GB2112519A - Hydrodynamic sample introduction system - Google Patents

Abstract

A sample introduction system comprises a sampling circuit (10-2-1-3) and a carrier stream circuit (8-4-1-5) where the two circuits share a volumetric conduit (1) which is at all times connected to and simultaneously opened to both sampling and carrier circuits.This system allows, by a controlled combination of hydrostatic and hydrodynamic forces, to create a well- defined sample zone within the volumetric circuit (1) and then to transport this zone, in a well-reproduced manner, into a continuous flow analyser (6) where an assay of sample solution components may be performed quantitatively, if necessary with the aid of chemical reactions. <IMAGE>

Description

SPECIFICATION Hydrodynamic sample introduction system The present invention relates to a sample introduction methodology by means of which a volume of a liquid sample zone, which is to be introduced into an unsegmented liquid carrier stream, can be defined on the basis of a controlled combination of hydrostatic and hydrodynamic forces, said well-defined sample zone subsequently being transported to a flowthrough analyzer in which a species present in the sample solution - possibly formed as a result of one or more chemical reactions taking place - can be evaluated quantitatively in a flow-through detector arrangement.

Assay by means of the Flow Injection Analysis (FIA) technique (see for example our U.S. Patents Nos. 4,022,575 and 4,224,033) requires that a sample solution to be analyzed is introduced into an unsegmented carrier stream as a well-defined sample zone, the volume and geometry of which is strictly reproducible. The conventional sample introduction techniques can be divided into three groups which are based on the following principles: (1) Direct injection of a precisely metered amount of sample solution into a carrier stream (see for example our U.S. Patent No. 4,022,575); (2) Insertion of a precisely metered amount of sample solution by means of a valve (see for example our U.S. Patent No. 4,224,033); and (3) Intercalation of a precisely metered amount of sample solution by means of a system of magnetic valves (see for example our U.S. Patent No.

4,177,677).

By the first-mentioned method of sample introduction, the sample solution is injected by means of a syringe provided with a hypodermic needle which is pierced through the wall of the conduit in which the carrier stream is propelled, but this method of introduction is however not always sufficiently reproducible, nor does it lend itself readily to automation.By the introduction method referred to in Group (2), the use of sliding or rotary valves with exact bores of precisely metered volume (or possibly also provided with external sample loops in order to accommodate larger sample volumes) - and where the sample bores partly can be brought in a position where they, with sample solution, are made to be part of the carrier solution circuit so that the samples can be brought to be transported by the carrier stream - is most common as it yields highly reproducible results and is easily automated. Its drawbacks are the high cost of the valves which must be very precisely machined, and the mechanical wear of the moving parts which must be kept leakproof even after thousands of injections.By the introduction method referred to in Group (3), use is made of several (at least four) magnetic valves which, in a certain sequence and at predetermined time intervals, can be opened and closed. Also this method of introduction lends itself readily to automation, but it requires obviously ancillary electronic timing circuitry. Its greatest drawback is however that the elastic components on which the magnetic open/close valves mechanically operate eventually become worn and deformed as a result of the repeated localized pressure exerted by the wedge of the magnetic valves, and thus with time might fail to open or close completely, which will result in a slowly increasing malfunction which can be extremely difficult to identify.

The common denominator of all three sample introduction designs mentioned above is that the metered volume of sample solution to be introduced is defined by the volume of a solid container (bore, loop length, etc.) which immediately prior to intro duction of the metered sample zone into the carrier stream is hermetically closed (that is, by introduction method 1 the metered volume of liquid sample corresponds to the volume trapped under the plunger of the hypodermic syringe; by introduction method 2 the liquid in the closed container is represented by that volume of sample liquid which is enclosed within the bore or sample loop of a sliding or rotary valve while the valve is being switched from the sampling to the introduction position; and by introduction method 3 the closed container, and the metered volume therein, corresponds to that volume which the magnetic valves entrap in a tube or conduit of a given length and diameter).

It will be demonstrated in the present invention that the volume of liquid sample zone, which is to be introduced into a carrier stream, equally well can be defined on the basis of a controlled combination of hydrostatic and hydrodynamic forces. Therefore, in our invention that container which serves for metering the volume of the sample zone can thus be permanently connected to and at all times opened to both the sampling and the carrier stream circuits; that is, be one for both circuits' common portion of conduit. The obvious advantage of such a sample introduction system is the simplicity of construction and the total absence of any moving parts, which not only makes the hydrodynamic sample introduction system extremely reliable but also, in fact, completely maintenance-free and thus long-lasting.

The invention will be described in more detail in the following, and in this connection reference will be made to the accompanying figures, of which Figure 1A states the components of the system which are: (a) a sample introduction container 1 consisting of a given length of conduit (e.g. tube) of small inner diameter (typically 0.5 mm i.d., and typically of a length of 5 to 100 cm, depending on the volume of sample solution which is to be introduced); (b) liquid propelling means 2,3,4 and 5 (e.g.

peristaltic pumps), partly to serve the sampling circuit by simultaneous operation of 2 and 3, and partly to serve the carrier stream circuit by simultaneous operation of 4 and 5; and (c) a timing device to control the liquid propelling aggregates 2, 3 and 4, 5, respectively, so that these can either be stopped (STOP) or activated (GO). It is essential that the liquids are delivered in the directions shown by the arrows on the figure, and that the liquid propelling devices used effectuate that the columns of liquid present in each individual circuit, except the one present in that portion of the conduit which is common for both circuits, is kept completely still when the liquid propelling devices (pumps) belonging to each individual circuit are not activated.Furthermore, it is necessary that the volumetric pumping rates in and out of the sampling circuit is as close to unity as possible, which requires that pumping aggregates 2 and 3 operate at exactly the same volumetric pumping rates. This is however very easily accomplished, for instance by using a two-channel peristaltic pump equipped with two identical pumping tubes. Exactly the same requirements to identify for in and out pumping of liquid apply for the carrier stream circuit, served by pumping devices 4 and 5.During the sampling cycle, sample solution 9 is drawn from a source 10 to be monitored (this might for instance be a reactor in which a chemical reaction takes place which has to be controlled, or it can be a pipe transporting a given solution, or it may possibly be a blood artery) by means of pumping devices 2 and 3 until the volumetric conduit 1 is thoroughly flushed and filled all along its length with sample solution.During the entire sampling cycle, pumping devices 4 and 5 are kept deactivated and therefore the columns of liquid to the left of conduit 1 will prevent any sample solution to enter the carrier stream circuit. After the sampling cycle has been completed, pumps 2 and 3 are stopped while pumps 4 and 5 are activated, thus introducing a well-defined sample zone (i.e., corresponding to the length of conduit 1) into the flowthrough analysis system 6, in which possible chemical reaction and subsequent detection of the introduced sample takes place. Because pumps 2 and 3 are now kept deactivated; that is, the columns of liquid to the right of conduit 1 are now stationary, only that amount of sample solution which was originally present in conduit 1 can be transported into the analyser system 6, namely by means of carrier solution 7 aspirated from reservoir 8.The carrier solution is thus, during this second cycle, the only moving liquid stream through the system, and pumps 4 and 5 are kept activated until the entire dispersed sample zone has passed the analyser system 6 which is indicated, on a recorder connected to the detector, by the registered signal returning to the baseline and thus reporting that the carrier solution cycle has been completed. Pumps 4 and 5 can then be stopped while pumps 2 and 3 may be restarted to begin a new measuring cycle. As the sampling and carrier cycles totally may be completed within one minute or less, the system is well-suited for e.g. continuous monitoring of industrial processes or medical applications such as critical patient care supervision.

By the application described above, the sample solution is introduced into the analysis system intermittently. It is however also possible to use the depicted system for continuous measurement of a given sample stream, while the hydrodynamic sample introduction principle is now used to verify the calibration of the applied flow-through analyser simply by introducing intermittently a standard solution of that species which is continuously being monitored; that is, it can be said that the roles of the sample and carrier streams here have been reversed. This may be illustrated by referring to Figure 1A where pumps 2 and 5, simultaneously and with identical volumetric pumping rates, now continuously aspirate that a solution 9 which is to be monitored, and which solution is propelled via conduit 1 to the analyser 6.During this procedure, pumps 4 and 3 are deactivated, and the columns of liquid belonging to this circuit - except the volume present in that portion of conduit which is common for both circuits, i.e. 1 - is kept still. When the analyser is to be adjusted or recalibrated, pumps 2 and 5 are stopped and pumps 4 and 3, which both pump with identical volumetric pumping rates, are activated. By this procedure the volumetric conduit 1 is filled with standard solution 7 from reservoir 8, and when pumps 4 and 3 are stopped and pumps 2 and 5 reactivated, the standard solution zone metered in conduit 1 will be transported by the sample solution 9 into the analyser 6 and here give rise to a signal which, in respect to the continuously registered sample signal, can be used for adjusting or recalibrating the flow-through analyser.

If the volume of sample material available is limited and/orthe sampling cycle has to be kept short, as is often the case when analyzing larger series of discrete samples, the hydrodynamic sample introduction system can be modified and further simplified, as depicted in Figure 1 B. Here, sample solution 9 is aspirated from a sample cup 11, placed for example on a sampler or a sample tray, via a conduit 12 which is made as short as practically possible, and runs from here into conduit 1, as drawn by activation of pumping device 3, the sampling cycle being limited to last as long as the volumetric conduit 1 is entirely flushed and filled with sample solution 9.As in the first-described example, pumps 4 and 5 are kept deactivated during the sampling cycle and are restarted only when the content of conduit 1 is to be introduced into the flow-through analyser 6 at which point of time pump 3 is stopped. It should be emphasized that in the absence of the controlling pump (sic 2 in Figure 1A), the volumetric pumping rates of pumps 4 and 5 must be exactly identical because (a) if pump 4 pumps faster than pump 5, then the difference in the volumetric delivery rates of the carrier stream 7 will cause that part of the carrier stream from reservoir 8 will be forced to cup 11 and thus diluting the sample material before the next sampling cycle; or (b) if pump 4 pumps slower than pump 5, then some of the sample material 11 will be aspirated even during the carrier cycle and thereby cause a false signal on the recorder, registered as an increase of the baseline signal. However, the fact that a satisfactory balance can be achieved, and reproducibility can be maintained, is demonstrated in Figures 2A, B and C, which figures are photographic reproductions of the recorder signals obtained in a series of spectrophotometric measurements as registered by the analysis system 6 equipped with a flow-through cell placed in a spectrophotometer which was connected to a chart recorder so that it was possible continuously to monitor the absorbance (abs) of the carrier stream, which in itself was colourless.Thus, by injecting a dye solution as sample solution 9 into the system and in the present case aqueous solutions of bromothymol blue (BTB) were used, the colour of which can be registered photometrically at 620 nm - the sample will during its passage of the analyser system 6 be registered as a peak, the height of which will be proportional to the intensity of colour present which again will be proportional on the one hand to the concentration of colour of the sample introduced into conduit 1 and on the other hand to the volume of sample metered in conduit 1; that is, at fixed sample volume (fixed volume of conduit 1) the peak height will be directly proportional to the concentration of colour in the sample solution 9.In Figure 2A there is first shown a series of 15 sample introductions where a sample volume of 25 us was used (that is, conduit 1 consisted of 12.5 cm tubing of an internal diameter of 0.5 mm), and where five different sample solutions of BTB of gradually increasing concentration were each introduced in triplicate; these solutions were prepared from an aqueous stock solution of BTB by successive dilution with water, the volumetric ratio of stock solution and water in the five solutions being 1:4,2:3,3:2,4:1 and 5:0 respectively.

Then the same experiment was repeated but this time 50 us aliquots of dye solutions were introduced (Figure 2B); that is, conduit 1 consisted of 25 cm of 0.5 mm i.d. tubing. As seen from Figures 2A and B, these two series of experiments demonstrated the excellent reproducibility which can be obtained by the hydrodynamic sample introduction method. The last series of sample introductions, shown in Figure 2C, comprises 23 sample introductions obtained over a period of 23 minutes (the attached recorder being run at a lower chart speed than in experiments 2A and B) and where each time 501l1 of the same 4:1 BTB sample solution was introduced. Not only does this experiment show excellent reproducibility of measurement, but the system exhibits furthermore a very high degree of stability in time.

With reference to Figure 1C, yet another embodi- ment of the hydrodynamic sample introduction system will be discussed. The sample solution pumping aggregate is replaced by a piston device such as a syringe 13, containing sample solution 9, which serves for introduction of sample solution via the sample circuit into the volumetric conduit 1, the length and cross-sectional area of which define the sample zone volume. Thus, only two means 4, 5 of solution propelling are needed such as, for example, a two-channel peristaltic pump which, after the sample circuit and conduit 1 have been filled with the sample solution, are started, thus introducing the sample zone into the carrier stream conduit and further into the analyser 6.A necessary prerequisite for satisfactory performance of this embodiment is that the piston in device 13 is held in a fixed position during the operational period of the carrier stream cycle, and that the pumping rates within channels 4 and 5 are identical. The advantage of this approach is the simplicity of the experimental setup; and the possibility of manipulating small sample volumes anaerobically from a donor source such as a patient, for example, into the analytical system. A possible drawback, if the syringe would be operated manual ly, is the necessity of skilled handling.

It should be emphasized that modifications of the invention described above do not affect its basic concept. Such modifications may comprise (a) Replacing one of the solution propelling aggregates, functioning in pairs and servicing the sample solution circuit (such as the pair 2,3 in Figure 1A) and/or the carrier stream circuit (such as the pair 4,5 in Figure 1A), by an open-closed valve which is in open position while the corresponding solution propelling means is active, and in closed position while the corresponding solution propelling means is inactive;; (b) Addition offurtherstreams (14,15 in Figure 1 D) to the system through which additional streams may be added, or withdrawn, from the analysis system 6, provided that the delivery rates are balanced so that exactly the same amount of liquid is delivered into the volumetric conduit 1 by means of propelling means 4 as is leaving it at the opposite end, which requires that the aspirational rate of means 5 must be equal to the net sum of delivery rates of means 4, 14 and 15.Alternatively, pumping aggregate 5 may be replaced by an open-closed valve, with the modifications described in paragraph (a); (c) Addition of one or several volumetric conduits 1,1 1 etc., as these can be placed in series in the sampling circuit so that each individual volumetric conduit is serviced by a separate carrier stream with the aim of performing analyses in a number of analysers 6,6', 6" etc., arranged in parallel, as all what is needed is hydrodynamic and hydrostatic balance and suitable sequential timing of the operating cycles of the sample and carrier stream circuits;; (d) The hydrostatic control can, for a short period of time, be replaced by a hydrodynamic control, as e.g. in the embodiment shown in Figure 1 one may continue to pump the sample solution 9 by means of the synchronized sample solution propelling means 2,3 even after the carrier stream circuit propelling means 4, 5 have been activated so that also the carrier stream 7 is in motion. Thus the volume of sample solution will be increased over that volume which may be accommodated within conduit 1 while solutions are still. The increase of the introduced sample volume depends on the length of the time period during which the operational cycle of the sampling circuit and the operational cycle of the carrier stream circuit overlap each other, and on the respective pumping rates generated by the solution propelling means 2,3,4 and 5. The advantage of this approach, which is characterized in that the hydrostatic control within the sampling circuit and volumetric conduit 1 is replaced during a well-defined period of time by a hydrodynamic control, is that it opens possibilities flexibly to vary the volume of the introduced sample solution by means of electronic control of the repetitive STOP/GO intervals comprising the operational cycles of the respective circuits.

The drawback of th is combined hydrostatic and hydrodynamic control is that the reproducibility of the introduced sample volumes depends on an exact timing of the operational cycles and on the pumping and aspiration rates of the liquid propelling means 2, 3,4 and 5. The previously described hydrostatic control of sample zone introduction, accommodated within the volumetric conduit 1, is independent on these parameters.

With this method of sample introduction, the sample can be pretreated before analysis in a quite simple manner. There can be inserted into the sample tube an ion exchanger, a dialysator, or an extraction apparatus for example, and the character of the sample can be completely changed by the treatment. Avery diluted sample can be concentrated, contaminants which might distort the analysis can be extracted or adsorbed into a column, or the substances of interest can be adsorbed into a column and the eluate be conducted to the analysis apparatus.

Though typical applications and embodiments of the present invention were illustrated by several example, it should be understood that further variations and modifications of the constructions, materials and components described above are possible without deviation from the spirit of the invention, the scope of which is defined in the following claims.

Claims (12)

1. A sample introduction system comprising a sampling circuit and a carrier stream circuit, said circuits sharing a volumetric conduit which is at all times connected to and simultaneously opened to both said circuits, said circuits supplying and withdrawing, on a well-defined time sharing basis, sample solution and non-segmented carrier stream solution with the aim of creating, by means of a controlled combination of hydrostatic and hydrodynamic forces, a well-defined non-segmented sample zone within the said volumetric conduit, said sample zone thereupon being transported by means of said non-segmented carrier stream through the carrier stream circuit with the aim of carrying said sample zone into a continuous flow analysis system provided with a detector.

2. A sample introduction system according to Claim 1, wherein said volumetric conduit, shared by the sampling and by the carrier stream circuit, is a narrow channel, the length and cross-sectional area of which determine the volume of said sample zone as said sample solution is first accommodated within said volumetric conduit and then swept by means of the carrier stream towards said continuous flow analysis system.

3. A sample introduction system according to Claims 1 and 2, wherein said carrier stream circuit is closed at all ends and the non-segmented columns of liquid within the closed carrier stream circuit are held still, with the exception of that section of liquid column which is situated within said volumetric circuit shared by the sampling and the carrier stream circuits while the sampling circuit is in operation, and wherein said sampling circuit is closed at least at one of its two ends so that the columns of liquid within the sampling circuit, with the exception of the column of liquid which is situated within said volumetric circuit, can be kept still while the carrier stream circuit is in operation.

4. A sample introduction system according to all of the preceding claims, wherein the time span of said sampling circuit operational cycle overlaps the start of said carrier stream circuit operational cycle with the aim of introducing a largervolume of the sample solution than that which can be accommodated within the volume of said volumetric conduit.

5. A sample introduction system according to Claims 1 to 4, wherein several volumetric conduits are connected in series, each said volumetric conduit being serviced by a separated carrier stream circuit, each said carrier stream circuit being connected to a corresponding continuous flow analysis system.

6. A sample introduction system according to Claims 1 to 4, wherein several volumetric conduits are connected in series, each said volumetric conduit being serviced by a separate sampling circuit while all said volumetric conduits are serviced by a single common carrier stream circuit.

7. A sample introduction system according to Claims 1 to 4, characterized in that a treatment station for the sample is arranged before the introduction system, said station comprising an ion exchanger, a dialysator or the like.

8. A sample introduction system substantially as hereinbefore described.

9. An apparatus for continuous flow analysis of discrete samples, utilizing a non-segmented carrier stream comprising the hydrodynamic sample introduction system described in the preceding claims; electronic means to control the duration and sequence of the operational cycles of the mechanical means of controlling the movement of liquids within said apparatus; means of propelling, aspirating or stopping liquids within conduits and circuits of said apparatus; flow-through analysis system and flow-through detector disposed to receive said carrier stream containing said sample solution.

10. An apparatus for continuous monitoring of the composition of a liquid stream according to all of the preceding claims.

11. An apparatus for continuous monitoring of the composition of a liquid stream according to Claims 1 to 7, wherein said continuous flow analysis system and the flow-through detector are situated in the sampling circuit through which the sample solution is transported continuously, with the exception of intermittent periods during which said continuous flow analysis system and flow-through detector are being recalibrated or readjusted by means of standard solution, which are for this purpose transported in the form of well-defined zones by the sample stream through the detector.

12. An apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.