WO1997014947A2

WO1997014947A2 - Container for calibration fluid

Info

Publication number: WO1997014947A2
Application number: PCT/GB1996/002553
Authority: WO
Inventors: David Stephen Josty; Paul Michael Williams; Roger Bernard John
Original assignee: Lion Laboratories Plc
Priority date: 1995-10-17
Filing date: 1996-10-17
Publication date: 1997-04-24
Also published as: WO1997014947A3; AU7313396A; GB9521260D0

Abstract

This invention relates to devices for providing vapour samples of volatile components of a solution and apparatus for allowing such samples to be tested. Two different sample containers (10 and 52) are described. In each, a volatile solution is retained so that the volatile component equilibrates with a headspace from whence it can be drawn off into testing apparatus. In the device (10), the volatile component is retained by a gas-permeable-hydrophobic membrane (14), whilst in the device (52) the solution is retained in absorbent material (56). The device (10) has associated apparatus (26), whilst the device (52) is complete in itself. In each case, when the testing apparatus is located on a sampling outlet port, it causes a valve to open allowing sampling to occur.

Description

CONTAINER FOR CALIBRATION FLUID

This invention relates to devices for providing a vapour sample of a volatile component of a solution and apparatus for allowing such samples to be tested. In many fields, such as breath testing for alcohol, there is a need to detect volatile components in gaseous samples and these are frequently detected by using a fuel cell, a semi-conductor detector or an infra-red detector. Each of these detectors requires regular calibration or checking and essentially two methods of providing a component standard have grown up. In the first a calibrated sample is provided from a pressurised cylinder or can from which gas is allowed to flow into the inlet port of a test apparatus and in the second a gas is bubbled through a wet bath until a head space above the fluid in the bath is in equilibrium. The former suffers from a relatively short shelf life and is susceptible to variations in the atmospheric pressure and ambient temperature. The second piece of equipment is extremely bulky, expensive, generally requires heating and cannot realistically be used in the field. From one aspect the invention consists in a device for providing a gas sample of a volatile component of a solution comprising a substantially closed container, absorbent material partially filling the interior of the container for absorbing the solution and for releasing the volatile component into at least part of the remaining interior space, an outlet communicating with the part of the space to allow a sample of the volatile component to be withdrawn and valve means for opening and closing the outlet. The valve means may be for opening the outlet in response to the connection of sample drawing apparatus,and may include a projection for engagement by the sample drawing apparatus as it is connected to the outlet to operate the valve means. The valve means may comprise a deflectable seal and means for urging the seal against the outlet. The container may include an inlet to the part of the space and valve means for closing the inlet, in which case the inlet valve means and the outlet valve means may be constituted by a common valve means such that the inlet and outlets are opened and closed together. The container may include a recess for temperature detection means such that the approximate temperature of the solution and/or the part of the space can be determined. The container may have a number of inwardly projecting walls so as to increase the internal surface area of the container. From another aspect the invention consists in a device for providing a gas sample of a volatile component of a solution, comprising an open-mouthed container having a base defining a reservoir for an aqueous solution of a volatile component, a hydrophobic gas-permeable membrane extending across the top of the reservoir to retain the solution therein and a head space for collecting the volatile component vapour and means for releasably sealing the mouth and hence the head space.

Preferably the membrane is also temperature resistant (within its working range) and/or chemically inert. For convenience, it may be mounted on a carrier and the membrane may have a pore size of between 0.02 and 5.0 μm. It is particularly preferred that the pore size is 0.2 μm. The membrane may be of a PTFE film and may conveniently be mounted on an open-weave carrier. The container may be formed in two parts and the membrane may be trapped between them or a container may define a seat around the reservoir and the membrane may be adhered, fixed or welded to that seat. The sealing means may comprise a foil attached across the mouth, in which case the foil may be pierceable, tearable or peelable to release a gas in the head space. In the case where a foil is peelable it may have an extension folded back over the container whereby the foil can be peeled by pulling the extension. In this case the container may have a breakable tab to which the free end of the extension is secured.

The base may be formed with a formation extending into the reservoir and define an external recess for receiving a temperature probe. Additionally or alternatively the base may have a self-sealing membrane through which the probe can be inserted into the reservoir. The base may have an opening for filling the reservoir and a bung for sealing that opening.

The device may have identification formations or machine readable markings thereon so that containers having different concentrations can be automatically distinguished. The volume of head space is in part determined by the volume of sample which is to be drawn (typically the head space is at least ten times the sample volume) ; partly by the need to prevent the pressure - equilibration venting not diluting the sample to any significant degree and partly to ensure the concentration equilibration time is not over long. It has been found that volumes between 12.5 and 18 cm³ meet these parameters for the described design at least and a volume of between 15 and 16 cm³ is preferred. The container may be made of amyl-butyl-styrene (ABS) which may be injection moulded or vacuum formed.

From another aspect the invention consists in a sample including a device as defined above and an aqueous solution of a volatile component in the reservoir. In one particular embodiment the volatile component may be ethanol and in any of these cases the solution may further contain copper sulphate as a preservative.

From a yet further aspect the invention consists in an apparatus for releasing a head space sample comprising a two part body, the parts being engageable to form a sealed enclosure for receiving a container containing a head space sample and for defining a sample chamber for receiving the head space sample, an outlet on the body and in communication with the chamber for connection to test apparatus, an outlet valve means for opening the outlet in response to connection of the test apparatus.

The valve means may include projection means for engagement by the test apparatus as it is connected to the outlet to operate the valve means. The valve means may comprise a deflectable seal and means for urging the seal against the outlet in which case the projection means acts by urging the seal away from the outlet. The apparatus may further include means for bleeding air into the chamber as the test apparatus is engaged to equilibrate the chamber at atmospheric pressure. The bleeding means may comprise an external taper profile on the outlet. The apparatus may further include temperature detection means for detecting the temperature of the solution and may further include means for detecting temperature of the head space sample. Additionally or alternatively it may include means for reading identification markings or formations on the device.

The apparatus may include electrical connection means for connecting the temperature detecting or identification detecting means to the test apparatus.

The apparatus as defined above includes an enclosure formed to receive a device as defined above and in particular the body may be dimensioned so that the top and or extension of the peelable embodiment can project out of the body when the two parts of the body are sealingly engaged.

The invention also includes a combination of the device, the apparatus and the test apparatus.

Although the invention has been defined above it is to be noted that it includes any inventive combination of the device as set out above or in the following description.

The invention may be performed in various ways and a specific embodiments will now be described with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through a device for providing a head-space sample with an external temperature probe located therein;

Figure 2 is a longitudinal section through apparatus for allowing the head-space sample to be passed to test apparatus.

Figure 3 is a longitudinal section through an alternative sample device;

Figure 4 is the corresponding view of the device of Figure 3 when engaged on breath testing apparatus; Figure 5 is an exploded view of the device of Figure 3; and

Figure 6 is a perspective view of the device of Figure 3 as assembled and part assembled.

A device for providing a head-space sample of a volatile component of an aqueous solution is generally indicated at 10. It comprises an open-mouthed container 11, which defines a reservoir 12 and a head space volume 13.

The reservoir 12 and head space volume 13 are separated by a gas-permeable hydrophobic membrane 14 which is affixed to a seat 15 which extends around the top of the reservoir 12.

The mouth of the container 11 is closed by a foil 16 which has a folded-back extension 17. The free end of the extension 17 is secured to a breakable tab 19 formed on the container 11. An inverted well 20 is formed in the base 21 of the reservoir 12 to receive a temperature probe 22 for monitoring or detecting the temperature of the solution. (The probe 22 is not part of the device 10.) The base 21 may also include a filling opening 23, which can be sealingly closed by a bung 24.

In use, the reservoir is filled with an aqueous solution containing the volatile component for which calibration is required and for the purposes of this specification it will be assumed that it is a solution of ethanol and the device is for use with breath testing apparatus. As can be seen in Figure 1 the reservoir 12 is filled with such a solution 25.

In manufacture, the container is formed (for example from ABS) by injection moulding or vacuum forming and the membrane and foil are then affixed to it. Finally the solution 25 is added through the opening 23 and the bung 24 is inserted. This procedure will be particularly suitable for mass manufacture. The membrane may be any suitable membrane, but PTFE membranes are particularly preferred and it has been found that for ethanol, a pore size of between 0.02 and 5.0 μm is particularly suitable and indeed a pore size of 0.2 μm is preferred. An example of an appropriate film is Gore-tex Microfiltration PTFE membrane 9530051 made by W.L. Gore & Associates. Such film has very little mechanical strength and it may be desirable to use it on a carrier, particularly to facilitate fixing the membrane 14 to the seat 15. Alternatively the container 11 could be formed in two parts so that the membrane 14 can be trapped between the two parts during manufacture. Any carrier must obviously equally be gas permeable and will possibly posses a larger pore size. In use, the volatile component diffuses through the membrane 14 into the head space volume 13 at a rate determined by Graham's Law of Diffusion and the membrane pore size, but the solution 25 is retained within the reservoir 12. The system will fairly quickly reach equilibrium and then, in accordance with Henry's Law, the concentration of the ethanol vapour in the head-space volume 13 will be directly dependent on the concentration of the ethanol in the solution and on the temperature of the solution. The solution temperature is significant because the diffusion coefficient of ethanol in an ethanol water system is temperature dependent and this in turn alters the equilibrium concentration for the head space for a given solution concentration. The head space volume therefore, for any particular temperature, contains a vapour sample of known concentration. This sample can be released in any appropriate manner to the test apparatus with which it is to be used. For example, the foil 16 could simply be pierced. However, for reasons which will become clear in the following description, it is particularly preferred that the foil 16 is peeled off by breaking a tab 19 off the container 11 and pulling the extension 17 away from the container 11 such that it peels back the foil 16. As described above, the volume of the head space volume 13 will depend on many criteria of the system involved, but when used with the apparatus described below and for calibrating hand-held breath testing equipment, a volume of between 12.5 and 18 cm³ has been found suitable and a volume of between 15 and 16 cm³ is particularly preferred.

Figure 2 illustrates an apparatus designed to allow the devices 10 to be used in conjunction with hand-held breath tester such as the LION ALCOLMETER (RTM) SL-400 manufactured By Lion Laboratories pic. The apparatus, which is generally indicated at 26, has a body 27 formed of two hinged parts, 28, 29 which can be locked together in their closed position by a catch 30. The body 27 defines a first enclosure 31, which contains a processor 32 and associated circuitry mounted on a printed circuit board 33 and a display 34, and a further enclosure 35 for receiving the device 10 and for allowing the sample in its head-space volume to be supplied to breath testing equipment. Thus, in connection with enclosure 35, part 28 defines a chamber 36 for receiving the device 10, whilst part 29 defines a further chamber 37 into which the head space volume sample can be released when the foil 16 is removed. The volume of the chamber 37 will define the time that will need to elapse for re-equibration of the sample to occur.This second chamber 37 is connected to an outlet 38 onto which the inlet port of a breath tester (not shown) can be engaged. For reasons which will become apparent, the outlet port 38 has a tapering external profile. The outlet port 38 is closed by a deflectable seal 39, which is mounted on a flat spring 40 that is fixed at its other end 41 to the part 29. A further seal 42 is engaged on the spring 40, intermediate the seal 39 and other end 41, and closes off an opening in the wall 43 of the part 29. This opening 44 receives and retains a projection 45. It will be noted that the height of this projection 45 is less than the height of the port 38. The spring 40 is also provided with an upstanding wall 46, which forms a labyrinth seal, between the port 38 and the opening 44, with a formation 47 on the wall 43. When breath testing apparatus is pushed onto the port 38, its body engages the projection 45 and displaces it inwardly into the chamber 37. This movement urges the head 48 of the projection 45 against the seal 42 and hence causes the spring 40 to be deflected downwardly opening the port 38.

As the projection 45 is shorter than the port 38, the seal 39 will not open until after the port 38 is partially inserted into the inlet of the breath tester. This prevents any substantial escape of the sample in the chamber 37. However, because the external profile of the outlet port 38 is tapered, air can bleed between the port 38 and the breath testing apparatus inlet into the chamber 37 so that it becomes equilibrated to atmospheric pressure, without any significant leakage of the sample to the atmosphere. The labyrinth seal prevents any direct leakage of air between the port 38 and the opening 44.

Once the breath tester is fully engaged the system is once more sealed and the apparatus can be instructed to suck out the sample from the chamber 37.

In use the device 10 is fitted into the chamber 36 with the body open. As it is inserted it engages with the temperature probe 22, which is mounted within that chamber. It may also engage a series of micro switches 49 mounted in that chamber. By providing suitable formations (eg 50)on the container 11, the micro switches 49 can be switched either on or off and hence produce an identifying code for the container and indicate to the processor 32 what concentration is within the container 10. (Machine readable barcodes and other identifying systems may also be used) . The temperature probe 22 is also connected to the processor 32. The processor 32 calculates the actual concentration of the sample in the head space and displays the value on the display so that the operator can calibrate or check the instrument in accordance with this figure. Alternatively this information may be supplied to the breath tester by a cable (not shown) for automatic calibration. In a third arrangement the cable (not shown) can be used to inform the breath tester of the concentration of the solution sample and the temperature of the solution so that a suitable compensation can be made by a processor in the breath tester. Once the container 10 is located in the chamber 36, the part 29 is closed down on it and a seal is formed with the O' ring 51 which extends around the mouth of the chamber 37. At this point the tab 19 extends outwardly of the body 27 and can be broken off and pulled so that the foil 16 is pulled out between the 'O' ring 51 and the part 28 to release the ethanol head-space vapour sample into the chamber 37 without any loss of the sample. The two parts 28, 29 are being held together under hand pressure at this time. They can then be clamped with the catch 30.

It will be understood from the above that the design of the container requires a balance to be struck between solution volume, headspace volume, sample volume and the desired equilibration time. Another factor in this "equation" is the surface area of the membrane between the solution volume and the head space volume because the diffusion rate is proportional to that area ie. a small surface area results in a slower diffusion rate and hence a slower rate of equilibration. Under certain temperature conditions, it has been found that water vapour can be formed in the head space volume 13. If such vapour forms then the reading taken by the breath testing apparatus may be affected. This problem may be dealt with in a number of ways: the software may be adjusted to take it into account; hydroscopic material may be provided in the head space for example along the surface of the container wall or the hydrophobic nature of the membrane may be improved. Figures 3 to 6 show an alternative device, 52, which also provides a solution to this problem and further effectively combines the functions of the device 10 of Figure l and the apparatus 26 Figure 2. The device 52 comprises a container 53 formed from upper and lower parts 54, 55. Absorbent material 56 is provided to line the inner walls of the parts 54 , 55 so as to partially fill the interior space, whilst leaving a head space 57. Grooves 58 are provided in parts of the absorbent material 56 so as to increase its surface area. In use the absorbent material 56 is impregnated with an ethanol solution (or a solution of any other volatile component to be tested) .

The lower container portion 55 contains inwardly projecting walls 59 which serve to guide a generally rectangular valve member 60. The valve member has lands 61,62 and 63. Lands 61 and 63 carry gasket material 64 on their bottom surface and form valve seats for an outlet 65 and an inlet 66 respectively. The central land 62 carries a downwardly extending projection 67 which is provided with a washer 68. The projection 67 extends through an opening 69 which can be sealed by the washer 68. A spring 70 acts to urge the valve member 59 into the closed position indicated in Figure 3. The spring 70 seats on the bottom of a well-forming projection 71 formed in the upper container part 54. The well 72 contains a thermistor 73.

In use the device 52 is engaged on breath testing apparatus 74 and this engagement forces the projection 67, and hence the valve element 59, upwardly opening both the inlet 66 and outlet 65. The breath tester 74 is then immediately operated and a sample from the head space 57 is drawn into the tester for calibration purposes as previously described. The open inlet 66 allows the head space 57 to be at atmospheric pressure and prevents any resistance to the sucking of the sample.

It will be understood that as in the previous example the solution of volatile component in the absorbed material will have equilibrated with the headspace and so the drawn sample will be of known concentration.

The thermistor 73 could be connected to a separate ^'computer element as in Figure 2, or it can simply be linked into the breath testing apparatus as shown in chain line in Figure 4. An even more preferred arrangement is that the breath testing apparatus could include a temperature probe which entered a well in the lower part 55 of the container when the breath testing apparatus is engaged on the device or, alternatively, the breath testing apparatus has an electrical contact which can engage directly with an electrical contact of the thermistor. Where the device 52 contains a memory, this could also inform the breath tester 74 of the concentration of the sample. Alternatively other identification means may be provided.

The provision of the inlet 66 can allow the device to be charged with the volatile component after assembly. Deflection of the projection 67 will open the inlet 66 and the container can then be filled with a known volume of volatile component, for example by a hypodermic syringe.

It is anticipated that the devices will probably be disposable. However, they could be re-charged as described above. Clearly the breath testing apparatus will require suitable software when it is taking readings directly from the thermistor.

Claims

1. A device for providing a gas sample of a volatile component of a solution comprising a substantially closed container, absorbent material partially filling the interior of the container for absorbing the solution and for releasing the volatile component into at leaεt part of the remaining interior space, an outlet communicating with the part of the space to allow a sample of the volatile component to be withdrawn and valve means for opening and closing the outlet. 2. A device as claimed in claim 1 wherein the valve means is for opening the outlet in response to the connection of sample drawing apparatus.

3. A device as claimed in claim 2 wherein the valve means includes a projection for engagement by the sample drawing apparatus as it is connected to the outlet to operate the valve means.

4. Apparatus as claimed in claim 3 wherein the valve means comprises a deflectable seal and means for urging the seal against the outlet. 5. Apparatus as claimed in any one of the preceding claims wherein the container includes an inlet to the part of the space and valve means for closing the inlet.

6. Apparatus as claimed in claim 5 wherein the inlet valve means and the outlet valve means are constituted by a common valve means such that the inlet and outlets are opened and closed together.

7. A device as claimed in any one of the preceding claims wherein the container includes a recess for temperature detection means such that the temperature of the solution and/or the part of the space can be determined.

8. A device as claimed in any one of the preceding claims wherein the container has a number of inwardly projecting walls so as to increase the internal surface area of the container.

9. An assembly of a device as claimed in any one of the preceding claims and a sample drawing means wherein the sample drawing means includes a temperature probe for location in the recess.

10. An assembly as claimed in claim 9 wherein the recess on the device is located such that the probe automatically enters the recess when the sample drawings means is engaged.

^"ll. An assembly as claimed in claim 9 or claim 10 wherein the sample drawing means is constituted by breath testing apparatus.

12. A device for providing a gaseous sample of a volatile component of a solution comprising an open-mounted container having a base defining a reservoir for an aqueous solution of the volatile component, a hydrophobic gas permeable membrane extending across the top of the reservoir to retain the solution therein and a headspace for collecting the volatile component in its gaseous state and means for releasably sealing the mouth and hence the head space. 13. A device as claimed in claim 12 wherein the membrane is a P.T.F.E film.

14. A device as claimed in claim 12 and claim 13 wherein the membrane is mounted on a carrier wherein the membrane is temperature resistant and/or chemically inert.

15. A device as claimed in any one of the preceding claims wherein the membrane pore size of between 0.5 and 2.5μm.

16. A device as claimed in claim 15 wherein the pore size is 0.2μm.

17. A device as claimed in any one of the preceding claims wherein the container is formed in two parts and the membrane is trapped between them.

18. A device as claimed in any one of the claims 12 and 16 wherein the container defines a seat around the reservoir and the membrane is adhered, fixed or welded to the seat.

19. A device as claimed in any one of claims 12 to 13 wherein the sealing means comprises a foil attached across the mouth. 20. A device as claimed in claim 19 wherein the foil is pierceable.

21. A device as claimed in claim 19 wherein the foil is peelable.

22. A device as claimed in claim 21 wherein the foil has an extension fold back over the container whereby the foil can be peeled by pulling the extension.

23. A device as claimed in claim 22 wherein the container has a breakable tap to which the free of the extension is secured. 24. A device as claimed in any one of claims 12 to 23 wherein the base is formed with a formation extending into the reservoir to define an external recess for receiving a temperature probe. 25. A device as claimed in any one of claims 12 to 24 wherein the base has an opening for filling the reservoir and a bung for sealing the opening.

26. A device as claimed in any one of claims 12 to 25 wherein the volume of head space is between 12.5 and 18cm³.

27. A device as claimed in claim 26 wherein the head space volume is between 15 and 16cm³.

28. A device as claimed in any one of claims 12 to 26 wherein the container is made of amylbutystyrene. 29. A device as claimed in any one of claims wherein the container is injection moulded or vacuum formed. 30. A device as claimed in any one of claims 1 to 8 or 12 to 29 having identification formations or machine readable markings thereon. 31. A sample including a device as claimed in any one of the claims 1 to 8 and 12 to 30 wherein there is an aqueous solution of volatile component.

32. A sample as claimed in claim 31 wherein the volatile component is ethanol. 33. A sample as claimed in claim 31 or claim 32 further including copper sulphate in the solution.

34. Apparatus for releasing a head space sample comprising a two part body the parts being sealingly engageable to form a sealed enclosure for receiving a container containing a head space sample and for defining a sample chamber for receiving the head space sample, an outlet on the body wall in communication with the chamber connection for to test apparatus and outlet valve means for opening the outlet in response to connection of the test apparatus.

35. Apparatus as claimed in claim 34 wherein the valve means includes projection means for engagement by the test apparatus as it is connected to outlet to operate the valve means.

36. Apparatus as claimed in claim 35 wherein the valve means comprises a deflectable seal and means for urging the seal against the outlet and wherein the projection means acts by urging the seal away from the outlet. 37. Apparatus as claimed in any one of the claims 34 to 36 further including means for bleeding air into the chamber as the test apparatus is engaged to equilibrate the chamber at atmospheric pressure. ^"38. Apparatus as claimed in claim 37 wherein the bleeding means comprises an external taper profile on the outlet.

39. Apparatus as claimed in any one of the claims 34 to 38 further including temperature detection means for detecting the temperature of the head space sample.

40. Apparatus as claimed in any of claims 34 to 39 further including means for reading identification marking or formations on the sample.

41. Apparatus as claimed in any one of claims 34 to 40 further including electrical connection means for connecting the temperature detecting means or identification means to the test apparatus.

42. Apparatus as claimed in any one of claims 34 to 41 including an enclosure formed to receive a device as claimed in any one of claims 1 to 8 and 12 to 35. 43. An assembly of an apparatus as claimed in any one claims 34 to 42, a device as claimed in any one claims 1 to 8 or claims 12 to 33 and testing or sample drawing apparatus.