GB2064779A - Flow-through analysis apparatus - Google Patents

Abstract

A flow-through analysis apparatus comprises a flow-through channel (44), a measurement probe (54) located in the channel (44) and means (52) for increasing the velocity of the medium to be analyzed in the vicinity of the measurement probe (54). The probe may be ion selective or photoelectric. <IMAGE>

Description

SPECIFICATION Flow-through analysis apparatus The present invention relates to measurement devices, and in particular, to a flow-through analysis apparatus for a liquid or gas which takes a plurality of measurements while the medium being monitored is in a continuous flow path using one or more flow-through channels.

Conventional devices utilized to obtain measurements of components in a flowing medium generally provide a canal or flow-through channel which has a constant cross-section over its entire length. The sensitive measuring surface of a probe extending into the flowing medium with the channel thus forms a continuation of the inner wall of the canal or channel in order to avoid cavities or protrusions extending into the flowing medium, thereby avoiding turbulence or dead space which may be introduced perpendicular to the direction of the fluid material to be measured.When very small amounts of test material are to be measured, it is the practice to keep the cross-sectional area of the flow-through channel as small as possible and to increase the width of the channel proximate the measuring probe or electrode thereby providing a measuring chamber so that the active portion or surface of the probe (i.e. an ion-selective electrode or photometric measuring device) may come into intimate contact with the medium to be analyzed. The dimensions of the chamber juxtaposed to the measuring surface of the probe generally has dimensions which are of the order of magnitude of the dimensions of the flowthrough channel since they cannot be reduced and still provide accurate measurements.

In all flow-through measuring devices a problem arises when two different samples, originally well separated, follow each other through the measuring apparatus. The original sharp spacing and definition between the test materials of different composition is not maintained. In the frontal area between the samples, a greater or lesser amount of mixing may occur. This effect is sometimes referred to as sample drag. Because of this sample drag, an increase in the time is needed to obtain a stable value of the analysis measurement so that the first material and the following material provide measurements which are correct for both samples, when both samples are of different material and flow sequentially through the system. In an analysis system which has a quick response time, the resulting measurement delay is caused solely by sample drag.The sample drag therefore has a substantial influence upon the minimum volume sample which may be utilized to obtain a reliable measurement and the number of sequential samples which can be analyzed in a given time will be determined by the amount of sample drag.

In many applications, the aforementioned factor is of great importance in the efficiency or speed of an automatic measuring system. It is of deep concern in automatic measuring equipment which is utilized in clinical chemistry for the analysis of serum samples. It is obvious that in a system, utilizing very small material samples and requiring that a large number of samples to analyzed per unit time, that increasing the speed of analysis, and obtaining more readings per unit of time, is particularly advantageous.

In other known systems where analytical measurements are made on small samples of medium, problems arise because of the trapping of air bubbles in the measuring channel or measurement chamber which interferes with obtaining the proper measurement of the medium flowing therethrough. The behavior of air bubbles in a miniaturized flow-through system with a low stream velocity is influenced more by internal barrier layer effects than by the mechanism used to drive the medium through the channel so that for example, a substantially spherical bubble whose diameter is greater than the diameter of the outflow channel of the measuring chamber can only be removed from the measuring chamber with great difficulty. The reason for this is that in order to deform an air bubble the energy required is greater than the energy transferred to the air bubble by the basis of the fluid flow.

The present invention seeks to provide an apparatus suitable for analysing a medium which has a minimum amount of sample drag.

According to the invention, there is provided a flow through apparatus for analysing a medium comprising a flow through channel provided an unobstructed path, free of dead zones, for the medium and a measurement probe in the flow through channel wherein means are provided for increasing the velocity of the medium in the vicinity of the measurement probe.

The invention will now be described in greater detail by way of example, with reference to the drawings in which: Figure 1 is a partial cross-sectional view, in elevation, of a conventional measuring probe cooperating with a conventional flow-through channel to measure a component of a medium flowing in the flow-through channel; Figure 2 is a partial cross-sectional view of a flow-through channel utilized with a measuring probe, according to the principles of the present invention; Figure 3 is a partial cross-sectional view in elevation of an alternative embodiment of a flowthrough channel cooperating with a measuring probe; Figure 4 is a partial view taken along the line 4-4 of Fig. 3;; Figure 5 is a partial cross-sectional view, in elevation, of a plurality of measuring probes cooperating with a flow-through channel fabricated in accordance with the principles of the invention; Figure 6 is a partial cross-sectional view of another embodiment of a flow-through channel of the invention cooperating with a plurality of measurement probes; Figure 7 is a partial view in cross-section of yet another embodiment of a flow-through channel, according to the invention, with a plurality of measuring probes cooperating therewith; Figure 8 is a cross-sectional view in elevation taken along the line 8-8 shown in Fig. 7;; Figure 9 is a cross-sectional view in elevation taken along the line 8-8 of Fig. 7 showing an alternative embodiment of the invention, providing a flow-through channel by inserting a member having a tapered cross-sectional which is symmetrical along the longitudinal axis of the flow-through channel; Figure 10 is a partial cross-sectional view in elevation of yet another embodiment of the invention which has measurement probes disposed in the narrowing member utilized to increase the velocity of the medium flowing the flow-through channel; and Figure 11 is a partial cross-sectional view of yet another embodiment of the invention shown in elevation.

In Fig. 1, a partial view of a prior art measuring arrangement 10 includes a housing 1 2 having an in-flow channel 1 4 and an outflow channel 1 6. The in-flow channel 14 terminates in a generally larger area 18 forming a measuring chamber 1 8. Generally, the in-flow and out-flow channels have a circular cross-section and terminate in a cylindrically-shaped measuring chamber 1 8. An aperture 20 is provided in the housing 1 2 for the purpose of receiving a sensor probe 22 therein.The sensor probe 22 may include an ion sensitive electrode, not shown, and is provided with a contact surface 24 which is in intimate contact with the measuring chamber 1 8. Therefore, any fluid medium flowing in the direction of arrows 26 will fill the measuring chamber 1 8 and come into contact with the sensing surface 24 of probe 22, thereby permitting the probe to generate a voltage relating to the component occurring with the flowing medium.

In addition to the apparatus shown, means are of course provided for moving the fluid medium in the direction of the arrows 26 and indicating means are coupled to the probe for providing a measurement of a component occurring in the medium. The medium may suitably be caused to move by the presence of a reduced pressure at a point in its path. The sensor probe 22 may be a radiation sensor device which may be combined with a radiation source on the opposite wall, not shown, to indicate the change in absorption of the medium flowing in the flow-through channel.

A measuring system may include three sequentially arranged probes 22 positioned as shown in Fig. 1 each containing a different sensor which may be sensitive to sodium, potassium and calcium occurring within the flowing medium and a further reference electrode constructed similarly, Other probes may be used to determine several other components in the same test medium. Heretofore, it has been shown that samples moving along and coming into contact with a plurality of probes in this type of system become contaminated and provide erroneous results since remains of a previous sample require a specific amount of time to be washed out of the flow path measuring chamber 1 8 occurring at the beginning of the flow path and therefore the sensing probes disposed downstream come into prolonged contact with samples of components from the preceeding material. Tests performed in accordance with the arrangement as set forth in Fig. 1 have been measured in a series of experiments whose results are summarized in the table of test results set forth hereinbelow designated experiments 1 and 2.

Referring now to Fig. 2 which shows a flow-through channel 30 having an in-flow and outflow portion, 32 and 34, respectively, joined by a constricting portion 36 where the sensing probe 38 is preferably positioned. The flow-through channel 30 provides a smooth continuous path for the medium to be measured to flow therethrough in the direction of arrows 40.

Preferably, in this embodiment the in-flow channel portion 32 and out-flow channel portion 34 is provided with a circular cross-section which gradually reduces the diameter until the constricting portion of the channel 36 is reached. The constricting portion 36 is concentric with the in-flow and outflow channels with the narrowing along the longitudinal axis thereof. Thus, with the configuration set forth the medium flowing in the flow-through channel 30 is permitting to flow undisturbed without turbulence of dead zones although the velocity of the medium will be increased as it flows through the constricted area 36. The measuring or sensing surface 42 of probe 38 thus will have a reduced barrier layer of the flowing material on the surface because of the materials increased velocity. This will permit a relatively rapid exchange of material across the measuring surface between neighbouring fluid samples. Air bubbles which may occur in the flow-through channel and generally lodge in the vicinity of the measuring chamber of prior art devices are not provided with a nesting area and thus, with the increased material velocity, will be moved away from the sensing surface 42 of the probe 38 permitting more reliable and accurate measurements to be made.

Of course, all the embodiments of the present invention also include the additional apparatus for moving the fluid medium and for indicating the component measurement.

An alternative embodiment of the present invention is disclosed in Figs. 3 and 4; Fig. 3 showing an elevational cross-section and Fig. 4 showing a cross-section along the line of 4-4 shown in Fig. 3. The flow-through channel A4 is provided with in-flow portion 46 and an outflow portion 48 and a constricting portion 50 to increase the velocity of a medium flowing in the direction of arrows 52 through the flow-through channel 44. The constricting portion 50 is formed by providing a protrusion 52 extending into the flow-through channel 44. The protrusion 52 in cross-section has the general contour of an airplane wing. Thus, a liquid or fluid flowing in the direction of arrows 52 will be caused to accelerate in velocity in the area of the constricting portion 50 and would reduce in velocity as it passed into the outflow portion 48 of the flowthrough channel.As shown in Figs. 3 and 4 the cross-section of the flow-through channel is substantially rectangularly shaped.

The measuring sensor or probe 54 may be ion selective and be of the type which is disclosed in U.S. patent application No. 037,232 filed May 8, 1979, and now U.S. patent No.

issued . This sensing probe includes a metal lead or contact 56, an ion conductive, oxygen impermeable coating and an ion selective membrane 60. The measurement of contact surface 62 of the probe 54 is positioned flush with the inner wall surface 64 of the constricting portion thereby providing a smooth surface for the medium to flow past without being subjected to any protrusions to cause unneeded and unwanted turbulence.

Fig. 5 shows in cross-section a flow-through measurement arrangement wherein a plurality of sensor probes 66, 68 and 70 are utilized in a housing 72 which is adapted to receive the probes and is also provided with a flow-through channel 74 through which a medium may flow in the direction of arrows 76. The flow-through channel 74 is provided with a plurality of protrusions 78, 80 and 82 which have the general shape, in cross-section, of an airfoil, thereby enabling the velocity of a medium flowing in the flow-through channel to be accelerated in the constricted areas of the channel. The protrusions are disposed opposite the sensing surfaces 84, 86 and 88 of probes 66, 68 and 70, respectively.The probes 66, 68, and 70 are of a type suitable for measuring sodium (Na+) potassium (K+) and calcium (C+ +), or any other ion selective electrodes or similar measuring probes and may also include a reference electrode disposed downstream or elsewhere in the flow-through channel, which is not shown. The number of sensing probes may vary depending upon the number of measurements to be made.

Preferably, the constricted portion increases the mean flow rate of the medium in the flowthrough channel by a factor of four and thus by increasing the speed in the vicinity of the probe each sensing surface is washed of the contamination of the previous sample measured so that the time appearing beneath the probe sensing surface is substantially reduced. With the configuration as set forth it is possible to measure several parameters of a single sample consecutively and continuously. The sample drag in such a system is markedly reduced when compared to the drag supplied in a conventional system because the residues that normally remain in a measurement chamber are required to be removed before the probe can get an accurate reading on the next sample of material to be measured.Experimental results tabulated in the chart hereinafter compares a conventional flow-through channel having measuring chambers of the conventional design with the flow-through channel as set forth in the instant invention. The improvement in the amount of time necessary for performing a stable measurement clearly indicates that the arrangement as set forth herein is superior to those devices known in the prior art.

A further embodiment of the present invention is disclosed in Fig. 6 wherein a housing 90 is adapted to receive a plurality of measuring probes 92, 94, 96 and 98 with each of their contact surfaces 100, 1 02, 104 and 106, respectively, being in contact with the flow-through channel 108 provided in the housing 90. The medium to be analyzed flows in the direction of arrows 110 and is caused to increase in velocity in the vicinity of the sensing surfaces of each of the probes because of the alternating airfoil-shaped protrusions 112, 114, 11 6 and 11 8 provided proximate each of the probes which alternate as they appear in position along the flow-through channel.

Referring now to Figs. 7 and 8 in which yet another embodiment of the present invention is disclosed, Fig. 7 is a cross-sectional view in elevation wherein a housing 1 20 is adapted to receive a plurality of sensor probes 1 22, 1 24, 126, 128, 130, and 1 32 with their contact surfaces flush with the inner wall 1 36 and 1 38 of flow-through channel 1 34. The medium to be analyzed flows in the direction of arrows 140 and by virtue of the constricting element is divided into two flow paths while being given an increased velocity in the vicinity of the measuring probes.As shown in Fig. 8, the constricting element 142 is sandwiched between the housing elements 1 20 and held together by a plurality of screws 144, 146, 148 and 1 50 forming the two constricting portions 1 52 and 1 54 of the flow-through channel 1 34.

In Fig. 9 yet another embodiment of the present invention is disclosed. Fig. 9 shows a crosssectional view taken along the line 8-8 of Fig. 7 wherein the housing 1 20 is provided with a flow-through aperture having 2 circular cross-section, is provided with a constricting element 1 56 having a circular cross-section and is tapered along the longitudinal axis of the flow-through channel 140 in a manner corresponding to that shown for constricting element 142 in Fig. 7.

Constricting element 1 56 is held in position by means of screws 1 58 and 1 60 which are received in counterbores 1 62 and 164 provided in the constricting element 1 56 thereby providing a reduction in the flow-through channel in the vicinity of probes 1 22, 1 24, 1 26, 128, 130, and 1 32 which will increase the velocity of a medium flowing in the flow-through channel 140 in the vicinity of the sensing probes. In the embodiments shown in Figs. 7 and 9 the reference sensing element (electrode) has not been shown since they may readily be located elsewhere in the fluid-flow path.

Providing two separate constricting areas in the flow-through channel has the advantage that a plurality of probes may be placed on one side and in contact with the flowing medium in one constricted area while the reference probe may be placed in the other constricted area (area of increased velocity) so that reference electrolytes used in the reference probe will be unable to affect the sensing probes placed in the other constricted channel thereby increasing their accuracy. When the embodiment shown in Fig. 9 is utilized, the screws 1 58 and 1 60 preferably made of synthetic material or a metal covered by an insulating synthetic material in order to avoid contact potentials which may be introduced by the presence of metals in the flowing medium.

Figs. 10 and 11 are cross-sectional views of yet other embodiments of the present invention which utilize constrictirg elements, in particular element 1 66 in Fig. 10 and 1 68 in Fig. 11, that extend in the longitudinal direction and are rotationally symmetrical. The sensing elements or probes 1 70, 1 72 and 1 74 and probes 176, 1 78 and 1 80 are disposed within the constricting elements 1 66 and 1 68 respectively and are placed at point of maximum velocity generated in the fluid-flow paths 184 and 1 86 respectively.The electrically conductive leads of the sensing probes extend through the support for the constricting element 1 66 where they are connected to an analysis apparatus 1 94. The support member 1 88 for the constricting element 1 66 is provided with a threaded portion 1 90 which cooperates with mating threads provided in the housing 1 92 in which the flow-through channel 184 is provided. The medium to be analyzed flows in the direction of arrows 1 96 and is led past the constrictive elements and past the support portion 1 88 and continues in the flow-through channel.The constricting elements may be removed from the fluid-flow path in order to modify or repair the probes if it should become necessary.

In the embodiments shown in Fig. 11 the supporting portion 1 98 with the constricting element 1 68 extends through the side wall of housing 200 which may be suitably retained therein by frictional forces or an epoxy. The leads from the measuring probes 176, 1 78 and 1 80 may extend through the support portion and be wired to the analysis equipment 202.

EXPERIMENTS Several experiments have been performed with the instant apparatus in order to indicate their improved performance over the devices heretofore utilized. Four different types of measuring arrangements have been compared. Each utilizes ion selective probes for sodium (Na+), potassium (K+) and calcium (Ca+ +). These tests have been performed with the arrangements as set forth below: Type 1 - utilizes a conventional prior art flow-through channel as shown in Fig. 1 with a single measuring block (housing). The measuring probe was placed in the block for each measurement. A reference electrode was placed elsewhere in the flow-through channel or stream after the measurement probe.

Type 2 - utilizes a conventional system and measurement block as shown in Fig. 1 with three probes inserted serially in a single block with the reference electrode placed downward in the flowing stream proximate to the measurement probes.

Type 3 - utilizes a system in accordance with the present invention as shown in Fig. 5.

Three separate probes were utilized. These probes were sensitive to sodium (Na+), potassium (K+) and calcium (Ca+ +). The probes were connected in series in a single block with the reference electrode similarly located downstream in the flowing stream in a subsequent unit of the same construction.

The geometry of the measuring arrangement preferably is so chosen that the increase of velocity in the location of the maximum protrusion is increased by a factor of approximately four.

Type 4 - the measurements were performed with a configuration shown in Fig. 5 with three similar probes plus a reference electrode in a row. The housing was fabricated from an acrylic glass block. The flow-through channel was provided with a rectangular cross-section having the dimensions of 2 mm by 1 mm and a total length of approximately 40 mm. The inflow channel and the outflow channels for the medium flowing therein was provided by polyvinyl chloride hoses. The constricting protrusions located in the medium flow path had a transverse cross section of an airplane wing with similar dimensions. Total length of the protrusion is approximately 6.7 mm with a maximum height of approximately 0,75 mm located 2,1 mm downstream from its point of connection with the base.

The first protrusion commences about 4 mm downstream from the leftmost edge of the measurement block. The free distance between two adjacent protrusions is approximately 5 mm.

With the measuring arrangement as set forth in Fig. 5, it has been found that the velocity increase is approximately four times since at this point a cross-sectional area of the channel is reduced to about one quarter. (Type 3) The dimensions of the conventional measuring system used for Type 1 and Type 2 experiments are substantially comparable to those of the measuring system used for Type 3 measurements. The cross-section of the channel used in Type 4 measurements has been further modified.

The measurements performed with the electrolyte solutions have a flow-through rate of 300 microliters per minute and are so arranged that in each change of composition of the test solution an air bubble is introduced to separate one solution from the other as they pass through the system. This technique is generally utilized when a plurality of individual test samples are to be evaluated. The test were performed by sucking the solution through the measuring equipment. The measurement solutions have been standardized utilizing standard solutions having components therein similar to blood. Solution No. 1 includes 0.8 mmol calcium ions per liter, 3 mmol potassium ions per liter, 110 mmol of sodium per liter. Standard solution No. 2 includes 3 mmol of calcium ions per liter, 7 mmol of potassium ions per liter, and 1 50 mmol of sodium ions per liter.In both solutions the anion is chloride in aqueous solution.

In the table shown below, the stabilization time (T) is defined as the time between t, at which a new test solution reaches the reference electrode and t2 the time at which the measuring indicator has reached approximately 99% of its new measured value. Additional tests were performed with Types 3 and 4 measuring setups utilizing blood as the test medium and the results are shown in the table.

A comparison of the stabilization times that are obtained using a measurement system of Type 1 and Type 2 shows that where several conventional measuring chamber are used in sequence the problem of sample drag and the increase in stabilization time is substantial. As indicated in the electrode probe measuring sodium, which is positioned in the first position in the multiple flow-through arrangement setup of Type 2, the response time is substantially the same order of magnitude as would be expected if the sodium electrode were utilized in an individual conventional measuring housing as shown in Fig. 1. With the second probe in the series being the potassium electrode of Type 2 there is already a substantial delay time when compared to an individual housing measurement.With a plurality of probes affixed in a housing, in the system of Type 2, the delay time with the calcium probe is even greater until stabilization is reached, when compared to a measurement taken in a single housing. Because of the sample drag, the calcium electrode has the longest stabilization time which is then followed by the potassium and the sodium electrodes.

The measurements clearly indicate that when utilizing a single flow-through housing that the calcium electrode has the quickest stabilization time when compared to the potassium or sodium electrodes. As indicated by the data obtained, substantial advantages have been gained when the multiple series flow housing arrangement is utilized as shown in Type 3 as compared to the multiple series flow-through system known in the prior art (Type 2) when an aqueous electrolyte was used for the comparison measurements. The stabilization times of the probes utilizing the construction of the instant invention are each less than one second. The sample drag is clearly substantially reduced with this construction and the relative stabilization time of each of the probes is maintained in accordance with the data obtained in utilizing an individual housing for each particular measurement probe.

The flow-through system fabricated in accordance with Fig. 5 utilizes unsymmetrical protrusions on the channel walls opposite the electrodes. If the flow in this type of system is reversed, then substantially increased drag times (time to stabilize) are observed (see the last line in the table under Type 4).

The results indicate that the probes positioned downstream take a much longer time to stabilize because of the dead zone areas which occur, thereby increasing sample drag. As indicated the flow-through channels having unsymmetrical forms are optimized for a unidirectional flow of material to be analyzed, for a bi-directional flow of material to be analyzed the symmetrical form of constricting the material flow in the channel is to be preferred.

A comparison of experiments 3a and 3b as well as 5a and 5b shows that the intended improvement caused by constricting the fluid flow to increase its velocity in the vicinity of the probe depends upon the test medium chosen.

Where blood is utilized as the test medium, a comparison of experiments 5b with 2 and 3b shows that a moderate increase in the flow of the material in the flow-through channel by a factor of 1.54 to 1 (see experiment 5b) gives a substantial improvement in the stabilization time.

It is also to be noted that a further increase in the velocity of the material being analyzed to 4 to 1 (see experiment 3b) does not yield a substantial improvement.

On the other hand, the stabilization time when using an aqueous electrolyte as the test medium are substantially decreased when the material flow velocity is increased four times (see the results of experiments 2, 5a and 3a).

Thus, these results indicate that a relatively small increase in the velocity of the material being analyzed in the vicinity of the sensing probe in the range of 1,1 7 until 5 to 1, typically of 1,54 to 1 lead to a reduction of the stabilization time for both blood and aqueous electrolyte substantially equivalent thereto.

This range is apparently particularly useful for systems which are intended for measurements for blood and aqueous solutions as well.

Hereinbefore has been disclosed a flow-through apparatus which is capable of substantially reducing the stabilization times of measurement probes utilized with automatic analysis equipment for analyzing large quantities of sample materials (liquids and gases) with a minimum of time between sample measurements.

TEST RESULTS Flow Through Experiment Test Medium Stabilization Time System Volume Type Number T (sec) (MI) Na+ K+ Ca++ aqueous Type 1 1 electrolytic 4-5 2-3 =1 =15 solution aqueous Type 2 2 electrolytic 4-5 11-12 16-18 =40 solution a) aqueous 3a electrolytic 0.85 0.58 0.54 Type 3 solution =50 3b b) blood 1.05 1.05 2.8 Type 3 aqueous (with reverse 4 electrolytic 5.5 2.8 =0.5 =50 direction of solution flow) a) aqueous 5a electrolytic 1.25 1.5 1.7 Type 4 solution =50 5b b) blood 1.6 1.73 2.1

Claims (14)

1. A flow-through apparatus for analyzing a medium comprising a flow-through channel provided an unobstructed path, free of dead zones, for the medium and a measuring probe in the flow-through channel wherein means are provided for increasing the velocity of the medium in the vicinity of the measurement probe.

2. An apparatus according to Claim 1, wherein the increase in velocity in the vicinity of the measurement probe relative to other portions of said channel is between 2:1 and 10:1.

3. An apparatus according to Claim 1 or 2 wherein the increase in velocity is between 4:1 and 6:1.

4. An apparatus according to Claim 1, 2 or 3 wherein the medium to be analyzed is moved through the flow-through channel by reduced pressure provided at a point in the channel.

5. An apparatus according to any one of Claims 1 to 4, wherein the means for increasing the velocity of the medium to be analyzed comprises means for reducing the cross-sectional area of the flow-through channel in the vicinity of the measurement probe.

6. An apparatus according to Claim 5, wherein the reduction of the cross-sectional area is in the range of 1:2 to 1:10.

7. An apparatus according to Claim 5 or 6, wherein the reduction of the cross-sectional area is between 1:4 and 1:6.

8. An apparatus according to Claim 5, 6 or 7, wherein the reduced cross-sectional area of the flow-through channel is concentric with the central axis of the channel.

9. An apparatus according to Claim 5, 6 or 7, wherein the means for increasing the velocity of the medium comprises a protrusion extending into the flow-through channel.

10. An apparatus according to Claim 9; wherein the protrusion extends longitudinally within the channel and has a symmetrical cross-section.

11. An apparatus according to Claim 9 wherein the protrusion extends longitudinally within the channel and has a generally winged-shaped longitudinal cross-section.

1 2. An apparatus according to Claim 9, 10 or 11 wherein a plurality of the protrusions are alternately disposed on opposite internal wall surfaces of the channel.

1 3. An apparatus according to Claim 5, 6 or 7, wherein the means for reducing the cross sectional area comprises a generally elongated pear-shaped body disposed in the flow-through channel.

14. An apparatus according to Claim 13, wherein the pear-shaped body is spaced from the inner wall of the channel.

1 5. An apparatus according to Claim 1 3 or 14 wherein the pear-shaped body is symmetrical about its longitudinal axis.

1 6. An apparatus according to claim 5 and any one of Claims 8 to 1 5 when appendent directly or indirectly from Claim 5, for alternative use for colloidal and aqueous fluids wherein the reduction of the cross sectional area is in the range of 1:1,1 7 to 1: 5.

1 7. An apparatus according to Claim 16, wherein the reduction in the cross-sectional area is 1:1,54.

1 8. A flow-through analyzing apparatus substantially as described herein with reference to the drawings.