GB2240622A - Controlling fluid flow through extraction cartridges - Google Patents

Abstract

In the extraction of substances from body fluids the fluid passes under gravity and suction from a reservoir through a cartridge. At the junction between reservoir and cartridge an infra-red light emitting diode (10) and phototransistor (11) provide an optical path through which the meniscus of the liquid passes as the reservoir empties. When there is no longer fluid in the optical path, the output of the detector circuit rises above the reference voltage of a comparator (15) to reset a NAND gate (16) which therefore passes a signal at (20) to shut a solenoid valve interrupting the suction thereby preventing entry of air into the cartridge. Where a number of such assemblies are operated signals through lines (18) and a NOR gate (19) set a start switch which is then used to open the valves by setting NAND gates (17) assuming the NAND gates (16) have been set by refilling the reservoirs. <IMAGE>

Description

A DEVICE FOR CONTROLLING FLUID FLOW THROUGH EXTRACTION CARTRIDGES This invention relates to apparatus for extracting substances from liquids.

The invention is concerned more particularly with apparatus for extracting substances from liquids such as body fluids, of the kind which comprises an extraction cartridge, a reservoir positioned above the extraction cartridge and connected to the inlet of the cartridge so that the liquid can be supplied through the reservoir to the cartridge, means for applying low pressure to the outlet of the cartridge so as to draw liquid from the reservoir through the cartridge, and means for collecting said liquid drawn from the cartridge.

Such apparatus is normally employed by first conditioning the cartridge with a specific solvent or solvents, and then adding a buffered sample. The cartridge is then washed with a solvent which washes interfering compounds off the cartridge and away to waste, while leaving the substances to be extracted attached to the material in the cartridge. These substances are then eluted by another solvent and collected. The different solvents, samples and wash solutions that are used are added sequentially to the reservoir.

Current multiple extraction devices permit a plurality of cartridges to be used simultaneously.

However there is no control of the flow rate through individual cartridges which leads to different emptying rates. Those which empty quickly therefore suck in air, while remaining full cartridges are emptying. Cartridges which dry out in this way have impaired performance, leading to reduced extraction efficiency. Commercially available extraction devices have a single tap as an accessory to control flow, but where multiple extraction devices are used, it is difficult accurately to control the flow through each cartridge.

An object of the invention is therefore to provide apparatus that overcomes the laborious and time consuming manual extraction of single samples and to provide automatic control of fluid flow through an extraction cartridge by the non-invasive detection of fluid level in the reservoir. A further object is to provide apparatus enabling the automatic control of fluid flow through multiple extraction cartridges enabling the preparation of many more samples in a given time period whilst improving reproducibility and standardising extraction efficiency.

According to the present invention there is provided apparatus for extracting substances from liquids such as body fluids, which comprises an extraction cartridge, a reservoir positioned above the extraction cartridge and connected to the inlet of the cartridge so that liquid can be supplied through the reservoir to the cartridge, means for applying low pressure to the outlet of the cartridge so as to draw liquid from the reservoir through the cartridge, and sensing means for sensing the meniscus surface of the liquid when in a location substantially between the bottom of the reservoir and a required top level of the liquid in the cartridge, the sensing means comprising a light emitter and a light detector mounted to provide an optical path from the light emitter to the detector extending through the said location, an electrically controlled valve for interrupting the low pressure applied to the cartridge, and an electronic reset latch connected for controlling the opening and closing of the valve and controlled by means responsive to the detector and to remote control for opening the valve and by the detector for closing the valve to interrupt the low pressure application, whereby the valve is opened when the meniscus is above the optical path and closed when below the optical path.

Conveniently the light emitter may be an infra-red light emitting diode and the light detector may be a phototransistor. The light emitter and the detector may very conveniently be mounted on a printed circuit board arranged to receive the reservoir above it and the cartridge beneath it.

Where fluid flow through multiple extraction cartridges is required, a plurality of precisely similar apparatus as aforesaid may advantageously be provided with the outputs of the reset latches connected to a single start switch for setting the reset latches, thereby providing remote control for opening the valves.

All switches, latches and control logic circuits may be mounted in a portable control box connected to the apparatus by a flexible cable.

In order that the invention may be clearly understood and readily carried into effect one apparatus in accordance therewith will now be described, by way of example, with reference to the accompanying drawings, in which: Fig.1 is a diagrammatic side elevation of apparatus for simultaneously automatically controlling the flow through a plurality of extraction cartridges; and Fig. 2 is a circuit diagram of electronic apparatus as used to control the flow through each of the cartridges of Fig.1.

Referring to Fig.1 the apparatus consists of a number of assemblies (five in this example), each comprising a reservoir 1 open at the top and narrowing at its lower end to fit into a neck 2 at the top of extraction cartridge 3. The reservoir 1 and neck 2 are made of translucent material. The outlet from the cartridge 3 fits on to the inlet of a solenoid valve 4.

The outlet of the solenoid valve 4 is connected to a vacuum box 5 (common to all five assemblies) which is connected in turn to a waste trap and vacuum pump. The reservoir and extraction cartridge pass through a hollow plastics detector block 6 in which an infra-red sensor is mounted substantially at the level of the neck 2.

Referring to the circuit diagram of Fig. 2, the portion of the circuit diagram inside the broken line frame constitutes the sensor latch and valve control circuits for one of the five assemblies. A similar circuit is provided for each of the other four assemblies. The sensor circuit board is carried in a hollow detector block 6 supported from the solenoid valve block by pillars (not shown) and formed with apertures through which the reservoirs 1 and cartridges 3 pass.

To each channel on the sensor circuit board is connected an infra-red light emitting diode 10 and a phototransistor 11 mounted on opposite sides of an opaque plastics sensor block with the bottom of the reservoir 1 or the top of the cartridge 3, depending on the cartridge design, interposed in the optical path between the light emitting diode 10 and the phototransistor 11.

The light emitting diode 10 is fed from a 9 volt stabilised supply via resistor 12 to set the current.

The phototransistor 11 is also fed from the 9 volt stabilised supply via a multi-turn potentiometer 13 on the sensor circuit board, inside the sensor block, which sets the current flowing through the phototransistor.

The current through the pohototransistor 11 is set so that transistor is just fully saturated when fluid is in the optical path. This means that when the fluid meniscus passes through the optical path, the increase in the optical density results in the phototransistor switching off, causing the voltage at the sensor circuiut output to rise. The phototransistor current adjustment by means of the potentiometer 13 is provided to compensate for variations between individual light emitting diodes and phototransistors and to enable sensor circuits designed for use with different extraction cartridges to be fitted.

A latching illuminated push-button switch 14 enables the user to render the phototransistor operative by switching on the light emitting diode 10. The output of the phototransistor is fed to a comparator 15 where it is compared to a preset reference voltage. When the fluid meniscus passes through the optical path, the phototransistor output voltage rises above the reference voltage, causing the comparator output to change state.

The comparator output is fed to one of the reset inputs of a R-S latch comprising two NAND gates 16, 17. The set input of the R-S latch is connected by a conductor 18 which, with similar conductors from the other four assemblies to a "start" non-latching push-button switch on the main printed circuit board mounted in the control box by way of an eight input NOR gate 19. Three inputs of the NOR gate 19 are short circuited to 0 volts, the remaining five inputs each being connected to one of the five sensor circuits. The "start" push button maybe on a control box connected by a flxible cable. The output of each sensor circuit, as shown in the example of Fig. 2, is connected at 20 via a driver stage to the associated solenoid valve 4 and to an associated indicator lamp 21 which indicates when the valve is open.The indicator lamp 21 is incorporated into a non-latching switch 22 which enables manual operation of the solenoid valve independently of the snesor circuit output. A second output 23 of the NOR gate 19 is connected, via a driver stage, to an indicator lamp in the aforesaid start pushbutton. In order to minimise the power requirements of the 9 volt voltage stabilizer, the solenoids and indicator lamps are fed from an unregulated 12 volt supply.

The sequence of operations of the apparatus will now be described. The required assembly or assemblies are selected by actuating the associated switch or switches 14 so as to render the corresponding light emitting diode or diodes 10 active. The appropriate reservoirs are then filled with fluid. At this point, the R-S latches are all reset so that the solenoid valves 4 are all shut, the lamps 21 are all extinguished and the indicator lamp in the start push-button is illuminated.

When the start push-button is pressed, the R-S latches 16, 17 are all set, e.g. by conductors 24, 25, the lamps 21 are illuminated to show that the valves 4 are open, and the fluid is drawn through such cartridges 3 as are joined to the filled reservoir or reservoirs by the vacuum in the suction box 5. When a descending fluid meniscus enters a particular optical path, the phototransistor output rises causing the associated comparator 15 to change state, resetting the R-S latch 16 so as to cause the solenoid valve for that particular assembly to close and its associated lamp 21 to be extinguished. When all the selected solenoid valves are closed, i.e. all the descending fluid menisci have reached optical paths, the output of the NOR gate 19 changes state, enabling the start push-button and illuminating its indicator lamp. The reservoirs can then be filled with the next fluid, and the process is repeated until all the desired reagents have passed through the cartridges. It will be seen that each solenoid valve is opened on receipt of two operational effects received by the R-S latch respectively from the latching switch 14 and from the start push-button through conductor 25 after the associated reservoir has been filled. The solenoid is closed as soon as the descending meniscus traverses the optical path and thereby counters the first of these two effects.

The sensor block can be designed to accomodate alternative types of reservoir and extraction cartridges.

Claims (8)

CLAIMS:

1. Apparatus for extracting substances from liquids such a body fluids, comprising an extraction cartridge, a reservoir positioned above the extraction cartridge and connected to the inlet of the cartridge so that liquid can be supplied through the reservoir to the cartridge, means for applying low pressure to the outlet of the cartridge so as to draw liquid from the reservoir through the cartridge, and sensing means for sensing the meniscus surface of the liquid when in a location substantially between the bottom of the reservoir and a required top level of the liquid in the cartridge, the sensing means comprising a light emitter and a light detector mounted to provide an optical path from the light emitter to the detector extending through the said location, an electrically controlled valve for interrupting the low pressure applied to the cartridge, and an electronic reset latch connected for controlling the opening and closing of the valve and controlled by means responsive to the detector and to remote control for opening the valve and by the detector for closing the valve to interrupt the low pressure application, whereby the valve is opened when the meniscus is above the optical path and closed when below the optical path.

2. Apparatus according to Claim 1, in which the light emitter is an infra-red light emitting diode and the light detector is a phototransistor.

3. Apparatus according to Claim 1 or Claim 2, in which the light emitter, the detector and reset latch are mounted on a detector block arranged to receive the reservoir above it and the cartridge beneath it.

4. Apparatus according to any one of the preceding claims, in which a comparator is interposed between the detector and the reset latch whereby when voltage applied to the comparator relatively to a pre-set voltage applied thereto, the reset latch is conditioned for opening or closing the valve.

5. Apparatus according to any one of the preceding claims, in which the electronic reset latch comprises two NAND gates connected respectively to the phototransistor and the said remote control and connectred in series to means for opening and closing the valve.

6. Apparatus according to any one of the preceding claims, consisting of one of a plurality of precisely similar apparatus and in which the outputs of the several reset latches are connected to a NOR gate connected to a start switch for setting the reset latches thereby serving as the remote control.

7. Apparatus according to Claim 6, in which the start switch is furnished with an illuminating lamp which is extinguished when the switch is operated to set the reset latches.

8. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.