U.S. patent number 4,269,804 [Application Number 06/099,704] was granted by the patent office on 1981-05-26 for self-contained gaseous contaminant dosimeter.
This patent grant is currently assigned to E. I. Du Pont de Nemours and Company. Invention is credited to Elbert V. Kring.
United States Patent |
4,269,804 |
Kring |
* May 26, 1981 |
Self-contained gaseous contaminant dosimeter
Abstract
A personal dosimeter for measuring the average concentration of
a gaseous contaminant over a given period of time is provided. The
dosimeter comprises a sealed pouch having a reaction chamber, which
contains a gas-collecting medium, and at least one compartment.
Each compartment can be separately sealed and can contain a
different reagent, the seals being individually breakable such that
the reagents can be separately released into the reaction chamber.
Into the pouch is sealed a gas diffusion device that permits the
contaminant to diffuse into the reaction chamber where it is
collected in proportion to its ambient concentration.
Inventors: |
Kring; Elbert V. (Wilmington,
DE) |
Assignee: |
E. I. Du Pont de Nemours and
Company (Wilmington, DE)
|
[*] Notice: |
The portion of the term of this patent
subsequent to June 17, 1997 has been disclaimed. |
Family
ID: |
26750217 |
Appl.
No.: |
06/099,704 |
Filed: |
December 3, 1979 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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69574 |
Aug 24, 1979 |
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922546 |
Jul 7, 1978 |
4208371 |
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Current U.S.
Class: |
422/86; 116/206;
338/34; 422/416; 422/88; 436/113; 436/117; 436/122; 436/902;
73/31.03; 96/10 |
Current CPC
Class: |
G01N
31/223 (20130101); Y10S 436/902 (20130101); Y10T
436/175383 (20150115); Y10T 436/186 (20150115); Y10T
436/178459 (20150115) |
Current International
Class: |
G01N
31/22 (20060101); B01D 053/22 (); B01D 059/10 ();
G01N 031/22 (); G01N 033/00 () |
Field of
Search: |
;422/61,83-88,119
;23/232R ;73/23,421.5 ;116/206 ;55/16,158 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Marcus; Michael S.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of co-pending
application Ser. No. 069,574, filed Aug. 24, 1979, abandoned, which
is a continuation-in-part of copending Ser. No. 922,546, filed July
7, 1978 now U.S. Pat. No. 4,208,371.
Claims
What is claimed is:
1. A personal dosimeter for measuring the average concentration of
a gaseous contaminant over a given period of time comprising:
a pouch-like receptacle of polymeric material having at least one
compartment, the compartment occupying less than the total volume
of the receptacle, leaving a reaction chamber, the compartment
containing a pre-determined quantity of a color-forming reagent and
being adapted to release the reagent into the reaction chamber
independently of any other reagents present in any other
compartments, and the reaction chamber containing a collecting
medium for the gaseous contaminant; and
a gas diffusion device which is sealed into a boundary of the
receptacle and through which the contaminant diffuses at a rate in
linear proportion to its concentration in the atmosphere, the
diffusion device providing the only communication between the
atmosphere and the interior of the reaction chamber.
2. The dosimeter of claim 1 in which the gas diffusion device
contains a plurality of through-and-through channels by which said
communication is provided.
3. The dosimeter of claim 2 in which there are 5-500 channels, each
having a diameter of 50-1000 microns and a length of 1.0-25.0
mm.
4. The dosimeter of claim 1 in which the gas diffusion device is a
membrane through which the gaseous contaminant passes at a rate in
linear proportion to its concentration in the atmosphere.
5. The dosimeter of claim 4 in which the membrane is constructed of
silicone rubber, polytetrafluoroethylene, or copolymers of silicone
and polycarbonate.
6. The dosimeter of claim 1, 2, 3, 4, or 5 wherein the collecting
medium is in the form of an absorbing solution.
7. The dosimeter of claim 6 wherein the absorbing solution is for
sulfur dioxide, nitrogen dioxide, or ammonia.
8. The dosimeter of claim 7 further containing at least one
color-forming reagent.
9. The dosimeter of claim 8 wherein the absorbing solution is a
solution of sodium tetrachloromercurate or potassium
tetrachloromercurate in water and the reagent is for determining
the presence of sulfur dioxide.
10. The dosimeter of claim 8 wherein the absorbing solution is a
solution of triethanol amine in water and the reagent is for
determining the presence of nitrogen dioxide.
11. The dosimeter of claim 8 wherein the absorbing solution is a
solution of sulfuric acid in water and the reagent is for
determining the presence of ammonia.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to a personal dosimeter for registering
gaseous contaminants in the atmosphere. More particularly it is
related to a self-contained dosimeter capable of integrating the
exposure level of a gaseous contaminant over a given period of
time.
2. Description Of The Prior Art
In response to the increasing concern about the health of workers
who are exposed to harmful pollutants in the air, it has become
necessary to monitor the concentration of the air-borne
contaminants. One development for this purpose involved a rather
large air pump which would force air to be sampled through a
filter, trapping particulate contaminants. This obviously is
unavailing for the monitoring of gas contaminants and, even for
particles, is not accurate to determine concentration of the
particles in the sampled atmosphere.
Personal sampling devices which are worn by individual workers and
which passively collect the contaminants have also been used. For
example, a device which utilizes the molecular diffusion of the gas
to be monitored to collect the sample has been described in
American Industrial Hygiene Association Journal, Volume 34, pages
78-81 (1973). This device, however, requires that the collecting
medium be removed therefrom, and carefully treated with reagents
which must be exactly-measured at each analysis.
The disassembly of the device and use of cumbersome reagents
required for each analysis are disadvantageous.
Therefore, there remains a need for a personal dosimeter for
gaseous contaminants which accurately integrates, that is,
indicates the average concentration of the gaseous contaminant over
a given time period, and which easily lends itself to analysis
without removal of the gas-collecting medium or bothersome addition
of other elements.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a personal
dosimeter for measuring the average concentration of a gaseous
contaminant over a given period of time comprising: a sealed
pouch-like receptacle of a pliable polymeric material, said
receptacle having a reaction chamber adapted to contain a
gas-collecting medium and at least one compartment separately
sealed and adapted to contain a testing reagent, the seals of each
compartment being individually breakable such that the reagents can
be separately released into the reaction chamber; and a gas
diffusion device which is sealed into a boundary of the receptacle,
the diffusion device providing the only communication between the
atmosphere and the interior of the reaction chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a magnified perspective view of a gas diffusion device
usable in the present invention.
FIG. 2 is a top view of a gaseous contaminant dosimeter utilizing
the diffusion device of FIG. 1.
FIG. 3 is a partial perspective view of the dosimeter of FIG.
2.
FIG. 4 is a perspective view of a gaseous contaminant dosimeter
utilizing a membrane as the gas diffusion device.
DETAILED DESCRIPTION OF THE INVENTION
The dosimeters of this invention collect a gaseous contaminant in
proportion to its average concentration in the atmosphere during
the collection period and provide for the expedient determination
of this concentration. This is achieved by passively sampling the
gaseous contaminant in ambient air in proportion to its
concentration therein by allowing the contaminant to diffuse into
an interior portion of the dosimeter where it is maintained until
it is analyzed. The dosimeter further contains specified
color-forming reagents, separately sealed in measured amounts
within the dosimeter but capable of being brought into contact with
the collecting medium.
The collecting medium, which is present in a measured amount, holds
the gaseous contaminant or its ions in a form that is more readily
analyzable than is the gaseous form. After collection, the medium
is treated with the appropriate reagents to product color, the
intensity of which is dependent upon the amount of gaseous
contaminant collected. The time-average ambient concentration can
then be determined, as later explained, with a
previously-calibrated colorimeter or spectrophotometer.
Generally, the collecting medium is a material that absorbs,
adsorbs, reacts or otherwise combines with the gaseous contaminant
being measured. Regardless of the manner in which the medium
interacts, as above, with the contaminant, the quantity or strength
of the collecting medium in the dosimeter should be sufficient to
interact completely with the total quantity of gaseous contaminant
which is anticipated to be collected. The collecting medium will
often be specific to the particular gaseous contaminant being
monitored. Examples, meant to be representative but not limiting,
include aqueous solutions of oxidizing agents or triethanol amine
to absorb nitrogen dioxide, solutions of potassium or sodium
tetrachloromercurate to absorb sulfur dioxide, and solutions of
sulfuric or other acids to absorb ammonia. Charcoal or powdered
carbon of high surface-area, powders of metals or metal salts, or
films can be used to adsorb may organic contaminants.
Methods for colorimetric analysis, for example, for sulfur dioxide,
nitrogen dioxide, and ammonia, in air, are described in National
Institute for Occupational Safety and Health method numbers
160(publication 121, 1975), 108 (publication 136, 1974), and
205(publication 121, 1975), respectively. The techniques therein
described are readily adaptable with respect to absorbing solution
and color-forming reagents for use in the dosimeter of the present
invention.
One embodiment of the present invention is shown in FIGS. 2 and 3
and is described and can be formed as follows. A base sheet 7 of
impermeable polymeric material, which is preferably pliable, is
provided with at least one depression 6. Normally, there will be
several depressions 6 which can be linearly spaced along a
periphery of the sheet 7 as shown. The sheet is preferably
transparent and thermoplastic and can be made of polymers of
olefin, halogenated polymers, polyester, or ionomer resins.
Preferred materials are shown in U.S. Pat. No. 3,264,272 issued
Aug. 2, 1966 to R. W. Rees. They are the ionic copolymers of
alpha-olefins and alpha, beta-ethylenically unsaturated carboxylic
acids of 3-8 carbon atoms having 10-90% of the carboxylic acid
groups neutralized with metal ions.
The size of sheet 7 is not critical but is preferably a size easily
adaptable for use in a personal dosimeter which is to be worn or
readily carried. The depressions 6 can easily be formed by applying
pressure to sheet 7 with an appropriate die, heated or
otherwise.
Pre-measured amounts of reagents are placed in any convenient
manner in the depressions 6. The collecting medium is placed in the
central portion of sheet 7. When the collecting medium is a liquid,
this can be more easily accomplished by first forming a depression
in the central portion of the sheet in a manner similar to that
used in the formation of depressions 6. This central depression is
normally larger than any of depressions 6.
After the reagents and collecting medium have been placed on sheet
7, a second, top sheet 8 corresponding to sheet 7 in composition
and substantially in size is placed over sheet 7. Heat and pressure
are then applied to the areas 4 surrounding the reagent-containing
depressions 6 with, for example, a conventional heat-sealing die,
thereby forming separate compartments for each reagent. The seals
along areas 4 are purposely made breakable by carefully controlling
the heat input or by forming only a narrow seal. Specifically, the
formation of the seals can be controlled to provide seals capable
of being later ruptured by the application of pressure to the
reagents in the compartments. Alternatively, adhesives or other
forms of bonding can be used, provided that rupturable bonds are
formed in these areas. Heat and pressure are then applied to the
three areas 3 to provide permanent, fluid-tight bonding at the
three corresponding edges of sheets 7 and 8.
An elongate gas diffusion device 1 having a plurality of
through-and-through channels 2 is positioned parallel and proximate
to the fourth, unbonded edge of base sheet 7 and parallel and flush
with the fourth, unbonded edge of top sheet 8. The open channels 2
of diffusion device 1 are thus oriented horizontally with respect
to the plane of sheet 7 and perpendicularly with respect to the
fourth edges of sheets 7 and 8. The diffusion device 1, thus
sandwiched between sheets 7 and 8, is bonded to said sheets by the
application of heat and pressure or by use of adhesives which
should be impermeable and chemically inert to the collecting medium
and reagents.
The bond between diffusion device 1 and each of sheets 7 and 8
should be liquid-tight and air-tight, thus completing the formation
of reaction chamber 5, this chamber being the interior of the
sealed receptacle formed between sheets 7 and 8 and containing the
collecting medium. The relative positions of diffusion device 1 and
sheets 7 and 8 are such that channels 2 provide the only
communication between the atmosphere and the interior of reaction
chamber 5.
It is also possible to form the dosimeter of FIGS. 2 and 3 saving
the placement of the reagents and collecting medium, when these are
liquids, for last. In such a case, the dosimeter is otherwise
formed as described above. The reagents and collecting medium can
be placed by piercing top sheet 8 at an appropriate spot with a
hypodermic needle and injecting a measured amount of the collecting
medium or reagent into the appropriate chamber or compartment. The
holes made by the hypodermic needle can then be thermally
sealed.
Diffusion device 1 allows the gaseous contaminant to diffuse
through each of channels 2 according to Fick's Law, which is
expressed in relevant form as
where
M=quantity of gaseous contaminant transferred (mg)
D=diffusion coefficient of the gaseous contaminant through air
(cm.sup.2 /min)
C=concentration of the contaminant in the atmosphere
(mg/cm.sup.3)
t=time of exposure (minutes)
A=cross-sectional area of the channel (cm.sup.2)
L=distance in direction of diffusion, herein channel length
(cm)
Values of D for various gaseous contaminants are readily available
from the literature. The purely diffusional nature of the transfer
of the gaseous contaminant through the channels, at a rate in
linear proportion to its atmospheric concentration, provides the
integrating character of the dosimeter.
Gas diffusion device 1 is preferably made from materials that are
non-hygroscopic and both chemically and physically inert to the
gaseous contaminant and to the collecting medium. Examples are
polyethylene, polypropylene, polymers or copolymers of
tetrafluoroethylene and hexafluoropropylene, and stainless steel.
The above-named polymers are preferred since they can be easily
injection-molded.
As can be seen from Fick's Law, the number and diameter of the
channels affect the quantity of gaseous contaminant collected since
they affect the total cross-sectional area available for transfer.
The quantity of contaminant collected is also inversely
proportional to the length of the channels. Although these
parameters are not necessarily critical to the integrating
operation of the diffusion device, it has been found that the use
of about 5-500 channels, preferably 10-100 channels each having a
diameter of about 50-1000 microns and a length of about 1.0-25.0
mm, preferably 3.0-8.0 mm, provides a device that is sufficiently
sensitive to low ambient contaminant concentrations but is still of
a conveniently small size.
Optionally, a porous, hydrophobic film of 15-1000 micron thickness
can be placed over the channel openings on the interior side 11 of
diffusion device 1, the side communicating with the interior of
reaction chamber 5. The film can be made, for example, of polymers
or copolymers of tetrafluoroethylene and hexafluoropropylene. The
function of the film is to prevent the absorbing solution, if that
form of collecting medium is used, from flowing into the channels
of diffusion device 1. Accordingly, the porosity of the film and
the size of its pores should be selected so that this function is
performed without interfering with the passage of the gaseous
contaminant from the interior ends of the channels to the absorbing
solution. That is, the diffusion of gaseous contaminant through
this film should be significantly greater than the diffusion
through the channels so that the overall rate of diffusion is
essentially controlled only by the channels. It has been found that
a film that is 50-80% porous with a pore size of 0.1-3.0 microns is
sufficient for this purpose when channels as previously-described
are used.
Other gas diffusion devices that can be used in the dosimeter of
this invention are gas-permeable, liquid-impermeable membranes
through which the gaseous contaminant can diffuse. Any of the
conventionally known membranes are suitable for use herein with the
proviso that the membrane be selected such that the rate of
diffusion of the gaseous contaminant therethrough varies linearly
with the atmospheric concentration of the contaminant through a
broad range of such concentrations. This insures that a dosimeter
using such membrane will integrate effectively. Where, for example,
a membrane passes a quantity of gas at high atmospheric
concentrations that is disproportionate to the amount passed at
lower concentrations, the correlation between the final quantity
collected and the average concentration in the atmosphere is
destroyed. The membranes are normally about 10-300 microns in
thickness and can be made, for example, of silicone rubber,
polytetrafluoroethylene, or copolymers of silicone and
polycarbamate.
A dosimeter of the present invention in which such a membrane is
used as the gas diffusion device is shown in FIG. 4. The
construction and description of this dosimeter are basically the
same as was described with respect to the dosimeter of FIGS. 2 and
3 but with the following changes. In addition to sheets 7 and 8
being sealed along areas 3 as in FIGS. 2 and 3, sheets 7 and 8 of
this dosimeter are also sealed in a similar manner on the fourth
side 3a, completing the formation of reaction chamber 5.
Top sheet 8, forming a boundary of reaction chamber 5, is provided
with a rectangular opening that is overlaid by a
correspondingly-shaped membrane 10 of the kind previously
described. A fastener 9, having the shape of the outline of a
rectangle, overlays membrane 10 such that the rectangularly-shaped
opening through fastener 9 exposes membrane 10 to the atmosphere.
Fastener 9 is of the same material as sheet 8 and can be bonded
thereto in a fluid-tight manner by the application of heat and
pressure. Membrane 10 is thus sealed into top sheet 8 and provides
the only communication between the atmosphere and the interior of
reaction chamber 5.
In addition to the gas diffusion devices described herein, other
devices usable in the present dosimeter are any of those that allow
diffusion, or permeation, of the gaseous contaminant therethrough
at a rate that varies linearly with the atmospheric concentration
of the contaminant. For example, hollow fibers of the kind
described in co-pending application Ser. No. 922,546 filed July 7,
1978 can be used.
Except for the inclusion of a diffusion device, the receptacle of
the present dosimeter is substantially similar to the test pack
shown in U.S. Pat. No. 3,476,515 issued Nov. 4, 1969. The
disclosure of this patent is incorporated by reference herein.
In use, the dosimeter is exposed to the air containing the gaseous
contaminant for a period of time for which the average contaminant
concentration is sought. After exposure, the selected reagent
compartments, containing the reagents necessary for analysis, are
broken, their contents being released into the reaction chamber and
mixed with the collecting medium therein. Breaking of the
compartment is most easily accomplished by the application of
pressure thereto, for example, by finger squeezing. The reagents
and collecting medium can be thoroughly mixed by application of a
light, pulsing force by the fingers on the pliable sheets forming
the reaction chamber.
Since the dosimeter is pliable and transparent, the contents of the
reaction chamber can be analyzed directly without withdrawing a
sample from the dosimeter. For analysis to be made photometrically,
the dosimeter can be clamped in a position where electromagnetic
radiation can be directed through the contents of the reaction
chamber with the unabsorbed (i.e., transmitted) radiation being
directed to an appropriate detector. The preferred method is to use
reagents which change the color of the collecting medium, depending
on the amount of gaseous contaminant collected, and then analyzing
with radiation in the range of visible light using a colorimeter or
spectrophotometer.
The dosimeter of this invention can be calibrated to give a direct
relationship between colorimetric or spectrophotometric readings
and average ambient concentration of the gaseous contaminant. This
can be accomplished by following a calibration procedure similar to
that described in co-pending application Ser. No. 922,546, filed
July 7, 1978. In such a procedure, several dosimeters are exposed
over a given period of time to various known concentrations of a
contaminant for which calibration is sought. The dosimeters contain
the same kinds and amounts of collecting medium and reagents.
Spectrophotometric readings, for example, are determined for at
least two dosimeters at each of several known concentrations, and a
straight-line is plotted, using a least-squares analysis, through
the data points thus obtained.
* * * * *