GB2025900A - Sampling apparatus - Google Patents

Abstract

A sampling apparatus is described which comprises an aspiration probe and a sample inlet assembly. The probe comprises coaxial inner 48 and outer tubes 50 joined at the sampling end so as to close the space between the tubes. A plurality of small diameter holes 54, 56, 58, 60 extend through the inner tube. The holes are axially and circumferentially spaced, and allow a diluent to be accurately and thoroughly mixed in said probe with an aspirated fluid sample. The sample is sucked into the probe through the open end of the tubes 48. The sample inlet assembly comprises a housing having a plurality of sealing septums through which the probe can be extended and retracted. The septums are spaced apart to define fluid chambers therebetween, and a fluid inlet extends into each chamber, whereby calibrating fluids can be introduced into the probe from the fluid chambers. <IMAGE>

Description

SPECIFICATION Sampling apparatus This invention relates fo fluid sampling apparatus and more particulary to a sample aspiration probe and a sample inlet assembly for use in said apparatus.

In fluid analysis, particularly in the analysis of biological fluids, it is necessary to dilute certain fluids, and it is desirable to minimize the sample volume required for analysis. To maintain accuracy in analysis, it is necessary that diluent added to the sample be accurately and thoroughly mixed with the sample. It is also necessary that one or more calibrating fluids be employed between actual samplings for instrument calibration to ensure accuracy of analysis.

Sampling apparatus and aspiration probes are well known. Dilution generally requires the collection of a substantial quantity of the undiluted fluid sample, enough to fill the probe and any connecting tubing, before a portion of the sample can reach the location in the apparatus where diluent is added. Alternatively, dilution is performed in the sample prior to aspiration, requiring careful sample preparation.

In order to maintain the accuracy of the analysis instrument, calibration fluids, comprising known chemical compositions, are tested between actual samplings. With typical prior art apparatus, a calibration fluid has to be tested as if it is an actual sample; e.g., placed in a specimen cup and aspirated to the instrument. As this procedure must be repeated for each calibration fluid, calibration of the prior art instruments is a cumbersome and time-consuming operation Alternatively prior art apparatus typically utilizes manual introduction of the calibration fluid or requires valving and complex tubing connections.

We have sought to provide sampling apparatus for which both dilution and calibration can be more easily accomplished. The present invention has arisen out of this work.

In accordance with a first aspect of this invention, we provide an aspiration probe comprising: an outer tube and an inner tube together defining spaces for fluid flow paths within said inner tube and in the space between said inner and outer tubes, one of said spaces being arranged for connection at one end to a source of negative pressure and being open at the opposite sampling end of said probe, the other of said spaces being arranged for connection to a source of diluent at one end and closed at the sampling end of said probe, and the inner tube being provided with a plurality of small diameter holes, circumferentially and axially spaced from each other, extending through the inner tube and providing a limited connection between said fluid flow paths, whereby diluent in said closed space may be accurately and thoroughly mixed with a fluid sample aspirated through said other space.

In a second aspect thereof, the invention provides a sampling apparatus comprising, in addition to the aspiration probe, a sample inlet assembly comprising a plurality of sealing septums supported in a housing and spaced apart to define at least one fluid chamber therein, and at least one fluid passage extending through said housing to each said fluid chamber; said probe being extendable through said septums for aspirating said fluid sample and into said chambers for aspirating said fluid from said chambers.

The invention is hereinafter more-particularly described by way of example only with reference to the accompanying drawings in which: Fig. 1 is a partly schematic side elevation of sampling apparatus in which the invention is embodied; Figs 2, 3 and 4 are enlarged sectional views illustrating different positions of the aspiration probe in relation to the sample inlet assembly in the apparatus of Fig. 1; Fig. 5 is an enlarged elevation view of the aspiration probe; and Fig. 6 is an enlarged sectional view of the aspiration probe with parts broken away.

Referring to Fig. 1, the illustrated sampling apparatus comprises a frame 1 0 supporting a sample aspiration probe 12. Probe 12 is held in a fixture 14 at the end of a threaded shaft 1 6. Shaft 1 6 extends through a rotatable nut 1 8 which is driven by motor 20 through gears 22, 24 to adjust the axial position of probe 12. Photoelectric sensors 26 co-operate with a flag 28 provided on the side of fixture 14 to detect the position of the probe 12. Below the fixture 14, a platform 30 supports a sample inlet assembly 32 through which probe 12 is shown extended.

As best shown in Fig. 5, probe 12 has an enlarged support casing 40 of stainless steel on one end. A sample tube 42 extends from the top of casing 40. A diluent tube 44 extends into the side of casing 40.

Probe 12 has a sampling tip 46 at an end opposite casing 40. As shown in Fig. 6, probe 12 comprises coaxial inner and outer stainless steel tubes 48, 50, which are fusion welded together at the sampling tip 46 so that the outer tube 50 is sealed. Inner tube 48 is open at the tip 46, and a diluent passageway 52 exists between the tubes 48, 50. Inner tube 48 has a series of four holes 54, 56, 58, 60, which are axially and circumferentially spaced in a helical arrangement adjacent to the tip 46. In the illustrated embodiment, the inner diameter of tube 48 is 0.0275 inches, and the holes 54, 56, 58 and 60 are 0.008 inches in diameter. Inner tube 48 is fusion welded inside casing 40 to sample tube 42 which in turn is fusion welded to casing 40.

Diluent tube 44 is welded to casing 40 and is connected to the diluent passageway 52.

In fluid sampling operation, probe 12 is extended into a sample fluid in a cup 62 (shown in dotted iines in Fig. 1), so that tip 46 is in the fluid sample. Suction is applied to the instrument end of sample tube 42, and the negative pressure draws the sample fluid into the inner tube 48. At the same time, diluent is forced through the diluent tube 44 into the passageway 52 and through holes 54, 56, 58, 60 into the inner tube 48. The diluent mixes with the sample as it is being aspirated. The spacing arrangement of the holes ensures complete mixing, as the diluent is introduced at four successive locations and from four different directions.The effect of pressure puises from the pump feeding the diluent on the amount of diluent added to the sample is minimized by the axial spacing of the holes, which in the illustrated embodiment are spaced apart 0.050 inches. The sample size of the holes also aids the mixing, because of the high velocity turbulent flow of the diluent as it passes into the inner tube 48. The thoroughly diluted sample then continues up through the probe 12 and through sample tube 42 to an instrument (not shown) where it is analyzed. The placement of the lowest hole 54 some distance above the tip 46, 0.050 inches in the illustrated embodiment, avoids diluent being forced out of the tip 46 should pressure pulses from the pump feeding the diluent cause momentary slight excesses of diluent to flow.

The flow rate for the diluted sample in a particular embodiment is about 0.40 ml/min. In the embodiment described the ratio of diluent to sample is about 2:1; approximateiy 0.26 mi/min.

of that flow is diluent, while the sample fluid is drawn up at a rate of about 0.14 mI/min. Diluting the sample at the tip reduces the amount of actual sample fluid required to be aspirated from the cup 62 for any giyen test.

Sample inlet assembly 32 is illustrated in greater detail in Figs. 2, 3 and 4. It comprises a housing 64 having a slot 66 along one side. A first plug 68 is secured in the top of housing 64. A centrally disposed conical bore 70 extends through plug 68. A spring washer 72 is positioned inside housing 64 between plug 68 and platform 30. A lock washer 74 prevents plug 68 from separating from platform 30.

Three sealing septums 76, 78 and 80 are axially aligned in housing 64 below bore 70 of plug 68. Septums 76, 78, 80, which are made of silicone rubber and lubricated with silicone oil, have slits 82, 84 and 86 extending therethrough.

Middle septum 78 is spaced apart from septums 76, 80 by a pair of supports 88, 90. This creates a pair of fluid chambers 92, 94 between the septums. Channels 96, 98 extend from the respective fluid chambers 92, 94 to calibration fluid tubes 100, 102, which exit from the housing slot 66. Each tube 100, 102 is connected to a different source (not shown) of calibration fluid. A bottom plug 104 having a centrally disposed conical bore 106 is secured to the bottom of the housing 64 by screw threads 108. When in place, bottom plug 104 holds the septums 76,78,80 and supports 88, 90 in the housing.

Septums 76, 78 and 80 seal the fluid chambers 92, 94 and prevent any leakage. However, bore 70, septums 76, 78, 80, chambers 92, 94, and bore 106 co-operate to form a continuous bore through the entire sample inlet assembly 32 through which the probe can pass, as shown in Fig. 4.

Calibration fluid passes through tubes 100, 102, so that the fluid fills the portions of the chambers 92, 94 which are unoccupied by probe 12. To calibrate the analyzing instrument between actual samplings, probe 1 2 is retracted from its normal sampling position so that the sampling tip 46 is in one of the chambers 92, 94. The calibration fluid in this chamber is then aspirated and analyzed. If an additional calibration test is desired, the probe 1 2 is extended or retracted so that the tip 46 is positioned in the other chamber.

The fluid in this chamber is aspirated and tested.

After the calibration the probe 12 may again be fully extended through the sample inlet assembly 32 into a specimen cup to aspirate another sample. The apparatus can also be cleaned by positioning the probe 12 in the conical bore 70 of the sample inlet assembly 32. Air is aspirated into the probe, and air bubbles clean the probe and tubing as they pass through.

Claims (12)

1. An aspiration probe comprising: an outer tube and an inner tube together defining spaces for fluid flow paths within said inner tube and in the space between said inner and outer tubes, one of said spaces being arranged for connection at one end to a source of negative pressure and being open at the opposite sampling end of said probe, the other of said spaces being arranged for connection to a source of diluent at one end and closed at the sampling end of said probe, and the inner tube being provided with a plurality of small diameter holes, circumferentially and axially spaced from each other, extending through the inner tube and providing a limited communication between said fluid flow paths, whereby diluent in said closed space may be accurately and thoroughly mixed with a fluid sample aspirated through said other space.

2. An aspiration probe as claimed in Claim 1, wherein one of said holes is positioned adjacent to and spaced from said sampling end and said holes are helically disposed about said inner tube.

3. An aspiration probe as claimed in either of Claims 1 or 2, wherein said inner tube is provided with four of said holes equidistantly spaced about the inner tube circumference.

4. An aspiration probe as claimed in any of Claims 1, 2 or 3, wherein the space between said tubes comprises said closed space, the outer tube being joined at the closed end to said inner tube.

5. An aspiration probe as claimed in any preceding claim, wherein said tubes are cylindrical.

6. An aspiration probe substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

7. A sampling apparatus comprising: an aspiration probe according to any preceding claim; and a sample inlet assembly comprising a plurality of sealing septums supported in a housing and spaced apart to define at least one fluid chamber therein, and at least one fluid passage extending through said housing to each said fluid chamber; said probe being extendable through said septums for aspirating said fluid sample and into said chambers for aspirating fluid from said chambers.

8. A sampling apparatus as claimed in Claim 7, wherein said septums are made of silicone rubber.

9. A sampling apparatus substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

10. A sample inlet assembly comprising a plurality of sealing septums supported in a housing and spaced apart to define at least one fluid chamber therein, and at least one fluid passage extending through said housing to each of said fluid chambers, whereby a probe may be extended through said septums and into said chambers for aspirating fluid fed into said chambers through said passages.

11. A sample inlet assembly according to Claim 10, wherein said septums are made of silicone rubber.

12. A sample inlet assembly substantially as hereinbefore described with reference to and as shown in Figs. 1 to 4 of the accompanying drawings.