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Claims  |
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What is claimed is:
1. A composition of matter useful for sensing the concentration of an ionic
component in a medium, comprising:
a matrix material having a cationic or anionic charge therewithin; and
a sensing component chemically bonded to said matrix material and being
effective to provide a signal in response to the presence of said ionic
component in said medium;
wherein said matrix material has sufficient cationic or anionic charge
distributed within said matrix material such that the apparent ionic
concentration sensed by said sensing component within said matrix material
is higher or lower than the actual ionic concentration in said medium.
2. The composition of claim 1 wherein said sensing component is covalently
bonded to said matrix material.
3. The composition of claim 1 wherein said ionic component is H.sup.+ or
OH.sup.-.
4. The composition of claim 1 wherein said signal varies as the
concentration of said ionic component in said medium varies.
5. The composition of claim 1 wherein said sensing component is an optical
indicator.
6. The composition of claim 1 wherein said sensing component is a
fluorescence indicator.
7. The composition of claim 1 wherein said matrix material is polymeric.
8. A composition of matter useful for sensing the concentration of an ionic
component in a medium, said composition comprising a combination of at
least two of:
(1) a matrix material having a cationic charge therewithin and a first
sensing component within said cationic matrix material, said first sensing
component within said cationic matrix material being effective to provide
a signal in response to the presence of said ionic component in said
medium in a first concentration range;
(2) a substantially nonionic matrix material and a second sensing component
within said nonionic matrix material, said second sensing component within
said nonionic matrix material being effective to provide a signal in
response to the presence of said ionic component in said medium in a
second concentration range; and
(3) a matrix material having an anionic charge therewithin and a third
sensing component within said anionic matrix material, said third sensing
component within said anionic matrix material being effective to provide a
signal in response to the presence of said ionic component in said medium
in a third concentration range;
wherein said first, second, and third sensing components are made from the
same indicator material.
9. The composition of claim 8 wherein said first, second, and third sensing
components are chemically bonded to said cationic, substantially nonionic,
and anionic matrix materials, respectively.
10. The composition of claim 8 wherein said first, second, and third
sensing components are covalently bonded to said cationic, substantially
nonionic, and anionic matrix materials, respectively.
11. The composition of claim 8 comprising the combination of all of (1),
(2), and (3).
12. The composition of claim 8 wherein said first, second, and third
sensing components are optical indicators made from the same optical
indicator material.
13. The composition of claim 8 wherein said first, second, and third
sensing components are fluorescence indicators made from the same
fluorescence indicator material.
14. The composition of claim 8 wherein said ionic component is H.sup.+ or
OH.sup.-.
15. An apparatus for measuring the concentration of an ionic component in a
medium, comprising:
sensor means including a matrix material having a cationic or anionic
charge therewithin, and a sensing component chemically bonded to said
matrix material and being effective to provide a signal in response to the
presence of said ionic component in said medium, wherein said matrix
material has sufficient cationic or anionic charge distributed within said
matrix material such that the apparent ionic concentration sensed by said
sensing component within said matrix material is higher or lower than the
actual ionic concentration in said medium; and
signal means capable of transmitting said signal from said sensing
component.
16. The apparatus of claim 15 wherein said sensing component is covalently
bonded to said matrix material.
17. The apparatus of claim 15 wherein said ionic component is H.sup.+ or
OH.sup.-.
18. The apparatus of claim 15 wherein said signal varies as the
concentration of said ionic component in said medium varies.
19. The apparatus of claim 15 wherein said sensing component is an optical
indicator.
20. The apparatus of claim 19 wherein said signal means comprises an
optical fiber.
21. The apparatus of claim 15 wherein said sensing component is a
fluorescence indicator.
22. The apparatus of claim 21 wherein said signal means comprises an
optical fiber.
23. An apparatus for measuring the concentration of an ionic component in a
medium, comprising:
sensor means including a combination of at least two of:
(1) a matrix material having a cationic charge therewithin and a first
sensing component within said cationic matrix material, said first sensing
component within said cationic matrix material being effective to provide
a signal in response to the presence of said ionic component in said
medium in a first concentration range; (2) a substantially nonionic matrix
material and a second sensing component within said nonionic matrix
material, said second sensing component within said nonionic matrix
material being effective to provide a signal in response to the presence
of said ionic component in said medium in a second concentration range;
and (3) a matrix material having an anionic charge therewithin and a third
sensing component within said anionic matrix material, said third sensing
component within said anionic matrix material being effective to provide a
signal in response to the presence of said ionic component in said medium
in a third concentration range; wherein said first, second, and third
sensing components are made from the same indicator material; and
signal means capable of transmitting said signals from said first, second,
and third sensing components.
24. The apparatus of claim 23 wherein said first, second, and third sensing
components are chemically bonded to said cationic, substantially nonionic,
and anionic matrix materials, respectively.
25. The apparatus of claim 23 wherein said first, second, and third sensing
components are covalently bonded to said cationic, substantially nonionic,
and anionic matrix materials, respectively.
26. The apparatus of claim 23 wherein said sensor means includes the
combination of all of (1), (2), and (3).
27. The apparatus of claim 23 wherein said ionic component is H.sup.+ or
OH.sup.-.
28. The apparatus of claim 23 wherein said first, second, and third sensing
components are optical indicators made from the same optical indicator
material.
29. The apparatus of claim 28 wherein said signal means comprises an
optical fiber.
30. The apparatus of claim 23 wherein said first, second, and third sensing
components are fluorescence indicators made from the same fluorescence
indicator material.
31. The apparatus of claim 30 wherein said signal means comprises an
optical fiber.
32. A method for sensing the concentration of an ionic component in a
medium, comprising:
contacting said medium with a composition comprising:
a matrix material having a cationic or anionic charge therewithin; and
a sensing component chemically bonded to said matrix material and being
effective to provide a signal in response to the presence of said ionic
component in said medium;
wherein said matrix material has sufficient cationic or anionic charge
distributed within said matrix material such that the apparent ionic
concentration sensed by said sensing component within said matrix material
is higher or lower than the actual ionic concentration in said medium; and
analyzing said signal to determine the concentration of said ionic
component in said medium.
33. The method of claim 32 wherein said sensing component is covalently
bonded to said matrix material.
34. The method of claim 32 wherein said ionic component is H.sup.+ or
OH.sup.-.
35. The method of claim 32 wherein said signal varies as the concentration
of said ionic component in said medium varies.
36. The method of claim 32 wherein said sensing component is a fluorescence
indicator.
37. The method of claim 32 wherein said matrix material is polymeric.
38. The method of claim 32 wherein said sensing component is an optical
indicator.
39. The method of claim 38 wherein said signal is transmitted prior to
being analyzed.
40. The method of claim 39 wherein said signal is transmitted by an optical
fiber.
41. A method for sensing the concentration of an ionic component in a
medium, comprising:
contacting said medium with a composition comprising a combination of at
least two of:
(1) a matrix material having a cationic charge therewithin and a first
sensing component within said cationic matrix material, said first sensing
component within said cationic matrix material being effective to provide
a signal in response to the presence of said ionic component in said
medium in a first concentration range; (2) a substantially nonionic matrix
material and a second sensing component within said nonionic matrix
material, said second sensing component within said nonionic matrix
material being effective to provide a signal in response to the presence
of said ionic component in said medium in a second concentration range;
and (3) a matrix material having an anionic charge therewithin and a third
sensing component within said anionic matrix material, said third sensing
component within said anionic matrix material being effective to provide a
signal in response to the presence of said ionic component in said medium
in a third concentration range; wherein said first, second, and third
sensing components are made from the same indicator material; and
analyzing said signal or signals provided by said sensing components to
determine the concentration of said ionic component in said medium.
42. The method of claim 41 wherein said composition comprises the
combination of all of (1), (2), and (3).
43. The method of claim 41 wherein said first, second, and third sensing
components are chemically bonded to said cationic, substantially nonionic,
and anionic matrix materials, respectively.
44. The method of claim 41 wherein said first, second, and third sensing
components are covalently bonded to said cationic, substantially nonionic,
and anionic matrix materials, respectively.
45. The method of claim 41 wherein said first, second, and third sensing
components are fluorescence indicators made from the same fluorescence
indicator material.
46. The method of claim 41 wherein said ionic component is H.sup.+ or
OH.sup.-.
47. The method of claim 41 wherein said first, second, and third sensing
components are optical indicators made from the same optical indicator
material.
48. The method of claim 47 wherein each said signal is transmitted prior to
being analyzed.
49. The method of claim 48 wherein each said signal is transmitted by an
optical fiber. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a system for sensing ionic components. More
particularly, the invention relates to compositions, apparatus and methods
useful for sensing ionic components, e.g., hydrogen or hydroxyl
ions-measured by pH, in fluids, such as blood.
It is often advantageous to determine the concentration of an ionic
component in a given fluid. For example, medical diagnostic and/or
treatment procedures may involve the determination of the pH value of a
patient's blood or other bodily fluid. Such determinations may be made
very frequently, even continuously, during treatment.
One problem which has arisen is that any one ionic component indicator,
e.g., pH indicator, is effective over only its "effective indicator
range", i.e., a limited range of concentrations of the ionic component,
e.g., a limited pH range, where reliable determinations can be obtained
using the given indicator. For example, each pH indicator has a unique pKa
associated with a unique pH response range. Therefore, each pH indicator
is useful over a limited pH range, e.g., of about one pH unit. Thus, if
the concentration of the ionic component in a given medium is outside the
"effective indicator range", reliable concentration determinations cannot
be obtained without changing the indicator. A pH indicator, e.g., dye,
with an appropriate pKa is needed for each pH range of interest. A
different indicator, e.g., dye, with a different pKa is needed outside
this range. It would be advantageous to use an indicator outside its
"effective indicator range". For example, in the medical area, it may be
useful to employ an indicator in the physiological range even though its
normal "effective indicator range" is located outside this range.
Indicators are often used in combination with matrix materials, such as
polymeric materials. For example, Seitz et al U.S. Pat. No. 4,548,907
teaches the use of a pH sensitive fluorophor
(8-hydroxy-1,3,6-pyrenetrisulfonic acid) which is electrostatically bound
to an ion exchange membrane, such as an anion exchanger. Seitz et al uses
the ion exchange membrane to immobilize the fluorophor to measure
physiological pH's by a ratioing technique.
Edwards U.S. Pat. No. 3,449,080 teaches a device for measuring the level of
electrolyte in body fluid for diagnostic purposes which comprises a
carrier containing a polymeric material having ion exchange
characteristics which is capable of exchanging ions with the electrolyte
whose level is to be measured, and a material which is color responsive to
the extent of the ion exchange. In effect, the species the color of which
the material is color responsive to is the product of the ion exchange.
Wang U.S. Pat. No. 4,473,650 also discloses a system in which an ion
exchange product is used to measure a characteristic of a test sample.
Sommer et al U.S. Pat. No. 4,543,335 discloses a method for preparing a
device for the quantitative determination of heparin in mammalian blood
plasma which involves coating a carrier matrix with a fluorogenic or
chromogenic substrate solution. Buffer is included in two layers of the
device because the rate of thrombin enzymatic reaction is pH dependent.
The pH of the buffer in both layers is designed to maximize the reaction
of thrombin and the substrate.
Harper U.S. Pat. No. 3,904,373 teaches bound pH indicators which include
any complex comprising an organic species covalently coupled via a silane
coupling agent to a carrier, preferably an inorganic carrier having
available hydroxyl or oxide groups. Such inorganic carriers include glass
silica gel, colloidal silica, woilastonite, and bentonite. Harper does not
teach carriers which are anionic or cationic after the coupling. Further,
Harper lists a large number of pH indicators, thus impliedly suggesting
that each indicator is to be used for a different pH range. Harper does
not teach extending the effective range of any pH indicator.
For biological fluids, a prior known sensor uses the fluorescent properties
of a dye in conjunction with the ionic permeability of a preformed
integral cellulose membrane sheet. In this sensor, the cellulose membrane
is chemically treated so as to introduce covalent bondable groups onto the
membrane. The dye is then covalently bonded to these groups to adhere the
dye to the membrane. Substantially all the covalently bondable groups
introduced onto the membrane are used to covalently bond the dye to the
membrane. Thus, the dye is adhered to a substantially nonionic matrix
material. A small disk is cut from the membrane sheet and is attached to a
cassette in association with an optical fiber bundle also attached to the
cassette. When the dye is excited by excitation light imposed on the dye
along the fibers, it undergoes fluorescence, emitting a wavelength of
light at a different wavelength than the excitation wavelength. The
emission light is measured as an indication of the pH.
SUMMARY OF THE INVENTION
A new system for sensing or measuring the concentration of an ionic
component in a medium has been discovered. This system, e.g. composition
of matter, apparatus and method, utilizes at least one ionically charged
matrix material to control the ionic environment to which an ionic
component indicator or sensing component is exposed. Ultimately, the
sensing component combined with an ionically charged matrix material is
able to effectively sense or measure concentrations of ionic components
over a broader concentration range and/or over a different concentration
range relative to the same sensing component combined with a nonionic or
ionically neutral matrix material. By controlling the charge density of
the matrix material, the concentration range over which a given sensor is
effective can be changed, as desired. Thus, a given indicator can be used
to provide reliable concentration determinations even at concentrations
which are outside the "effective concentration range" of the indicator.
In one broad aspect, the invention involves a composition of matter useful
for sensing or measuring the concentration of an ionic component in a
medium. This composition comprises a cationic or anionic matrix material
and a sensing component chemically bonded, preferably covalently bonded,
to the matrix material and being effective to provide a signal in response
to the presence of the ionic component in the medium. An apparatus for
measuring the concentration of an ionic component in a medium comprises a
sensor means including the above-noted composition and signal means
capable of transmitting the signal from the sensing component.
In another broad aspect, the invention involves a mixed composition useful
for sensing or measuring the concentration of an ionic component in a
medium. This composition comprises a combination of at least two of: (1) a
cationic matrix material and a first sensing component associated
therewith and being effective to provide a signal in response to the
presence of the ionic component in the medium in a first concentration
range; (2) a substantially nonionic matrix material and a second sensing
component associated therewith and being effective to provide a signal in
response to the presence of the ionic component in a second concentration
range; and (3) an anionic matrix material and a third sensing component
associated therewith and being effective to provide a signal in response
to the presence of the ionic component in the medium in a third
concentration zone. Preferably, the first, second and third sensing
components are substantially identical. An apparatus for measuring the
concentration of an ionic component in a medium comprises a sensor means
including this mixture and a signal means capable of transmitting signals
from the sensing components.
The present invention is particularly useful in sensing the concentration
of hydrogen ions (H+) or hydroxyl ions (OH.sup.-). In this embodiment, the
pH of the medium is the most often determined.
The signal provided by the sensing component or components in response to
the presence of the ionic component in the medium preferably varies as the
concentration of the ionic component in the medium varies. The sensing
component is preferably an optical indicator, more preferably an
absorbance indicator or a fluorescence indicator. Many sensing components
useful to provide a signal in response to the presence of ionic components
are conventional and well known in the art.
Any suitable sensing component may be employed in the present invention,
provided that such sensing component can be effectively chemically bound
to the desired matrix material. Suitable pH sensing components include
many well known pH indicators and/or functionalized derivatives of such
indicators. Among these pH indicators are hydroxypyrenetrisulfonic acid
and salts thereof, phenolphthalein, fluorescein, phenol red, cresol red,
pararosaniline, magenta red, xylenol blue, bromocresol purple, bromophenol
blue, bromothymol blue, metacresol purple, thymol blue, bromophenol blue,
tetrabromophenol blue, brom-chlorphenol blue, bromocresol green,
chlorphenol red, o-cresolphthalein, thymolphthalein, metanil yellow,
diphenylamine, N,N-dimethylaniline, indigo blue, alizarin, alizarin yellow
GG, alizarin yellow R, congo red, methyl red, methyl orange, orange I,
orange II, nile blue A, ethyl bis (2,4-dinitrophenyl) acetate,
gamma-naphthoibenzein, methyl violet 6B, 2,5-dinitrophenol, and/or the
various functionalized derivatives of the above species. Even when an
indicator cannot be chemically bound unchanged with retention of indicator
activity, one or more of its derivatives can often be chemically bound
with satisfactory results.
Sensing components for other ionic components can be made from organic
species which include fluorescein, diiodo-fluorescein, dichlorofluorescin,
phenosafranin, rose bengal, eosin I bluish, eosin yellowish, magneson,
tartrazine, eriochrome black T and others.
The preferred pH indicator selected from the group consisting of
hydroxypyrenetrisulfonic acid, derivatives thereof and mixtures thereof.
The cationic and/or anionic matrix material useful in the present invention
is preferably substantially insoluble in the medium being sensed or
analyzed. Also, the matrix material should be permeable to the ionic
component being sensed. That is, the matrix material should be structured
s that the ionic component being sensed can physically permeate the matrix
material. It should be noted that the charges on the matrix material may
act to repel the ionic component. However, even in such event, the matrix
material should be physically structured to be permeable to the ionic
component, i.e., so that, the ionic component can substantially freely
permeate the matrix material.
The matrix material is preferably a polymeric material. In one embodiment,
the matrix material comprises a base polymer and a plurality of anionic or
cationic groups, as desired. For example, the base polymer may be
derivatized to chemically bond cationic or anionic groups to the base
polymer. Macromolecular hydrophilic polymers which are substantially
insoluble and permeable to the ionic component of interest are useful as
base polymers in systems to be used in aqueous media. Such base polymers
include, for example, cellulose, high molecular weight polyvinylalcohol
(i.e., PVA), polyurethanes, quaternarized polystyrenes, sulfonated
polystyrenes, polyacrylamides, polyhydroxyalkyl acrylates, polyvinyl
pyrrolidones, hydrophilic polyamides, polyesters and mixtures thereof. In
systems used to measure pH, cellulose, high molecular weight PVA and
mixtures thereof are preferred.
The base polymer can be made anionic or cationic in character, as desired,
using conventional and well known techniques. For example, the base
polymer, or a functionalized derivative thereof may be reacted with an
acidic component, such as an organic sulfonic acid, a carboxylic acid and
the like, to form an anionic matrix material; or may be reacted with a
basic component, such as an organic amine and the like, to form a cationic
matrix material. Also noted above, such anionic and cationic matrix
materials can be produced using conventional and well known procedures.
Therefore, such procedures need not be discussed in detail here.
Chemical bonding of the sensing component to the matrix material can be
accomplished either by direct coupling of the sensing component to
reactive sites on the matrix material, as for instance, the hydroxyl
groups on either cellulose or PVA, or through indirect coupling utilizing
a substituent group which is coupled or chemically bound to the matrix
material. For example, alkylamines can be first joined to at least a
portion of the hydroxyl groups on the cellulose backbone by forming an
ether between the alkyl portion of the alkylamine and the cellulose
backbone. This leaves the amino functionality of the alkylamine available
for reaction with the sensing component, e.g., dye, to join the sensing
component to the matrix material or backbone. The use of alkylamines also
acts to impart cationic character to the matrix material. The amount of
alkyl amine employed can be controlled, as desired, to impact the desired
degree of cationic character to the matrix material.
It is preferred to form a covalent bond between the optical indicator and
the matrix material, either directly or indirectly through a substituent
group. This assures that the sensing component is fixedly and irreversibly
bound to the matrix material for improved performance of the sensor.
The substituent groups utilized in conjunction with the matrix materials
are preferably organic and more preferably contain about 2 to about 20
carbon atoms. These substituent groups may be straight chain aliphatic,
branched chain aliphatic, cyclo aliphatic or aromatic, or mixed
aliphatic/aromatic. The substituent groups may include additional groups
located thereon which are hydrophilic such as --OH, --NO.sub.2, carboxyl,
sulfonate or the like. In one embodiment, the substituent group is a
aminoalkyl group. Preferably the aminoalkyl group includes about 2 to
about 8, more preferably 2 or 3, carbon atoms.
In one embodiment, the starting material for the matrix material is a
solid, finely divided polymeric material, e.g., a powder. However, the
starting material for the matrix material may be present in a different
state, such as a liquid. For convenience however, utilization of a solid
powder polymeric material is preferred.
The sensing component is preferably an optical indicator, more preferably
either an absorbance or a fluorescence indicator sensing component.
Particularly good results are obtained with fluorescence indicators. For
use with a pH sensor, sensing components such as hydroxypyrenetrisulfonic
acid and its salts, fluorescein and beta-methylumbelliferone are
preferred.
For an illustrative pH sensor of this invention, cellulose is utilized as
the polymeric material. Aminoethylated cellulose is commercially available
in a powdered form, as for instance from Sigma Chemical, St. Louis, Mo. If
desired, free amine groups can be generated on aminoethylated cellulose.
For example, if commercial aminoethylcellulose is utilized, the material
as received from the manufacturer can be first treated to generate free
amine groups. This is easily accomplished by simply treating the
aminoethylcellulose with a sodium carbonate solution and drying.
The hydroxypyrenetrisulfonic acid, hereinafter referred to as HPTS, is
first converted into an active species. It is of course realized that this
material could be used as the free acid or as a suitable salt, e.g., an
alkali metal salt or an alkaline earth metal salt. For use with
aminoethylcellulose or other aminoalkylcellulose, a suitable active
species is a sulfonic acid chloride. The HPTS is first acetylated to
protect the hydroxy function of the HPTS and then it is converted to a
suitable acid chloride.
The acid chloride derivative of the HPTS is reacted with
aminoethylcellulose to covalently bond the HPTS to the cellulose backbone
material utilizing sulfonylamido linkages. As is evident from the reaction
of an acid chloride with an amine, hydrochloric acid is generated as a
byproduct. This byproduct hydrochloric acid tends to react with other
amine groups on the aminoethylcellulose. In view of this, the HPTS can be
stepwise reacted with the aminoethylcellulose by first treating with a
first batch of the HPTS acid chloride followed by treating this product
with sodium carbonate solution, and further reacting with additional HPTS
acid chloride. It is evident that the desired amount of HPTS which is to
be loaded onto the cationic cellulose can be controlled by either
stoichiometric control of the amount of HPTS which is added to any
particular amount of cellulose or by control of the stepwise reaction
noted above.
If desired, some of the amino groups can be blocked to control the cationic
character of the matrix material. This blocking can be conveniently done
by acetylating these amines, e.g., by utilizing an acetyl blocking group.
Blocking substantially all of the remaining amino sites results in a
substantially nonionic matrix material to which is covalently loaded a
sensing component.
A stronger positively charged matrix material can be obtained by
quaternarizing the unreacted amino groups on the matrix material.
Conventional and well known quaternarizing reactions, e.g., utilizing
alkyl halides such as methyl iodide, may be employed to produce quaternary
amino groups on the matrix material. Such quaternarization preferably
takes place after the cellulose matrix is regenerated. To increase the
density of positively charged groups on the matrix more aminoalkyl groups
can be introduced into the cellulose matrix by known methods.
If desired, an anionic matrix material may be utilized. Such an anionic
matrix material may be produced by reacting the unreacted amino groups on
the aminoalkyl cellulose (after chemically bonding the sensing component)
with a di-functional acid derivative, such as a dicarboxylic acid
anhydride or chloride. Again, to increase the density of anionic groups on
the matrix additional aminoalkyl groups can be introduced into the matrix
which can be reacted further with the difunctional acid derivatives.
The degree of cationic or anionic character of the matrix material can be
controlled by controlling the density of aminoalkyl groups on the
cellulose, and/or controlling the degree of quaternarization or acid
reaction, respectfully, to which the aminoalkyl cellulose is subjected.
For strongly cationic matrices, such as found in commercially available ion
exchange resins, it may not necessary to covalently bond HPTS. Due to the
multianionic character of HPTS, ionic bonding may be sufficiently stable.
The matrix can be formed on the optical surface and then dipped into a
solution containing HPTS to form the sensing element.
Once the sensing component has been chemically bound to the matrix
material, the material is preferably taken up into the solution. With
cellulose, three basic types of solutions can be formed. The first of
these is based on inorganic complexes, the second is based upon organic
complexes and the third utilizes hemi esters or sulfur complexes.
The cellulose can be regenerated from any of these solutions by acid
treatment. Such acid treatment typically entails utilizing a diluted acid
such as the common mineral acids, e.g., sulfuric acid and the like.
In any event, after the cellulose is solubilized, an appropriate aliquot of
the solubilized cellulose is then loaded onto an optical surface of an
optical fiber or on an optical surface which interfaces with the optical
fiber. The solubilized polymeric material is then regenerated so as to
form a solid matrix of the sensing component-containing cellulose material
on the optical surface of the optical fiber.
If desired, additional solubilized polymeric material can be added to the
existing regenerated material already on the optical surface of an optical
fiber. The further addition is followed by a further regeneration acid
dip. This allows for the build up of a final matrix of a precise
dimension. Since the solubilized cellulose adheres to both the regenerated
cellulose matrix and to the glass of the optical fiber, it is possible to
repeatedly add new aliquots of solubilized cellulose onto the existing
regenerated cellulose to stepwise build up a sensor of any desired
dimension.
For increased ion permeability of the final polymeric matrix on the end of
the optical fiber, permeability enhancing agents can be added. These
generally will be added either in the solvent for the cellulose, the
regeneration solution for the cellulose or both of these. Suitable for use
as such permeability enhancing agents are low molecular weight molecules
which are hydrophilic and are water soluble. Such compounds include
sugars, polyols and the like. For instance, glycerol can be added to both
a solvent solution for the cellulose and to an acid regeneration bath.
Another specific suitable permeability enhancing agent is low molecular
weight water soluble PVA.
After regeneration of the cellulose on the optical fiber, the cellulose can
be quaternarized or reacted with di-functional acid anhydrides or
chlorides to obtain the desired cationic or anionic character. After this,
the cellulose on the optical fiber can be overcoated with a suitable
overcoating material serving to enhance certain properties of the sensor.
An overcoat material would be chosen so as to be ionic component permeable
as is the cellulose. Suitable for an overcoating material would be
cellulose which is impregnated with carbon black and the like.
In use, the sensor on the end of an optical fiber is positioned in the
appropriate test solution. If a fluorescent sensing component is utilized,
an excitation light wavelength from a light source is channeled down the
fiber toward the sensor. The light strikes the sensing component and the
sensing component fluoresces and emits an emission light which is
dependent on the concentration of the component of interest to which the
sensing component is exposed. The emission light is then channeled back up
the fiber to a light sensor for electrical readout of the same. This
procedure is similar to that described in Lubbers et al, U.S. Pat. No. Re.
31,879 and Heitzmann, U.S. Pat. No. 4,557,900 each of which is
incorporated in its entirety by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic illustration of a sensor apparatus according to the
present invention.
FIG. 2 is an enlarged, fragmentary sectional view of an alternate
embodiment of the sensor apparatus shown in FIG. 1.
FIG. 3 is a side elevational view, partly broken away, showing a composite
bundle of overcoated sensors.
FIG. 4 is an end elevational view in section about the line 4--4 of FIG. 3.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a suitable physical sensor 10 of the invention. An optical
fiber 12 is connected to an appropriate light transmitting apparatus 14.
The light transmitting apparatus 14 generates the excitation light. The
optical fiber 12 is also connected to a light receiving apparatus 16. The
light receiving apparatus 16 receives and analyzes the emission light from
the fluorescent dye as is described in the above referenced Lubbers et al
and Heitzmann patents.
Located on the optical surface 18 of the fiber 12 is a cationic polymeric
matrix 20, as for instance, a cellulose matrix containing HPTS as a
fluorescent pH indicator and quaternary amino groups to provide matrix 20
with the desired degree of cationic character. The matrix 20 adheres to
the optical surface 18 and slightly down along the sides 22 of the end of
the fiber 12. An opaque overcoating 24 can then be applied over the
totality of the matrix 20 and down further along the side 22 of the fiber
12.
In use, the optical fiber 12 bearing the matrix 20 and the overcoat 24
thereon is placed in an appropriate solution. Excitation light of an
appropriate wavelength from the light transmitting apparatus 14 is fed to
the fiber 12. This interacts with the HPTS in the matrix 20 causing the
HPTS to fluoresce. The emission light from the fluorescence is fed to
light receiving apparatus 16.
The cationic character of matrix 20 tends to repel H.sup.+ ions so that the
pH in matrix 20 is increased relative to the pH in the solution. For
example, when the pH in the solution is 6, the pH in the matrix is 7; and
when the pH in the solution is 7, the pH in the matrix is 8. By using
matrix 20 of controlled cationic character, one can effectively measure
the pH of a solution having a pH in the range of 6 to 7 with a pH
indicator having a range of 7 to 8 pH. In effect, the controlled ionic
character of the matrix 20 allows one to controllably change the effective
range of a pH indicator.
The present invention can be further illustrated by a matrix 20 which is
anionic in character, having a controlled amount of free sulfonic acid or
carboxylic acid groups. This anionic matrix 20 tends to attract H.sup.+
ions so that the pH in matrix 20 is decreased relative to the pH in the
solution. Thus, when the pH in the solution is 8 to 9, the pH in the
anionic matrix 20 is 7 to 8, respectively. The anionic character of matrix
20 allows one to controllably change the effective range of the HPTS pH
indicator from 7 to 8, to 8 to 9.
As appreciated by those of ordinary skill in the art, the cationic and
anionic matrix materials set forth in the present specification and
examples have cationic or anionic charge which is distributed within and
throughout the matrix materials. As appreciated from the discussion above,
the cationic or anionic charge of the matrix materials of the present
invention is sufficient such that the apparent ionic concentration sensed
by the sensing component within such matrix materials is either higher or
lower (depending upon whether or not the matrix is cationic or anionic)
than the actual ionic concentration in the tested medium.
The sensor 10 as is evident from FIG. 1 is of a size domain approximately
that of the optical fiber 12. Thus, typically, the sensor 10 would only be
slightly larger than a typical 125 micron diameter fiber. The thickness of
the matrix 20 would be chosen so as to be approximately three to four mils
thick.
FIG. 2 illustrates an embodiment of a sensor structured similarly to sensor
10 except that cationic polymeric matrix 20 is replaced by a hydrophilic
matrix material 21 which includes cationic polymeric particles 23,
nonionic polymeric particles 25 and anionic polymeric particles 27
randomly distributed throughout. Except as expressly stated herein, the
sensor illustrated in FIG. 2 is structured and functions identically to
the sensor 10 illustrated in FIG. 1.
Hydrophilic matrix material 21 can be any ionpermeable polymeric material
which is compatible with the other components of the system. Examples of
such materials include polyacrylamides, hydrogels, cellulose,
polyurethanes, PVA and the like. The cationic polymeric particles 23 and
anionic polymeric particles 27 can be produced in a manner similar to th | | |
