SAMPLE DILUTER

Abstract: A sample diluter comprising means for extracting a measured quantity of a sample from a sample chamber, means for passing a measured quantity of diluent into the sample chamber and means for passing the extracted sample back into the sample chamber.

Description: 1 SAMPLE DELUTER The invention relates to a device for diluting a sample such as a sample of blood or urine which is being examined for example in an impedance particle sizing system. The invention also relates to sample measuring systems comprising a sample diluter. Various systems are known for measuring the properties of samples such as blood, urine or yeast where properties such as particle concentration within a sample are required to be known. Such a sample measuring system is an impedance particle sizing system which can count the number of particles of a certain size which pass through an orifice for a given sample flow rate thereby to calculate particle concentration. However, it has been found that the measured concentration does not accurately reflect the actual particle concentration over all particle concentrations. That is, the measured concentration does not vary monotonically with actual concentration and for example the response can go through a maximum at a given actual concentration after which the measured concentration is believed to be decreasing in spite of increasing actual concentration. Additionally, it is desirable to be able to dilute a sample which is measured in a system in order to check that the values obtained for the diluted sample meet predicted results thereby to corroborate results achieved for the initial sample. Accordingly, the invention seeks to provide a device for diluting samples in a measuring system and also a sample measuring 2 system comprising a sample diluter. There is a further object of the invention to provide an automated system which enables on line dilution of a sample thereby automatically to check measurements on a sample. According to a first aspect of the invention there is provided a sample diluter comprising means for extracting a measured quantity of a sample from a sample chamber, means for passing a measured quantity of diluent into the sample chamber and means for passing the extracted sample back into the sample chamber. Beneficially therefore, the sample diluter can be a stand alone unit which comprises requisite pumps and tubing to enable extraction and presentation of sample and diluent to a sample chamber of a measuring system. Preferably, the sample extraction/presentation tube and/or diluent presentation tube are movable between an operable position wherein the tubes are within the sample chamber and a second position wherein the tubes are removed from the sample chamber. Accordingly, the invention enables measurements to take place on a sample before the sample diluter is moved first to extract a measured quantity of the sample from the sample chamber whereafter the remaining sample can be removed from the sample chamber according to the apparatus in use. Once the sample chamber has been emptied and cleaned, the sample diluter according to the invention 3 then presents the extracted measured quantity of sample back into the sample chamber together with a measured quantity of diluent. For example, it is possible to dilute the sample by any required ratio simply by calibrating the measured quantity of sample to measured quantity of diluent. For example, a ratio in the order of 1 to 2 or 1 to 9 might be appropriate. Another aspect of the invention provides a sample measuring system such as an impedance particle sizing system, comprising a sample chamber from which a property of the sample is measured, means for emptying the sample chamber and means for cleaning the sample chamber, and further comprising a dilution device comprising means for extracting a measured quantity of sample from the chamber, and means for presenting a measured quantity of diluent to the sample chamber. Another aspect of the invention provides a method of measuring a concentration dependent parameter of a sample, such as concentration itself, comprising the steps of:- making a first measurement at a first concentration. diluting the sample and making a second measurement at a second concentration, analysing the first and second measurements and comparing the result with a predetermined expected behaviour, determing the value of the parameter if the expected result is 4 advanced, repeating the step of diluting the sample and making a further measurement at the further concentration analysing the further measurement with respect to at least one of the earlier measurements and comparing the result with a predetermined expected behaviour and repeating the dilution, measurement and analysis steps until the result agrees with the predetermined expected behaviour. The method can use an impedance measuring technique. The dilution between measurements is preferably approximately constant. The dilution between measurements is preferably in the order of about 1 in 2 and about 1 in 20. The dilution between measurements is more preferably in the order of about 1 in 9. Preferably the analysis is made between the most dilute concentration and the previous measurement at the next most dilute concentration. Also the predetermined expected behaviour is preferably a monotonic variation in the value of the measurement in proportion to the amount of dilution between successive measurements. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- 5 FIGURE 1 is a schematic drawing of a sample measuring system according to the invention comprising a sample diluter; FIGURE 2 is a schematic perspective view of sample diluter according to the invention; and FIGURE 3 is a schematic graph of measured concentration versus actual concentration obtained using as impedance particle sizing apparatus. Referring to Figure 1 there is shown a sample diluter 10 according to the invention comprising a sample extraction and presentation tube 12 which is connected to a pump 14. There is further provided a diluent presentation tube 16 connected to a pump 18 which in turn is connected to a reservoir 20. Figure 1 also shows a sample measuring system 30, such as an impendence particle sizing apparatus, comprising a sample chamber 32 having an inlet aperture into which tubes 12 and 16 can pass. System 30 further comprises an exhaust tube 34 and pump 36 which enable extraction of the sample from sample chamber 32. System 30 further comprises a sample presentation device such as a hand-held device or wand 38 comprising a pump 40 and presentation tube 42. Device 38 enables extraction of a sample from a sample tube say into tube 42 and then presentation of the sample into sample chamber 32 by reverse operation of pump 40. 6 System 30 in this example further comprises a second chamber 44 having a diluent presentation tube 46 which in this example is connected to diluent tube 16 via a three way valve 48. An exhaust pipe 50 is provided to enable extraction of the contents of chamber 44 using pump 36 and three way valve 52. Finally, an actuator 60 and arm 62 are provided to enable movement of tubes 12 and 16 into and out of chamber 32. Finally, a controller 64 is provided to control the operation of pumps 14,18,36 and possibly 40, and valves 48 and 52, and actuator 60. Controller 64 can be a programmable device such as a microcontroller or microprocessor. In use, a sample is presented to sample chamber 32 using device 38. The system 30 then operates in its usual manner as described for example in our earlier Patent application number GB-A- 9724611.0 to measure particle sizes or particle concentration in this example. This entails measuring the difference in impedance through an electrically conductive path provided between sample chamber 32 and second chamber 44 which path passes through a narrow orifice through which particles from the sample are caused to flow for example by providing suction at exhaust tube 50 which causes sample in the chamber 32 to pass into chamber 44. Details of the impedance measuring system are not shown but can be found in GB-A- 9724611.0. After the measurement is completed, sample extraction tube 12 is lowered into chamber 32 using actuator 60 and a measured quantity 7 is extracted from the sample chamber using pump 14. The extracted sample is retained in tube 12 whilst sample chamber 32 is evacuated using exhaust tubes 34 and pump 36. Similarly chamber 44 is preferably emptied using tube 50 and pump 36 also. Both chambers 32 and 44 can then be cleaned using diluent which is pumped into chambers 32 and 44 using pump 18 and tubes 16 and 46 respectively. Again, the chambers are evacuated and this process can be repeated as necessary. When sample chamber 32 is clean and empty, the measured volume of sample held within tube 12 is pumped back into sample chamber 32 together with a measured volume of diluent from reservoir 20 using pump 18 and tube 16. A further measurement can thereby be made on the diluted sample using system 30. After the measurement is completed, the process of extracting part of the sample, including cleaning the chambers and representing the measured sample back into the chamber 32 and diluting it by a further amount, can be repeated any number of times. Beneficially therefore, the change in measured concentration for example can be checked to ensure that all measurements are made along a desired monotonic region. Alternatively, as shown in Figure 3, it is possible to determine that the measurements are being made above a maximum CM. The controller 64 analyses the concentration measurements, in 8 this example from the number of detected particles versus sample flow rate through the aperture between chambers 32 and 44, to determine the region of measurement against actual concentration as shown in Figure 3 and whether the measurements are in the monotonic region. If they are not sample dilution continues until the measurement is made in the monotonic region and finally the original concentration of the sample can be determined from the number and amount of dilutions which have taken place. Referring to Figure 2 there is shown a stand alone diluter 10 according to the invention which comprises a case C housing many of the components shown in Figure 1. However, in this embodiment valve 48 and tube 46 are not provided, nor is the sample chamber etc. The other components are the same and are given the same reference numeral. Accordingly, diluter 10 comprises a sample extraction/presentation tube 12 connected to a pump 14, and a diluent tube 16 connected to a pump 18 which in turn is connected to a diluent reservoir 20. Diluter 10 further comprises an actuator 60 which operates a pair of arms 62 which carry tubes 12 and 16. Slots S are provided in part of case C in order to enable movement of arm 62 and tubes 12 and 16 up and down. For example, actuator 60 can provide an electric motor. Device 10 is also shown in Figure 2 to comprise a controller 64 such as a micro-controller or micro-processor programmed to actuate pump 14, pump 18, and actuator 60 according 9 to a predetermined sequence or on instructions from a system controller (not shown) to which controller 64 can be in communication via an input/output port 66. Alternatively or as well, controller 64 can be operated independently by a user for example using a button B on case C. For example, pressing B can effect lowering of tube 12 into a sample chamber and extraction of a predetermined amount of sample followed by a raising of arm 12. The user is then able to clean the sample chamber as required and by pressing button B again, tubes 12 and 16 are lowered back into the sample chamber and the sample stored in tube 12 is presented to the sample chamber together with a measured volume of diluent 16. Preferably diluter 10 comprises a lid L which enables access to diluent reservoir 20 thereby to enable the reservoir to be topped up. For example, a sample chamber 32 might hold up to 50 ml of liquid. In order to provide a 1 in 9 dilution of the primary sample, it would be appropriate to extract 5 millilitre of the sample using tube 12 and to represent the 5 ml of sample with 40 millilitre of diluent back into the sample chamber. The controller 64 analyses the concentration measurements, in this example from the number of detected particles versus sample flow rate through the aperture between chambers 32 and 44, to determine the resion of measurement against actual concentration as shown in Figure 3 and whether the measurements are in the 10 monotonic region. If they are not, sample dilution continues until the measurement is made in the monotonic region and finally the original concentration of the sample can be determined from the number and amount of dilutions which have taken place.

Claims: CLA S: 1. A method of measuring a concentration dependent parameter of a sample, such as concentration itself, comprising the steps of:- making a first measurement at a first concentration, diluting the sample and making a second measurement at a second concentration, analysing the first and second measurements and comparing the result with a predetermined expected behaviour, determing the value of the parameter if the expected result is achieved or, repeating the step of diluting the sample and making a further measurement at the further concentration, analysing the further measurement with respect to at least one of the earlier measurements and comparing the result with the predetermined expected behaviour and repeating the dilution measurement and analysis steps until the result agrees with the predeterrnined expected behaviour, such that the value of the parameter can be accurately determined. 2. The method of Claim 1 wherein an impedance measuring technique is used. 3. The method of Claim 1 or 2 wherein the dilution between measurements is preferably approximately constant. 4. The method of Claim 1, 2 or 3 wherein the dilution between measurements is preferably in the order of about 1 in 2 and about 1 in 20. 5. The method of Claim 4 wherein the dilution between measurements is preferably in the order of about 1 in 9. 6. The method of any of Claims 1 to 5 wherein analysis is made between the most dilute concentration and the previous measurement at the next most dilute concentration. 7. The method of any of Claims 1 to 6 wherein the predetermined expected behaviour is a monotonic variation in the value of the measurement in proportion to the amount of dilution between successive measurements. 8. A sample diluter comprising means for extracting a measured quantity of a sample from a sample chamber, means for passing a measured quantity of diluent into the sample chamber and means for passing the extracted sample back into the sample chamber. 9. A sample diluter according to Claim 8 further comprising a tube locatable within the sample chamber and means for moving the tube between a first position wherein part of the tube is operably within the sample chamber and a second position wherein the tube is operably removed from the sample chamber. 10. A sample diluter according to Claim 8 or 9 comprising a separate sample extraction/presentation tube and diluent presentation tube. 11. A sample diluter according to Claim 10 comprising means for moving both said sample tube and diluent tube between first positions wherein part of the respective tube is within the sample chamber and a second position wherein the respective tube is removed from the sample chamber. 12. A sample diluter according to any of Claims 8 to 11 comprising a reservoir of diluent. 13. A sample diluter according to any of Claims 8 to 12 wherein the diluent transfer means comprises means for measuring a specific quantity of diluent, such as a pump. 14. A sample diluter according to any of Claims 8 to 13 wherein the means for extracting sample comprises means for measuring the quantity of sample such as a pump. 15. A sample diluter according to any of Claims 8 to 14 comprising a controller, such as a microprocessor, for determining a predetermined dilution of extracted sample in a measured quantity of diluent. 16. A sample diluter according to any of Claims 8 to 15 wherein the diluter is an integral unit comprising, amongst other things, requisite pumps and tubing to enable extraction and presentation of sample and diluent to a sample chamber of a measuring system. 17. A sample measuring system such as an impedance particle sizing system, comprising a sample chamber from which a property, such as particle size or particle concentration, of the sample is measured, means for emptying the sample chamber and means for cleaning the sample chamber, and further comprising a dilution device having means for extracting from and representing to the sample chamber a measured quantity of sample, and means for presenting a measured quantity of diluent to the sample chamber. 18. A sample measuring system according to Claim 17 having the features of any of Claims 9 to 16.

Inventors: WOOD MICHAEL ANTHONY, WOOD, MICHAEL, ANTHONY
Applicants: MICROBIAL SYSTEMS LTD, WOOD MICHAEL ANTHONY, MICROBIAL SYSTEMS LIMITED, WOOD, MICHAEL, ANTHONY
Application year: 1999
Main classification: G01N15
IPC codes: G01N1, G01N15, G01N27