since
saturated hydrocarbons are not readily reacted at low or
atmospheric temperatures. Carbon monoxide which may be present in
the gas stream can be removed with selectively permeable membranes.
Alcohols, if present, can be removed by passing the gas stream
through a water scrubber. Furthermore, gases such as NO, NO.sub.2,
and SO.sub.2 can be detected and measured by suitable modification
of the detecting and measuring unit. These materials at the
electrochemical cell undergo a change in valency state.
Moreover, in the case of detecting alcohol in the blood stream by
determining the concentration of alcohol in a breath sample, an
alternative arrangement to that shown in FIG. 2 would be to utilize
a detector having two electrochemical cells. A gas stream which
would contain alcohol vapors, and carbon monoxide in addition to
air, would be split in two streams after entering the intake means
with one stream being fed to cell A while the other stream is first
bubbled through water prior to entering cell B. The output of cell
A will consist of current derived from the oxidation of carbon
monoxide and alcohol, while the output of cell B will consist only
of the oxidation of carbon monoxide since the ethanol is scrubbed
out in the water. By measuring the difference between the two, the
output signal for alcohol can be determined. With this embodiment,
selectively permeable membranes or the like are not required for
the detection of alcohol even if carbon monoxide may be present,
for example, with sniffer devices.
The various modifications described above are within the ability of
one skilled in the art and fall within the scope of the present
invention.
* * * * *