EP0910447A1

EP0910447A1 - Method for the colorimetric quantification of ions

Info

Publication number: EP0910447A1
Application number: EP97934036A
Authority: EP
Inventors: Ronald L. Bruening; Garold Lee Goken; Krzysztof E. Krakowiak; David Cameron Seely; Wolfgang Hans Strehlow
Original assignee: IBC Advanced Technologies Inc; Minnesota Mining and Manufacturing Co
Current assignee: IBC Advanced Technologies Inc; 3M Co
Priority date: 1996-07-12
Filing date: 1997-07-07
Publication date: 1999-04-28
Also published as: CA2256747A1; JP2000515968A; WO1998002224A1

Abstract

A method for the colorimetric quantification of a targeted ion from a source solution, which may contain other ions in greater concentrations, comprises bringing a measured volume of the source solution into contact with a porous web or membrane having enmeshed therein an ion recognition substrate which has a selective affinity for the targeted ion. The ion recognition substrate selectively and quantitatively traps the targeted ion, for example, through covalent, or ionic bonds, chelation, complexation or organo-metal dative bonds. Following removal of the source solution, the concentration of the targeted ion in the original solution, may be detected and quantified by, for example, visual comparison or densitometric techniques. The ions which are trapped in the web or membrane can be (a) self-colored through interaction with the ion recognition substrate or (b) subjected to a second solution whicn contains a developer. The developer, which may be colorless or of a different color, is chosen because it will 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 can be correlated to the concentration of the targeted ion in the measured source solution.

Description

METHOD FOR THE COLORIMETRIC QUANTIFICATION OF 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 which Pb²⁺, Hg^2*, Mn²\ Fe⁺, Fe³\ Co²⁺, Ni²⁴, Cu²⁺ , Cu\ Zn²⁺, Cd²⁺, Hg²⁺, Pd²⁺ , As0₄ ^3", As0₃ ^3~, Sn^2*, Sn\ Au\ Au³\ Ag⁺, Rh^3*, 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 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 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 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 ligands; 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 ligands; 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. 5,078,978 to Tarbet et al . discloses pyridine-containing hydrocarbon ligands; 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. 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 (μg) , compared to a flask which might weigh 300 grams providing that the differences in weight would be 300.0000 g s 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. 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 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 μg . 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 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 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. 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⁺ , Ni^2* , Cu²⁺ , Cu⁺ , Zn²⁺ , Cd²⁺ , Hg^: 2+

Pd²⁺ , As0₄ ^3" ^" , As0₃ ^3~ , Sn²⁺ , Sn⁴⁺ , Au⁺ , Au³\ Ag⁺ , Rh³⁺ , Ru³\

Ir³ , Bi³⁺ , SbO\ Ga³\ Al³\ Tl^* , Tl^3* , 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. 4,943,375; 4,960,882; 5,179,213 and 5,393,892 which are incorporated herein by reference. Appropriately selected polyamines, polythioethers, polyamino acids, polyaminophosphonic acids, polypyridine amines and polythiol amines "M" can selectively bind targeted ions "T" such as Pb^2*,

Hg^2* , Mn²⁺ , Fe^2* , Fe^3* , Co^2* , Ni^2* , Cii^2*, Cu^*, Zn^2*, Cd^2*,

Hg^2* , Pd^2* , As0₄ ^{3 "} , As0₃ ^3~ , Sn^2* , Sn^4* , Au^*, Au^3*, Ag^*, Rh^3*,

Ru^3* , Ir^3* , Bi^3* , SbO^* , Ga^3* , Al^3* , TTl⁺, Tl^3*, 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 ('U.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 quantification 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 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

where X is a grouping having the formula: ( CH₂ ) _a ( OCH₂CHR¹CH₂ ) _b wherein R¹ 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 CI, 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 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)_c-(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 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 μm 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 μm, preferably less than 1 to 12 μm.

When the porous matrix is PTFE, the process for making webs as used in the present invention can be as disclosed, for example, in U.S. Patent Nos. 4,153,661 and 5,071,610, which are incorporated herein by reference. Specifically, the PTFE 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 μms and an average diameter less than 0.5 μm.

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 may be desirable to increase the wettability of the component fibers .

2. Macrofibβrs 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 μm to 1000 μm. 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- ebber™, 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 Kodel™ 43UD (Eastman Chemical 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., Melty™ 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. 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 μm and 1000 μm) 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 subsequent 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 art; see, for example, WO93/01494, which is incorporated herein by reference. Microfibrous webs of the present invention have average fiber diameters up to 50 μm, preferably from 2 μm to 25 μm, and most preferably from 3 μm to 10 μm. Because the void sizes in such webs range from 0.1 μm to 10 μm, preferably from 0.5 μm to 5 μm, flow through these webs is not as great as is flow through the macroporous webs described above . 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 . 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 aromatic polyamide fibers are those of the nylon family.

Suitable pulps for providing the sheet materials of the present invention include ara id pulps, preferably poly (p-phenyleneterephthalamide) (Kevlar™, Dupont and polyacrylonitrile (PAN) and derivatives thereof. Kevlar™ 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 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, preferably 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 μm. 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 μm, 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" 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 dia ine, 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 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 required 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 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 substrate, having an average particle size in the range of 8 to 10 microns, was embedded in circular Empore™ (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 #F3074-1) . One liter (1000 ml) samples of solutions, having Hg concentrations varying from 5μg/0 to 500 μg/C, 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 μg Hg which corresponds to 5 μg/Q Hg in 1 liter of feed solution. The Hg color density differences were visually readily distinguished at various levels of 5 μg bound Hg up to 1000 μg bound Hg . No variation in developed color density was detected with any change in Hg bound above 5 mg(5000μg) 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 μg, 10 μg, 20 μg, 50 μg, 100 μg, and 500 μg .

Example 2 In this example the same ion selective substrate (Superlig®308 from IBC Advanced Technologies, Inc.) embedded in a circular Empore™ 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 μg and 100 μg of Hg respectively. The disks were then individually washed out using 5 mL of 10-15 megaoh water. Finally -0.2 mL of 0.1 M Na₂S Individual 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-CH₂-0-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 Empore™ (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 μg, 20 μg, 100 μg, and 1000 μg, 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 μg Pb which corresponds to 1 μg/C Pb in the original solution. The Pb color density could be visually readily distinguished at levels of 1 μg bound Pb up to 1000 μg 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 μg 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 μg intervals between 5 and 50 μg . Spectrophotometric measurements of the relative light intensity reflected at the specular angle (using a zero to 100 calibration scale established with white and black surfaces) were as follows: 96.7, 95.4, 89.5, 82,5, and 76.0.

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 Empore™ (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 a ine donor atoms present in the Superlig material. A blue color was detectable with as little as 5 μg Cu which corresponds to 5 μg/C Cu in the original solution. The blue color density could be visually readily distinguished at levels of 5 μg bound Cu up to 500 μg 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 g 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 μg intervals between 5 μg and 100 μg Cu. Spectrophotometric measurements of the relative light intensity reflected at the specular 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.

Claims

CLAIMSWe claim:

1. A method for the concentration and quantification of a targeted ion from a source solution which comprises a) bringing a measured volume of said source solution into contact with a porous web or membrane having enmeshed therein, in particulate form, an ion recognition substrate having an affinity for the targeted ion and thereby forming a complex between said targeted ion and said ion recognition substrate enmeshed in said web; b) removing said volume of said source solution from contact with said web; and c) determining the concentration of said targeted ion in said measured volume of source solution by means of colorimetric analysis of said targeted ion complexed to said ion recognition substrate enmeshed in said web.

2. The method according to Claim 1 wherein said targeted ion complexed to said ion recognition substrate results in a quantifiable color having density which correlates to the concentration of the targeted ion in the measured volume of source solution.

3. The method according to Claim 1 wherein, following step b) , a developer solution is brought into contact with said web or membrane wherein said developer interacts with said targeted ion complexed to said ion recognition substrate resulting in a quantifiable color having density which correlates to the concentration of the targeted ion in the measured volume of source solution.

4. The method according to Claim 1 wherein said ion recognition substrate has the general formula:

M-L-S wherein M is an ion recognition moiety, L is an organic spacer and S is a solid support and wherein M is covalently bound to L which is in turn covalently bound to S, and wherein S is a particulate having a particle size of between about 0.1 and 150 microns.

5. The method according to Claim 4 wherein M is a member selected from the group consisting of crown ethers, aza crowns, thioether crowns, cryptands, polyamines, polythioethers, polyamino acids, polyaminophosphonic acids, polypyridine amines, polythiol amines, and mixtures thereof.

6. The method according to Claim 5 wherein S is a member selected from the group consisting of silica, zirconia, titania, alumina, nickel oxide, glass beads, phenolic resins, polystyrenes and polyacrylates.

7. The method according to Claim 6 wherein said web or membrane is a porous sheet material selected from the group consisting a fibrous nonwoven polymer; a porous membrane; a fibriHated polymer; a nonwoven inorganic fibrous material; a fibrous polymer pulp; or a blend of fibrous polymer pulps; or combinations and chemical modifications of any of the foregoing.

8. The method according to Claim 7 wherein S is member selected from the group consisting of silica, silica gel, silicates, zirconia, titania, alumina, nickel oxide and glass beads and L is represented by the formula: Z

I -Si-X- z I where X is a grouping having the formula:

(CH₂)_a(OCH₂CHR¹CH₂)_b wherein R¹ 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 and each Z is independently selected from the group consisting of CI, Br, I, alkyl, alkoxy, substituted alkyl or substituted alkoxy and S.

9. The method according to Claim 7 wherein S is member selected from the group consisting of phenolic resins, polystyrenes and polyacrylates and L is represented by the formula:

-<CH₂)_d-(Y)_c-(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 and benzyl with the proviso that at least one of c, d or e must be at least 1.

10. The method according to Claim 9 wherein c is 1.

11. The method according to Claim 1 wherein said web or membrane 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 μm and a pore volume of between about 20 to 80%.

12. The method according to Claim 1 wherein said targeted ion is an ion selected from the group consisting of Pb^2* , Hg^2* , Mn²⁺ , Fe^2* , Fe^3* , Co^2* , Ni^2* , Cu^2*

Cu^* , Zn^2* , Cd^2* , Hg^2* , , Pd^2* , , As0₄ ^3" , As0₃ ^{3 "} , Sn^2* , Sn^4* , Au^* ,

Au^3* , Ag^* , Rh^3* , Ru^3* , , lr³⁺ , , Bi^3* , , SbO^* , Ga³ \ Al³ '^*, TΓ

Tl^3* , F\ I^" and Br^" .

13. The method according to Claim 3 wherein said developer solution contains a developer selected from the group consisting of Na₂S, dithizone, ammonia, ethylene diamine, 4- (2-nitrophenylazo) resorcinol, pyridylimidazole, and 2- (4-nitrophenylazo) chromotropic acid.

14. The method according to claim 7 wherein said web or membrane comprises aramid polymer pulp.

15. The method according to Claim 7 wherein said web or membrane is a polyolefin.

16. The method according to Claim 7 wherein said web or membrane is polytetrafluoroethylene .

17. The method according to Claim 1 wherein said colorimetric analysis consists of visually comparing the density of the quantifiable color against visual standards present as a color chart.

18. The method according to Claim 1 wherein said colorimetric analysis consists of reading the density of the quantifiable color on a densitometer and comparing said reading against the values on the same meter for known standards.

19. The method according to Claim 1 wherein said web or membrane is a disk and said disk comprises water insoluble indicia on a surface thereof indicative of the targeted ion that can be concentrated or quantified by said disk.

20. The method according to Claim 19 wherein said indicia is the chemical name of said targeted ion .

21. The method according to Claim 19 wherein said indicia is the chemical symbol of said targeted ion.

22. A colored complex having any of the formulae : M-L-S-T, M-L-S-T-D, and T-D where

(a) wherein M is an ion recognition moiety covalently bound to L; L is an organic spacer which is in turn covalently bound to S; and S is a particulate solid support having a particle size of between about 0.1 and 150 microns;

(b) T is a targeted ion, selectively trapped, by means of covalent bonding, chelation, complexation or organo-metal dative bonding, to ion recognition moiety M or developer D ; and

(c) D is a developer which, when in contact with T or M-L-S-T forms a colored complex.

23. The colored complex according to Claim 22 which is enmeshed in a porous web or membrane.

24. The colored complex according to Claim 22 wherein the color of said complex has a density that is a function of the amount of targeted ion T .