GB2104657A - Apparatus for flow injection analysis - Google Patents

Abstract

Apparatus for FIA (Flow Injection Analysis) consists of an operating panel on which there may be mounted a sample injection valve, a measuring cell, measuring instruments and flow connections such as couplings, T- branches. The sample injection valve consists of two bodies (11, 12) in sealing contact with each other and movable in relation to each other so that in two different positions of the valve bodies ducts (13a-f) in one body (11) are connected in various manners to ducts (14a-e) in the other body (12) and an intermediate position (C) all communication through the valve is closed off. The solutions are fed by the application of a constant gas pressure from a reservoir or reservoirs. The valve operates to advance a carrier flow, inject a predetermined amount of sample solution into the carrier flow, and add an additional one or more reagents and/or washing solutions. Connecting lines have the same diameter as the ducts and each is attached with an elastic sealing ring 19 which surrounds the line. The measuring cell may be for potentiometric photometric or spectrophotometric measurement. <IMAGE>

Description

SPECIFICATION Apparatus for flow injection analysis Flow Injection Analysis (FIA) is based on the formation and use of the carefully controlled concentration gradients arising upon injection of a sample in a continuously flowing carrier flow, to which additional reagent flows may be added. It is quite essential that these gradients be able to be controlled with complete precision, and therefore all sample valve designs up to now have used a by-pass.

Our own Swedish Patent 76101 f O 4 0--4 relates to a sample injection device for FIA analyzers, in which a measured sample loop of a predetermined length is alternatingly coupled into an intake line to be filled with a predetermined sample amount, and into the path of the continuously flowing carrier solution to supply the exact sample amount to the carrier solution. A by-pass is continually coupled parallel to the sample injection device, and the sample loop is coupled parallel thereto.

The by-pass has a fluid resistance which is greater than that of the sample loop.

This by-pass prevents pressure from building up in the system when the valve is turned from one position, intake, to the other position, injection.

The build-up of pressure would otherwise cause changes in the speed of the carrier flow and thus affect the precision of the concentration gradient.

This disturbance would be further accentuated if a multi-line system were used without a by-pass, as pressure build-up in the injection line would of course change the mixing ratio between the sample and reagent.

According to the invention, however, the bypass can be eliminated under certain special conditions. The feeding of the fluid flow or flows must take place in a system which always assures constant flow rates regardless of the position of the injection valve, i.e. the pressure in the system must always be constant and pressure must not be built up at any time.

In our previous design, the solutions were fed up to the analyzer itself with pumps, preferably hose pumps. When the flow is cut off, such a pump builds up a pressure in the outgoing line, and this causes a surge in pressure at the valve opening during the very short switch-over delays when injecting samples. The by-pass has served to eliminate such surges in pressure.

According to the invention, however, the fluid flows are advanced by the action of compressed air or another inert gas with a constant pressure from a common pressure reservoir for one or more lines, or possibly separate pressure reservoirs for the lines. At the very low pressure used, as a rule at most 1 bar, and preferably 0.2 to 0.5 bar, a pressure regulator for the gas can also compensate for changes in pressure caused by the change in fluid level in the reservoirs. The actual measurement can then be made in a special flowthrough cell which has also been developed in conjunction with the invention. The analysis results can then be obtained in less than 20 seconds with a reproducibility of better than 1%, using sample sizes of a few microliters and reagent amounts of less than a milliliter.By arranging the various parts of the apparatus on a panel as a "plug-in system" connected with thin hoses, the various components can be interchanged simply and rapidly, easily adepting the apparatus to different analyses.

The invention will now be described in more detail with reference to the accompanying drawings of which; Figs. 1 a and b show schematically the sample injection in a conventional FIA system, Figs. 2a and b show schematically sample injection without a by-pass, Fig. 3 shows schematically sample injection according to the invention with an additional reagent flow, Fig. 4 shows the sample valve according to the invention, Fig. 5 shows the sample valve in Fig. 4 in another position, Fig. 6 shows a section along the line VI--VI in Fig. 5, and Fig. 7 shows a section through the measuring cell according to the invention.

The previous sample injection is shown in Figs.

1 a and b.

The carrier solution flows through the line 1 and through the sample injector 2 or the by-pass 3 and continues through the line 4 to the measuring apparatus.

The addition of an additional reagent after the sample injection through a line 5 is shown in Fig.

1 b. A number of such addition lines can be used in certain analyses. The fluid flows are achieved with a peristaltic pump, preferably for several lines.

Fig. 2a illustrates the new sample injection without any by-pass and with constant pressure in the system. The by-pass can be removed here without any complications, starting from the system in Fig. 1 a and using gas pressure for feeding the solutions. However, it is not possible to immediately go from the system in Fig. 1 b to the system in Fig. 2b without taking further steps, since otherwise the fluid flows in the system 2b would be mixed in different ratios at different points in time depending on whether the injection valve line is open or closed. Thus in order to eliminate the by-pass in a multi-line system, another valve design is necessary in which it is possible to stop simultaneously the flow in all the lines and thus assure constant mixing ratios at all times. Such a system is shown in Fig. 3.The sample is added to the line 1 and the lines 1 and 5 are open or closed simultaneously. Thus the mixing pattern at point 7 is always constant.

One embodiment of a valve design according to the invention is shown in Figs. 4-6. The actual sample valve 10 consists of two discs 11, 12, which are fixed on top of each other with a central screw and are rotatable in relation to each other.

The discs can be made of metal, glass, plastic or any other material which is inert to the solutions used in the analysis and which does not corrode or contaminate the solutions in any way.

In the lower disc there are six ducts, 1 3a,b,c,d,e,f and in the upper disc there are five ducts, 1 4a,b,c,d,e. The ducts in the lower disc extend radially inwards from the edge of the disc and then turn perpendicularly upwards and opn into a hole 1 5a,b,c,d,e,f on top of the disc. There are corresponding holes 1 6a,b,c,d,e in the bottom of the upper disc and the ducts extend from the holes right through the disc. Fig. 6 shows the ducts 13a and 14a in cross section with the holes 1 5a and 1 6a directly opposite each other. If the apparatus with the sample injection valve is not to be placed on a panel, but mounted in another manner, the ducts can of course be drilled straight through the lower disc and the hoses fixed to the bottorn, which would simplify manufacture.

The outermost portion of the ducts is broadened 1 7a,b,c,d,e,f, and the outermost portion is internally threaded 1 8a,b,c,d,e,f. A hose for inflow or outflow with the same diameter as the duct with a surrounding elastic ring 1 9 can be inserted into the outer portion 1 7 of the duct providing an effective seal when a sleeve 20 is screwed into the internally threaded outer portion 18.

The ducts in the upper disc are made in the same manner for connecting hoses thereto.

The lower disc 11 is provided with two stops 21,22, and the upper disc with a handle 23 which abuts against the stops when the disc is rotated.

In the first position against the stop 21, a sample enters into ducts 1 3a through the holes 1 spa and 1 6a in a loop 24 between the ducts 1 4a and 1 4d and continues out through the holes 1 sod, 1 5d, the duct 1 3d and the corresponding hose. In the same manner, the carrier solution goes through the ducts 1 3b, 1 4b, a loop 25, and out through the ducts 1 4e and 1 3e and the corresponding hose.

When the upper disc is rotated and the handle 23 abuts the stop 22 (position B), the sample loop 24 is coupled into the carrier flow path between ducts 13b and 13e.

In position A the duct 1 4c in the upper disc is connected to the duct 1 3c and in position B to the duct 1 3f. These ducts can be used in various ways.

a) Reagent is added either through duct 1 3f or 1 3c to duct 1 4c, which connects to the line from duct 1 3e, i.e. the carrier flow. When the valve position is changed from A to B, there will be a simultaneous stop in all the lines. The purpose of this is to compensate for the lack of a by-pass and to compensate for all changes in the composition of the flows taken together when the branch pipe has more than one line.

b) in the same manner as in a), reagent is fed both through 1 3f and 1 3c, but by placing the valve in the stop position C between A and B, all flows through the valve are shut off simultaneously for stop-flow analysis.

c) To save reagent, water is fed through duct 1 3c and 1 4c in position A when the sample loop is charged with sample solution. This permits continuous washing of the system. Reagent is added only when the valve is placed in position B through ducts 1 3f-1 4c.

d) The same coupling is used as in c) to save reagent, but water or washing solution is coupled to duct 1 3c and reagent to duct 1 3f. It can also be used to effectively wash out the system of all deposits formed in the reactions between sample and reagent. One example is washing with EDTA solution to remove deposits of barium sulphate in determination of sulphate by nephelometry (Ba++ + -BaSO4).

To increase the washing effect, the pump speed for the washing solution can be increased, thus intensifying the washing.

e) Either 1 3c or 1 3f is blocl < ed so that reagent is added to the carrier flow only during the sample charging.

The design has been shown here with the sample addition valve consisting of two round discs in which the ducts are arranged, but the valve can of course also be made as two discs which are displaced longitudinally or as two concentric tubes which are turned to various positions.

The operation of the valve can be done manually but also entirely automatically controlled by the computer used for the analysis. The entire valve need not be in one piece, but can be divided up into a number of small units each controlled separately by the computer according to the desired program.

The valve can of course also be expanded with a number of ducts for charging of two or more reagents at desired locations in the path of the carrier flow.

Measuring cells of various cells can be coupled to the flowing sample solution. A suitable measuring cell for potentiometric measurement consists of a tube through which solution flows, and in which two electrodes are fixed, suitably a reference elctrode and an indicator electrode.

The sample can also be fed directly into the nebulizer of an atom absorption spectrophotometer.

A suitable embodiment of a measuring cell for photoelectric measurement consists of a transparent plastic hose 30 curved in hair-pin shape and fixed in a plug 31 of opaque material.

The same hose can be used in the rest of the apparatus. The hose 30 is held in the plug 31 in the same manner as the hoses to the sample valve with threaded holes 32 in the plug, in which sleeves 20 are screwed, the hose being clamped in place with an elastic ring 19.

The actual hair-pin curve 33 in the hose goes diametrically across a hole 34 in the plug, so that a beam of light 35 can pass straight through to a spectrophotometer. To avoid light diffusion, the plug is placed in a transparent container 36 filled with a transparent liquid 37, for example silicon oil, with approximately the same index of refraction as the material in the hose.

As can the sample charging valve, the measuring cell can also be mounted on the operating panel. A method which we have found to be very practical for putting together the analysis apparatus, is the so- alled Lego systemR in which building blocks provided with cavities can be snapped onto a board provided with projections. On such a LegoR board, the valve, measuring cell, measuring instruments etc. can be snapped into the desired positions and be connected with hoses and then be moved as defied for simple adaption to various analyses.

The apparatus according to the invention can be used for developing new methods of an analysis in a simple and inexpensive manner by virtue of its great flexibility. A single apparatus can be used for all the different FIA analyses required in a laboratory with a wide range of analysis required and can replace other specific and rarely used analysis apparatii.

Claims (14)

1. Method of Flow Injection Analysis, FIA, characterized in that various solutions are fed from a container by applying a constant pressure inside the same, to a sample injection valve which, in addition to ducts for injecting a specific sample amount, also has ducts and lines for injecting additional reagent and/or washing solution, that the measurement is done in a flow-through cell, and that the various units in the apparatus are portably and interchangeably mounted on a control panel.

2. Method according to Claim 1 , characterized in that the connecting lines are of equal or slightly smaller diameter than the ducts in the valve and are fixed to the ducts with an elastic sealing ring placed outside the line.

3. Method according to Claim 1 or 2, characterized in that the valve has a first position for a through carrier flow, for measuring out a specific amount of sample solution and for adding additional reagent or washing solution; a second position in which the measured out sample is introduced into the carrier flow and additional reagent may be added; and an intermediate position in which all ducts are closed.

4. Method according to one of the preceding claims, characterized in that the pressure for feeding the solutions is produced with air or inert gas.

5. Apparatus for FIA consisting of a sample injection valve, a measuring cell, reaction coils, couplings and connections etc., characterized in that the sample injection valve consists of two movable bodies which seal against each other with ducts in one body which connect with ducts in the other body in such a manner that in a first position the carrier flow passes through the valve, a certain amount is defined and additional reagent and/or washing solution or water is possibly added; in a second position the defined sample amount is introduced into the carrier flow and additional reagent is possibly added; and in a third position all the ducts are closed.

6. Apparatus according to Claim 5, characterized in that said valve has additional ducts for injection of reagent or other solutions.

7. Apparatus according to Claim 5 or 6, characterized in that said movable bodies consist of two discs rotatably joined to each other.

8. Apparatus according to Claim 5, characterized in that the measuring cell for photometric measurement consists of a transparent hose bent to hair-pin shape, and that the hair-pin curve has a straight portion through a beam of light can be conducted to a measuring instrument, said straight portion being immersed in a liquid with essentially the same index of refraction as the material in the hose.

9. Apparatus according to Claim 8, characterized in that the liquid consists of silicon oil.

10. Apparatus according to Claim 5, characterized in that the measuring cell for potentiometric measurement consists of a tube through which the solution flows, and in which two electrodes are mounted, preferably an indicator electrode and a reference electrode.

1 Apparatus according to Claim 5, characterized in that the measuring cell consists of an atom absorption spectrophotometer, the sample being conducted directly into the nebuíizer.

12. Apparatus according to Claims 5-11, characterized in that the sample injection valve the measuring cell and the accompanying parts are detachably and movably mounted on a control panel.

13. Method of Flow Injection Analysis, FIA, substantially as described hereinbefore with reference to the accompanying drawings.

14. Apparatus for FIA, substantially as described hereinbefore with reference to the accompanying drawings.