WO1989002596A1

WO1989002596A1 - Solid state test device

Info

Publication number: WO1989002596A1
Application number: PCT/US1988/003036
Authority: WO
Inventors: Kenneth Allan Blake; Katharine Gentry Johnston; Edwin Michael Presnal, Jr.
Original assignee: Environmental Test Systems, Inc.
Priority date: 1987-09-03
Filing date: 1988-08-31
Publication date: 1989-03-23
Also published as: AU2626188A

Abstract

A sheath (11, 12) enclosed reagent incorporated matrix (13) (SERIM) type device (10) is presented which allows the pretreatment of the fluid being tested prior to such fluid contacting the primary reagent. The solid state device (10) essentially comprises porous matrices (13, 18) which incorporate reagents, the primary or first reagent being reactive with the analyte being detected in the test fluid and the secondary reagent being used to pretreat the fluid. The first (13) and second (18) matrices are in contiguous relationship such that the fluid being detected must first pass through the second reagent before it contacts the first or primary reagent.

Description

SOLID STATE TEST DEVICE

FIELD OF THE INVENTION

The present invention relates to unitized solid state test devices and methods for determining the quantity of analyte (substance being detected) in fluids which require a pretreatment step prior to the test fluid contacting a reagent which is specifically reactive with the analyte or a conversion product thereof in the test fluid. More particularly, the invention relates to solid state test devices which include reagents impregnated into or incorporated with bibulous or porous matrices which are encased in or covered with fluid impervious sheaths having placement and size controlled openings for directing the fluid into and through the matrices, which devices or test systems require a pretreatment step prior to the fluid contacting the reagent in the matrix or the separation of reagent components into contiguous matrices or the contacting of the fluid being analyzed sequentially with two or more separated reagents.

BACKGROUND OF THE INVENTION

The science of analytical chemistry and particularly simple tσ-use solid state test devices using analytical chemistry principles has made dramatic progress over the past decade or so. At one time such devices simply gave an indication of the presence of a substance or a gross condition of the fluid being analyzed, such as, for example, the use of litmus paper to determine if the fluid was acidic or basic. Now such devices can give answers which are as precise, specific and sensitive as those obtained using laboratory procedures and conditions. Moreover, such devices can quite often be used without accompanying instrumentation which permits their use in the field or "on-site" to give instant answers. This obviously eliminates the need for preserving sample integrity, simplifies record keeping and allows the user to take . rapid corrective measures.

Present simple to use solid state testing devices usually take the form of either (1) a paper matrix pad impregnated with a reagent which develops a color when the entire pad is immersed in or contacted with an analyte in solution or (2) a reagent impregnated bibulous or porous matrix which is enclosed in a fluid impervious sheath or covering which restricts the flow of fluid being tested to a defined opening, usually an end portion of the sheath. In use, this latter type device is contacted with the fluid being tested such that the opening is exposed to the fluid which wicks up or into the bibulous matrix by capillary action (or is pulled or pushed into and through the porous matri ) , wherein an analyte or a conversion product thereof in the fluid reacts with the reagent in the matrix to form a localized reaction product giving a visual response as the fluid moves through the matrix.

The pad type device is usually made quantitative or semi-quantitative by using a chromogen in the reacting mixture which responds proportionally to the amount of analyte in the fluid being tested. This response can either be read visually by comparison to a developed color chart or by inserting the pad in a reflectance photometer which electronically "reads" the amount of color formed and interprets this as a quantitative value. The photometer obviously gives the analysis a higher degree of precision and sensitivity.

The sheath enclosed reagent incorporated matrix (SERIM) type device is interpreted by measuring the reaction of the analyte with the reagent as the fluid moves through the matrix. This is accomplished by effecting a localized visual change in the matrix by such reaction until the analyte is exhausted from the moving front of the wicking fluid. Depending ^'on the type of chemical reaction involved between the analyte and the reagent composition, the reagent can either be simply impregnated into the matrix or can be physically or chemically attached thereto. For example, if the reaction forms an insoluble product, such as a precipitate, the reagent can be simply impregnated into the matrix, whereas if the reaction comprises the formation of a fluid soluble color reactant, then the reagent must be attached to the matrix. The sheath enclosing the matrix usually contains a means such as spaced marking lines and a numerical scale for measuring the extent of the chemical reaction. The number opposite the visual change is then compared to a calibration chart to give a quantitative result; however, if the device can be fabricated consistently, the numbers on the device can be the actual values for the concentration of analyte in the fluid being tested.

Whereas the pad type devices have the advantage of simplicity and speed of reaction, they suffer in that a subjective estimation of the color change must be made by the user. Color blind individuals cannot use such devices for obvious reasons. SERIM type devices on the other hand offer greater sensitivity and do not rely on subjective color judgments by the user. They are versatile and offer the user an economical way to effect an immediate result.

As advantageous as SERIM type devices are, they nevertheless suffer from certain drawbacks. As presently configured they are homogenous type systems in that the fluid being tested is drawn through a single reagent composition. In other words all of the components of the reagent composition must be intermixed and incorporated into a single matrix. Incompatibilities can pose serious problems for reagent formulators. Moreover, certain analytical chemical reactions must be accomplished sequentially, that is, one reaction must be completed before the next can be started. This obviously cannot be accomplished in a single matrix. An additional drawback of SERIM devices is that occasionally an interfering component or condition of the fluid must be either removed, neutralized or complexed. All of these drawbacks can be alleviated by the utilization of a second matrix containing one or more pretreatment second reagents being placed between the first, or primar reagent impregnated matrix, and the fluid being tested.

DESCRIPTION OF THE PRIOR ART

U.S. Patent No. 3,620,677 discloses and claims basic SERIM type devices which are manufactured by Environmental Test Systems, Inc. of Elkhart, Indiana and sold under the registered tradename QUANTAB.

While the above noted U.S. patent discloses a basic SERIM device, several others disclose devices comprising multiple reagent impregnated matrices and means for controlling the flow of test fluid through such matrices to achieve a desired result. U.S. Patent No. 3,811,840 discloses and claims a device wherein the fluid being tested is forced to flow through an aperture in a matrix having a reagent immobilized therein, this first matrix being backed up with a second matrix to force additional fluid through the aperture. All reactions involved in these pad type devices are of the colorimetric or color producing variety and are read in the aperture or device opening.

Another device approaching but distinct from the SERIM type is disclosed and claimed in U.S. Patent No. 4,301,139. The basic configuration described in this patent is a specific binding immunoassay column device which uses a portion of the device as a "capillary pump" to force additional fluid through the reagent impregnated part of the device. Readout is accomplished by using radioactive labels and sophisticated instrumentation.

SUMMARY OF THE INVENTION

The present invention accordingly relates to a SERIM type device which includes a means to (1) pretreat a sample to remove an interfering substance prior to the fluid contacting the primary reagent, (2) neutralize or complex an interfering constituent in a fluid being tested prior to that fluid contacting the primary reagent, (3) separate incompatible reagents and/or, (4) effect a sequential reaction process in a single device. All of these objectives can be accomplished by the utilization of a second matrix containing one or more second reagents or chemical components in contiguous relationship with the first matrix of a SERIM type device, which first matrix contains a first or primary reagent, and configuring the resulting device such that the fluid being tested contacts and passes through the second matrix (and reagents) before it passes through the first matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a front view of a device of the present invention wherein the first and second matrices are elongated and flat and are contained in a single continuous sheath.

Figure 2 is a longitudinal sectional view of the device of Figure 1 taken along the line 2-2.

Figure 3 is latitudinal sectional view of the device of Figure 1 taken along the line 3-3.

Figure 4 is an exploded partial front view of a device of the present invention wherein the second matrix is mounted external to the first matrix.

Figure 5 is a longitudinal sectional view of the device of Figure 4 taken along the line 5-5.

Figure 6 is a front view of the assembled device shown in Figures 4 and 5.

Figure 7 is a perspective front view of a cylindrical device wherein the matrices are contained in tube-shaped sheaths and are connected by a removable plastic coupling ring.

Figure 8 is a longitudinal sectional view of the device shown in Figure 7 taken along the line 8-8.

Figure 9 is a device similar to that shown in Figure 7 wherein the second .matrix consists of several connected matrices each containing separate pretreatment reagents, the sheaths containing the first and second matrices being held together by a plastic coupling ring.

Figure 10 is a longitudinal sectional view of the device shown in figure 9 taken along the line 10-10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, the following definition^'s apply: analyte is defined as the chemical substance or condition being detected; reagent is defined as one or more chemical substances which react with the analyte to give a visually perceptible response thereto; test fluid is defined as the liquid environment which contains the analyte; matrix is defined as the inert bibulous or porous support for the reagent; sheath is a test fluid impervious, transparent or translucent (light transmissive) material which intimately covers and encloses the matrix; first matrix is used herein to designate the matrix which contains the primary reagent which reacts with the anaiyte or a conversion product thereof to give a visual response; second matrix is used to designate the matrix which contains the pretreatment reagent or reagents and may consist of more than one matrix, each of which contains a separate reagent but are interconnected, or several reagents spaced apart from each other in one matrix, such that the fluid being tested flows therethrough before it reaches the first matrix; matrix localized reaction product means that the visually perceptible substance formed by reaction of the analyte with the reagent is retained at the site in the matrix where the reaction takes place; coupling means refers to a mechanism for attaching a first and second matrix or one or more matrices making up the second matrix such that the matrices are in contiguous relationship and the fluid being tested will flow from one to the other; SERIM is an acronym for sheath enclosed reagent incorporated matrix type devices as disclosed herein; and basic SERIM device refers to a test means which comprises a first matrix and primary reagent contained in a sheath.

A first preferred embodiment of the present invention comprises the use of flat, paper or paper-like matrices which are encased or laminated between sheets of plastic film. The matrices are usually elongated strips of paper which has be^"en impregnated with reagent. The end portions of the plastic film are cut off exposing the matrix to the prevailing environment. The lower end is for contact with the fluid being tested and the upper end is opened to permit air to escape from the device which is replaced with the test fluid. In such a device the second pretreatment matrix and reagent can be placed in or on the lower end in contiguous relationship to the first matrix contain the primary reagent.

Another preferred embodiment comprises the use of cylindrical, filter tip type matrices in which the reagents are contained in the filter tip material and the sheath is a continuous tube of material which surrounds the matrices. First and second matrices are positioned in the same relationship as the in the flat, paper type matrices laminated between sheets of plastic film. The resulting cylindrical devices are used in the same manner as the flat devices but have the advantage of increased volume and are more amenable to pulling the fluid through the column by means of a negative pressure exerted on the upper opening.

Referring now to the drawings, Figures 1 and 2 show a front view and a side sectional view respectively of a SERIM device 10 wherein a strip of reagent impregnated paper 13 forming a first matrix is laminated between two sheets of transparent plastic 11 and 12, the face portion of the front sheet 12 being printed with marking lines 16 and a numerical scale 17 for ease of reading the extent of reaction. The upper end of the matrix 13 is covered with a signal string 14 which is likewise laminated between plastic sheets 11 and 12 but exposed to the atmosphere at opening 19. The lower end of the first matrix 13 is butted up against a second matrix 18 which is also laminated between plastic sheets 11 and 12 and extending to the lower end thereof forming an opening 15 such that fluid must enter the second matrix 18 prior to contacting the first matrix 13. The front sheet 12 must be light transmissive; however, the rear sheet 11 may be opaque to enhance the reading of the extent of the reaction in the matrix 13. Figure 3 is a cross sectional view of device 10 at line 3-3 showing matrices 13 and 18 laminated between plastic sheets 11 and 12.

Figures 4 and 5 show exploded front and longitudinal sectional views of a lower end portion of a basic SERIM device 20 consisting of a first reagent impregnated matrix 23 laminated between sheets of plastic 21 and 22, the device having an opening 24 exposing the first matrix 23 to contacting fluids. The device 20 is assembled with the second matrix 32 by forming the matrix into a "U" shape and attaching it to the end portion of device 20 by pressing adhesive layers 33 against the front and back sheets of plastic laminate 21 and 22 thereby covering the opening 24. Figure 6 shows the device 20 assembled with the second matrix 32.

Figure 7 shows a perspective front view of a cylindrical, filter-tip type SERIM device 40, wherein the first matrix 43 and the second matrix 44 are porous webs containing the primary and pretreatment reagents respectively. These matrices are encased in tubular plastic film sheaths 41 and 42 which are held in contiguous relationship by means of a snug fitting connecting or coupling tube 45. The sheath 41 contains spaced marking lines of which 46 is representative and a numerical indication of line placement of which 47 is representative. The end portions of the device 40 are open at the upper end 49 and the lower end 48. In use the lower end opening 48 is placed in sufficient fluid to fill the device but not to the extent that it can enter the upper end opening 49. Figure 8 is a cross sectional view of the lower end of device 40 taken along line 8-8.

Figure 9 is a SERIM device 50 similar to that shown in figure 7, except that sheath 52 comprises three matrices 54, 55 and 56 held in contiguous relationship with first matrix 57 contained in sheath 51 by means of coupling tube 53. Figure 10 is a cross sectional view of the lower end of device 50 taken along the line 10-10.

Basic SERIM type devices using flat paper type matrices are fabricated as follows: 1. porous or bibulous paper is impregnated or incorporated with a reagent which reacts specifically with the analyte being detected to give a visual response; 2. the paper is dried, if necessary, and cut into elongated strips, the length and width depending on the wicking action desired; 3. the strips are then "laminated" between sheets of transparent plastic material such that the plastic material is in intimate contact with the reagent paper and the edge portions of the plastic surrounding the reagent are sealed; and, 4. the end portions are then opened to expose the paper. In use, one end portion of the resulting SERIM device is immersed into the fluid being tested which fluid moves through the matrix of the device. The analyte reacts with the reagent in the matrix until the analyte is exhausted, at which location on the matrix the reaction ceases. The fluid minus analyte continues through the matrix until reaching the top at which time the degree of reaction is "read" . The extent of the reaction along the matrix is then measured and compared to a calibration chart to give a quantitative result.

As shown in Figures 1 and 6, pretreatment second matrices can be attached to the basic flat SERIM device by either laminating the second matrix within the sheath or by attaching it externally around the lower end of the sheath such that it covers the end portion of the basic SERIM device.

Basic cylindrical type SERIM devices are fabricated as follows: 1. continuous filament material such as cellulose acetate or polyester is woven and shaped into cylindrical rods; 2. this porous material is impregnated with reagents and dried; 3. the impregnated rods are then encased into tightly fitting transparent plastic sheaths and cut to length; and, 4. the plastic sheaths are either initially provided with or are later printed with graduated markings.

Pretreatment second matrices and reagents are prepared in a manner similar to that described next above, cut to the desired length and attached to the basic cylindrical SERIM device by means of a tightly fitting tube or by wrapping the sheaths together end to end using plastic adhesive tape.

The raw materials used in constructing or fabricating the devices of the present invention are many and diverse; however, basically the matrix materials must be porous to the fluids being tested and the sheath or laminating materials must be impervious to such fluids in order to direct its flow into and through the device. Moreover, the matrix must be inert to both the reagents and the analyte. It must, however, be capable of containing the reagents and, if necessary, holding the reagent in place while the test fluid is flows through the matrix. This can be accomplished by either adsorbing the reagent onto the matrix or chemically attaching the reagent to the reagent such as by chemical bonding. Common matrix substances are cellulosic materials such as filter paper, glass fibers, porous polymer materials and combinations of such materials. Some examples of such materials include cellulose or derivatives of cellulose such as a wide array of substituted ion-exchange celluloses, continuous filament synthetic cellulose acetate or polyester filter materials, ion exchange resin loaded materials, and, in addition, a wide range of adsorbants such as silica gel, activated alumina, diatomaceous earth, silicas and derivatives thereof, and activated carbon. Common sheath materials include Mylar film, polyethylene, polypropylene, polyesters, and other transparent or translucent (light transmissive) film forming or heat shrinkable materials. The choice of sheath material is dependent on the type of device, the fluid being tested and the lamination or encasement process.

The choice of reagent system used is likewise within the purview of the formulator. Basically, the reagent must be capable of quickly reacting with the analyte to form a visual indication of such reaction as the test fluid moves through the matrix. Such chemical reactions may involve precipitation, ion exchange, ion retardation, complexation, and so forth. The reaction proceeds until the analyte is exhausted from the test fluid which location is registered as a visually perceptible line of demarcation between test fluid containing the analyte'and that which does not. ^' The position of this line as compared to a numerical scale is indicative of the quantity of analyte in the test fluid. The test fluid then proceeds through the matrix until it reaches the upper end portion of the matrix. A signal string impregnated with a chemical which is visually responsive to the fluid can be utilized at the upper end of the matrix to emphasize completion of the fluid flow through the matrix and enhance venting to potentiate completion of the reaction process.

As previously noted, the present invention comprises the utilization of a second matrix incorporated with a second reagent which is positioned with respect to the first matrix (and first reagent) such that the fluid being tested must first pass through the second matrix before it contacts and reacts with the reagent contained in the first matrix. By such an expedient, several advantageous objectives can be realized: 1. the fluid being tested can be "pretreated" to remove an interfering constituent from a mixture of components in the test fluid including the analyte; 2. the second reagent can neutralize or change an interfering constituent in the test fluid to one which does not affect the final reaction; 3. the second reagent can be an essential part of the reaction between the first reagent and the analyte but be incompatible therewith; and, 4. the second reagent can react with the analyte to convert it into a product which then sequentially reacts with the first reagent. The above noted advantages are not necessarily mutually exclusive and in certain circumstances more that one advantage may be realized in a single SERIM type test device using the second matrix, second reagent concept.

Moreover, as also previously noted, the second matrix may comprise a single porous carrier containing one or more second reagents or several porous materials positioned end to end, each containing individual reagents. The rationale for the latter type of second matrix is that it may be more expedient to separately incorporate the individual reagents in porous matrices and physically connect such matrices to form the second matrix. The advantage of such a configuration is that sequential reactions can be effected on the test fluid prior to contacting the same with the first reagent and primary matrix. Moreover, such a configuration can be advantageous from a reagent compatibility standpoint.

The following illustrations describe in a general way the utility of the present invention. The above noted first advantage can be accomplished by the utilization of a chelating agent to remove a metal from the test fluid. The second advantage can be achieved by using an acidic or basic material in the second matrix to neutralize an alkaline or acid test fluid which would interfere with the reaction between the analyte and the reagent in the first matrix. The third and fourth advantages can be simultaneously realized by the utilization of a reducing agent in the second matrix to change the analyte to a conversion product which is capable of reacting with the first reagent but which reducing agent would be incompatible with such first reagent.

In use, the open lower end of the SERIM type devices of the present invention are simply immersed about halfway into the fluid being tested. The fluid is allowed to travel by capillary action up the matrices until it reaches the upper end of the first matrix at which time the device is removed from the fluid and the extent of reaction along the first matrix noted. This value is then either compared to a calibration chart which is derived from using the device with known solutions of analyte or the result read directly from the device itself. Alternatively, the reaction may be accelerated by using a suction means to draw the fluid into and through the matrices. If the visually perceptible reaction between the analyte and the first reagent is permanent then the fluid can be stripped from the device and the device retained as a permanent record of the test result.

A particularly advantageous application of the present invention can be found in the testing of concrete for chloride ion or salt. The common SERIM device for chloride testing utilizes a first matrix impregnated with silver dichromate which when contacted with chloride ion forms an insoluble white silver chloride precipitate. Accordingly, the length of white precipitate formed in the first matrix or column is proportional to the amount of chloride ion present in the test fluid. However, when this device is used to test concrete, which is extremely alkaline, the pH of the fluid entering the device causes a brownish-black silver oxide or hydroxide precipitate which obscures the visualization at lower concentration levels of the white silver chloride precipitate, making the test unreliable at such concentration levels. This problem can be alleviated or obviated by the use of a second matrix in contiguous relationship with the first or silver dichromate reagent impregnated matrix such that the fluid from the concrete mix must first travel or pass through a neutralizing second matrix before contacting the first matrix. An example of such a device is described below.

The following Examples are illustrative of the present invention.

EXAMPLES 1-6

Tests for Chloride Ion in Concrete

Note: In Examples 1-6 which follow, commercially available SERIM devices, i.e. QUANTAB chloride titrators, Product No. 1175, Control Code 0023086 were used as the first matrix and first reagent. This product is basically strips of paper impregnated with silver dichromate which are laminated between two thin sheets of plastic film, the top film being transparent and containing marking or calibration lines to measure the extent of reaction of the chloride to the dichromate reagent in the paper. The devices are open at the bottom and have a signal string laminated between the films in contact with the top of the impregnated paper. The signal string is impregnated with a dyestuff responsive to an aqueous fluid which serves to mark the end of the test procedure as well as providing a vent for the wicking mechanism.

Example 1.

Test for Chloride in Mortar using Standard SERIM Devices

The lower ends of three SERIM devices having no pretreatment capability were immersed about two cm into fresh mortar having a sodium chloride concentration of about 100 ppm. Fluid from the mortar wicked up the device in about 6-7 minutes. The extent of reaction in the reagent matrix was obscured by the formation of a brownish-black precipitate making the test devices unusable. Example 2

Test for Chloride in Mortar Using Modified Standard SERIM Devices

Example 1 above was repeated except that devices with a rectangular piece of ion exchange filter paper impregnated with about 45 % by weight of R-SO H ion exchange resin was folded over the open lower end of the device as shown in Figures 4-6. No sign of brownish-black precipitate was found in the device and reading of the reaction line was easily accomplished.

Example 3

Example 2 was repeated except that a cellulose phosphate (-0 PO H ) paper was used in place of the ion exchange impregnated paper. Results were similar to those obtained in Example 2.

Example 4

Example 2 was repeated except that carboxymethy- cellulose was used instead of the ion exchange impregnated paper. Results were similar to those obtained in Example 2.

Example 5

Example 2 was repeated except that the lower end portion of the sheath enclosing the first matrix was extended one cm and a strip of ion exchange paper was incorporated in this sheath as shown in Figures 1-2 hereof. This obviated the need to attach the second matrix to the SERIM device. Example 6

Example 5 was repeated except that filter paper impregnated with activated carbon was used in place of the ion exchange paper. This device was used to test grape juice for the presence and amount of chlorides therein. The activated carbon removed all traces of purple coloration from the fruit juice which would completely obscure the reaction in the first reagent matri .

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Claims

WHAT IS CLAIMED IS:

1. In a solid state device for testing fluids for analytes, the device consisting of an elongated porous first matrix incorporating a first reagent which is specifically reactive with the analyte or a reaction product thereof to form a visually perceptible matrix localized reaction product and a light transmissive, fluid impervious covering material for the first matrix, the device having a controlled opening in the first matrix to allow test fluid to enter, the improvement which comprises placing a second matrix containing a second reagent in contiguous relationship with the first matrix such that the fluid being tested must come into contact with the second matrix before it comes into contact with the first matrix.

2. A device as in Claim 1 wherein the second matrix is an extension of the first matrix and is enclosed in the same covering material.

3. A device as in Claim 1 wherein the first matrix is a flat, paper-like material.

4. A device as in Claim 1 wherein the second matrix covers the lower end opening in the first matrix.

5. A device as in Claim 1 wherein the first and second matrices are cylindrically shaped.

6. A device as in Claim 5 wherein the second matrix is detachably mounted on the first matrix.

*__.•

7. A device for testing wet mortar for the presence and amount of chlorides comprising a first matrix having incorporated therein silver dichromate and a second matrix having incorporated therein an acidic reagent, the first and second matrices being in contiguous relationship such that the fluid from the wet mortar must first contact the second matrix and reagent before it contacts the first matrix and reagent.

8. A device as in Claim 7 wherein the second matrix and reagent is an acid ion exchange material.

9. A method for testing fluid from wet mortar for the presence and amount of chlorides comprising contacting the wet mortar with a second matrix and reagent containing an acidic material, allowing the fluid from the wet mortar to flow therethrough and thereafter allowing the fluid to contact a first matrix and reagent consisting of silver dichromate reagent wherein the second matrix and reagent is encased in a light transmissive, fluid impervious material, and observing the resultant reaction through the encasing material after the fluid has flowed through the first matrix..

10. A method as in Claim 9 wherein the first matrix is a flat paper like bibulous material.

11. A method as in Claim 10 wherein the second matrix contains an acid ion exchange resin.

12. A method as in Claim 10 wherein the second matrix and the first matrix are contained in a contiguous relationship in a common encasing material and the lower end of the encasing material containing the second matrix is contacted with the wet mortar.

13. A method as in claim 9 wherein the matrices comprise a bibulous material and the wet mortar is allowed to travel through the matrices by capillary action,

14. A method as in claim 9 wherein the matrices comprise a porous material and the wet mortar fluid is pulled into the device by placing negative pressure at the upper end of the device.