WO1990003564A1

WO1990003564A1 - Analytical reaction vessel

Info

Publication number: WO1990003564A1
Application number: PCT/US1989/003179
Authority: WO
Inventors: Theodore J. Larsen; Raymond F. Cracauer; John G. Pumphrey; Walter C. Mahoney
Original assignee: Kallestad Diagnostics, Inc.
Priority date: 1988-09-30
Filing date: 1989-07-20
Publication date: 1990-04-05
Also published as: EP0436563A1

Abstract

Disclosed is a reaction chamber (12) and an optical detection chamber (13) adapted to be used in an assay where the presence of the analyte in the sample is detected by optical means.

Description

ANALYTICAL REACTION VESSEL FIELD OF THE INVENTION

This invention relates to an assay device and method for use in analyzing fluids for specific chemical components and particularly to a device and method for delivering measured quantities of reagents employed during such analysis.

BACKGROUND OF THE INVENTION

In the area of diagnostics, various devices and methods have been developed to improve the speed, sensitivity and accuracy of analytical chemical procedures designed to determine whether a particular chemical species (an analyte) is present in a biological sample. Typically, these procedures involve seq-uential delivery of premeasured quantities of several different reagents to a liquid sample suspected of containing the analyte. Reagents dissolved in solution are commonly added by pipetting, either manually or automatically. Reagents in a dry form are added in measured quantities as a dry powder membrane or a pellet or the like.

As reagents are transferred from one container to another, some of the reagents may be left on the tool or device used in such transfer, thus reducing the accuracy of the assay. When reagents are present in a dry form in a vessel prior to addition of a liquid sample, the sequential addition of reagents to the reaction vessel is precluded unless the reagents are compartmentalized. Again, transfer of the components from one compartment to the next may result in loss of some of the reagent during transfer.

In order to overcome these problems, an assay- device that allows precise quantities of reagents to be sequentially added to a liquid sample during an analysis is desired.

SUMMARY OF THE INVENTION The present invention provides a self-contained single use reaction vessel that carries within it the necessary reagents for an assay in premeasured quantities and in such a manner that the reagents can be delivered to a liquid sample in sequential order as the analysis progresses.

The vessel comprises a container having a hollow interior adapted to receive a liquid sample and an opening, an elongated stalk having a longitudinal axis slidably receivable in the container opening and movable inwardly to expose segments of the stalk length to the container interior. The vessel further includes means for providing and maintaining a liquid-tight seal between the stalk and container opening.

The vessel may also include means for mixing the liquid sample in the container which desirably comprises a mixing ring element having a hollow core, the outside diameter of the element having a diameter that is slightly smaller than the inside diameter of the vessel container and its hollow core having a larger diameter than the outside diameter of the stalk. The element is sized so that it may move longitudinally within the container and about the outside of the stalk without touching the stalk.

In one embodiment, the vessel further includes a housing defining a channel extending outwardly from and being sealingly connected to the container about the opening. The channel is sized to allow the stalk to be slidingly received therein, When the stalk is in its storage position (the top end of the stalk is flush with the interior floor of the container) the housing desirably extends the length of the stalk providing a protective sheath.

In another embodiment, the sealing means is a narrow rib carried on the periphery of the stalk, extending radially from the longitudinal axis of the stalk and sized to contact the container opening to form a liquid-tight seal. The stalk may include a plurality of such ribs spaced from each other along the length of the stalk and dividing the stalk into segments, each rib being adapted to contact the container opening and the inner wall of the housing to form a liquid-tight seal.

The reaction vessel may be particularly adapted for use in an analysis process that involves the sequential ordered contacting of liquid in the container with reagents carried by the stalk. In this embodiment, the stalk includes a plurality of segments, each segment bearing one or more of the reagents employed in the analysis. The segments are arranged in a predetermined order along the length of the stalk so the reagents become exposed to the interior of the container in said predetermined order as the stalk is moved through the opening.

Yet another embodiment of the invention is a method of analyzing for the presence of an analyte in a liquid sample employing a reaction vessel comprising a reaction chamber having an opening therethrough and an optical detection chamber attached to and in communication with the interior of the reaction chamber; an elongated stalk having a longitudinal axis slidably carried in the reaction chamber opening and movable inwardly through the opening to expose segments of its length to the interior of the chamber and the liquid sample contained therein; and means for providing and maintaining a liquid-tight seal between the stalk and the opening.

The method comprises placing a predetermined amount of sample into the reaction chamber; moving the stalk inwardly through the opening to expose a segment of its length to the container interior, the stalk segment bearing a pair of reagents wherein at least one of said reagents is capable of reacting with the analyte, one of which has a detectable label. The degree of binding reagent:analyte complex formation being related to the amount of analyte present in the sample. The stalk is then moved inwardly through the opening to expose another segment of its length to the chamber interior, the segment having immobilized thereon a second reagent capable of binding the analyte, the labeled first reagent or a product formed by reaction between the analyte and first reagent; and detecting the presence of labeled reagent remaining in solution or bound to the immobilized reagent to determine the amount of analyte present in the sample. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a perspective view of a reaction vessel of the invention.

Figure 2 shows an exploded view of the components of the reaction vessel of Figure 1.

Figure 3A through Figure 3C show cross-sectional views of the reaction vessel in various stages of being used in an analytical procedure.

Figure 4 shows a perspective view of an embodiment of a mixing ring of the invention.

Figure 5 shows a cross-sectional view of the mixing ring of Figure 4 within a reaction vessel of the invention. Figure 6 shows a cross-sectional view along 6-6 of the mixer shown in Figure .

Figure 7 shows a standard line used with a method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in Figures 1-3, the reaction vessel comprises a container 11 having a reaction chamber 12 and an optical detection chamber 13 and is particularly adapted to be used in an assay in which the presence of analyte in the sample is detected by optical means. The reaction chamber has a hollow interior 14 and an opening 15. As typified in Figures 1 and 2, the reaction chamber is cylindrical in shape; however, it may be of any size or shape. It is made of any suitable material that is substantially air and liquid impenetrable and generally inert to the reagents used in the assay and the material which is to be assayed including, for example, a thermoplastic material such as polyethylene, polypropylene, polyurethane, polystyrene and polycarbonate or glass, metal, ceramic and the like.

The optical detection chamber 13 has a hollow interior 16 communicating with the hollow interior 14 of the reaction chamber. The optical detection chamber may be of any suitable size or shape. It is made from any suitable material is substantially air and liquid impenetrable and generally inert to the reagents used in the assay and the material to be assayed and in the embodiment shown it is made of a material that is substantially transparent to light in given wave lengths to enable the detection of absorbance, fluorescence, or luminescence therefrom.

The container may be formed as a single piece, including both the reaction chamber and the optical detection chamber, or it may be assembled with two separately molded pieces. The reaction and detection chamber may be molded from substantially different materials as necessary for a particular assay.

In the embodiment shown in Figures 3A-3C, a solid elongated stalk 20 carried within the opening 15 of the reaction chamber 12 is slidably received in the opening and movable inwardly through the opening to expose segments of its length to the container interior. The stalk is desirably made of any suitable material that is substantially rigid and generally inert to the reagents used in the assay so that it will not interfere with the assay being performed, such as a thermoplastic material, glass and the like.

As shown in Figure 2, the stalk 20 may include along its length, segments (shown as 21, 22, 23, 24) adapted to carry a reagent employed in the assay. The stalk may be molded as a single piece with the segments delineated by radially extending ribs or by spaces on the stalk where no reagent is carried or it may be made of various segments molded separately and adapted to fit together. In the latter case, the segments may be of various lengths and diameters, although the outside diameter of the segments must be less than diameter of the opening of the reaction chamber so that the stalk can be slidably received therein.

Referring to Figure 3, a housing shown as 30 projects downwardly from the reaction chamber opening 15 and is sealingly connected to the chamber about the opening. The housing has a channel 31 aligned symmetrically along the vertical axis of the reaction chamber and desirably extends a sufficient length to form a protective sheath about the stalk when it is in its storage position. The reaction vessel also includes means for providing and maintaining a liquid-tight seal between the stalk and the reaction chamber opening. The sealing means may be any suitable type such as an O-ring, gasket or the like carried at the chamber opening or on the periphery of the stalk such as the ribs typified as 25 in Figures 2 and 3. The ribs desirably extend radially from the longitudinal axis of the stalk and are desirably spaced from each other along the length of the stalk. Each rib is sized and shaped to form a liquid-tight seal with the reaction chamber opening and the inner wall of the housing.

In use, the stalk is initially positioned in its storage position so that an end 29 is received in the reaction chamber opening so that it is flush with the inner wall of the chamber and a first rib is providing liquid sealing contact between the chamber opening and the stalk. After liquid sample has been placed into the reaction chamber, the stalk is moved upwardly into the chamber until a portion of its length bearing a predetermined quantity of reagent has been exposed. As the stalk is moved up the first rib moves out of sealing contact with the reaction chamber opening and the second rib on the stalk moves into place to provide a liquid-tight seal. It is important therefore when this embodiment of the invention is utilized for the ribs on the stalk to be in sealing contact with the inner walls of the housing so that as the second rib moves into place it wipes the inner walls of the housing and carries any liquid on the wall into the reaction chamber as it is received in the chamber opening. The ribs 25 may be integrally molded as a part of the stalk or as separate pieces. They are desirably made of a material capable of forming liquid-tight seal between the container opening and the stalk and the housing wall and the stalk.

As shown in Figure 3, the wall 32 of the channel 31 desirably has indentations 33 adapted to receive within them the radially projecting ribs 25 of the stalk 20, the indentations being sized so that the outer edges of the ribs are under minimal compression when the ribs are received within the indentations. The indentations are provided so that when the reaction vessel is not in use, the phenomenom of "cold flow" in the outer edges of the stalk ribs and/or the housing walls is prevented. Nevertheless, when the stalk is positioned so that its ribs are received within an indentation, the seals provided by the ribs and indentation in the housing walls are designed to be liquid-tight for the shelf life of the device.

In the embodiment shown in Figure 3, the vessel further includes means for mixing liquids contained in the reaction chamber. The mixer is designed to establish preferential fluid flow past the reagent-containing stalk in the reaction chamber to enhance reaction of liquid-dispersible reagents with immobilized reagents. As shown in Figure 3, the mixer 60 is a simple sleeve and is sized so that its outside diameter (OD) is slightly smaller than the inside diameter (ID) of the reaction chamber forming a gap 61 between them, the difference in diameter being preferably about 0.008-0.012 inches. Another gap 62 is formed between the mixer and the stalk with the ID of the mixer being slightly larger than the OD of the stalk, with a difference in diameters of about 0.030 inches. The presence of a larger gap on the interior side of the mixer and about the stalk establishes a preferential fluid flow path through that gap. The gap formed between the mixer and stalk ensures that the fluid moves past the stalk with a volumetric flow rate equivalent to the volume swept by the mixer. Additionally, the narrow gap imparts relatively high velocity to the fluid as it moves past the stalk. This is particularly important as the fluid moves into the region of the chamber above the stalk. The relatively high velocity of the fluid causes it to "jet" into the bulk volume of fluid above the stalk, thus inducing mixing in this fluid.

The mixer dimensions may vary with the size of the stalk and the reaction chamber and must be selected to obtain the proper gap size and swept volume. The mixer diameters are selected to ensure that significant fluid motion is prevented on the side of the mixer next to the interior of the reaction chamber. The gap between the mixer and the stalk and the height and width of the mixer should be selected so that the displaced or swept volume of fluid is substantially greater than the volume of fluid that can be contained in the gap between the mixer and the stalk. On each stroke, the swept volume and thus the fluid transfer from top to bottom is desirably at least twice the volume of fluid contained in that gap so that with each stroke a substantially "fresh" volume of fluid passes the stalk. If the swept volume is less then the volume in that gap the fluid contained therein is not cleared with each stroke and exchange of fluid into the bulk volume of fluid above the stalk is not effectively achieved.

A second embodiment of mixing means useful with this invention is shown in Figures 4-6. The generally tubular mixer 70 includes an inwardly projecting lip 71 at its top end 72 which forms a constriction having a diameter that is slightly greater than the OD of the stalk to form a radial gap of about 0.015 inches. The constriction ensures that as the mixer is moved downwardly about the longitudinal axis of the stalk that displaced fluid will jet into the bulk fluid above the stalk at a high velocity. The lower portion of the mixer includes a flange having slots 75 formed axially therewithin to define blades 76 projecting inwardly toward the stalk to constrict the flow of fluid about the stalk as the mixer is moved upwardly about the stalk to cause additional mixing of the fluid below the stalk. The mixer also includes a plurality of axially-extending slots 77 therethrough, the slots desirably being spaced from the top of the element and extending a portion of the length of the wall ending before the blades begin. The slots also induce turbulence in the fluid as it passes about the stalk and enters the lower portion of the reaction chamber. The slots and blades speed up the dissolution of reagents borne by the stalk and enhance binding rates of reagents or analyte dissolved or dispersed in the fluid to reagents immobilized on the stalk.

In use, both mixer embodiments are moved along the longitudinal axis of the stalk through any suitable means. For example, the mixer may be constructed in part from ferromagnetic materials or similar materials or include an iron or ferromagnetic steel collar and external magnets would then be able to induce the desired reciprocal vertical motion. This motion displaces fluid as shown by the arrows 63 in Figure 3 from either the bottom of the chamber as the mixer is moved down or from top to bottom when the direction of mixer travel is reversed.

The reaction vessel of this invention desirably is used in conjunction with an instrument which performs one or more of the following functions to automate the analytical procedures being performed. The instrument may automatically dispense a premeasured quantity of the liquid sample to be analyzed (along with any diluent buffer required) into the reaction chamber of the container, and physically move the vessel to and from one or more discrete electromechanical stations within the instrument as the analysis progresses. At each station, the instrument desirably has camming means or the like for moving the stalk upwardly a predetermined distance within the container opening to expose a segment of the stalk length to the sample present in the reaction chamber. The instrument also desirably maintains the contents of the reaction vessel at a constant temperature as the analysis progresses, provides motive power for mixing means carried in the reaction vessel; and aspirates liquid and dispenses buffer to wash the reaction chamber and the portion of the stalk exposed within it as required in a particular analysis. The instrument also desirably detects transmitted light, scattered light, or fluorescence emitted light from the reaction vessel, depending upon the requirements of the analytical procedure being used to determine the presence of analyte in the sample. Furthermore, the instrument may maintain precise timing of the sequence of steps of the analysis as it moves the vessel among the stations, track the identity and physical location of the vessel within the instrument at all times, and calculate the quantity of analyte in the sample from the optical readings obtained.

This invention allows the sequential addition of precise quantities of any reagent to a reaction chamber additionally, any combination or order can be used in a variety of analytical procedures. The invention is particularly well suited for use in the detection of a particular analyte in biological fluids such as blood, serum and urine, including, for example, the following immunoassay types: simultaneous, sequential, delayed addition of a solid phase in either a competitive or sandwich format, double antibody or secondary capture approach. These assays may employ monoclonal-antibodies, polyclonal-antiserum, other members of specific binding pairs and other participants in binding and recognition reactions. As used herein, "specific binding pair" refers to a pair of compounds of which one is capable of recognizing a particular spacial and polar organization and is capable of binding to that compound. The reagents useful in this invention can be any chemical species commonly employed in analytical procedures such as enzymes, enzyme substrates, antibodies, antibody fragments, antigens, haptens, inorganic and organic reagents, buffers, salts, and the like, as well as radioactively labeled or fluoroescent reagents of the above-mentioned types and including nonisotopic labels such as enzymes, luminescent agents, microparticulates and the like. Solid phase analytical procedures in which at least one reagent is immobilized (covalent or non-covalent) on an insoluble surface are particularly suited for use with this invention. In a solid phase assay, a reaction generally occurs between a first immobilized reagent and a second mobile reagent that is liquid-soluble or liquid-dispersible. Typically, in analytical procedures with biological fluids, the immobilized reagent is a member of a specific binding pair that binds to the analyte being assayed, or to the second mobile reagent another reagent that reacts with the analyte in an amount that is related to the amount of analyte present in the sample. The second mobile reagent is typically labeled with an enzyme or other compound that can produce a detectable signal.

When the invention is used in an analytical procedure, the reagents can be applied to the stalk by any suitable means, including for example, ink-jet application, nebulization, pipetting reagent onto the surface, immobilization on the stalk and the like.

The invention is further demonstrated by the following illustrative examples. Example 1. Analysis for Digoxin^*

An immunoassay for a small molecule (hapten) analyte, for example digoxin, was carried out employing the reaction vessel of this invention as follows. The stalk was manufactured in segments or portions. The largest portion or segment served as a solid-phase. Goat anti-rabbit antiserum, was immobilized to the stalk using polyglutaraldhyde using the following procedure, This procedure is in part described in US Patents 4,267,235 and 4,410,634. Preparation of the Solid Phase,

A 4% solution of gluteraldhyde (Sigma or Aldrich Chemical Co.) was prepared in a sodium carbonate-bicarbonate buffer, pH 10.0. This solution was stirred using a magnetic mixer for 18 hours at room temperature. The resulting product was measured by taking a UV/visible spectrum between 200-400 nm of a 1:100 dilution in water. The concentration of the polygluteraldhyde in the resulting solution was adjusted so that the optical density at 234 nm was greater than 0.45. The resulting solution was added to stalks washed in 50% ethanol and the mixture incubated for 40 hours at room temperature. The stalks were then washed thoroughly with water. Goat anti-rabbit antiserum was diluted to a concentration of 10 ug/ml of goat anti-rabbit IgG in 20 mM sodium phosphate, 0.15 M NaCl, pH 6.0. The antiserum was then added to the polyglutaraldehyde-treated stalk segment at a volume of 3 mis/stalk. The addition was done within 30 minutes of the dilution of the antiserum. The resulting mixture of stalks and antiserum was incubated at room temperature for 18 hours, under constant movement of the solution. Following the incubation period, the stalks were washed with a solution of 20 mM sodium phosphate, 0.15 M NaCl, and 0.1% sodium azide at pH 7.0. The washed stalks were stored in a solution of 10 mM HEPES, 0.15 M NaCl, 0.5% bovine serum albumin, and 0.1% sodium azide until they were dried prior to placement in the reaction vessel.

The antiserum-immobilized stalks were dried in a variety of ways. For purposes of illustration, one approach is described here. Briefly, the solid phase from above was washed with water. The stalks were then coated with a solution of 2% polyvinyl alcohol (PVA) . The PVA coated stalks were then dried in a wind tunnel as described in the teachings of US Patent 4,063,367. Application of Reagents to Other Stalk Segments

Assay reagents for a competitive digoxin assay (rabbit anti-digoxin and digoxin-alkaline phosphatase conjugate) were prepared according to commonly known immunoassay methods The antibody was titered to 1:120,000 and the digoxin-alkaline phosphatase conjugate diluted to 1:50,000. It was then determined that using 50 ul of each reagent and 20 ul of sample allowed the generation of an assay standard line with an appropriate slope and sensitivity. The reagents were then concentrated by vacuum dialysis so that the precise amount of reagent necessary for the assay could be ink-jetted onto the stalk segment in a 100 nl volume. A volume of reagent was placed into a commercially available ink jet head having a piezo electric crystal that generates a pulse wave which causes the expulsion of droplets from the ink jet head. 100 nl of liquid is equivalent to about 500 droplets. A drop counter and controller were used to set the ink jet apparatus so that a sufficient number of droplets of reagent would be applied to each stalk. Once the ink-jet head was loaded with sufficient reagent, a segment of the stalk was targeted and held about 2 and 1/2 inches from the head and the reagents shot onto its surface and dried in a wind tunnel as described in US Patent 4,063,367. Rabbit anti-digoxin and digoxin-alkaline phosphatase conjugate were shot onto the same stalk segment . Other ink-jet heads including, for example, the Hewlett-Packard Think-Jet head and the ink-jet apparatus disclosed in European Patent Application EP 87116861 can be used in the application of reagents.

A paste containing 1 mM 4-methylumbelliferyl phosphate (an alkaline phosphatase substrate) in water was applied to a lower stalk segment by means of a pipet. After the reagents necessary for the digoxin assay had been applied to appropriate segments, the stalks were inserted into the housing channel of the reaction vessel so that the top of the stalk was flush with the floor of the reaction chamber. The stalk was assembled as shown in Figure 2 with the top segment 21 containing the rabbit anti-digoxin and digoxin alkaline phosphatase, the next segment 22 containing the immobilized antibody and the third section 23 containing the 4-methylumbelliferyl phosphate. The segments used included ribs so that when the stalk was assembled each stalk segment was bounded by ribs as shown in Figure 2. Digoxin Assay

20 ul of patient sample suspected of containing digoxin was added to the reaction chamber of the vessel along with 300 ul of buffer (0.5 M TRIS, 2.O M MgCl, ImM MnCl, 0.1 mM ZnCl, 0.05% Tween 20 (polyoxyethylene sorbitan monooleate) , and 0.05% bovine serum albumin, pH 8.0). The reaction was initiated by pushing the stalk upwardly into the reaction chamber to expose the top segment containing rabbit anti-digoxin and digoxin akaline phosphatase and the middle segment which was the solid phase containing immobilized antibody. Endogenous digoxin in the sample reacted with the rabbit anti-digoxin and the digoxin alkaline phosphatase conjugate as those reagents dispersed in the fluid. Because rabbit anti-digoxin was present in limiting amounts a competition reaction occurred between the endogenous digoxin and the digoxin alkaline phosphatase conjugate for binding sites on the antibody. The amount of digoxin-alkaline phosphatase conjugate binding to the anti-digoxin antibody depends inversely on the amount of endogenous digoxin originally present in the sample. After 20 minutes at 37 degrees C, with mixing, the reaction was stopped by the aspiration of the contents of the reaction chamber and the chamber and stalk were washed using 2.5 mis of water. Following aspiration of the water, 1.2 mis of substrate buffer (0.1 diethanolamine, DEA) was added. The stalk was then pushed upwardly to expose the third segment containing 4-methylumbelliferyl phosphate, a liquid-dissolvable compound. The 4-methylumbelliferyl phosphate was converted to the fluorescent derivative 4-methylumbelliferone by the action of alkaline phosphatase present on the stalk. In this assay the amount of 4-methylumbelliferone produced is inversely related to the amount of digoxin in the patient sample. The measured rate of formation of the fluorescent product was detected using a conventional fluorometer, adapted to allow constant mixing of the contents of the reaction chamber, and transformed to a number representing the amount of analyte in the sample using a standard line. The reaction vessel was then discarded. The standard line is shown in Figure 7. Example 2. Glucose Measurement

The reaction vessel was used for a more traditional clinical chemistry assay in the measurement of glucose concentration in a serum sample. A solid phase was not used in this assay.

Glucose specific reagents (glucose oxidase 400 U/ml and horseradish peroxidase 120 U/ml) were dissolved in 0.1 M phosphate buffer pH 7.0 and were ink-jetted onto a segment of the stalk, after being concentrated as described in Example 1. The stalk was then assembled with the reagent-containing segment at the top followed by a segment bearing an acceptor compound. The stalk was inserted into the housing channel and moved upwardly toward the reaction until its top was flush with the inner wall of the reaction chamber.

20 ul of patient sample and 300 ul of buffer were added to the reaction chamber and the reaction initiated by pushing the stalk upwardly until the first reagent-containing segment was exposed to the liquid in the reaction chamber to allow the glucose specific reagents to dissolve therein. Glucose present in the sample was in part modified to H₂0₂ and other products through the action of glucose oxidase. The resulting H O was used as an oxidant by the peroxidase to produce light or a colored solution, in the presence of an appropriate acceptor. The acceptor was added to the reaction mixture by moving the stalk inwardly into the container to expose the stalk segment upon which it was carried. For example, acceptors such as luminol (light) or ABTS (2,2'-azino-di- S-ethyl-benzthiazolone-e-sulfonic acid, color) were added to react as shown below.

Glucose oxidase Glucose + O2 Products+ H2O2

Peroxidase H2O2 + luminol or ABTS ^{• •} -^Products + light or color

ABTS was used in this example and the increase in absorbance of color was directly related to the level of glucose in the sample. If luminol is used as an acceptor, light is generated in an amount directly proportional to the level of glucose in the sample (Carter, T.J.N. Whitehead, T.P., and Kricka, L.J. [1982] Telanta 29: 529-531).

Claims

WHAT IS CLAIMED IS:

1. An analytical reaction vessel comprising a container having a hollow interior adapted to receive a liquid sample and having an opening, an elongated stalk having a longitudinal axis slidably receivable in the opening and movable through the opening to expose segments of its length to the container interior, and means for providing and maintaining a liquid-tight seal between the stalk and the container opening.

2. The vessel of claim 1 wherein the container comprises a reaction chamber having an opening and an optical detection chamber connected to the reaction chamber and having a hollow interior communicating with the hollow interior of the reaction chamber.

3. The vessel of claim 1 wherein the means for providing and maintaining a liquid-tight seal comprises a rib carried by the stalk that radially extends outwardly from the longitudinal axis of the stalk.

4. The vessel of claim 3 further comprising a housing defining a channel extending outwardly from the container opening and sealingly connected to the container about the opening, the channel being sized to receive the stalk therein.

5. The vessel of claim 4 wherein the stalk further comprises additional ribs extending radially outwardly from the longitudinal axis of the stalk positioned along the length of the stalk and sized to provide a liquid-tight seal between the stalk and inner wall of the housing.

6. The vessel of claim 5 wherein the stalk comprises a plurality of segments.

7. The vessel of claim 6 wherein the stalk segments are separated from each other along the length of the stalk by the ribs.

8. The reaction vessel of claim 1 particularly adapted for use in a chemical detection process for analyzing a liquid sample for a given analyte, the stalk having a segment bearing a reagent employed in said chemical detection process.

9. The reaction vessel of claim 8 wherein the stalk includes another segment along its length bearing a different reagent employed in the chemical detection process.

10. The reaction vessel of claim 9 wherein at least one of said reagents is immobilized upon the surface of the stalk.

11. The reaction vessel of claim 9 wherein at least one of said reagents borne by the stalk is freely dispersible in an aqueous solution.

12. The reaction vessel of claim 11 wherein the liquid-dispersible reagent is applied to the stalk by spraying the reagent onto the stalk with an ink jet device.

13. The reaction vessel of claim 9 wherein the chemical detection process involves the sequential, ordered contacting of liquid in the container with said reagents in a predetermined order, the reagents being ordered along the length of the stalk so as to become exposed to the interior of the container in said predetermined order.

14. The reaction vessel of claim 2 wherein said optical detection chamber is substantially transparent to light in a given wave length to enable the detection of the absorbance of light by a liquid sample in that portion to be detected.

15. The reaction vessel of claim 1 further comprising mixing means carried in the container and reciprocably movable axially of the stalk to mix liquid contents of the container.

16. The reaction vessel of claim 15 wherein said mixing means comprises a generally tubular mixer receivable loosely over the stalk when the stalk is moved into the container.

17. The reaction vessel of claim 16 wherein the tubular mixer has an inner diameter greater than the outer diameter of the stalk and wherein the mixer has an outer diameter less than the inner diameter of the container and the difference in diameter between the stalk outer diameter and the inner diameter of the mixer is greater than the difference in diameter between the outer diameter of the mixer and the container inner diameter to provide a preferential flow path between the mixer and the stalk.

18. The reaction vessel of claim 16 wherein the mixer comprises a thermoplastic polymer containing particles of a ferromagnetic material.

19. The reaction vessel of claim 16 wherein the mixer includes a collar of a ferromagnetic material carried by the mixer and adapted to move the mixer axially of the stalk in response to an externally applied magnetic field.

20. The reaction vessel of claim 15 wherein said mixing means comprises a generally tubular mixer receivable loosely over the stalk when the latter is moved into the container, the mixer having an inner surface of non-uniform cross section to create turbulence between it and the stalk as the mixer is reciprocated.

21. The reaction vessel of claim 20 wherein the inner surface of the mixer is configured to define, at one end of the mixer, an inwardly projection flange closely confronting the stalk and forming a liquid flow constriction therebetween.

22. The reaction vessel of claim 21 wherein said flange includes slots formed axially therewithin and wherein walls of the mixer include axially-extending slots therethrough, the inner mixer surface further including, adjacent its other end, and inwardly extending lip closely confronting the stalk and forming a liquid-flow constriction therebetween.

23. A method of analyzing for the presence of an analyte in a liquid sample, in which method reagents of the analysis are combined in sequential steps, comprising: placing a predetermined amount of sample into a container having an opening; and moving an elongated stalk inwardly through the container opening to sequentially expose segments of the stalk's length to the interior of the chamber, each reagent bearing stalk segment employed in the chemical analysis to perform the steps of the analysis.

24. A method of analyzing for the presence of an analyte in a liquid sample, in which reagents of the analysis are combined in sequential steps, comprising: providing a reaction vessel comprising a container having an opening; an elongated stalk, slidably receivable in the opening and movable inwardly through the opening to expose segments of its length to the interior of the chamber and having a plurality of segments along its length, each reagent bearing employed in the chemical analysis; placing a predetermined amount of sample into the containe ; moving the stalk inwardly through the opening to sequentially expose the reagent-bearing segments to the container interior allowing the reagents borne by the segments to sequentially contact the sample to perform the analysis steps.

25. Method of analyzing for the presence of an analyte in a liquid sample, in which method the liquid sample is contacted with an analytical reagent, comprising: placing a predetermined amount of sample into a container having an opening beneath the level of the liquid sample, and moving upwardly through said opening in a liquid tight manner an elongated stalk bearing a segment containing said reagent to bring said reagent into contact with the sample.

26. A method of analyzing for the presence of an analyte in a liquid sample, in which reagents of the analysis are combined with the sample in sequential steps to produce a detectable product comprising: placing a predetermined amount of sample into a container having an opening; moving an elongated stalk inwardly through the container opening to sequentially expose segments of the stalk's length to the interior of the chamber, each reagent bearing stalk employed in the chemical analysis; and determining the presence of the analyte by detecting the product of reactions of the reagent.

27. The method of claim 23 further comprising mixing the liquid sample about the stalk to facilitate reactions among reagents and the analyte.

28. The method of claim 27 wherein the mixing is accomplished by axially reciprocating mixing means about the stalk.

29. The method of claim 28 further comprising preferentially flowing liquid past the stalk to produce mixing using a generally tubular mixer, the tubular- mixer having an inner diameter greater than the outer diameter of the stalk and wherein the mixer has an outer diameter less than the inner diameter of the container and the difference in diameter between the stalk outer diameter and the inner diameter of the mixer is greater than the difference in diameter between the outer diameter of the mixer and the container inner diameter.

30. The method of claim 27 wherein the mixing is accomplished by axially reciprocating a generally tubular mixer having an inner surface of non-uniform cross section about the stalk.

31. The method of claim 23 further comprising waiting a predetermined time after a reagent-bearing segment is exposed to the container interior and contacts the liquid sample to allow the reagent to react with analyte or products formed by reactions between the analyte and other reagents before the next reagent-bearing segment is moved inwardly through the container opening.

32. The method of claim 23 further comprising moving the stalk inwardly through the container opening until a rib positioned below the stalk segment being exposed to the container interior and extending radially from the longitudinal axis of the stalk sealingly engages the container opening.

33. The method of claim 23 further comprising moving the stalk through a housing having a wall extending outwardly from the container opening, the housing wall defining a channel closely receivable about the stalk, to sealingly contact a plurality of ribs dividing the stalk into reagent-bearing segments and extending radially from the longitudinal axis of the stalk before moving the stalk inwardly through the container opening.