WO2009156746A2

WO2009156746A2 - Sampling devices and methods

Info

Publication number: WO2009156746A2
Application number: PCT/GB2009/001623
Authority: WO
Inventors: Stephen John Taylor
Original assignee: Smiths Detection-Watford Limited
Priority date: 2008-06-26
Filing date: 2009-06-26
Publication date: 2009-12-30
Also published as: WO2009156746A3; GB0811687D0

Abstract

A sampling device including a preconcentrator and a gas flow device, the preconcentrator including an adsorbent surface over which a sample gas is passed, the adsorbent surface being provided in the region of an orifice of the preconcentrator and the gas flow device being arranged to cause gas to flow through the orifice and radially outward of the orifice.

Description

SAMPLING DEVICES AND METHODS

Field

This invention relates to sampling devices and methods.

Background

Atmospheric sampling, such as to detect hazardous substances in air, can be carried out using a preconcentrator. Air is directed over the surface of the preconcentrator selected such that the analyte substance of interest is adsorbed to the surface of the preconcentrator. Analyte substances may be present in very low concentration levels in the air, below that which can be detected reliably by conventional detectors. By passing the air over the preconcentrator for an extended period of time the level of adsorbed substance can be accumulated and increased. The accumulated substance can subsequently be released (such as by heating the preconcentrator) in a short period of time to produce a bolus of a higher concentration of the substance at a level that can be detected reliably.

The preconcentrator may be attached to the inlet of a suitable detector, such as, for example, an ion mobility spectrometry (IMS), gas chromatograph (GC), mass spectrometer (MS) infrared (IR), or Raman detector or any combination of these detectors. Alternatively, the preconcentrator may be provided in a separate sampling device at a location remote from the detector, which is connected to the detector after it has been running for sufficient time. This latter arrangement enables one detector to be used to detect substances at a number of different locations and allows the detector to be remote from the sampling device, reducing risk of contamination of a detector that cannot readily be decontaminated. The preconcentrator can be highly sensitive to contamination so it is very important that it is protected from contamination during handling and use. This presents particular problems where the preconcentrator is a replaceable component in a sampling device. Typically, the sampling device would include a fan or some other form of air-moving device and some form of seal with the preconcentrator so that air flow was appropriately confined and directed. When the preconcentrator is replaced by a new preconcentrator, it would necessarily contact the seal, which could be contaminated by substance from the previous sampling. This can lead to problems if it is important to know how the concentration of the analyte substance is varying with time, or if the sampling device is moved to sample at a different location.

Accordingly, there is a need to provide an alternative sampling device and method.

Summary

According to one embodiment there is provided a sampling device including a preconcentrator and a gas flow device, the preconcentrator including an adsorbent surface over which a sample gas is passed, the adsorbent surface being provided in the region of an orifice of the preconcentrator and the gas flow device being arranged to cause gas to flow through the orifice and radially outward of the orifice.

According to another embodiment there is provided a sampling device including a preconcentrator and a gas flow device, the preconcentrator including an adsorbent surface over which a sample gas is passed, the adsorbent surface being provided in the region of an orifice in a plate member, and the plate member being supported at one side only and unsupported along other sides. According to another embodiment, there is provided A sampling device including a preconcentrator and means for causing flow of a sample gas over an adsorbent surface of the preconcentrator, the adsorbent surface being provided in the region of an orifice of the preconcentrator and the means for causing flow of the sample gas being arranged to cause gas to flow through the orifice and radially outward of the orifice.

According to another embodiment, a sampling device including a preconcentrator and means for causing flow of a sample gas over an adsorbent surface of the preconcentrator, the adsorbent surface being provided in the region of an orifice in a plate member, and the plate member being supported at one time only and unsupported along other sides.

Other features, objects, and advantages of the present invention are apparent in the detailed description that follows and in the claims. It should be understood, however, that the detailed description, while indicating embodiments of the invention, is given by way of illustration only, not limitation. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description

Figures

Figure 1 is a cross-sectional side elevation view of an exemplary device. Figure 2 is a plan view of the exemplary device of Figure 1.

Description

One embodiment provides a sampling device including a preconcentrator and means for causing flow of a sample gas over an adsorbent surface of the preconcentrator. The adsorbent surface can be comprised of any suitable material. This will be determined by the sample gas to be detected. The sample gas may, for example, include low to high boiling organics, such as methane, propane, n-pentane, acetone, isopropanol, toluene, m-xylene, 1 ,2- dichlorobenzene, n- dodecane, nicotine, 1-dodecanol, ethanol, methanol, and thiodiethanol, as well as inorganic components, such as HCN and ammonia. Other compounds/components include carbon monoxide, butane, methyl ethyl ketone, hydrogen sulfide, and agents such as, for example, sarin, mustard gas, tabun, and VX.

A suitable adsorbent surface is one which adsorbs a sufficient amount of the sample gas for this to be detected. Examples of suitable material include charcoal, Anasorb®, Anasorb® GCB2, Anasorb® GCBl, Anasorb® CMS, carbon, such as carbon molecular sieve, Chromosorb®, Chromosorb-102®, Chromosorb- 104®, Chromosorb- 106® Chromosorb- 108® Florisil® 226, Porapak®, Poropak-N®, Porapak-Q®, Porapak-R®, Porapak-T®, polyurethane foams (PUF)5 silica gel, Tenax®, Tenax® 226, Tenax® GR, Tenax® TA, XAD®, XAD®-2, XAD®-4, XAD®-7, and/or a combination of one or more sorbent materials.

The adsorbent surface can be provided in the region of an orifice of the preconcentrator and the means for causing flow of the sample gas can be arranged to cause gas to flow through the orifice and outwardly of the orifice. In one embodiment the gas can flow radially outwardly of the orifice.

Any suitable means for causing flow of gas can be used. Gas can be transferred using, for example, a fan, a compressor, a blower. In one embodiment, the gas moving means includes a centrifugal fan. In one embodiment, the preconcentrator can be a planar or substantially planar member with the orifice located near or within the edges of the member. In an embodiment, the preconcentrator can be supported towards one end only, away from the adsorbent surface.

According to an aspect there is provided a sampling device including a preconcentrator and means for causing flow of a sample gas over an adsorbent surface of the preconcentrator, the adsorbent surface being provided in the region of an orifice in a plate member and the plate member being supported at one side only and unsupported along other sides.

The plate member can be supported in any suitable way, such as, for example, at an open end of a wallet or similar structure into which the plate member can be slid after use.

According to a further aspect there is provided a method of sampling including providing an adsorbent surface on a member having an internal and external surface, causing a sample gas to flow over the adsorbent surface from the external surface to the internal surface where it is caused to flow away from the adsorbent surface.

Referring to the accompanying figures, the sampling device can include a preconcentrator 1 and a centrifugal fan arrangement 2 arranged to direct air or other sampling gas over a part of the preconcentrator. The preconcentrator 1 can be removable from the sampling device so that, after the sampling time, which can be a predetermined time, the preconcentrator can be taken to a suitable detector and replaced by a new preconcentrator.

The preconcentrator 1 can include member 10 of any suitable material. The member 10 may be in the form of a plate. The plate 10 can be made of, for example, a thin, rigid or semi-rigid material. The plate 10 can be any suitable thickness. In one embodiment, the plate member 10 can be from 0.1-1 mm thick. In another embodiment, the plate 10 can be about 0.5mm thick. In an embodiment, the plate 10 can be any suitable shape, including square or substantially square, substantially rectangular, substantially circular, or substantially oval.

In another embodiment, the member 10 can be a rectangular plate extending horizontally and supported only at one end 11 in the open end 12 of a similar- shape housing or wallet 13. The other three sides of the plate 10 can be unsupported and are not contacted by any part of the sampling device. In an embodiment electrical connection can be made via the outside surface of a flange 14 attached to the free, edge 14' of the plate. The other three sides of the wallet 13 can be closed. The plate 10 can be slidable into or out of the wallet 13 so that, after use, it can be slid into the wallet and sealed by the flange 14. The wallet 13 can protect the plate 10 from contamination during handling and transport. The plate 10 can include a circular region of any suitable size that provides an orifice through the thickness of the plate in that this region is perforated with multiple openings 16. The multiple opening can form a filigree-like appearance when viewed from above.

In one embodiment, the substantially circular or circular region of the plate 10 can be from about 15 mm to about 5mm in diameter. The orifice region 15 can be located centrally of the plate 10, within its four edges. The surfaces of the orifice openings 16 and the immediate periphery around the region 15 can be coated with an adsorbent material 17 selected to be adsorbent to the analyte substance or range of substances of interest. Any suitable adsorbent material can be used such as those set out above. In one embodiment, the adsorbent material 17 can be a polydimethylysiloxane. The plate 10 has an upper, external side 18 and a lower, internal side 19.

The fan arrangement 2 can include an electric motor 20 mounted beneath a horizontal baffle plate 21 extending parallel to the preconcentrator plate 10 and of about the same size. The shaft 22 of the motor 20 can be fixed to the centre of a centrifugal fan blade 23 of conventional form and circular, disc shape. The upper surface of the fan blade 23 can be open and its lower surface can be closed. The diameter of the fan blade 23 can be greater than that of the orifice region 15. In one embodiment, the diameter of the fan blade can be approximately two to three times the diameter of the orifice region. The motor shaft 22 and the centre of the fan blade 23 can be aligned with the centre of the orifice region 15. It is not essential that the orifice region 15 be located centrally or that it be axially aligned with the fan blade 23 providing that part of the fan diameter is covered by the imperforate boundary region outside the orifice region. The underside of the fan blade 23 can be closely spaced from the upper surface of the baffle plate 21, sufficient to ensure that the blade does not contact the baffle plate during use. The upper surface of the fan blade 23 can be similarly closely spaced from the underside of the preconcentrator plate 10 sufficient to avoid any risk of contact with the plate during use.

In operation, the motor 20 rotates the fan blade 23 about a vertical axis so that air or other sampling gas can be drawn down in to the centre of the upper surface of the blade and expelled radially or substantially radially around its outer edge. It can be seen, therefore, that this will cause air to be drawn down into the sampling device from the external side 18 to the internal side 19 of the plate 10 through the orifice region 15. Air or sampling gas can then move radially outwardly in all directions by the fan 2 away from the centre of the orifice region 15. As the air or sampling gas flows through the plate 10 it flows over the adsorbent surface 17 and any analyte substances are adsorbed to the central region 15 of the plate. The radial flow of air or sampling gas can minimize the opportunity for gas vortices or other disturbed flow patterns to form of the kind that could pass air, sampling gas or particles from the fan blade to the lower preconcentrator surface 19.

Using radial flow means in this way enables air or other sampling gas to be drawn efficiently through the orifice region 15 of the plate 10 without any need to contact the plate and thereby risk cross-contamination to the plate or to subsequently attached plates.

It will be appreciated that there are other means by which a radial flow of gas could be produced, such as, for example, by means of a radial arrangement of corona discharge sources such that their combined electric winds cause a radial air flow.

When the sampling device has been operating for a length of time, the motor is turned off and the plate 10 can be slid carefully to the left, back into its protective wallet 13. The preconcentrator 1 comprising the wallet 13 and plate 10 then can be removed from the sampling apparatus and taken to an appropriate detection instrument for desorption and detection or analysis. The detection instrument can be any suitable instrument including an IMS, GC, MS, IR, Raman, or any combination of these detectors. In one embodiment, the detection instrument is an IMS, A new preconcentrator can then placed on the sampling device, its plate slid to the right, out of the wallet into an operative position and the fan is restarted to commence a new collection.

It can be seen that during the operation, removal and replacement of the preconcentrator, the preconcentrator plate does not at any time contact any surface of the sampling device, thereby ensuring that it does not pick up contamination from the device, and ensuring that it does not transfer any contamination to the sampling device. The present invention, therefore, avoids the need to clean the sampling device when a new preconcentrator is put on the device, making the sampling device particularly useful for field use.

Claims

1. A sampling device including a preconcentrator and a gas flow device, the preconcentrator including an adsorbent surface over which a sample gas is passed, the adsorbent surface being provided in the region of an orifice of the preconcentrator and the gas flow device being arranged to cause gas to flow through the orifice and radially outward of the orifice.

2. A sampling device as claimed in claim 1, wherein the gas flow device is a fan, a blower or a compressor.

3. A sampling device as claimed in claim 1, wherein the gas flow device is a centrifugal fan.

4. A sampling device as claimed in any preceding claim, in which the preconcentrator is a substantially planar member.

5. A sampling device as claimed in claim 4, in which the orifice of the preconcentrator is located away from the edges of the planar member.

6. A sampling device as claimed in claim 5, in which the orifice is located centrally of the planar member.

7. A sampling device as claimed in any preceding claim, in which the preconcentrator is supported towards one end only.

8. A sampling device including a preconcentrator and a gas flow device, the preconcentrator including an adsorbent surface over which a sample gas is passed, the adsorbent surface being provided in the region of an orifice in a plate member, and the plate member being supported at one side only and unsupported along other sides.

9. A sampling device as claimed in claim 8, in which the plate member is supported at an open end of a wallet into which the plate member can be slid after use.

10. A sampling device including a preconcentrator and means for causing flow of a sample gas over an adsorbent surface of the preconcentrator, the adsorbent surface being provided in the region of an orifice of the preconcentrator and the means for causing flow of the sample gas being arranged to cause gas to flow through the orifice and radially outward of the orifice.

11. A sampling device including a preconcentrator and means for causing flow of a sample gas over an adsorbent surface of the preconcentrator, the adsorbent surface being provided in the region of an orifice in a plate member, and the plate member being supported at one time only and unsupported along other sides.

12. A method of sampling including providing an adsorbent surface on a member having an internal and external surface, causing a sample gas to flow over the adsorbent surface from the external surface to the internal surface where it is caused to flow away from the adsorbent surface.