HK1058238B - Device for separating electrolyte chambers within an electrochemical sensor - Google Patents

Description

Device for separating electrolyte chambers in electrochemical sensors

Technical Field

The present invention relates to an electrochemical sensor. More particularly, a separator device for use in a reference cell having a non-axial flow path therethrough is disclosed.

Background

Electrochemical sensors for measuring pH, ORP, or other specific ion concentrations typically consist of three parts: a multi-ion electrode, a reference cell, and an amplifier that converts the signal into usable information that can be read. For example, in the case of a pH sensor, the multi-ion electrode may be a hydrogen ion sensitive glass bulb with millivolt output that varies with the relative hydrogen ion concentration inside and outside the bulb. In contrast, the reference cell output does not vary with hydrogen ion activity.

The reference cell is of such a construction, where most problems can occur within the electrochemical sensor. The reference cell is typically composed of three main parts: an internal component such as a metal-metal salt, e.g. Ag/AgCl, Pt/Hg₂Cl₂Etc., a filling solution such as an electrolyte; and a liquid junction through which the fill solution contacts the sample desired to be measured.

In particular, the reference cell is used to maintain a common potential in the case of measuring the sample fluid. The fill solution or electrolyte provides a conductive bridge to the sample fluid and surrounds the reference element with an electrochemically stable environment. This liquid junction must be held in place in order to obtain an accurate reading. In an ideal liquid junction, electrolytic contact between the reference element and the sample liquid provides the necessary communication, and also prevents mixing of the sample liquid with the electrolyte. However, various liquid junctions may not be perfect. This is because there is contact between the electrolyte and the sample fluid in order for ion flow to occur and therefore mixing may eventually occur.

In the case of early pH meters, the liquid junction was simply a very tiny hole in a glass or ceramic barrier through which ionic communication could be established between the two solutions. However, under long term use, it has been found that various single-hole junctions become susceptible to plugging. Accordingly, recently, various liquid junction designs have typically included ceramic or other frit materials, porous materials such as quartz, or casing junctions. Some porous materials, e.g. wood, Teflon^TMWicks, frosted glass dots, or the like may also be used.

In us patent No.3,440,525, the use of a large junction surface consisting of wood or a porous ceramic material is disclosed. As a result wood is particularly a good material to use, since the electrolyte contact can be maintained by a number of small capillaries or natural grooves extending radially (in the direction of the wood grain) between the electrolyte and the sample liquid. While the use of wood or other porous materials provides an effective liquid junction, it is desirable to extend the useful life of various electrochemical sensors by prolonging the useful life of the wood or other porous materials used in the sensors.

In U.S. patent re.31,333, the use of a larger cork assembly is disclosed, which is made up of a number of smaller corks combined. An adhesive sealant such as epoxy is used to seal the abutting end surfaces of the large plugs prior to assembly. Thus, when the wooden plug is assembled and filled with electrolyte and the epoxy is in place, the ion flow path is non-linear. In other words, due to the presence of the epoxy barrier, ions must pass back and forth between a series of non-axially aligned wooden plugs.

In us patent 5,630,921, an electrochemical sensor is disclosed, comprising: a first longitudinal series of semi-permeable plugs, the semi-permeable plugs being impregnated with electrolyte; a second series of semi-permeable plugs disposed in an overlapping relationship with the first series to have an interlocking fit; and a series of impermeable plugs. Each plug from the second semipermeable plug passes through each impermeable plug so as to maintain an ion path. Thus, although an impermeable plug is used to prevent poisoning of the reference cell, the ion path is maintained by the semipermeable plug.

In U.S. Pat. No. 6,054,031, a junction for ionic communication is described, which is essentially a channel extending between the inner surface of the housing and the outer surface of the inner body. The grooves are designed to have a relatively small cross-section for providing ion continuity, but also to provide a long, tortuous groove length, thereby increasing the transit time of ions through the groove. By using this design, ion exchange between solutions separated by channels is limited and significantly slowed. This design avoids problems associated with clogging because the cross-section can be larger than that described in previous designs. In particular, a spiral groove is disclosed that includes these properties.

Summary of the invention

The invention relates to a salt bridge for an electrochemical sensor, comprising: (a) at least two chambers for containing electrolyte liquid; (b) a plug for separating the at least two chambers, said plug being substantially impermeable to the electrolyte fluid; (c) a narrow bore through the plug, the bore providing a non-axial flow path for ionic communication between the at least two chambers in the presence of the electrolyte liquid. In a more detailed aspect according to an embodiment of the invention, a salt bridge for an electrochemical sensor includes: (a) at least two chambers for containing electrolyte liquid; (b) a plug for separating at least two chambers, said plug comprising a material that is substantially impermeable to an electrolyte fluid; (c) an axial direction defined by the linear distance between at least two chambers; and (d) a non-axial orifice extending axially through the plug, the non-axial orifice defining a non-axial flow path between the at least two chambers, wherein the non-axial flow path is within the non-axial orifice, the non-axial flow path providing ionic communication between the at least two chambers when electrolyte liquid is present in the at least two chambers.

Further, a separation device for separating a plurality of chambers within an electrochemical reference cell is disclosed, the separation device comprising: (a) a first liquid-impermeable barrier having a liquid-facing surface and comprising at least one open channel for enabling ionic communication between the plurality of cells in the presence of a continuous electrolytic liquid; and (b) a second liquid-impermeable barrier having a liquid-blocking surface that mates against the liquid-facing surface such that the open channel closes to form a channeled flow path. In a more detailed aspect according to an embodiment of the invention, a separation device for separating a plurality of chambers within an electrochemical reference cell, comprises: (a) a first liquid-impermeable barrier having a liquid-facing surface and comprising at least one open channel for enabling ionic communication between the plurality of chambers in the presence of a continuous electrolyte liquid; and (b) a second liquid-impermeable barrier having a liquid-blocking surface that fits against the liquid-facing surface such that the open channel closes to form a liquid flow path, wherein the first and second liquid-impermeable barriers are formed in the shape of discs, each disc having an axially central aperture, and wherein one disc has a larger outer diameter and a larger central aperture than the opposing disc.

Each of these embodiments is preferably used within an electrochemical sensor for measuring ionic properties of a liquid sample. The device preferably comprises a reference cell having: a first chamber adjacent to a liquid sample to be measured; a second chamber, the second chamber remote from the liquid sample; a substantially impermeable plug for separating the first chamber from the second chamber; a non-axial flow path through the plug fluidly connecting the first chamber to the second chamber; a continuous electrolyte liquid within the first chamber, the second chamber, and the non-axial flow path; and a liquid interface region for contacting the continuous electrolyte liquid with the liquid sample. In addition, an electrolyte sensing element, such as a metal-metal salt, may be present in the second chamber and in ionic communication with the continuous electrolyte liquid, and a sample sensing electrode or multi-ionic electrode may also be in such conductive communication with the electrolyte sensing element that a potential difference may be measured.

Also disclosed is a method of determining pH in comparison to a reference, the method comprising the steps of: (a) forming a reference cell; (b) contacting a solution sample with a multi-ion sensor; (c) creating a flow of electrons from the first chamber to a second chamber between the reference cell and the solution sample, across a small non-axial ion flow path through another impermeable plug; and (d) measuring any potential difference. In a more detailed aspect according to an embodiment of the invention, a method of determining pH in comparison to a reference comprises: (a) forming a reference cell; (b) contacting a sample of solution with an ion sensor; (c) forming an electron flow between the reference cell and the solution sample from the first chamber through a small non-axial ion flow path to a second chamber, wherein the non-axial flow path is non-axial with respect to the axial direction defined by the linear distance between the first chamber and the second chamber, and the non-axial flow path passes through a plug comprising a substantially impermeable material separating the first chamber from the second chamber; and (d) measuring the potential difference between the reference cell and the solution sample.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings;

FIG. 1 is a cross-sectional view of an electrochemical sensor implemented in accordance with an aspect of the present invention;

FIG. 2 is a cross-sectional view of a portion of FIG. 1;

FIG. 3 shows two perspective views (3a and 3b) of a first impermeable plug or barrier having a liquid-facing surface and a concentric annular surface; and

fig. 4 shows two perspective views (4a and 4b) of a second impermeable plug or barrier having a liquid-retaining surface and a concentric annular surface.

Detailed description of the invention

Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular process steps and materials disclosed herein as such process steps and materials may vary somewhat. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims and equivalents thereof.

Referring to fig. 1, fig. 1 shows a cross-sectional view of an electrochemical sensor 10. Generally, the sensor 10 is supported by a housing 12, the housing 12 being comprised of an outer layer 14, an inner layer 18 and an insulating solution ground path 20, the outer layer 14 having ridges 16 formed to receive a sensor protector or cap (not shown). The outer layer 14 is formed in a cylindrical shape and may be made of a rigid material that is inert or otherwise chemically compatible with the sample solution to be tested. Polyvinylidene fluoride plastic is a typical material having these properties, but other materials may be used as known to those skilled in the art. The inner layer 18 may likewise be composed of a structurally rigid material that is inert or otherwise chemically compatible with the sample fluid to be tested and which is in direct contact with the electrolyte solution.

Inside the inner layer 18 are three semipermeable plugs 22, all of which plugs 22 are machined in an annular shape. The semipermeable plugs 22 are preferably made of a wood material such that the wood grain follows a generally radial path 24. The outer diameter 26 of the semipermeable plug 22 preferably presses snugly against the inner surface of the inner layer 18 so that any electrolyte (not shown) or displaced sample fluid (not shown) does not readily escape the semipermeable plug 22.

The semipermeable plugs 22 are actually separated from one another by one or more fluted impermeable plugs, which will be described below. At the proximal end 28 of the device 10, the semipermeable plug 22 contacts the sample fluid to be tested. At the distal end 30, an electrolyte sensing element 32 is present and in ionic communication with the electrolyte liquid.

Inside the inner diameter 34 of the annular semipermeable plug 22 is a sample sensing electrode 36. The sample sensing electrode 36 may fit neatly inside the inner diameter 34 of the semipermeable plug 22 such that liquid does not quickly escape the semipermeable plug 22.

The semipermeable plug 22 is separated by a pair of impermeable plugs 38, the impermeable plugs 38 being formed in a circular sheet shape with an axial central bore (not shown) through the plugs 38. Specifically, a first impermeable plug 40 and a second impermeable plug 42 are shown, the plugs 40, 42 being seen in more detail in fig. 2.

Turning to fig. 2, fig. 2 shows a cross-section of a portion of the pair of impermeable plugs 38. Specifically, the first impermeable plug 40 is defined by two surfaces. One surface has a series of ridges 44, the ridges 44 being concentrically disposed such that they are pressed into the semipermeable plug 22 so as to inhibit significant rapid migration of any poisons migrating into the semipermeable plug. Opposite the concentric ridges 44 is a flat surface 46, the flat surface 46 acting to block the escape of electrolyte from the open channels, as will be explained below.

The second impermeable plug 42 is generally comprised of two sections 42a, 42 b. Both portions 42a and 42b are joined to form a second impermeable plug 42. Although the second impermeable plug 42 is shown in two portions 42a, 42b, one skilled in the art will appreciate that the second impermeable plug need not be split into two portions, but may be a unitary plug. Similar to the first impermeable plug 40, the exposed surface of the portion 42a has a series of concentric ridges 44, which concentric ridges 44 are pressed into the semipermeable plug 22 in such a way as to inhibit the significantly rapid migration of any poisons that migrate into the semipermeable plug. Opposite the concentric ridges 44, and on the portion 42b, there is a liquid-facing surface 48 for facing liquid in a non-axial direction to form a non-axial flow path 50. The flat or blocking surfaces 46, the surfaces each having concentric ridges 44, and the liquid-facing surface 48 can be seen more clearly in fig. 3 and 4.

Fig. 2 also shows a first aperture 52 and a second aperture 54. The first aperture is defined radially by the inner layer 18 and a first impermeable plug 40, and axially by the semipermeable plug 22 and a second impermeable plug 42. The second aperture is defined radially by the second impermeable plug 42 and the sample sensing electrode 36, and axially by the semipermeable plug 22 and the first impermeable plug 40.

In the design of this embodiment, the first impermeable plug 40 has an axial bore (not shown) that fits snugly around the sample sensing electrode 36 while providing a substantially sealed fit. The outer diameter (not shown) of the first impermeable plug 40 is shaped to leave a gap or hole 52 adjacent the inner layer 18. In contrast, the second impermeable plug 42 is designed such that the outer diameter (not shown) fits snugly against the inner layer 18 to provide a substantially sealed fit. In addition, an internal central aperture (not shown) is shaped to leave a gap or aperture 54 near the sample sensing electrode 36. The outer diameter and central bore of the first impermeable plug 40 are both smaller than the outer diameter and central bore, respectively, of the second impermeable plug 42. However, while the first impermeable plug 40 has been described as generally smaller in outer diameter and central bore, it will be understood by those skilled in the art that the impermeable plugs 40, 42 may be varied in size such that the first permeable plug is generally larger in outer diameter and central bore. In other words, the first impermeable plug may function to seal against the inner layer of the housing, while the second impermeable plug may function to seal against the sample sensing electrode without altering the basic function. Accordingly, the first impermeable plug 40 is said to be smaller for convenience only. However, it is preferred for this particular embodiment that all of the impermeable plugs 40, 42 be dimensionally identical so that one seals against the inner layer 18 and the other seals against the sample sensing electrode 36.

Turning now to fig. 3, fig. 3 shows a first view 3a and a second view 3 b. In the first view 3a, the portion 42b is shown generally. On portion 42b is a liquid-facing surface 48, which surface 48 includes a series of open grooves 60, which open grooves 60 are shaped radially between a central bore 62 and an outer diameter 64. In a second view, 3b, the portion 42a is shown generally. On portion 42a is a surface having concentric ridges 44 to prevent any poisons that may migrate into the semipermeable plug from migrating rapidly and thus contaminating the open channels 60.

In fig. 4, a first view 4a and a second view 4b are shown. In a first view, fig. 4a, a blocking surface 46 is shown. The blocking surface 46 shown in fig. 4a is generally pressed against the liquid-facing surface 48 (shown in fig. 3 a) to prevent liquid from escaping from the open channel 60. Thus, the blocking surface 46 and the liquid-facing surface 48 cooperate to provide a radially extending tunnel-like channel through which liquid can flow. Fig. 4b shows a surface with several concentric ridges 44. This surface also functions as described above for fig. 3 b.

In view of these figures, a salt bridge for an electrochemical sensor comprises: (a) at least two chambers for containing an electrolyte liquid; (b) a plug for separating the at least two chambers, said plug being substantially impermeable to the electrolyte fluid; and (c) a narrow bore through the plug, the narrow bore providing a non-axial flow path for ionic communication between the at least two chambers when the two chambers are in the presence of the electrolyte liquid. In a more detailed aspect according to an embodiment of the invention, a salt bridge for an electrochemical sensor includes: (a) at least two chambers for containing electrolyte liquid; (b) a plug for separating at least two chambers, said plug comprising a material that is substantially impermeable to an electrolyte fluid; (c) an axial direction defined by the linear distance between at least two chambers; and (d) a non-axial orifice extending axially through the plug, said non-axial orifice defining a non-axial flow path between the at least two chambers, wherein at least a portion of the non-axial flow path is within the non-axial orifice, said non-axial flow path providing ionic communication between the at least two chambers when electrolyte liquid is present in the at least two chambers. In addition, an electrochemical sensor for measuring ionic properties of a liquid sample is also disclosed. Such a device preferably comprises: a reference cell having a first chamber adjacent to a liquid sample desired to be measured; a second chamber remote from the liquid sample; a substantially impermeable plug for separating the first chamber from the second chamber; a non-axial flow path through the plug fluidly connecting the first chamber to the second chamber; a continuous electrolyte liquid within the first chamber, the second chamber, and the non-axial flow path; and a liquid interface region for contacting the continuous electrolyte liquid with the liquid sample. An electrolyte sensing element may be present in the second chamber and in ionic communication with the continuous electrolyte liquid. In addition, a sample sensing electrode may be in conductive communication with the electrolyte sensing element such that a potential difference may be measured. In each of these embodiments, the non-axial flow path preferably comprises a linear path, although other non-axial flow paths, such as helical, zig-zag, etc., may be used. It is also preferred that the non-axial flow path be confined to the interior of the plug body. In addition, to avoid problems associated with clogging, a relatively large orifice and/or multiple ion flow paths may be machined into the plug.

The substantially impermeable plug preferably comprises a first barrier layer having a liquid facing surface and a second barrier layer having a liquid blocking surface. The liquid facing surface and the liquid blocking surface may then cooperate so as to form a tunneled non-axial flow path. Most preferably, the first barrier and the second barrier are a pair of discs, each having an axially central bore. In this embodiment, one of the discs has a larger outer diameter and larger bore diameter than the face sheet, with holes provided at each end of the flow path. In addition, the liquid-facing surface preferably consists of an array of radially symmetrical open channels extending from the central bore to the outer diameter. Thus, if one open cell becomes plugged, other open cells maintain ionic communication in the presence of the electrolyte solution.

The reason for having different sized axially centered holes for different sized wafers is that the holes can be formed between a housing near the outer diameter and the multi-ion sensor near the center hole. For example, the housing and the multi-ion sensor may be arranged concentrically such that the central bore of each wafer is large enough for the multi-ion sensor to pass through and the outer diameter of each wafer is large enough to fit within the housing. In this embodiment, one of the pair of discs may fit snugly to the multi-ion sensor, while the opposite disc may fit snugly to the housing. The pair of discs then provides a mechanism to seal one chamber for the loading of electrolyte from the other, i.e. one disc is sealed at the housing and the other disc is sealed at the multi-ion sensor and the pair of discs are bonded to each other except at the open channel where the tunneled ion flow path is maintained.

Although not required, the chambers containing the electrolyte fluid may be provided with semipermeable plugs impregnated with an electrolyte as described in U.S. Pat. No. RE 31,333, which is incorporated herein by reference. Various woods are useful as semipermeable plugs because they contain natural axial channels for electrolyte and sample fluid flow. Furthermore, the present invention is useful in many ways over the prior art in that: if semi-permeable plugs are used, they may be impregnated with an electrolyte solution prior to assembly. This allows for a more simplified manufacturing method.

Either impermeable barrier layer may further comprise a surface having a series of concentric ridges that are pressed into one of the semipermeable plugs, particularly against the area proximate to contact with the sample fluid to be tested. This is done so that any poisons that migrate into the semipermeable plug do not migrate significantly into the non-axial flow path or the tunnel-like channel.

Also disclosed is a separation device for separating a plurality of chambers within an electrochemical reference chamber, the separation device comprising: (a) a first liquid-impermeable barrier having a liquid-facing surface and comprising at least one open cell for enabling ionic communication between the plurality of chambers in the presence of a continuous electrolytic liquid; and (b) a second liquid-impermeable barrier having a liquid-blocking surface that mates against the liquid-facing surface such that the open channel closes to form a tunneled flow path. In a more detailed aspect according to an embodiment of the invention, a separation device for separating a plurality of chambers within an electrochemical reference cell, comprises: (a) a first liquid-impermeable barrier having a liquid-facing surface and comprising at least one open channel for enabling ionic communication between the plurality of chambers in the presence of a continuous electrolyte liquid; and (b) a second liquid-impermeable barrier having a liquid-blocking surface that fits against the liquid-facing surface such that the open channel closes to form a liquid flow path, wherein the first and second liquid-impermeable barriers are formed in the shape of discs, each disc having an axially central aperture, and wherein one disc has a larger outer diameter and a larger central aperture than the opposing disc.

Although this is not required in terms of a liquid impermeable barrier, the flow line may be non-axial. Further, the impermeable barrier layer preferably comprises an elastomeric material known to be impermeable to liquids. So that only where liquid communication is permitted is the flow path through the element. In addition, the barrier layer is preferably in the form of discs each having an axially central bore, wherein one disc has a larger outer diameter and a larger central bore diameter than the opposing disc, as described above. Other similar elements that may be present in a preferred embodiment include: (a) having an array of radially symmetrical open channels extending from a central aperture to an outer diameter, (b) having a central aperture on each wafer large enough for the multiple ion sensor to pass therethrough, (c) having at least one of a first liquid-impermeable barrier and a second liquid-impermeable barrier, the barriers further comprising a second surface having a series of concentric ridges, and as described above, (d) having a non-axial flow path.

In addition to the disclosed structure, a method of determining pH against a benchmark is disclosed, the method comprising the steps of: (a) forming a reference cell; (b) contacting a sample of the solution with a multi-ion sensor; (c) creating a flow of electrons between the reference cell and the solution sample from a first chamber to a second chamber across a small non-axial ion flow path that penetrates the otherwise impermeable plug; and (d) measuring any potential difference. In a more detailed aspect according to an embodiment of the invention, a method of determining pH in comparison to a reference comprises: (a) forming a reference cell; (b) contacting a sample of solution with an ion sensor; (c) forming an electron flow between the reference cell and the solution sample from the first chamber, through a small non-axial ion flow path, to a second chamber, wherein the non-axial flow path is non-axial with respect to an axial direction defined by the linear distance between the first chamber and the second chamber, and the non-axial flow path through a plug comprises a substantially impermeable material separating the first chamber from the second chamber; and (d) measuring the potential difference between the reference cell and the solution sample.

While the invention has been described with reference to certain preferred embodiments, those skilled in the art will appreciate that various modifications, changes, omissions, and changes may be made without departing from the spirit of the invention. Accordingly, it is intended that the invention be limited only by the scope of the following claims.

Claims (21)

1. A system for use in an electrochemical sensor, comprising:

(a) at least two chambers for containing electrolyte liquid;

(b) a plug for separating at least two chambers, said plug comprising a material that is substantially impermeable to an electrolyte fluid;

(c) an axial direction defined by the linear distance between at least two chambers; and

(d) a non-axial bore through the plug, relative to the axial direction, the non-axial bore defining a non-axial flow path between the at least two chambers, wherein the non-axial flow path is within the non-axial bore, the non-axial flow path providing ionic communication between the at least two chambers when electrolyte liquid is present in the at least two chambers.

2. The system of claim 1, wherein the non-axial flow path is linear.

3. The system of claim 1, wherein the non-axial flow path is confined within the plug body.

4. The system of claim 1, further comprising at least two apertures through the plug.

5. The system of claim 1, wherein said plug includes a first barrier having a liquid facing surface and a second barrier having a liquid blocking surface, said liquid facing surface and said liquid blocking surface cooperating such that said non-axial flow path is formed.

6. The system of claim 5, wherein the first barrier and the second barrier are a pair of discs each having an axially central bore, and wherein one disc has a larger outer diameter and a larger central bore diameter than the opposing disc.

7. The system of claim 6, wherein the liquid-facing surface includes an array of radially symmetrical open channels extending from its central aperture to the outer diameter.

8. The system of claim 6, further comprising a housing and a concentrically disposed multi-ion sensor, wherein the central bore of each disk is large enough for the multi-ion sensor to pass therethrough, and the outer diameter of each disk is small enough to fit within the housing.

9. The system of claim 8, wherein one of the pair of discs is snugly held against the multi-ion sensor, and wherein the opposite disc is snugly held against the housing.

10. The system of claim 1, wherein at least two of the chambers contain a semipermeable plug impregnated with electrolyte.

11. The system of claim 10, wherein the semipermeable plug is wood.

12. The system of claim 10, wherein the semipermeable plug is impregnated prior to assembly.

13. The system of claim 6 wherein at least two of the chambers contain electrolyte-saturated semipermeable plugs and said first barrier further comprises a surface having a series of concentric ridges that press into one of said semipermeable plugs, and wherein said second barrier further comprises a surface having a series of concentric ridges that press into a different semipermeable plug such that any poisons moving into the semipermeable plug do not substantially move into the non-axial flow path.

14. The system of claim 1, wherein the at least two chambers include a first chamber proximate the fluid sample to be measured and a second chamber distal from the fluid sample, and wherein the continuous electrolytic fluid is within the first chamber, the second chamber, and the non-axial bore, said system further comprising:

(e) a liquid interface region for contacting the continuous electrolyte liquid with the liquid sample,

(f) an electrolyte sensing element in the second chamber and in ionic communication with the continuous electrolyte liquid, an

(g) A sample sensing electrode, which is electrically conductively connected to the electrolyte sensing element in such a way that a potential difference can be measured.

15. A separation device for separating a plurality of chambers within an electrochemical reference cell, comprising:

(a) a first liquid-impermeable barrier having a liquid-facing surface and comprising at least one open channel for enabling ionic communication between the plurality of chambers in the presence of a continuous electrolyte liquid; and

(b) a second liquid-impermeable barrier having a liquid-blocking surface that fits against the liquid-facing surface such that the open channel closes to form a liquid flow path, wherein the first and second liquid-impermeable barriers are formed in the shape of disks, each disk having an axially central bore, and wherein one disk has a larger outer diameter and a larger central bore diameter than the opposing disk.

16. The separator arrangement of claim 15 further comprising an axial direction defined by the linear distance between two chambers separated by said separator arrangement, and wherein said liquid flow path is non-axial with respect to said axial direction.

17. The separation device of claim 16 wherein said non-axial flow path is linear.

18. The separation device of claim 15, wherein at least one of the first liquid-impermeable barrier and the second liquid-impermeable barrier comprises an elastomeric material.

19. The separation device of claim 15, wherein the liquid-facing surface is an array of radially symmetric open channels extending from its central aperture to the outer diameter.

20. The separation device of claim 15, wherein at least one of the first liquid-impermeable barrier and the second liquid-impermeable barrier further comprises a second surface having a series of concentric ridges.

21. A method of determining pH in comparison to a reference comprising:

(a) forming a reference cell;

(b) contacting a solution sample with a multi-ion sensor;

(c) forming an electron flow between the reference cell and the solution sample from the first chamber, through a small non-axial ion flow path, to a second chamber, wherein the non-axial flow path is non-axial with respect to the axial direction, said axial direction being defined by the linear distance between the first chamber and the second chamber, and the non-axial flow path passes through a plug comprising a substantially impermeable material separating the first chamber from the second chamber; and

(d) the potential difference between the reference cell and the solution sample is measured.