GB2192278A

GB2192278A - Apparatus for and method of flow injection analysis

Info

Publication number: GB2192278A
Application number: GB08615979A
Authority: GB
Inventors: David Malcolm-Lawes; Raymond Newton
Original assignee: BIOTECH INSTR Ltd
Current assignee: BIOTECH INSTR Ltd
Priority date: 1986-07-01
Filing date: 1986-07-01
Publication date: 1988-01-06
Anticipated expiration: 2006-07-01
Also published as: GB2192278B; GB8615979D0; GB8700075D0

Abstract

A sample duct 12 in a carrier line 10 may be isolated by three-way valves 14, 16, blocking the flow of carrier or flushing liquid from reservoirs 24, 26. The sample duct 12 may be connected to a suction source 18, 20 and a sample reservoir 17 respectively by the valves 14, 16. When the sample duct 12 is connected into the carrier line 10 pressurised carrier fluid may convey the sample for analysis through a manifold 38 comprising valves 40 through which reagents may be introduced from reservoirs 42. The sample then passes through a thermostatically controlled reaction tube 46 to a valve 50 which switches it between waste and an outlet 48 leading to a detector for analysis. The carrier and flushing fluids and the reagents are pressurised by gas from an inlet 30 which is conveyed via an overpressure vent 32 to the reservoirs 24, 26, 42 by lines 28, 44. Rigid inert tubing is used throughout the carrier line 10, sample duct 12, manifold 38 and reaction tube 46. <IMAGE>

Description

SPECIFICATION Apparatus for and method of flow injection analysis Field of the invention This invention relates to apparatus for and a method of flow injection analysis.

Background to the invention Flow injection analysis (FIA) is employed in wet chemistry for the analysis of chemical samples. A defined volume of the sample is conveyed by a liquid carrier stream to a flow through detector in which the sample is analysed. Provision is made for the addition of a reagent to the sample being conveyed, whereafter the conveyed sample and reagent pass through a reaction tube before entry into the detector.

Prior art Apparatus for fluid injection analysis is known from U.K. Specification No. 2104657, wherein a relatively complex valve is provided which in a first position acts to divert the flow of carrier fluid through the valve independently of the sample duct, thereby to enable the sample duct to be loaded, and in a second position passes the carrier flow through the sample duct, the valve acting while passing betweeen the first and second positions to cut off the flows of carrier, sample and reagent. In this known analysis system, the carrier liquid is conveyed by positive pressure displacement instead of by the use of a peristaltic pump, as is the conventional practice.

Object of the invention It is an object of this invention to provide improved apparatus for and an improved method of flow injection analysis which are flexible in operation and offer high versatility in usage.

The invention According to one aspect of the invention, there is provided apparatus for flow injection analysis wherein a sample to be analysed is loaded into a sample duct of predetermined volume from which it is conveyed by pressurised carrier fluid through a manifold at which a pressurised reagent can be added before the sample is passed to a reaction tube, and wherein the sample duct is positioned in the carrier line between isolating valves operable to check the flow of carrier fluid and to isolate the sample duct from the carrier line in order to enable the sample duct to be loaded.

According to another aspect of the invention, there is provided a method of flow injection analysis wherein a sample to be analysed and contained in a sample duct is conveyed by pressurised carrier fluid through a manifold at which a pressurised reagent can be added before the sample is passed to a reaction tube, wherein the sample duct is located in the carrier line between upstream and downstream isolating valves, the method including the steps of operating the valve or valves on one side of the sample duct to connect a sample inlet to the sample loop and isolate the sample duct from the carrier line, operating the valve or valves on the other side of the sample duct to connect the sample loop to a suction inlet and isolate the sample loop from the carrier line, loading the sample into the sample duct, and operating the valves to connect the sample duct into the carrier line on both the upstream and downstream sides.

In a preferred arrangement, two three-way isolating valves are provided, one on the upstream and one on the downstream side of the sample duct.

Between the isolating valves and between the sample duct and the valve providing for connection to the suction inlet, an additional three-way valve is preferably provided, enabling sample surplus to the said predetermined volume to be passed to waste.

On the upstream side of the upstream isolating valve, one or more further three-way valves may provide for the carrier line to be connected to any one of a plurality of carrier and/or flushing liquids.

On the downstream side of the downstream isolating valve, but upstream of the reagent manifold, a still further three-way valve may provide for priming, allowing for intake of a small amount of sample and its ejection to waste before loading the sample duct with the predetermined volume to be analysed.

The sample loading means may conveniently comprise a solenoid operable syringe which acts via the upstream isolating valve to suck the sample into the sample duct via the downstream isolating valve.

The reagent manifold may comprise a series of three-way valves, each providing for connection with an individual reagent reservoir.

Any one or more of the said series of valves may be provided for addition of any one or more reagents to the sample to be analysed.

Downstream of the reagent manifold, the reaction tube is preferably thermostatically controlled, and may be followed by yet another three-way valve which provides connections either to waste or to an outlet leading to the detector.

Both the carrier and/or flushing liquids and the reagents are driven by positive pressure displacement, pressurisation preferably being effected from a common gas inlet and protected by an overpressure vent. Conveyance by positive pressure displacement enables rigid tubing or ducting to be employed throughout the apparatus, thus affording greater precision than the flexible tubing normally used with systems driven by peristaltic pumps.

The sample is drawn from a sample reser voir which may readily be incorporated in an automatic sample changer, and programmed control is possible for example to enable onstream monitoring or a succession of analyses for different sequential samples each for one or more analytes.

The various three-way valves employed in the apparatus may be operated manually, or automatically in a programmed sequence in the case of computerised control.

Description of drawings The apparatus and method in accordance with the invention will now be exemplified with reference to an embodiment described in conjunction with the accompanying drawing, in which: the single figure shows the apparatus in diagrammatic form.

Description of embodiment Referring to the drawing, the reference 10 generally denotes a carrier line. The line 10 includes a sample duct 12 which is located between upstream three-way isolating valve 14 and downstream three-way isolating valve 16. The valves 14 and 16 enable the sample duct 12 either to be connected on-stream in the carrier line 10 or to be isolated from the carrier line and be connected on the downstream side to a sample reservoir 17 and on the upstream side to a sample loading means comprising a load syringe 18 operable by a solenoid 20.

A three-way valve 22 upstream of the upstream isolating valve 14 enables either a carrier liquid from a reservoir 24 or a flushing liquid from a reservoir 26 to be taken into the carrier line. More than two such carrier/flushing agent reservoirs may be provided, together with the appropriate number of threeway valves.

Supply of carrier liquid (or flushing agent) into the carrier line 10 is by positive pressure displacement, enabled by a gas line 28 supplied with gas such as nitrogen gas under pressure from a gas inlet 30 via an overpressure vent 32. A suitable gas supply pressure is of the order of 5 to 15 psig, giving a flow rate through a downstream detector (not shown but conveniently a computer controlled spectrophotometer) of 0. 1 to 5 ml per minute, with 1 ml per minute possibly being a preferred value.

A three-way valve 34 connectable to waste is provided between the upstream isolating value 14 and the sample loop 12, and another three-way valve 36 connectable to waste is connected in the carrier line just downstream of the downstream isolating valve 16.

Downstream of the sample loading system, the carrier line 10 leads to a reagent manifold 38, where a series of three-way valves 40 enable any one or more of a number of reagents contained in reservoirs 42 to be added to a sample being conveyed along the carrier line. Supply of reagent is also by positive pressure displacement, enabled by the gas line 44 fed from the same gas inlet 30.

The sample/reagent mixture passes to a thermostatically controlled reaction tube 46 and thence to an outlet 48 leading to the detector via a three-way valve 50 having an alternative outlet to waste. The reaction tube will typically be controlled to operate in the range from room temperature up to 100 degrees Celsius.

All ducting 12, 38 is in the form of rigid tubing.

In use, sample (typically in an amount from 20 to 200 microlitres) is drawn into the sample duct 12 by operating the load syringe 18 while the isolating valves 14 and 16 are operated to isolate the region of carrier line between them which contains the sample duct.

Surplus sample is passed to waste by operating valve 34, releasing the load syringe 18 and then operating the upstream isolating valve 14 to flush the space between said valve 14 and said waste valve 34.

After sample loading, the isolating valves 14 and 16 are operated to reconnect the sample duct 12 into the carrier line 10, whereby operation of the valve 22 causes carrier liquid to enter the carrier line to convey the sample downstream. As the reagent passes any one or more of the valves 40 in the reagent manifold 38, the appropriate valve 40 is operated to cause a selected reagent or reagents to be added. For this purpose the appropriate valve 40 is operated several times to inject a required amount of reagent, typically ten times for a period of 1 second each time in order to supply 200 microlitres of reagent for mixing with a 200 microlitre sample. Flow then continues to take the sample/reagent mixture to the reaction tube 46.

The sample loading system permits priming between samples by intake of a small amount of sample, followed by its ejection through the downstream waste valve 36. Full flushing of the system is enabled by opening the valve 22 to a flushing agent reservoir and valve 50 to waste. It is to be noted, however, that priming and/or flushing is not an essential intermediate step between successive samplings, which is advantageous if several sample aliquots are to be successively drawn from the same reservoir, for example to test for different analytes.

It is to be noted that incorporation of an automatic sample changer is readily possible, and also that there is no limit to the number of reagent reservoirs which may connect with the reagent manifold.

The system may be computer controlled with any chosen program which produces repeated valve operations, sample loadings, and reagent loadings in any chosen sequence, for example for on-stream monitoring or a com plex series of analyses involving differing samples, differing analytes and differing reagents.

The system is particularly suited to use in the field, since a 12 volt d.c. supply is sufficient for the operation of electrical components and a nitrogen cylinder is sufficient to enable flow by positive gas displacement. This last mentioned means of fluid conveyance is also advantageous to the use of a detector in the form of a visible/UV spectrophotometer, since the pulsating flow associated with the use of peristaltic pumps is avoided.

Another important advantage of the system is that it enables the flows of carrier, sample and reagent to be carried out by means of rigid inert tubing and inert valves, enabling use with both organic materials and strong inorganic acids and bases, which is generally not possible with systems driven by peristaltic pumps.

Various modifications of the illustrated and described arrangement are possible within the scope of the invention hereinbefore defined.

Claims

1. Apparatus for flow injection analysis wherein a sample to be analysed is loaded into a sample duct of predetermined volume from which it is conveyed by pressurised carrier fluid through a manifold at which a pressurised reagent can be added before the sample is passed to a reaction tube, and wherein the sample duct is positioned in a carrier line between isolating valves operable to check the flow of carrier fluid and to isolate the sample duct from the carrier line in order to enable the sample duct to be loaded.

2. Apparatus according to claim 1 in which two three-way isolating valves are provided one on the upstream and one on the downstream side of the sample duct.

3. Apparatus according to claim 1 or claim 2 in which a three-way valve is provided between the isolating valves and between the sample duct and the valve providing for connection to the suction inlet, enabling sample surplus to the said predetermined volume to be passed to waste.

4. Apparatus according to any one of the preceding claims in which one or more threeway valves on the upstream side of the upstream isolating valve provide for the carrier line to be connected to any one of a plurality of carrier and/or flushing liquids.

5. Apparatus according to any one of the preceding claims in which a three-way valve on the downstream side of the downstream isolating valve, but upstream of the reagent manifold, provides for priming, allowing for intake of a small amount of sample and its ejection to waste before loading the sample duct with a predetermined volume to be analysed.

6. Apparatus according to any one of the preceding claims in which the sample loading means comprises a solenoid operable syringe which acts via the upstream isolating valve to suck the sample into the sample duct via the downstream isolating valve.

7. Apparatus according to any one of the preceding claims in which the reagent manifold comprises a series of three-way valves, each providing for connection with an individual reagent reservoir.

8. Apparatus accordng to any one of the preceding claims in which the reaction tube downstream of the reagent manifold is thermostatically controlled.

9. Apparatus according to claim 8 in which the reaction tube is followed by a three-way valve which provides connections either to waste or to an outlet leading to a detector.

10. Apparatus according to any one of the preceding claims in which the carrier liquid and the reagent are both driven by positive pressure displacement.

11. Apparatus according to claim 10 in which pressurisation for the positive pressure displacement is effected from a common gas inlet and protected by an overpressure vent.

12. Apparatus in which rigid tubing is used throughout the carrier time, the sample tube and the reaction tube.

13. A method of flow injection analysis wherein a sample to be analysed and contained in a sample duct is conveyed by pressurised carrier fluid through a manifold at which a pressurised reagent can be added before the sample is passed to a reaction tube, wherein the sample duct is located in a carrier line between upstream and downstream isolating valves, the method including the steps of operating the valve or valves on one side of the sample duct to connect a sample inlet to the sample duct and isolate the sample duct from the carrier line, operating the valve or valves on the other side of the sample duct to connect the sample duct to a suction inlet and isolate the sample duct from the carrier line, loading the sample into the sample duct, and operating the valves to connecct the sample duct in to carrier line on both the upstream and downstream sides.

14. Apparatus for flow injection analysis substantially as herein described with reference to the drawing.