| Method and apparatus for pumping and diluting a sample -> Monitor Keywords |
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Method and apparatus for pumping and diluting a sampleRelated Patent Categories: Pumps, Successive Stages, Fluid Motor For One Stage Supplied From Another StageMethod and apparatus for pumping and diluting a sample description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060104827, Method and apparatus for pumping and diluting a sample. Brief Patent Description - Full Patent Description - Patent Application Claims
PRIOR APPLICATIONS [0001] This application claims benefit of Patent Cooperation Treaty Application Number PCT/GB2003/003564, filed Aug. 14, 2003, which claims priority from Great Britain Application Number 0218949.6, filed Aug. 14, 2002. FIELD OF THE INVENTION [0002] This invention relates to a method and apparatus for pumping a sample to analysis equipment and diluting the sample before it is analysed, or for any other reason. [0003] The invention is described herein with reference to liquid samples which require dilution before they are analysed in a mass spectrometer. However, the invention is not limited to liquid samples or mass spectroscopy and can equally apply to dissolved or suspended samples and any other test or analysis equipment. DESCRIPTION OF THE RELATED ART [0004] Analysis equipment for analysing trace elements in liquids have a limited capability of measuring samples which have relatively high levels of dissolved solid material, or matrix (such as CaCO.sub.3 or dissolved salts in water, or the like). The trace elements of interest to the user are often only a few parts per billion, or lower, whilst the matrix can be many parts per million, or higher. Such high levels of matrix can have undesirable effects on the analytical equipment, for example, materials can be deposited on orifices, glassware and ion optical elements. It is, therefore, necessary to dilute the sample prior to analysis. [0005] Inductively coupled plasma mass spectrometers (ICP-MS) typically require a total dissolved solid level of less than 2000 mg/l to avoid such deleterious effects. The dissolved solids can become deposited on components within the instrument, for example on the cones which sample the plasma and skim off a portion of the supersonic jet, thus significantly reducing the reliability of the test result and the results of any other subsequent test. If deposition of materials occurs, the instrument has to be thoroughly cleaned before accurate testing can resume. [0006] Test laboratories are often required to analyse many samples quickly where the matrix content of each sample varies widely. Typically, the user would wish to dilute each sample by a certain amount to determine the analytes present in each sample, and whether the sample can be analysed undiluted. If dilution is required, this initial test provides an indication of the dilution factor necessary to bring the total dissolved solids down to a level tolerated by the instrument. [0007] Such manual intervention is too cumbersome, time consuming and costly if many samples per day require analysis. Presently, samples which introduce too great a loading of dissolved solids for the instrument to cope with are re-analysed once the analyser has been cleaned. Analysis must stop for cleaning, and samples inadvertently analysed after contamination of the analyser must be re-analysed. This requires considerable operator intervention. Such a limit to the throughput of samples is undesirable and operator intervention is costly. [0008] Automated dilution systems have been used previously and, referring to FIG. 1, such an automated system 10 known in the art is shown in highly schematic form. A sample 12 is drawn from a container by a sample pump 14 to a mixing tube 16. Similarly, a diluent 18 is drawn by a diluent pump 20 to the mixing tube 16 from a separate diluent container. The sample is diluted in the mixing tube where it is completely mixed with diluent. An instrument pump 22 draws the diluted sample from the mixing tube and into the instrument or analyser, not shown in FIG. 1. [0009] Both the sample and diluent pumps have to be able to maintain accurate flow rates to ensure the sample is diluted precisely. If the dilution is not maintained to a known level and within a relatively tight tolerance, the accuracy of the analysis results may be unacceptable. Likewise, the instrument flow must be maintained at an accurate flow rate to ensure the diluted sample is pumped to the analyser's input at a known, controllable rate. Thus, all the pumps (and their associated flow rates) need to be controlled accurately to maintain accurate test results. [0010] Presently, peristaltic pumps are used to pump the sample, diluent and diluted sample through the dilution system. Typically, dilutions ratios of 50:1 of diluent to sample are used for mass spectroscopy. Hence, the diluent pump rate is typically fifty times greater than the sample pump rate. Peristaltic pumps have a limited range of flow rates and the sample and diluent pumps often operate at the extremes of their flow rate range. Also, the limited flow rate for peristaltic pumps limits the dilution factor by which the sample can be diluted; the maximum dilution occurring whilst the diluent pump operates at a maximum flow rate and the sample pump operates at a minimum flow rate. [0011] The rate at which the diluted sample should enter the instrument (not shown) depends on the type of instrument being used but is relatively low and typically a few millilitres per minute. If this rate is exceeded the instrument will become swamped with diluted sample which will cause problems in the spectrometer and have a detrimental effect on the analysis results. Typically, the combined flow rates of the sample and diluent pumps far exceeds the instrument pump flow rate. This is because all the pumps have relatively similar ranges of flow rates, and at dilution factors greater than ten, for example, the diluent pump 20 must operate at a high flow rate. This high flow rate typically exceeds the flow accepted by the analysis instrument. It is, therefore, necessary to provide a waste outlet 24 to prevent build up of pressure in the system; excess diluted sample not pumped to the instrument flows to a waste container 26. At high dilution factors, the solution flowing to waste can exceed the flow entering the instrument by a factor of fifty. Materials in the waste container are discarded and, since the high quality diluent necessary for accurate test results is relatively expensive, this wastage is an additional economic burden on test laboratories. [0012] Another automated pumping system 28 known in the art is shown in FIG. 2 in highly schematic form. Sample 29 is pumped along a first pipe 30 by a syringe pump 31 to fill the syringe (not shown). A valve 32 is closed to prevent fluid entering the syringe from the pump discharge pipe 33. When the pump is charged with an appropriate amount of sample, the valve is opened and the syringe plunger driven at a constant rate to provide a flow of sample along pipe 33 in the general direction indicated by arrow Z. A one way valve in the pump (not shown) prevents the sample from flowing back to the container 29 during the phase when the sample flows along pipe 33. [0013] A mixing region 34 of the pipe is defined by a second pipe 35 adjoining pipe 33 in a generally "T" or "Y" shaped configuration. As solution is aspirated by the instrument pump system (for example, a nebuliser), an uncontrolled pressure drop is produced in pipe 35. This causes an uncontrolled flow of solution along pipe 33' from the mixing region 34. This flow rate is a combination of a controlled flow of solution from the syringe pump, and an uncontrolled flow of diluent along pipe 35. The inability to control the flow of diluent results in an uncontrolled dilution factor. There is no instrument pump to pump the diluted sample to the analyser in this arrangement. [0014] Problems arise with systems which rely on this arrangement. For instance, there are limits to the dilution factor this system can provide, especially if the analyser requires the diluted sample to be pumped at a specific rate. This problem could be overcome by providing an instrument pump and pressure relief system similar to that shown in FIG. 1. However, the problems associated with the system in FIG. 1 now become prevalent with the system, for example, diluent wastage. [0015] Pumping systems known in the art are disclosed in U.S. Pat. No. 4,245,509 (Instrumentation Laboratory Inc.) and U.S. Pat. No. 5,007,297 (Pacific Scientific Company). [0016] Furthermore, contamination of the pump parts exposed to the sample during operation can cause subsequent samples to become contaminated, thus resulting in inaccurate analysis results. This so called "memory effect" problem is particularly troublesome with highly sensitive analysis instruments. As test instruments become more sensitive, this problem further increases. (For example, we have found this problem has very little effect on analysis results when samples are tested using the relatively insensitive atomic absorption analysis instruments, but can be problematic when samples are tested using highly sensitive ICP-MS analysis tools). [0017] Also, certain fluids can damage pump components. Such damaged components can lead to inaccurate flow rates, or more seriously, render the pump unusable without lengthy repair or regular servicing. [0018] At present, peristaltic pumps are used; the liquid being pumped is only in contact with the tubing in such pumps (which can be made of resilient material). However, peristaltic pumps have inadequate flow rate range and accuracy to dispense a sample solution at a sufficiently low flow rate to avoid discharging qualities of fluid to waste, as previously described. Furthermore, the use of peristaltic pumps limits the dilution factor achievable, because of their limited effective flow rate range. SUMMARY OF THE INVENTION [0019] It is an aim of the present invention to ameliorate the problems associated with the prior art. [0020] More precisely, there is provided a pump apparatus for pumping a sample to an analyser for analysis, comprising; a first pump arranged to pump the sample into a buffer region at a first flow rate, and a second pump arranged subsequently to pump a second fluid into said buffer region at a second flow rate to cause at least a portion of the sample to be displaced from the buffer region to the analyser, said second pump being operable so that the second flow rate is more accurately controllable than the first flow rate. Continue reading about Method and apparatus for pumping and diluting a sample... Full patent description for Method and apparatus for pumping and diluting a sample Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and apparatus for pumping and diluting a sample patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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