Sensor Apparatus

In the present invention, the solid contacted ISE and the solid contacted reference are based on a conductive porous network with a solid contact and membrane disposed thereon. The porous networks are not only mechanically stable, but also provide pore structure for the solid contact and membrane to intercalate, which enhances the life time and stability of the sensors. The invention further incorporates a unique fluidic fitting sensor and sealing mechanism so that measurements can be taken at high pressures. The fitting design has many benefits, such as low cost and disposability, which allows them to be mass manufactured. These sensors can be produced for detection of many different kinds of ions by applying different types of ion selective membranes, including polyvinylchloride (PVC) based ion-selective membranes and fluorous matrixes based ion-selective membranes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1depicts an electrochemical cell203assembly of the prior art comprising a membrane based ion selective electrode200, a voltmeter201, and an external reference electrode202. The ion selective electrode200is inserted into the sample solution204where the analyte and other matrix chemicals interact with the ion selective membrane205to create a complex boundary potential at the membrane liquid interface. The internal reference electrode207is in contact with the inner filling solution206, which is in contact with the ion selective membrane205that is in contact with both the inner filling solution206and the sample solution204. The internal reference electrode207typically is comprised of a silver wire coated with silver chloride (Ag/AgCl). This electrode can be replaced by another coated electrode material as is readily understood by those skilled in the art. The external reference electrode202can be chosen from any typical reference electrode such as is commonly known in the art.

In operation, the electrochemical cell203is inserted into a sample solution204to measure selected components in the liquid phase. An electromotive force develops between the ion selective electrode200and the external reference electrode202which is measured with a voltmeter201. Since the membrane is selective for the target ion, the voltage measured will indicate the presence of the target ion in sample solution204.

The inner filling solution206typically comprises a mixture of the target ion dissolved in a buffer. The freshly produced ion selective membrane205is typically exposed to inner filling solution206and is equilibrated and aged in a sample solution204that significantly matches the composition of the inner filling solution206. Typically the inner filling solution206is buffered and can contain primary ion and/or one or more potentially interfering ions to reduce the effect of transmembrane fluxes on the measured signal. The inner filling solution206can also incorporate a number of ion exchangers, anti oxidants, or buffers that will stabilize the inner filling solution206or provide a chemical sponge for primary ion or potentially detrimental reaction products that may be produced over time.

An external reference electrode202incorporates a liquid junction301between the bridge electrolyte solution210and sample solution204. In this case, the reference electrode internal electrode302is immersed in a reference electrolyte solution211. This liquid junction301can be comprised of various inert porous materials including porous ceramics, porous glass, porous polymers, and porous metals. Alternatively, a porous polymer or silica monolith may be cast and cured. The purpose of this configuration is to prevent the bridge electrolyte solution210from reacting with and fouling the electrode surface. This liquid junction301provides a tortuous path for diffusion and significantly increases the time for the bridge electrolyte solution210to migrate through the liquid junction to the sample solution.

One embodiment of the present invention uses a Ag/Ag2S internal reference electrode207and a Ag/Ag2S reference electrode internal electrode302to make the respective internal references less susceptible to chemical attack by inner filling solutions206that might react with it. Inner filling solutions206could react with AgCl, resulting in undesirable reactions of the components in these inner filling solutions. Such reactions include oxidation and desulfurization. Importantly, a slow decrease in the inner filling solution ion concentration results in a shift in the phase boundary potential at the interface of the inner filling solution of the ISE and the ion-selective membrane. For example, xanthate desulfurization by AgCl will gradually convert AgCl to Ag2S, resulting in changes in the phase boundary potentials between (a) the silver precipitate and the Ag wire and (b) the silver precipitate and the inner filling solutions. Shifts in these three phase boundary potentials will manifest themselves (a) in a slow drift of the measured potentiometric response, requiring frequent recalibration, and (b) in an increased temperature sensitivity of the calibration curve due to the resulting differences between the internal reference electrode and the external reference electrode relative to which the potential of the ISE is measured. Therefore, a reference electrode design based on Ag2S-coated Ag wires is an alternative embodiment. It is anticipated that other embodiments using other electrode materials and their sulfide coatings could be used as alternative internal reference electrodes207.

Using Ag2S-coated Ag wires as internal reference electrodes207eliminates the driving force for desulfurization. Solid-state ISEs based on Ag2S for the measurement of sulfide and Ag+are well established and take advantage of the high conductivity of Ag2S [Koebel, M.; IbI, N.; Frei, A. M.,Conductivity and kinetic studies of silver—sensing electrode. Electrochimica Acta 1974. 19: p. 287-95], which is about three orders of magnitude higher than that of silver halides, and the very low solubility of Ag2S (solubility product, Ksp, 4.3×10−50, as compared to 1.6×10−10for AgCl). As all suitable setups for external reference electrode and internal reference electrodes, the Ag2S/Ag system has a very small temperature coefficient (reported to be in the range of −0.04 to −0.08 mV/° C., as compared to −0.08 mV/° C. for AgCl/Ag).

In an another embodiment, external AgCl/Ag reference electrode internal electrode302is replaced with a Ag2S/Ag-based reference electrode because (a) identical reference electrode internal electrode302and internal reference electrode207minimizes the temperature dependence of the measured EMF, and (b) because this eliminates complications and improves real-life lifetimes due to sulfide and hydroxide from samples diffusing past the liquid junction301into the bridge electrolyte solution210of the reference electrode, leading there to the reaction of AgCl to Ag2S or Ag2O.

FIG. 2of the present invention is an alternative embodiment to the electrochemical cell described inFIG. 1. The ion selective electrode system272is comprised of a working electrode230and a external reference electrode250. Similar to the electrochemical cell inFIG. 1, a voltmeter201is used to measure the potential between the working electrode230and the external reference electrode250when brought into contact with the sample solution204.

Now with particular attention to the working electrode230, the electronically conducting member231is attached to the central conductor wire236of a low loss coaxial wire232. The central conductor wire236be can be stranded or solid wire and is typically constructed from copper or silver coated copper. Solid vs stranded central conductor wire236wires tend be more electrically stable and an air gap between the central conductor wire236and the shield237can deliver superior performance. The connection between the central conductor wire236of the low loss coaxial wire232and the electronically conducting member231can be made with any number of crimping or gluing methods as is commonly known in the art. Appropriate glues include silver or carbon filled epoxy. In the case of epoxy, appropriate curing time and good adhesion to both the central conductor wire236of the low loss coaxial wire232and the electronically conducting member231is required to prevent an electrical short or a highly resistant electrical connection. The requirements for this connection include adhesion and sufficient conductivity so as to not significantly contribute (i.e. <<1%) to the overall electrical resistance. Total electrical resistance of the connection between the electronically conducting member231and central conductor wire236wire of the low loss coaxial wire232should typically be less than 1 k ohm. In some cases, during use, the coaxial cable232needs to rotate independent of the working electrode. This requires a different central conductor wire236to electronically conducting member231design as will be discussed inFIG. 3andFIG. 6. The electronically conducting member231can also be directly soldered to the instrumentation amplifier of voltmeter201, preventing losses due to connections.

Now, the electronically conducting member231can be fabricated from many different materials. The key feature is to provide a conductive porous network255disposed within and or upon the surface of the electronically conducting member231. In one embodiment in the present invention, it is fabricated from iso molded graphite carbon rods. To make the rods, graphite is ground and exfoliated in an organic dispersant or binder with subsequent extrusion/molding. Organic dispersants include glues of organic origin such as polyester or acrylate oligomers and monomers. The rod diameter ranges from 0.1 mm to 200 mm in diameter. The carbon that makes up the rod is typically graphitic and is mixed with a binder such as epoxy or polyester or clay and extruded, molded, or cast into rods or flat ribbons. The rods are porous with a large pore size distribution; pores range from 1-100 nm. The porosity can be increased by removing the organic (non clay) binder at 500-1000° C. One commercial product that is suitable as a substrate is fine isomolded graphite carbon rods obtained from the GraphiteStore.com. Isomolded rods tend to be more consistently electrically uniform compared to extruded rods. However, extruded rods provide acceptable performance if the carbon is fine enough and the binder content is low.

In some cases, it is preferred that the working electrode230be encapsulated disposed between insulative substrates. In this case the electronically conducting member231is a thin conductive film that is covered with solid contact member and membrane respectively. The thicknesses of the conductive trace can range from several microns to several hundred thousandths of an inch. The film is typically solution cast or printed onto a inert substrate that can be selected from any number of plastics that will provide good adhesion to the central conductor body and good insulating properties. Encapsulation of conductive traces by an insulative substrate is commonly practiced in the art.

The thin conductive film may be an ink formulated from graphite, buckyballs, nanotubes and fluorinated versions of these materials can be used provided it is compounded at a high enough percentage to provide electron transport and acceptably low resistance. Ink formulations include a solvent, a solid conductive material, an optional nano dimensioned porogen, and an optional binder. For example, carbon can be compounded up to 70% w/w in an acrylate formulation comprising a oligomer, a monomer, and a photoinitiator and photocured with UV light. There are many such formulations found in the art. An example formulation includes 50% exfoliated graphite, buckyball, or carbon nanotubes, 10% isobornyl acrylate, 5% 2,4 diisocyanato-1-methyl-benzene, and 20% 2-methyl, 2-hydroxyethyl, 2-propenoic acid. Nano sized porogens include polymers, carbon, and metals and are available for purchase at Sigma Aldrich nano materials. A wide variety of nanoparticles are available from Sigma Aldrich. Alternatively, nanoparticles such as sliver nanoparticles can be introduced into the matrix and may or may not be removed upon curing. Nanoparticles that have been selected and/or prepared to achieve or produce a particular property in the resulting electronically conducting member231, are intended to be within the scope of the present invention. For example, nanoparticles that may be used herein include well-known nanoparticles that have been made from metals (for example, Pd, Cu, Fe, Ag, Ni), intermetallics (for example, Al52Ti48), and metal oxides (for example, TiO2, Y2O3, ZnO, MgO, Al2O3). In certain embodiments, the nanoparticle is crystalline or amorphous. Other anticipated nanoparticles include carbon based nano materials such as graphene, nano tubes, or buckyballs. Graphite may or may not be exfoliated as is commonly described in the art. The binder such as epoxy or poly urethane can be optionally removed after casting and curing at 1000° C. under nitrogen to make nano dimensioned pores which allow for high capacitance and direct ion to electron transduction. There are a wide variety of inks that are formulated with carbon that are also suitable for porous or nonporous conductive carbon coatings.

In another embodiment, the electronically conducting member231is fabricated from a porous metal conductor or a metal ink containing a porogen. High quality metal coated pins are not usually sufficient to maintain adhesion between the solid contact member235, and the electronically conducting member231. The nonporous metal conductors can be made porous by treating the metal pin surface with porous metal particles or metal nano particles with subsequent annealing to provide adhesion. Metal frits are suitable and are the preferred embodiment because they offer a off the shelf porous metal option. The porous metal may be electroplated with any suitable inert metal.

The electronically conducting member231may or may not have a ion to electron transducer, referred to as solid contact member235. In some cases where the porosity of the electronically conducting member231is closely controlled around a monodisperse 100 angstroms, the solid contact member may not be required. This can be accomplished using a layer of porous particles that have monoporosity such as carbon coated silicas as are commercially available from United Science. The solid contact member235can be conducting polymers. An example of a conducting polymer is polyoctylthiophene (POT) with a average MW of 10,000-60,000 daltons. Other examples include poly(3,4-ethylenedioxythiophene), poly(thiophene-3-[2-(2-methoxyethoxy) ethoxy]-2,5-diyl) or polypyrrole or any number of conductive coatings. Typically, the organic semiconductor is dissolved in carbon tetrachloride and is cast on the electronically conducting member231dropwise. The carbon tetrachloride evaporates leaving the electronically conducting member231coated. Several coatings are required to fully coat the central conductor body uniformly.

The solid contact member235can be a metal transducer comprised of metal redox pairs. Metal redox pairs include ferrocene/ferrocenium redox couple, cobalt(II)/cobalt(III) redox couple, Au cluster and any other metal redox couples. Typically, these redox pairs are dissolved into tetrahydrofuran with into ion selective membranes205and drop casted onto electronically conducting member231. The tetrahyrofuran evaporates leaving the electronically conducting member231coated. Several coatings are required to fully coat the electronically conducting member231uniformly. The solid contact member235may be mixed with membrane234or membrane205to provide a continuous single phase.

When the electronically conducting member231has a high enough surface area such as is found with nano porous carbon materials described above, then the solid contact member235may not be needed to obtain a stable Nernstian response.

With respect to ion selective membrane205, any coating that is described in the art may be used. The membrane may be based on fluorous matrixes or may be based on hydrocarbon polymeric membranes as is described in the art. Typically, the membrane is cast dropwise over the end of the electronically conducting member231that is coated with organic semiconductor. Up to three coats with 1-2 hr cure time in between may be required to provide a consistent pin hole free coating.

If the electronically conducting member231is porous, care must be taken to allow penetration of the membrane mixture into the pores for adhesion and larger surface area contact. This can be accomplished by vacuum and sonication.

With respect to external reference electrode250, external reference electrode202as described inFIG. 1will suffice. However, in certain circumstances, the reference electrode can follow the same construction as working electrode230is discussed inFIG. 2. However, the reference electrode membrane234should not be selective for any particular ion of interest as is ion selective membrane205. These membranes are commonly based on lipophilic salts, such as tetrabutyl ammonium tetrabutyl borate (TBA-TBB) or ionic liquids, such as 1-methy-3-octylimidazolium bis-(trifluoromethylsulfonyl)imide ([C8mim+][C1C1N−]). The reference electrode membranes234are coated in the same way as is ion selective membrane205.

This basic electrode design can be used to create some highly useful ion selective sensors.FIG. 3shows a sensor fitting350, comprised of a ¼-28 threaded fitting351, a electronically conducting member231coated with solid contact members235as described inFIG. 2, resilient polymeric member354, and an fluid sealing member353. In this case, the electronically conducting member231is a nano porous, iso molded graphite carbon rod, which has been machined to maintain the outer diameter dimension to within +/0.001, −/0.000 inches. The resilient polymeric member354is made of heat shrink PVC, FEP, or PTFE. A through hole365in the ¼-28 nut 351 has been machined to allow a 0.0005-0.003″ compression fit of the heat shrink encapsulated electronically conducting member231. The distal end355of the ¼-28 threaded fitting351as been threaded to receive a coaxial cable assembly610(FIG. 6) that will transmit the sensor signal to the high input impedance device100ofFIG. 10.

The electronically conducting member231is either pressed into the nut or is pulled through the hole365of threaded fitting351. The pull through procedure involves shrinking an extended length of resilient polymeric member354onto the electronically conducting member231. The shrink tubing is then pulled through hole365from the distal end355to the proximal end360. The extended piece of resilient polymeric member354that pulled the electronically conducting member231through the nut is then trimmed with a diamond razor blade and the carbon polished before adding the solid contact member and membrane to face361. Subsequently, the ion selective membranes205or reference electrode membrane234are applied to the first sensor face361of the electronically conducting member231. The rod may protrude from the face of the proximal end360or it may be flush with the face depending on the requirements of the receiving device. The fluid sealing member353provides a fluidic seal between the analysis fluid and the outside of the device. Suitable sealing members include ferrules, o-rings, or chisel points.

It should be noted that the membrane205can partially dissolve this resilient polymeric member354when it is cast on the face361, thereby producing a fluid tight seal. Alternatively, polymeric matrix can be coated on the inside of a tube that the membrane is not soluble in. Then, when it is cast onto face361, it will dissolve into the coating that has been coated onto the non-soluble resilient polymeric member. Such non-soluble resilient polymeric member354may include PTFE or FEP. This coating effectively acts like a glue.

The fitting350, can be any threaded or non threaded nut commonly described in the art. Threaded nut examples include 10-32 threaded nuts, ¼-28 nuts, and Swagelok hardware including all metric equivalents. The fitting350can be a threaded nut made from stainless steel, Tefzel, PEEK or any other material commonly used in the art. It is anticipated that the sensor could be adapted to any common fluidic fitting including quick disconnects and Luer nuts. The fitting350need not be threaded provided there is sufficient axial and radial compression to prevent leakage. A pressed in fitting350with no threads is desirable from the standpoint that there is no radial torsional force applied to the sensor face361which may damage it in the case that the conductor protrudes from face361. This design can withstand several thousand pounds of hydrostatic pressure and not leak.

The fluid sealing member353sealingly engages the fitting350to a female threaded or non threaded seat that is commonly known in the art. The fluidic seal can be accomplished with a coned ferrule or flangeless fitting or super flangeless fitting as is commonly known in the art. The materials are understood to cover the full range of materials commonly known in the art such as stainless steel, PEEK, PTFE, FEP, and combinations of these materials.

Quick disconnect fittings such as are commercially available from Colder Products, are desirable to eliminate the need to rotate the fitting to thread it into a receiving seat. Rotation torsional force applied to the face361. In this case, it is understood that the assembly technique and the fabrication materials can be altered to accommodate any diameter fitting.

The electronically conducting member231can be made from any material that satisfies the criteria set forth in the discussion ofFIG. 1. The length of the electronically conducting member231can vary as mentioned above. Upon installation, the distal end362of the electronically conducting member231should align with thread location363. This is necessary because the coaxial cable threads into end355. If the electronically conducting member231is too short, the electrical connection will fail and the ISE will not work.

The resilient polymeric member354material should be selected to provide chemical compatibility with the fluid and adhesion to the ion selective membrane or reference electrode membrane. The wall thickness of the tubing typically ranges from 0.001 to 0.010″. The thicker the wall, the greater the compliance for pulling or pressing the electronically conducting member231into the through hole365.

FIG. 4shows an example of an additional embodiment. Assembly400is a single sensor comprised of a electronically conducting member231, coaxial cable232, resilient polymeric member354, and a protective housing401. The electronically conducting member231follows the construction guide outlined inFIG. 1. Electrical connection of the coaxial cable232to the electronically conducting member231will also follow those guidelines established in the specification underFIG. 1. Methods and assemblies for improved shielding of the electronically conducting member231can follow the guide given in the discussion ofFIG. 1. The method of assembly and variations follow the guidelines outlined in the discussion aroundFIG. 3. However, it is important to note that the resilient polymeric member354can extend to cover the electronically conducting member231to cable connection and can extend to cover the entire length of the coaxial cable232. The protective housing401can be any resilient or non resilient material including stainless steel, PVC tubing, PEX tubing, PTFE tubing or any other material that provides protection to the sensor.

Multi-lumen sensor assembly405is a muli sensor design similar to assembly400. The construction comprises a plurality of insulated electronically conducting member231, a plurality of electrical cables402. The electrical cables402may be combined into a single mutt conductor shielded cable as is commonly known in the art. The insulation layer403provides electrical isolation for electronically conducting member231. Heat shrink tubing or conformal coatings provide these insulative characteristics. The insulation layer403provides a resilient layer around the electronically conducting member231to shield and seal the connections to the multi lumen holder. A multi-lumen structure408provides the compression on the outer diameter of the electronically conducting member231. The multi-lumen structure408can be made from epoxy, FEP, PTFE, PVC, or any other solution castable potting agent. Alternatively, the multi-lumen structure can be an extruded or machined structure. The outer housing401provides a protective body to the sensor array and can be any resilient or non resilient material including stainless steel, PVC tubing, PEX tubing, PTFE tubing or any other material that provides protection to the sensor.

FIG. 5shows an alternative embodiment of a multi-lumen sensor assembly405installed into a multi lumen catheter500. In this case, a plurality of working electrodes230and reference electrode250are glued or installed into the lumens408of a venous or arterial catheter. A French 22 gage catheter is a commonly used for these purposes. Either glue or compression is used to sealingly engage the electrodes to the catheter500. Glue can be epoxy, acrylate, or any other glue that allows the insulated electronically conducting member231to sealingly engage the catheter500. Typically, there are a plurality of open lumens505for guide wire, drug, liquid or calibration solution delivery to the sensor head location. This catheter assembly501can be installed in the superior or inferior vena cava to monitor the onset of hyponatremia during surgery or in the intensive care unit.

FIG. 6shows an example of an electrical coaxial cable assembly610that is used in conjunction with the sensor fitting350shown inFIG. 3. It is comprised of a low loss electrical connector600, low loss coaxial cable232, a spring loaded electrical connector pin602, and a fitting assembly comprising a ferrule assembly603and a cable assembly fitting604. The low loss electrical connector600can be configured to receive multi conductors or a single conductor. This connector600is electrically engaged with the high input impedance device100ofFIG. 10. The low loss electrical connectors600are commercially available from many vendors but the high input impedance device is an object of the present invention. The connector600is optionally waterproof. The coaxial cable232can be muti-conductor or single conductor. In the case of a single conductor, a single spring loaded electrical connector602is soldered to the central conductor wire236of the coaxial cable. This spring connector602is gold plated and has a high electrical conductivity. The use of a spring loaded pin602is desirable since it can accommodate dimensional variances and tolerances in the fitting and in the axial location of the electronically conducting member231. The pin602also allows torsional degree of freedom so that the assembly603can rotate around the central axis with out breaking the electrical connection.

The ferrule assembly603is crimped onto the outer surface of the connector pin602to hold the pin in electrical engagement with the electronically conducting member231. The ferrule assembly603connected to the pin is threaded into the threaded proximal end355of sensor fitting350to create an electrical connection. The ferrule mechanically engages the distal end362of the electronically conducting member231providing axial support to the electronically conducting member231. When the electronically conducting member231is large diameter (>1 mm), it is important to provide axial support under high hydrostatic pressures (>3000 psi). High hydrostatic pressure on face361can displace the electronically conducting member231axially through the threaded fitting351.

The two piece sensor assembly comprising coaxial cable assembly610and fitting350is desirable to be used as a single piece design shown inFIG. 4if a controlled and sealed fluidic interface is required. Examples of fluidic interfaces that benefit from a two piece sensor assembly include a high performance liquid chromatography flow cell, a manifold, a micro fluidic chip, a bioreactor, a process stream or a valve.

In an alternative embodiment, the ISE fitting350shown inFIG. 3can be adapted to give rotational and translational freedom in light of the design shown inFIG. 6. In this case, the electronically conducting member231is not compressed within fitting350and has translational axial and radial freedom. The electronically conducting member231loose within fitting350but is spring loaded from the distal end355with a spring loaded conductor pin602as shown inFIG. 6. The electronically conducting member231is pressed by the spring load against a polymeric or PTFE-supported ion sensing membrane that is sealingly attached to face361.

In the case of PTFE ion selective membranes, they can easily be adhered to nut face360with any number of glues or ultrasonic welding. A series of co-radial chisel points can also be machined into the face360to provide sealing points for the nut against the receiving seat. This is an important feature for fluidic sealing as rotation of the ISE membrane against a receiving seat is not recommended. Ferrule techniques are also effective at sealing.

The fitting350and cable assembly fitting604shown inFIG. 3andFIG. 6can be completely eliminated with any of these designs. These fittings are only required when a fluidic seal is required or when a two piece disposal sensor design is required such as in single use bioreactor sensing. In the case that no fitting is required, resilient polymeric member354is still used to hold and connect the electronically conducting member231to an coaxial cable232. The coaxial cable232may be directly connected to electronically conducting member231as shown inFIG. 2or it can be connected with a spring connector as in connector600.

FIG. 7illustrates a manifold device790incorporating a plurality of sensor fitting350, electrical coaxial assembly610, hetero phase fluid removal assembly710, and a fluidic manifold720. The fluidic manifold720has a plurality of inlets721, outlets722, and sensor ports723. The manifold can have a plurality of fluidic channels730, however, for simplicity, only one channel is shown in this illustration. In this case the channel incorporates a static fluid mixer to provide optimal mass transfer to the sensor. The fluidic manifold720can be fabricated from any number of materials including stainless steel or plastics. The inlets721, outlets722, and sensor ports723can be configured to accommodate many different fitting types and styles from any manufacturer. Unused ports can be sealed with a plug735.

Hetro phase fluid removal assembly710is shown as a press fit assembly. In this case, the hetro phase removal unit is designed to separate immiscible fluids. When oriented properly, fluid entering from inlet721that is hetro phaseic, separates in fluidic channel730. The less dense fluid rises to the top of the manifold when it is oriented vertically and is removed through the removal assembly710. The removal assembly can be activated by a conductivity sensor or other ultrasonic sensor designed to detect a change in fluid phase.

FIG. 8shows an example of a flexible and configurable fluidic system890that utilizes the fluidic manifold720detailed inFIG. 7. The system is comprised of fluid reservoirs800, process fluid inlet overflow reservoir801, fluid conditioning unit802, fluidic manifold720, sensors805, solenoid valves810, outlet fluid pump820, high input impedance device100, and biphasic fluid removal unit830. Pumps820and valves810are actuated and controlled via a configurable routine that is defined by the user. The manifold incorporates grounding channels and temperature measurement channels. These are not shown.

The fluid reservoirs800contain buffers, calibrants, and wash solutions. The calibration routine is simple and programmable with a PLC as is commonly used in the art. First, the flow of fluid from the process is shut. The solenoid valve810from the appropriate reservoir800opens. Pump820turns on for enough time to flush the system. The sensor takes a reading. The process is repeated for any number of cleaning, buffering, and calibration routines.

The process fluid inlet reservoir801is either a regulated pressure inlet that incorporates a solenoid valve or an overflow sampling reservoir as is commonly used in the art. This second method is preferred. If the process inlet fluid is an overflow sampling reservoir, then unit802must incorporate a pump, valve or combination of both to provide fluid flow. Unit802preconditions the fluid for the manifold by cooling or heating the fluid. It is desirable that the temperature of the fluid be around 30° C. for most applications. There are many feedback heating and cooling devices on the market that may be implemented to allow cooling and heating. It also incorporates an ultrasonic sensor as is commonly available in the art to detect multi phase fluids.

Unit802may also include a nafion membrane pre ion selection.

The process of sampling and measuring the process flow with a sensor805is simple and programmable. First, the solenoid valve in unit802is opened. Then pump820turns on, drawing fluid from overflow reservoir801, through heater/cooler unit802and into the manifold device790. The device can optionally be flushed with a cleaning solution or calibrant before and after the process is sampled. The pump can oscillate flow forward and backward to maintain a mixed solution provided bubbles do not form. In the case that the fluidic channels are narrow, a pump may be installed between802and790to provide process fluid to be analyzed under positive pressure.

FIG. 9shows details for the biphasic fluid removal component that interfaces with the manifold. Unit830will include a pump that receives a feedback signal from the ultrasonic detector in unit802. The pump will turn on when the signal threshold is triggered, thus removing the biphasic fluid from the manifold. The ultrasonic sensor could be incorporated onto the manifold if required. Upon pump actuation, the fluid is drawn through the apparatus shown in the figure. The apparatus990is comprised of a press in holder900, a membrane filter901, a flared tubing902, an o ring903, and a fitting904. The membrane filter is PTFE can can separate gasses from liquids. The pore size of the filter membrane is less than 3 micron. A complete fluidic seal provided by flare tubing902and o ring903is required for to isolate and sealingly engage the seat in press in holder900.

FIG. 10shows a high input impedance device100that enables measurement of high impedance samples or high impedance working electrodes. The input impedance of the device is at least 1 teraohm. The device incorporates a high impedance instrumentation amplifier on a ceramic chip. Other infinite impedance devices include optical transmit and readout. Examples of high impedance sensors include those fabricated from highly resistant fluorous membranes. High impedance for the purposes of this disclosure are impedances greater than 100 MOhm. Other sensor membranes with high impedance that may benefit from the device100as well. The device100can also be used to measure the resistivity of samples that are high impedance such as soil or concrete. The device100incorporates a sensor health relay array to occasionally measure the resistance and health of the sensor. The array is comprised of a series of resistors and a series of relays that are sequentially checked to monitor the resistance of the membrane. When the membrane resistance varies over a threshold quantity, then the user is informed that the sensor needs to be replaced.

FIG. 11. Describes an application of the devices described above. A chloride selective working electrode, a reference electrode, a high input impedance device100and low loss connectors600were installed in a low dead volume (5-10 uL) fluidic PEEK “tee” and plumbed into the flow path of a high pressure liquid chromatograph. The chloride detector could be installed on the high pressure side, upstream of the column or on the low pressure side, downstream of the column. It is advantageous to be installed upstream as there is a more accurate real time response and shorter delay time. Furthermore, there is no sample to foul the sensor. A salt gradient from 5% to 100% of 10 mM chloride over 5 minutes was programmed into the chromatograph. The chloride sensor followed the mixing online and in real time. A fluorous PFOS sensor was then plumbed in downstream of the detector and PFC standards were injected onto the column. The PFOS sensor could detect the PFCs upon elution from the column. A pH gradient was programmed into the HPLC unit and monitored using the system and sensor configuration shown inFIG. 11. Step gradients could be detected and monitored in real time.

FIG. 12shows the typical construction of a low loss coaxial cable. The cable is comprised of a central conductor wire236, an insulator105, a foil shield110, a braided wire shield120, and a jacket130. The central conductor wire236is typically a solid wire of copper coated silver but it can be stranded. The insulator can be any number of materials but is typically PTFE or FEP. It can also incorporate an air gap. The foil is typically silver coated copper or silver foil. The braided wire shield is woven over an additional insulator105. The jacket covers the braid and protects from external elements.

FIG. 13shows the composite cable131of the present invention. This cable uses conductive coatings106to replace or augment the metal shields110and shields120described inFIG. 12. Conductive coatings106incorporating single wall nanotubes of different lengths and aspect dimensions dispersed in conducting polymers formulations can be used to reject and shield central conductor wire236from various frequencies. This approach can also be used as a general coating for radiation sorption. For example, a formulation of 10 micron length by 1 nm diameter single wall nanotube will disperse a certain frequency of energy. When dispersed in a conducting polymeric layer, it is then useful as a coating that will absorb and drain radiation. A plurality of organic coatings106and formulations may be placed on top of one another or be sandwiched between insulators105. Alternatively, organic semiconductors may be coated to form electron dense or electron deficient coatings. Foam insulators are coated inside and outside to give unique frequency shielding. Coating uniformity is assured by formulation into a UV cure coating107or by multi layer coatings. Sprayed or powder coated PTFE nanoparticles can replace most insulators. There are many different types of organic conductors that are soluble in organic solvents. When these are mixed with nanoparticles that will absorb radiation, they can be used in place of metallic shields110and shields120. The coatings106eliminate expensive polymer extrusion, wire braiding, and foil operations in some cases.

FIG. 14shows an example of a calibration curve for some of the devices described above. The devices described inFIG. 3,FIG. 6, andFIG. 10were fabricated. The working electrode was formulated to be selective for chloride. This figure shows that we are able to get a Nernstian response and use the devices with traditional chloride sensing membranes.

FIG. 15shows a fluorous sensor for PFOS using the device constructions detailed inFIG. 4,FIG. 6, andFIG. 10. Low limits of detection and Nernstian responses were obtained.

The fluorous ion selective cocktail was applied onto the PTFE membranes.

Cocktail: linear perfluoropolyether solution of 0.25 mM tetraalkylphosphonium and 1 mM electrolyte salt (fluorophilic tetraalkylphosphonium as cation and tetraphenylborate as aninon).

Conditioning process: The electrodes were first condition in 1 μM PFOS-K+ for 2 days and 0.1 nM PFOS-K+ for another 2 days.

The calibration curve was obtained by addition from 10−10M PFOS-K+. Detection limit was determined as 4.63E-9 M.

The solid contact reference electrode250is prepared using an ionic liquid for the potential of miniaturization, elimination of liquid junction301and dryness of inner electrolyte solutions, and therefore improvement of performance and lifetime.

To prepare the electrode, a graphite carbon rod (d=7 mm) is inserted into a heatshrink tube to avoid the contact with sample solution and therefore the shortcut. One of its end is soldered with metal wire for the connection to cable. Another end is well-polished and covered with poly(octyl thiophene) (POT) by drop casting its solution (POT is dissolved in chloroform at a concentration of 0.25 mM). After it is dry, new solution is added and this process is repeated for three times. The reference electrode membrane is ortho-nitrophenyl octyl ether (o-NPOE) plasticized poly-(vinyl chloride) (PVC) membrane doped with the ionic liquid 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)-imide (IL). For the best performance, PVC/IL/o-NPOE ratio of 2:1:2 (w/w) is used.

The prepared solid contact reference electrode250showed a Nernstian response of with a glass pH electrode which indicates the excellent performance of thus prepared solid contact reference electrode. A similar reference electrode250but with different solid contact has been found for excellent potential stability, with potential drifts as low as 42 μV/h over 26 days.

We tested the high input impedance device100with a commercially available glass pH electrode. The glass pH electrode was chosen because it had very stable and reproducible response. We monitored the potential of pH electrode at pH 4.0, 7.0 and 10.0 vs a glass double junction reference electrode202. Theoretical Nernstian response (Slope=58 mV/decade concentration change) was obtained with glass pH electrode in different pH buffers by using the device100.

We tested the device100with prepared fluorous electrodes. All electrodes were solid contact electrodes with carbon rods as solid contacts. The PTFE membranes were glued onto the end of Tygon tubing. There was no polyoctylthiophene (POT) layer between the carbon and the PTFE membrane for electrode 1 and 2 (E1 and E2) and there were POT layers between the carbon and the PTFE membranes for electrode 3 and 4 (E3 and E4). Linear perfluoropolyether solution of 0.25 mM tetraalkylphosphonium cation and 1 mM electrolyte salt (fluorophilic tetraalkylphosphonium as cation and tetraphenylborate as aninon) was applied onto the PTFE membranes. A gold pin, one end of which is in contact with the carbon rod, was soldered to a coaxial cable and connected via BNC connector to a commercially available low input impedance datalogger housed in a Faraday cage or the high input impedance device of the present invention without a Faraday cage. Before measurements, the electrodes were conditioned in 10 nM PFOS−K+. We used the two voltmeters to measure the PFOS−response of E3, while we spiked in the PFOS−to change the sample concentration. The response slopes were identical.

Noise and real-time response was measured with the glass pH electrode at pH 7.0 using the high input impedance device100without a faraday cage. The response reached a stable state in 5 minutes. This is similar to the measurements carried out by commercially available voltmeter in faraday cage. The noise of response was about 0.4 mV.

The response of glass pH electrode in pH 7.0 buffer was continuously monitored with the high input impedance device100of the present invention for 2 days. After the response reached a stable value, the long term drift of the electrode was determined to be 5 μV/h.

Due to the extremely high electrical resistance of fluorous electrodes, we have to carry out the measurement in a Faradic cage in the past; otherwise, the response of electrode would be very noisy and the response time will be long. But by using the high input impedance device100and coaxial cables with low loss connections, the noise was greatly decreased as shown in curve A ofFIG. 16even when measurements were carried out in open air and measured with the commercially available low input impedance voltmeter. Experiment with high impedance voltmeter in the present invention was performed in open air and faradic cage was not used for shielding either.FIG. 16shows that the response, measured by the high input impedance device (curve C), was more stable with much less noises and spikes compared to the experiment performed with a commercially available low input impedance datalogger without Faraday cage. The noise is about, 0.4 mV, which is at the same level as the response measured in Faraday cage with standard datalogging equipment (curve B). Moreover, after the change of concentrations, we could observe quick change of potentials and achievement of stable potentials in the measurement with high input impedance device. The response times were shorter compared to that using standard datalogging equipment.

Real-timeresponse in 10 nM PFOS−with an ISE based on membranes consisting of tetraalkylphosphonium cation 1 (0.25 mM) and electrolyte salt (1 mM) in perfluoropolyether measured by high input impedance device100of the present invention for 2 days. After the sensor was stable, the long drift of the electrode was determined to be 30 μV/h.