Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR THE COLORIMETRIC QUANTIFICATION O~: IONS.
FIELD OF THE INVENTION
This invention relates to a method for the
colorimetric quantification by visual or densitometric
means of selected, targeted ions in a solution which
are first selectively and quantitatively trapped in a
porous matrix or membrane having a suitable ion
recognition substrate.
BACKGROUND OF THE INVENTION
Current methods for the quantification and or
separation and removal of inorganic ions at low, i.e.
sub ppm, levels such as transition metal cations of
hi h Pb2+ Hg2+ Mn2+ Fe2+, Fe3+, Co2, Ni , Cu , Cu ,
Zn2, Cd2+, Hg2+, Pd2+, Aso43-, Aso33-, Sn2+, Sn4, Au , Au3,
Ag , Rh3, Ru3, Ir3, Bi3, SbO+, Ga3, Al3, Tl , Tl3, F,
I and Br- are illustrative, from aqueous solutions
which may also contain high levels of other cations,
including H+, and anions do not provide the levels of
precision that modern technology requires without the
use of large and expensive instruments such as the
inductively coupled plasma (ICP), inductively coupled
plasma-mass spectroscopy (ICPMS), graphite furnace
atomic absorption spectroscopy (graphite furnace AA)
or preconcentrative ion chromotography
(preconcentrative IC). These prior art methods may
also have insufficient detection limits due to their
lack of preconcentration. The preconcentrative IC
method employs ion exchange resins and/or organic
ligands adsorbed onto silica gel, packed into glass or
plastic columns. Purification methods that employ a
packed column technique must maximize several
interrelated parameters in order to be useful. The
type of packing must be selected to perform the
desired function, e.g., cation exchange resin for the
exchanging of Mg2+ for Na+. The particle size must be
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optimized to present the largest surface area to the
solution to be cleaned and yet, if the particle size
becomes too small, e.g. less than 60 microns, the flow
of test solution is slowed below acceptable limits.
Particle packing presents a second problem in that
when particles are packed, interparticle spaces and
channels are formed. The interparticle spaces allow
target ions from the test solution to pass through the
column without being trapped. One solution to this
problem has been to increase the volume of the packing
material used, thereby increasing the probability that
all ions will contact a trapping molecule or moiety.
However this alternative presents cost considerations,
as well as the realistic limitations on the physical
size of a column. One solution to such a problem is
to place the column under extreme pressure, thereby
compressing the interparticle spaces. In conjunction
with high pressure it has been found that small
particles e.g. ~2 micron, could be efficiently used
because the high pressure forced the flow rate into
- acceptable ranges. Although high pressure liquid
chromatography, HPLC, does allow for significant
chemical separation, the method presents additional
problems associated with the use of liquids under high
pressures. The most significant problem with HPLC
columns, as pertains to the present invention, is the
limited volume and speed at which an HPLC column will
produce results. Typical pressures range between ~2-
25 atmospheres, with corresponding flow rates measured
in mL/h. If one were to analyze a test solution of 10
to 20 liters using HPLC, thousands of hours would be
required.
The problems found in the prior art can be
summarized by the offsetting relationship between the
desire for small particle size and thereby larger
surface area and the desire for a faster flow rate
through the particles. The fastest flow rates are
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achieved through the use of large particles, whereas
better selectivity and efficiency are obtained through
the use of small particles, but then the flow rate is
prohibitively slow or requires high pressure. The
limitations mentioned, as well as others, have
prevented the formulation of a rapid method for the
quantification and isolation of targeted ions from
solution. Furthermore, the costly and heavy equipment
required have made these analyses difficult to perform
in the field.
In addition to the need for rapid flow of a large
volume of solution, the solid phase extraction resin
must also selectively and efficiently bind the ion of
interest. Effective methods for the concentration and
quantification of a selected ion from a solution that
will often contain a variety of ions, both cationic
and anionic, across a wide pH range, represents a real
need in the modern era of advanced technologies. A
significant improvement in the art does exist which
provides for the concentration and/or removal of a
selected ion from a solution using an organic
recognition ligand that is covalently bound, through
an organic spacer, to a solid support such as silica
gel, glass beads, alumina, titania, zirconia nickel
oxide, polyacrylate, or polystyrene. The organic
ligand provides for coordinative or chelative ion
bonding with significant levels of selectivity. The
combination of organic ligand and solid support
provides for the incorporation of the ion recognition
substrate into a column for subsequent use much as
pure silica gel is used in column chromatography. By
passing a solution containing ions, wherein one ion
is desired to be trapped to the exclusion of any other
ions, through a column containing a suitable ion
recognition substrate designed to trap the targeted
ion, the targeted ion is selectively and exclusively
removed from the test solution. The trapped ion may
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be flushed or "un-trapped" by passing a second
solution through the column. The second solution is
formulated such that it has a greater affinity for the
trapped ions than the ion trap does, allowing for the
trapped ions to be flushed from the column. In this
manner the targeted ion is selectively removed from
any other ions in the test solution.
Ion selective or recognizing substrates
comprising ion binding organic ligands covalently
attached to solid supports through organic spacers,
such as described above, are illustrated in numerous
patents, of which the following are representative:
U.S. Patent No. 4,952,321 to Bradshaw et al. discloses
amine-containing hydrocarbon ligandsi U.S. Patent Nos.
5,071,819 and 5,084,430 to Tarbet et al. disclose
sulfur and nitrogen-containing hydrocarbons as ion-
binding ligands; U.S. Patent Nos. 4,959,153 and
5,039,419 to Bradshaw et al. disclose sulfur-
containing hydrocarbon ligands; U.S. Patent Nos.
4,943,375 and 5,179,213 to Bradshaw et al. disclose
ion-binding crowns and cryptands as ligandsi U.S.
Patent No. 5,182,251 to Bruening et al. discloses
aminoalkylphosphonic acid-containing hydrocarbon
ligands; U.S. Patent No. 4,960,882 to Bradshaw
discloses proton-ionizable macrocyclic ligands; U.S.
Patent No. S,078,978 to Tarbet et al. discloses
pyridine-containing hydrocarbon ligandsi U.S. Patent
No. 5,244,856 to Bruening et al. discloses
polytetraalkylammonium and polytrialkylamine-
containing hydrocarbon ligands; U.S. Patent No.
5,173,470 to Bruening et al. discloses thiol and/or
thioether-aralkyl nitrogen-containing hydrocarbon
ligands; and U.S. Patent No. 5,190,661 to Bruening et
al. discloses sulfur-containing hydrocarbon ligands
also containing electron withdrawing groups. These
ligands are generally attached to the solid support
via a suitable hydrocarbon spacer.
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However, if it is desired to know the quantity of
the target ion in the test solution using ion-binding
organic ligands covalently attached to solid supports
through an organic spacer, several problems present
themselves. Although the methods disclosed in the
above patents provide a manner through which a
targeted ion may be selectively and exclusively
removed from a test solution, no method is provided
whereby the trapped, targeted ions may be quantified.
One method to obtain quantification of the ions might
be to weigh the ion recognizing substrate before and
after use. Employment of a weight difference method
would be highly unreliable due to small differences in
large weight values. A second weight difference
calculation would involve the weight of the product
obtained through use of the above column. This
calculation suffers from the same source of error as
the previous weight difference method, namely the
calculated difference in weight would be a small
difference on large numbers. More particularly the
weight of the targeted ion may be as little as 1
microgram (~g), compared to a flask which might weigh
300 grams providing that the differences in weight
would be 300.0000 gms compared to 300.0001 gms. Even
under precision balance techniques 1 microgram is
smaller that the margin of error on the balance.
One solution to the column packing problem is
presented in U.S. Patent Nos. 4,153, 661 and 5,071,610
wherein is provided a method for the suspension of
particles in a porous, fibrillated
polytetrafluoroethylene (PTFE) sheet. This method
provides a particle-loaded sheet having uniform
porosity. U.S. Patent No. 4,810,381 relates to a
chromatcgraphic article of the '610 patent.
Particle-loaded nonwoven fibrous articles useful
for separations have been disclosed in U.S. Patent
Nos. 5,328,758 and 5,498,478.
... .. . ..
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U.S. Patent No. 3,971,373 discloses webs of blown
microfibers, preferably polyolefin webs, and particles
incorporated in such webs by known procedures. Glass
and ceramic nonwoven webs are known and particles can
be incorporated in such webs as is known in the art;
see, for example, WO 93/01494. Non-woven webs made
from large-diameter fibers are also known.
Particle-loaded solid phase extraction sheets for
direct measurement of radioactivity have been
disclosed in International Application No.
PCT/US95/13107 (International Publication No. WO
96/14931).
OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION
It is an object of the present invention to
provide a method for the detection and quantification
of a target ion regardless of the concentration of the
target ion or the concentration of other ions in the
test solution, by passing the test solution through a
porous web, such as a disk or membrane, containing
enmeshed ion-recognition substrates with subsequent
optional color development of the disk or membrane and
colorimetric analysis of the disk or membrane by
visual or densitometric means.
It is a further object of the present invention
to provide a method whereby the concentration of a
selected ion, which may be present in as little as sub
parts per trillion (ppt) levels, in a test solution
that may also contain other charged ions in much
greater concentration than the ion of interest, may be
determined with speed and precision.
It is also an object of this invention to provide
a method whereby the ions that have been caused to be
selectively and exclusively trapped by an ion
recognition moiety in the web, e.g., disk or membrane,
form a color or are subsequently caused to chemically
react with a developer substance which has been
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selected so as to selectively react chemically with
the targeted ion to produce a colored product.
It is a further object of this invention that
even when the targeted ion is present in the solution
to be tested in only trace amounts, the ion
recognition substrate enmeshed in a three dimensional
porous web will function exclusively and selectively
capture the targeted ion.
It is an additional object of this invention that
the selected developer will produce a visually or
densitometrically detectable product from the reaction
between the developer and the ion captured in the disk
of a diameter of about 20 mm if the amount of the
captured ion in the disk or membrane is at least 1 ~g.
An additional object of the present invention is
to provide a method whereby the trapped, targeted ion
which has been caused to form a colored product
through reaction with the ion-selective moiety or a
developer, may be densitometrically detected and
quantified through visual comparison, densitometric or
other known means with equipment sufficiently light
weight and inexpensive to be used in the field.
These and other objects are accomplished by means
of first passing a measured volume of solution
containing the targeted ion as well as other ions that
are desired to remain undetected, through a porous web
into which has been enmeshed an ion recognizing
substrate, which substrate was selected because it
would selectively and exclusively trap the targeted
ion, for example through ionic or covalent bonds,
chelation, complexation, or organo-metal dative bonds.
The ions that are trapped by or in the web can be (a)
self-colored through interaction with the ion
recognition substrate or (b) subjected to a second
solution or mixture that contains a developer, which
may be colorless or of a different color, but that has
been chosen because at least a component thereof will
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selectively react with the targeted ion or, because of
the presence of the targeted ion, cause the formation
of a colored or color changed product. The density of
the color, which density can be correlated to the
concentration of the targeted ion in the measured or
sampled volume of original solution, may then be
quantified through either visual comparison or
densitometric techniques.
Due to the porous nature of the web, the solution
is exposed to a large surface area of the supported
ion recognition substrate allowing optimum contact and
capture of the targeted ions by the corresponding ion
recognition substrate. If the binding of the targeted
- ion to the ion recognition substrate does not cause
the formation of a quantifiable color, a suitable
organic or inorganic developer is brought into contact
with the porous web and at least a component of the
developer reacts with the captured ions to produce a
visually detectable color whose density is a function
of the amount of ion present in the measured volume of
solution. The color is detectable at low targeted ion
concentrations of analytical interest.
More particularly, this invention pertains to a
method for the detection and quantification of the
ions of a selected element or complex which are
present in a solution or mixture that may contain
other ions in much greater concentration than the ion
of interest. Targeted ions are separated from the
starting or test solution by first selectively and
quantitatively trapping them by means of ion
recognition substrates enmeshed in a porous solid web
such as a disk or membrane. If a quantifiable color
is not developed by the trapping action of the ion
recognition substrate, the trapped ions may be caused
to chemically react with a developer that is known to
change color or become colored when reacted with the
targeted ions, which color can then be detected
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visually and/or densitometrically. The magnitude of
the color density detected can be correlated to the
concentration of the targeted ion in the test solution
sample. The associated apparatus used in carrying out
this method can be portable and sufficiently simple to
allow for field operation as well as in-house
laboratory use.
In this application "rapid" means the rate at
which an ion-containing solution may be passed through
a web without sacrificing selectivity or quantitative
capture of a targeted ion.
"Trace" means that the targeted ion can be
present in single digit parts per billion (ppb)
amounts.
"Ion" means any cationic or anionic charged
species.
"Web" and "matrix" are used synonymously to refer
to a porous sheet material comprising a three-
dimensional web or network which can be a fibrous
nonwoven polymer, fibrillated polymer, nonwoven
inorganic fibrous material such as glass or ceramic
materials, or a fibrous polymer pulp or a blend of
fibrous pulps or chemical modifications or blends of
any of the above.
~Membrane" means a sheet material which is a
solid with pores therein.
"Disk" means a sheet material having a regular
shape, preferably a circular shape.
"Enmeshed" or "embedded" or "trapped" are used
synonymously to refer to particulate forms of ion
recognition substrate which are physically contained
and held within a three-dimensional porous matrix,
disk or membrane.
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DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
INVENTION
In carrying out the present invention, an ion
recognition substrate is imbedded in a porous web in
the form of a disk or membrane.
The ion recognizing substrate is a combination of
an ion recognizing moiety covalently bound through an
organic spacer grouping to a solid inorganic or
organic polymer support.
The ion recognizing substrate may be represented
by the formula:
M-L-S
wherein M represents the ion recognition moiety or
ligand; L represents an organic spacer grouping and S
is a solid support. The ion recognition moiety or
ligand M is covalently bound to the spacer portion L
which is in turn covalently bound to the solid support
S.
The ion recognizing moiety ~M~ is selected from
organic ligands such as crown ethers, aza crowns,
thioether crowns, cryptands, polyamines,
polythioethers, polyamino acids, polyaminophosphonic
acids, polypyridine amines, polythiol amines, and
mixtures of the above which can selectively form
ionic, coordinate or chelate bonds with selected
specific ions.
Appropriately selected crown ether, aza crown,
thioether crown and cryptand ligand moieties "M" can
selectively bind targeted ions "T" such as Pb2+, Hg2+,
Mn2+ Fe2+ Fe3+ Co2+ Ni2+ Cu2+ Cu+ Zn2+ Cd2+ Hg2+
Pd2+, Aso43-, Aso33-, Sn2+, Sn4+, Au+, Au3+, Ag+, Rh3+, Ru3+,
Ir3+, Bi3+, SbO+, Ga3, Al3+, Tl+, Tl3+, F-, I- and Br-.
Typical crown ether, aza crown, thioether crown and/or
cryptand ligands, bound to solid supports, are
illustrated in U.S. Patent Nos. 4,943,375i 4,960,882;
5,179,213 and 5,3g3,892 which are incorporated herein
by reference.
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Appropriately selected polyamines,
polythioethers, polyamino acids, polyaminophosphonic
acids, polypyridine amines and polythiol amines "M"
can selectively bind targeted ions "T" such as Pb2+,
Hg , Mn , Fe , Fe , Co , Ni , Cu , Cu , Zn , Cd ,
Hg2+, Pd2+, Aso43-, Aso33-, Sn2+, Sn4+, Au+, Au3+, Ag+, Rh3+,
Ru3+, Ir3+, Bi3+, SbO+, Ga3+, Al3~, Tl+, Tl3+, F-, I-, and
Br~. Typical classes of these ligands, bound to solid
supports, are illustrated in the following patents
which are incorporated herein by reference; polyamines
(U.S. Patent 4,952,321); polypyridineamines (U.S.
Patent 5,078,978); polytetraalkylammonium and
polytrialkylamines ~U.S. Patent 5,244,856);
polyaminophosphonic acids (U.S. Patents 5,182,251 and
5,273,660); polythiolamines PU.S. Patents 5,071,819,
5,084,430 and 5, 173,470) and polythioethers (U.S.
Patents 4,959,153, 5,039,419 and 5,190,661.
In certain instances the trapped targeted ion
combined with the recognizing substrate may result in
a color change which is indicative of the
concentration of trapped ion in a measured volume of
solution. Hence, the use of a separate developer
solution may not be necessary. However, prior to the
present invention, there has been no available means
to use any such color change using an ion-recognizing
substrate as a ~uantification means.
The solid support "S" is an organic and/or
inorganic support material which is particulate or can
be made into particulate and has a particle size in
the range of between about 0.10 and 150 microns.
Preferably the particle size will be between about 1
and 100 microns and most preferably between about 1
and 40 microns. Typical solid support materials "S"
are selected from the group consisting of silica,
silica gel, silicates, zirconia, titania, alumina,
nickel oxide, glass beads, phenolic resins,
polystyrenes and polyacrylates. However, other organic
, . . .
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resins or any other hydrophilic organic and/or
inorganic support materials meeting the above criteria
can be used.
As noted above, the organic ion binding ligands
represented by M are attached to a solid support via a
suitable spacer L. U.S. Patents 4,943,375; 4,952,321;
4,959,153; 4,960,882; 5,039,419; 5,071,819; 5,078,978;
5, 084,430; 5,173,470; 5,179,213; 5, 182,251; 5,190,661;
5, 244,856; 5,273,660; and 5,393,892, referenced above,
disclose various spacers which can be used in forming
an organic ligand attached to a solid support as an
ion recognition substrate and are therefore
incorporated herein by reference.
When the solid support S is an inorganic material
such as silica, silica gel, silicates, zirconia,
titania, alumina, nickel oxide and glass beads the
spacer L may be represented by the formula:
z
-Si-x-
I
z
where X is a grouping having the formula:
~CH2)a (OCH2CHR CH2) b
wherein Rl is a member selected from the group
consisting of H, SH, OH, lower alkyl, and aryl; a is
an integer from 3 to about 10; b is an integer of 0 or
1. Each Z is independently selected from the group
consisting of Cl, Br, I, alkyl, alkoxy, substituted
alkyl or substituted alkoxy and S.
When the solid support S is an organic resin or
polymer, such as phenolic resins, polystyrenes and
polyacrylates, it will generally be a hydrophilic
polymer or polymer derivatized to have a hydrophilic
surface and contain polar functional groups. The ion
recognition moiety or ligand M will then generally
contain a functional grouping reactive with an
activated polar group on the polymer. The spacer L
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will then be formed by the covalant bonding formed by
the reaction between the activated polar group from
the polymer and the functional group from the ligand
and may be represented by formula:
-(CH2)d~(Y)~~(CH2)e~
where c is an integer or 0 or 1, d and e are
independently integers between 0 and 10 and Y is a
functional group or aromatic linkage such as an ether,
sulfide, imine, carbonyl, ester, thioester, amide,
thioamide, amine, alkylamine, sulfoxide, sulfone,
sulfonamide, phenyl, benzyl, and the like. Preferably
c is 1.
It is to be emphasized that the present invention
does not reside in the discovery of an ion selective
or ion recognizing substrate. Hence, it is not claimed
that M-L-S is novel. Rather, it is the discovery that
such substrates, in particulate form, can be enmeshed
in a porous web or matrix so as to enable the
selective trapping of the targeted ion "T" from a
measured solution sample by the ion recognizing
substrate when the solution sample is rapidly passed
through the porous web or matrix and that the trapped
ion can be visually or densitometrically quantified.
The ion recognizing substrate, in particulate
form, is enmeshed in the sheet material comprising a
porous matrix or membrane which can be a fibrous
nonwoven polymer such as polyolefin (e.g.,
polypropylene, polyethylene) and copolymers thereof,
polyacrylonitrile, fibrillated polymer such as
polytetrafluoroethylene (PTFE), nonwoven inorganic
fibrous matrix such as glass or ceramic materials, or
a fibrous polymer pulp or a blend of fibrous pulps
such as those comprising aramids such as poly (p- or
m-phenyleneterephthalamide) or chemical modifications
thereof, optionally blended, for example, with
polyolefin fibers, or polyacrylonitrile fibers, each
with ion recognizing substrate particles enmeshed
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therein. It is within the scope of this invention for
the porous matrix or membrane to comprise combinations
or chemical modifications of any of the forementioned
materials. The web or membrane preferably has a
thickness in the range of between about 0.05 to 5.0
mm, a pore size of between about 0.1 to 10 ~m and a
pore volume of between about 20 to 80 percent.
1. PTFE Pourous Web
In a more preferred embodiment, the present
invention provides an article having a composite
structure and method therefore, the composite
structure preferably being an essentially uniformly
porous, composite sheet comprised of ion recognition
substrate particles distributed essentially uniformly
throughout a matrix formed of intertangled,
polytetrafluoroethylene (PTFE) fibrils. In such a
structure, almost all of the ion recognition substrate
particles are separated one from another and each is
isolated and not adhered one to another in a cage-like
matrix that restrains the particle on all sides by a
fibrillated mesh of PTFE microfibers.
The preferred extraction sheet material of this
invention, which can comprise any of the porous
matrices disclosed above, when it is a single layer
of solid phase extraction medium or a disk, has a
thickness in the range of 0.05 to 5.0 mm, and has a
tensile strength of at least 20 KPa and even as high
as 700 KPa
Fibrous pulps can comprise main fibers surrounded
by many smaller attached fibrils, resulting in a high
surface area material. The main fiber generally can
have a length in the range of 0.8 mm to 4.0 mm, and an
average diameter in the range of less than 1 to 20 ~m,
preferably less than 1 to 12 ~m.
When the porous matrix is PTFE, the process for
making webs as used in the present invention can be as
.
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disclosed, for example, in U.S. Patent Nos. 4,153,661
and 5,071,610, which are incorporated herein by
reference. Specifically, the PT~E composite article
of the invention is prepared by mixing the particulate
or combination of particulates employed, PTFE and
lubricant, until a uniform mixture is obtained. PTFE
and lubricant can be added as a PTFE resin emulsion
which is commercially available from DuPont. It has
been found that to optimize separation techniques in
the resultant article, lubricant in the mixture, or
subsequently added lubricant, i.e., water or water-
based solvent or organic solvent, should be present
sufficient to be near or to exceed the lubricant
sorptive capacity of the particles preferably by at
least 3 weight percent up to 200 weight percent. This
range can be optimized for obtaining the desired mean
pore sizes for different types of ion recognition
particles and for the different types of separations
- to be performed. PTFE fibrils can have a diameter in
the range of 0.025 to 0.5 ~ms and an average diameter
less than 0.5 ~m.
Useful lubricants as well as blending, mixing,
and calendaring procedures are disclosed in U.S.
Patent Nos. 4,153,661 and 5,071,610, which are
incorporated herein by reference.
In other embodiments of the present invention,
the membrane (web) can comprise a solution-cast porous
membrane or a non-woven, preferably polymeric macro-
or microfibers which can be selected from the group of
fibers consisting of polyamide, polyolefin,
polyacrylamide, polyester, polyurethane, glass fiber,
polyvinylhalide, or a combination thereof. (If a
combination of polymers is used, a bicomponent fiber
can be obtained.) If polyvinylhalide is used, it
preferably comprises fluorine of at most-75 percent
(by weight) and more preferably of at most 65 percent
(by weight). Addition of a surfactant to such webs
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16
may be desirable to increase the wettability of the
component fibers.
2. Macrofibers
Macrofibrous webs can comprise thermoplastic,
melt-extruded, large-diameter fibers which have been
mechanically-calendered, air-laid, or spunbonded.
These fibers have average diameters in the general
range of 50 ~m to 1000 ~m.
Such non-woven webs with large-diameter fibers
can be prepared by a spunbond process which is well-
known in the art. (See, e.g., U.S. Patent Nos.
3,338,992, 3,509,009, and 3,528,129, which are
incorporated herein by reference, for the fiber
preparation processes of which are incorporated herein
by reference.) As described in these references, a
post-fiber spinning web-consolidation step (i.e.,
calendering) is required to produce a self-supporting
web. Spunbonded webs are commercially available from,
for example, AMOCO, Inc. (Naperville, IL).
Non-woven webs made from large-diameter staple
fibers can also be formed on carding or air-laid
machines (such as a Rando-WebberTM, Model 12BS made by
Curlator Corp., East Rochester, NY), as is well known
in the art. See, e.g., U.S. Patent Nos. 4,437,271,
4,893,439, 5,030,496, and 5,082,720, the processes of
which are incorporated herein by reference.
A binder is normally used to produce self-
supporting webs prepared by the air-laying and carding
processes and is optional where the spunbond process
is used. Such binders can take the form of resin
systems which are applied after web formation or of
binder fibers which are incorporated into the web
during the air laying process. Examples of such resin
systems include phenolic resins and polyurethanes.
Examples of common binder fibers include adhesive-only
type fibers such as KodelTM 43UD tEastman Chemical
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Products, Kingsport, TN) and bicomponent fibers, which
are available in either side-by-side form (e.g.,
Chisso ES Fibers, Chisso Corp., Osaka Japan) or
sheath-core form (e.g., MeltyTM Fiber Type 4080,
Unitika Ltd., Osaka, Japan). Application of heat
and/or radiation to the web "cures~' either type of
binder system and consolidates the web.
Generally speaking, non-woven webs comprising
macrofibers have relatively large voids, preferably
having a mean pore size in the range of 5.0 to 50
micrometers. Therefore, such webs have low capture
efficiency of small-diameter particulate (reactive
supports) which is introduced into the web.
Nevertheless, particulate can be incorporated into the
non-woven webs by at least four means. First, where
relatively large particulate is to be used, it can be
added directly to the web, which is then calendered to
actually enmesh the particulate in the web (much like
the PTFE webs described previously). Second,
particulate can be incorporated into the primary
binder system (discussed above) which is applied to
the non-woven web. Curing of this binder adhesively
attaches the particulate to the web. Third, a
secondary binder system can be introduced into the
web. Once the particulate is added to the web, the
secondary binder is cured (independent of the primary
system) to adhesively incorporate the particulate into
the web. Fourth, where a binder fiber has been
introduced into the web during the air laying or
carding process, such a fiber can be heated above its
softening temperature. This adhesively captures
particulate which is introduced into the web.
Of these methods involving non-PTFE macrofibers,
those using a binder system are generally the most
effective in capturing particulate. Adhesive levels
which will promote point contact adhesion are
preferred.
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Once the particulate (reactive supports) has been
added, the loaded webs are typically further
consolidated by, for example, a calendering process.
This further enmeshes the particulate within the web
structure. See U.S. Patent No. 5,328,758 for
consolidation techniques.
Webs comprising large diameter fibers (i.e.,
fibers which have average diameters between 50 ~m and
1000 ~m) have relatively high flow rates because they
have a relatively large mean void size.
3. Microfibers
When the fibrous web comprises non-woven
microfibers, those microfibers provide thermoplastic,
melt-blown polymeric materials having active
particulate dispersed therein. Preferred polymeric
materials include such polyolefins as polypropylene
and polyethylene, preferably further comprising a
surfactant, as described in, for example, U.S. Patent
No. 4,933,229, the process of which is incorporated
herein by reference. Alternatively, surfactant can be
applied to a blown microfibrous (BMF) web subse~uent
to web formation. Particulate can be incorporated
into BMF webs as described in U.S. Patent No.
3,971,373, the process of which is incorporated herein
by reference. Glass and ceramic nonwoven webs are
known and particles can be incorporated in such webs
as is known in the arti see, for example, WO93/01494,
which is incorporated herein by reference.
~icrofibrous webs of the present invention have
average fiber diameters up to 50 ~m, preferably from 2
~m to 25 ~m, and most preferably from 3 ~m to 10 ~m.
Because the void sizes in such webs range from 0.1 ~m
to 10 ~m, preferably from 0.5 ~m to S ~m, flow through
these webs is not as great as is flow through the
macroporous webs described above.
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19
In this embodiment of the present invention, the
particle-loaded fibrous article, which preferably can
be a microfibrous article, can be compressed to
increase its density and decrease interstitial
porosity and comprises in the range of 30 to 70 volume
percent fibers and particulate, preferably 40 to 60
volume percent fibers and particulate, and 70 to 30
volume percent air, preferably 60 to 40 volume percent
air. In general, pressed sheet-like articles are
disclosed in U.S. Patent No. 5,328,758, and they are
at least 20 percent, preferably 40 percent, more
preferably 50 percent, and most preferably 75 percent
reduced in thickness compared to unpressed articles.
The article comprises pores having a mean pore size in
the range of 0.1 to 10 micrometers, preferably 0.5 to
5 micrometers.
Blown fibrous webs are characterized by an
extreme entanglement of fibers, which provides
coherency and strength to an article and also adapts
the web to contain and retain particulate matter. The
aspect ratios (ratio of length to diameter) of blown
fibers approaches infinity, though the fibers have
been reported to be discontinuous. The fibers are
long and entangled sufficiently that it is generally
impossible to remove one complete fiber from the mass
of fibers or to trace one fiber from beginning to end.
4. Solution-Cast Porous Membranes
Solution-cast porous membranes can be provided by
methods known in the art. Such polymeric porous
membranes can be, for example, polyolefin, including
PTFE and polypropylene, and polyamide, polyester,
polyvinyl acetate, and polyvinyl chloride fibers.
Membranes that include ion recognition substrate
particles have sufficient porosity to allow passage of
fluids.
.
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5. Fibrous Pulps
When the porous matrix is a polymer pulp, sheet
materials can be prepared by dispersing the polymer
pulp(s) generally with particulate, preferably using a
blender, in the presence of a suitable liquid,
preferably water or water-miscible organic solvent
such as alcohol or water-alcohol. The dispersion is
poured through a fine screen preferably having pores
of about 0.14 mm (100 mesh) to provide a wet sheet,
which can then be pressed to remove additional liquid.
The sheet is then dried, preferably by heating, to
provide a dry sheet preferably having an average
thickness in the range of about 0.1 mm to less than 10
mm, more preferably 0.2 mm to 9 mm, even more
preferably 0.3 mm to 5 mm, and most preferably 0.4 mm
to 3 mm. Up to 100 percent of the liquid can be
removed, preferably up to 90 percent. Calendaring can
be used to provide additional pressing or fusing, when
desired. This general method is provided in U.S.
Patent No. 5, 026,456, which is incorporated herein by
reference. The sheet resembles porous, unglazed paper
that may have color, depending upon its components.
The color density of the sheet can be differentiated
by visual or by densitometric methods.
Generally, the fibers that make up the porous
polymeric pulp of the SPE sheet of the present
invention can be any pulpable fiber (i.e., any fiber
that can be made into a porous pulp). Preferred
fibers are those that are stable to radiation and/or
to a variety of pHs, especially very high pHs (e.g.,
pH = 14) and very low pHs (e.g., pH = 1). Examples
include polyamide fibers and those polyolefin fibers
that can be formed into a pulp including, but not
limited to, polyethylene and polypropylene. Aromatic
polyamide fibers and aramid fibers are particularly
preferred when stability to both radiation and highly
caustic fluids is desired. Examples of useful
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aromatic polyamide fibers are those of the nylon
family.
Suitable pulps for providing the sheet materials
of the present invention include aramid pulps,
preferably poly(p-phenyleneterephthalamide) (KevlarTM,
Dupont and polyacrylonitrile (PAN) and derivatives
thereof. KevlarTM fiber pulps are commercially
available in three grades based on the length of the
fibers that make up the pulp. Blends with polyolefin
pulps, such as at least one of polypropylene and
polyethylene, can be used to optimize the physical and
sorptive properties of the sheet materials. Ratios of
aramid pulps to polyolefin pulps can be in the range
of 1 to 100 weight percent to 99 to 0 weight percent,
preferably 10 to 90 weight percent to 90 to 10 weight
percent.
Regardless of the type of fiber(s) chosen to make
up the pulp, the relative amount of fiber in the
resulting SPE sheet (when dried) ranges from about
12.5 percent to about 30 percent (by weight),
preferably from about 15 percent to 25 percent (by
weight).
- Preferably, fibrous SPE sheets useful in the
invention comprise polymeric pulps, at least one
binder, and ion recognition particulate of the
invention. A binder is used to add cohesive strength
to the fibrous SPE sheet once it is formed by any of a
number of common wet-laid (e.g., paper-making)
processes.
Useful binders in the SPE sheets of the present
invention are those materials that are stable over a
range of pHs (especially high pHs) and that exhibit
little or no interaction (i.e., chemical reaction)
with either the fibers of the pulp or the particles
entrapped therein. Polymeric hydrocarbon materials,
originally in the form of latexes, have been found to
be especially useful. Common examples of useful
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binders include, but are not limited to, natural
rubbers, neoprene, styrene-butadiene copolymer,
acrylate resins, and polyvinyl acetate. Preferred
binders include neoprene and styrene-butadiene
copolymer. Regardless of the type of binder used, the
relative amount of binder in the resulting SPE sheet
(when dried) is about 3 percent to about 7 percent,
pre~erably about 5 percent. The preferred amount has
been found to provide sheets with nearly the same
physical integrity as sheets that include about 7
percent binder while allowing for as great a particle
loading as possible. It may be desirable to add a
surfactant to the fibrous pulp, preferably in small
amounts up to about 0.25 weight percent of the
composite.
Desirably, the average pore size of the uniformly
porous sheet material can be in the range of 0.1 to 10
~m. Void volumes in the range of 20 to 80% can be
useful, preferably 40 to 60%. Porosity of the sheet
materials prepared from polymer pulp can be modified
(increased) by including adjuvant hydrophilic or
hydrophobic fibers, such as polyacrylonitrile,
polypropylene or polyethylene fibers of larger
diameter or stiffness which can be added to the
mixture to be blended. Fibers can have an average
size (diameter) of up to 20 ~m, and up to an average
length of 4 mm; preferably any adjuvant fibers added,
for example, to control porosity, are non-sorptive.
Up to 99 weight percent of the total fiber content can
be adjuvants.
When the binding of the targeted ion "T" to the
ion recognition substrate "M-L-S" does not result in
the formation of a quantifiable color, a solution
containing a suitable organic or inorganic developer
"D" must be brought into contact with the porous disk
or membrane in order for the developer, or a component
thereof, to react with the trapped targeted ions "T"
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to produce a visually detectable color whose density
is a function of the amount of ion present over the
detection range in the volume of solution passed
through the disk or membrane. The volume or
concentration of the solution can be adjusted so that
the color density falls with the detection limits of
the method.
A second solution containing a developer "D" is
chosen because a component of the developer will react
chemically with the trapped targeted ion "T", which is
now bound to the ion recognition substrate "M-L-S"
enmeshed in the porous web or membrane, to produce a
densitometrically detectable change. The color
producing developing reaction is caused to take place
in the disk or membrane.
Suitable developers "D" include Na2S, dithizone,
ammonia, ethylene diamine, 4-(2-
nitrophenylazo)resorcinol, pyridylimidazole, 2-(4-
nitrophenylazo)chromotropic acid and the like which
may be dissolved or suspended in solvents such as
water, lower alkanols or other solvents. Typically, a
concentration of about 0.001 to 0.03M of the developer
is sufficient to bring about the desired effect. The
color is formed by precipitation, chelation, or
similar reactions known in the art. The requirement of
the developer "D" is that it, or a component thereof,
form a color when in contact with the targeted ion "T"
quantitatively preconcentrated in a membrane
containing an ion recognition substrate such that a
color is formed that is differentiable from the normal
color of the membrane and developer solution. If
needed, the excess developer can be washed out of the
membrane prior to the densitometric analysis or
reading of the color.
The colored complex formed can be represented by
any of formulae:
M-L-S-T, M-L-S-T-D, and T-D
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24
where M is the ion recognition moiety, L is an organic
spacer group and S is a solid support, all as defined
above. M-L-S thus represents the ion recognition
substrate, T is the targeted ion which can be captured
by the ion recognition substrate, and D is the
developer or component of developer which causes the
formation of the colored complex.
Such colored complex (M-L-S-T-D, M-L-S-T, or T-D)
remains on and in the porous membrane or web, e.g., a
disk.
After the developing reaction has occurred, the
disk with the colored complex enmeshed therein is
submitted to visual or densitometric analysis from
which one skilled in the art can determine the
concentration of the targeted ion in the original test
solution.
Colorimetric analysis can be performed either by
comparing the color of the membrane having the
targeted ion quantitatively trapped thereon against
several visual standards present as a color chart, or
by reading the color density using, for example, a
Macbeth 1200 Series Densitometer ~Macbeth Corp., New
Windsor, NY) or a Beta Color Densitomer ~Beta
Industries, Carlstadt, NJ) against the values on the
same meter for several known standards. Meter
readings can also involve reading the disk against a
blank or known standards for a calibration curve.
Colorimetric analysis by visual means can be
accomplished with the help of a color comparison chart
which can be a preprinted rendition of distinguishable
color densities of a given colored complex over its
detection range.
A specific color comparison chart may be re~uired
for a given ion recognition substrate ~M-L-S), target
ion ~T) and developer ~D) combination. The color
comparison chart allows the analyst to match a color
density rendition to the color density of a disk after
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an amount of target ion has passed through the disk
and has caused a colored complex to form. The density
of the colored complex corresponds to the amount of
target ion (T) that is present.
Also preprinted on the color comparison chart in
numerical and alphanumerical form for each of the
color density renditions are the amount and the type
of the ion that would have to pass through the disk to
cause a corresponding color density to appear on the
disk.
The color comparison chart allows the analyst to
directly read the amount and type of ion in the
sample.
To facilitate the selection of appropriate disks
or membranes for a specific targeted ion, the name or
chemical symbol of the ion to be trapped by an ion
recognition substrate enmeshed in the disk or membrane
can be contained on the surface of the disk or
membrane. Preferably, this will be by means of
printing the appropriate name, symbol or other indicia
on the surface of the disk or membrane with a water
insoluble ink.
The following examples of selective binding,
removal, and subsequent color development of trace
level ions for analysis are given as illustrations.
These examples are illustrations only, and are not
comprehensive of the many analyses possible using the
process within the scope of this invention.
Example 1
In this example, a particulate ion selective
substrate available from IBC Advanced Technologies,
Inc., American Fork, Utah, under the tradename
Superlig~ 308 was used. In this ion selective
substrate, the ligand (M) was a polythioether, the
spacer (L) was -CH2-CH(OH)-CH2-CH2-CH2- and the solid
support (S) was silica gel. The ion selective
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26
substrate, having an average particle size in the
range of 8 to 10 microns, was embedded in circular
EmporeTM (PTFE) disks of 1.1 mm thickness and 2. 2 cm
effective diameter. The disks were placed in disk
holders, such as one provided by Baxter Scientific
Products catalog #F3074~ One liter (1000 ml)
samples of solutions, having Hg concentrations varying
from 5~g/Q to 500 ~g/Q, were passed individually
through the disks (one solution per one disk) at a
flowrate of 20 ml/min. using a peristaltic pump. Each
disk was then individually washed using 5 ml of 10-15
megaohm/cm water. Finally - 0.2 ml of 0.01 M Na2S
individual developer solution was placed on each disk.
A brown to gray Hg color was detectable with as little
as 5 ~g Hg which corresponds to 5 ~g/Q Hg in 1 liter of
feed solution. The Hg color density differences were
visually readily distinguished at various levels of 5
~g bound Hg up to 1000 ~g bound Hg. No variation in
developed color density was detected with any change
in Hg bound above 5 mg(5000,1lg~ which defined the upper
limit of the detection range for this disk. The upper
limit of the detection range can be extended by proper
dilution of the sample before analysis. Differences in
color densities were readily distinguishable between 5
~g, 10 ~g, 20 ~g, 50 ~g, 100 ~g, and 500 ~g.
Example 2
In this example the same ion selective substrate
(Superlig~308 from IBC Advanced Technologies, Inc.)
embedded in a circular EmporeTM disk as in Example 1
was used having 1.1 mm thickness and 1.0 cm effective
diameter. The disks were placed in disk holders as in
Example 1. These disks with a smaller effective
diameter than those in Example 1 were loaded with 10
~g and 100 ~g of Hg respectively. The disks were then
individually washed out using 5 mL of 10-15 megaohm
water. Finally ~0.2 mL of 0.1 M Na2S Individual
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developer solution was placed on each disk. As
expected, for a given mass loaded the brown to gray Hg
color density produced was more intense than the color
produced in Example 1.
Example 3
In this example, a particulate ion selective
substrate available from IBC Advanced Technologies,
Inc., American Fork, Utah, under the tradename
Superlig~ 601 was used. In this ion selective
substrate, the ligand ~M) was a crown ether, the
spacer (L) was -CH2-CH2-O-CH2- and the solid support
(S) was silica gel. The ion selective substrate,
having an average particle size in the range of 8 to
10 microns was embedded in circular EmporeTM (PTFE)
disks of 1.1 mm thickness and 2.2 cm effective
diameter. The disks were placed in disk holders as
shown in Example 1. Using appropriate feed
solutions and flow times, five disks were loaded with
1 ~g, 20 ~g, 100 ~g, and 1000 ~g, of Pb respectively.
These disks were color developed with 0.1 M Na2S. A
tan to brown Pb color was detectable with as little as
1 ~g Pb which corresponds to 1 ~g/~ Pb in the original
solution. The Pb color density could be visually
readily distinguished at levels of 1 ~g bound Pb up to
1000 ~g bound Pb at which level the Pb color density
was at or near full visual density. No variation in
developed color density was detected with any change
in Pb bound above 1000 ~g Pb which defined the upper
limit of the detection range for this disk. The upper
limit of the detection range can be extended by proper
dilution of the sample before analysis. Differences
in color density were readily distinguished at 5 to 10
~g intervals between 5 and 50 ~g. Spectrophotometric
measurements of the relative light intensity reflected
at the specular angle (using a zero to 100 calibration
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28
scale established with white and black surfaces) were
as follows: 96.7, 95.4, 89.5, 82,5, and 76Ø
Example 4
In this example, a particulate ion selective
substrate available from IBC Advanced Technologies,
Inc., American Fork, Utah, under the tradename
Superlig~ 304 was used. In this ion selective
substrate, the ligand (M) was a
polyamine, the spacer (L) was -CH2-CH(OH)-CH2-CH2-CH2-
and the solid support (S) was silica gel. The ion
selective substrate, having an average particle size
in the range of 8 to 10 microns, was embedded in
circular EmporeTM (PTFE) disks of 1.1 mm thickness and
2.2 cm effective diameter. The disks were placed in
disk holders as in Example 1. Solutions of 1000 ml
volume and varying Cu concentrations and also
containing 0.1 M sodium acetate were individually
passed through the disks at a flow rate of 20 ml/min.
using a vacuum. The disks were then washed out using
5 ml of 10-15 megaohm water. These disks naturally
turned blue due to reaction of the Cu with the amine
donor atoms present in the Superlig material. A blue
color was detectable with as little as 5 ~g Cu which
corresponds to 5 ~g/Q Cu in the original solution. The
blue color density could be visually readily
distinguished at levels of 5 ~g bound Cu up to 500 ~g
bound Cu at which level the color density was at or
near full visual intensity. No variation in color was
detected with any change in Cu bound above 5 mg which
defined the upper limit of the detection range for
this disk. The upper limit of the detection range can
be extended by proper dilution of the sample before
analysis. Differences in color density were readily
distinguished at 10 to 20 ~g intervals between 5 ~g
and 100 ~g Cu. Spectrophotometric measurements of the
relative light intensity reflected at the specular
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29
angle (using a zero to 100 calibration scale
established with white and black surfaces) were as
follows: 95.2, 94.3, 90.8, 83.9 and 72.8.
Various modifications and alterations of this
invention will become apparent to those skilled in the
art without departing from the scope and spirit of
this invention, and it should be understood that this
invention is not to be unduly limited to the
illustrative embodiments set forth herein.
.
