Detector inlet and sampling method

A detector comprising an analytical apparatus for detecting a substance of interest, and a detector inlet. The detector inlet comprises a flow passage for carrying a flow of fluid, the flow passage comprising a sampling volume, and a sampling inlet adapted to collect samples of the fluid from the sampling volume as the fluid flows past the sampling inlet, and to provide the samples to the analytical apparatus, wherein the flow of fluid carries particulates. The detector inlet also comprises a flow director arranged to vary a spatial distribution of the particulates carried by the fluid to increase a relative proportion of the particulates carried past the sampling inlet along the flow passage without entering the sampling volume.

The present disclosure relates to detection methods and apparatus, and more particularly to methods and apparatus for obtaining samples for detectors, still more particularly to methods and apparatus for obtaining samples of vapours in the presence of particulates, these methods and apparatus may find particular application in spectrometry, for example ion mobility spectrometry and mass spectrometry.

Some detectors operate by “inhaling” a stream of fluid, such as air, into a detector inlet and sampling that air with an analytical apparatus to detect substances of interest. That inhaled stream of air can be sampled from the detector inlet using a sampling inlet such as a pinhole, capillary or membrane inlet.

Often, hand held, or portable devices may be needed for example for use by military and security personnel. These personnel frequently operate in hostile environments in the presence of large quantities of dust and grit and other particulate matter. Such particulates may obstruct the sampling inlet, or otherwise damage the detector. In some cases, particulates carried by the stream of air may comprise substances to which the detector is sensitive. If these accumulate in a detector or its inlets they may contaminate the detector, and may cause recovery time issues.

In the drawings like reference numerals are used to indicate like elements.

Embodiments of the disclosure relate to detectors for detecting substances of interest, and to detector inlets arranged to obtain samples for analysis in the detectors.

To obtain a sample, a fluid can be inhaled into a detector inlet and flowed to an outlet along a flow passage. A sampling inlet is coupled to the flow passage to provide samples of the fluid to an analytical apparatus. Where particulates are present in the environment they are carried by the inhaled flow, and are spatially distributed throughout it. Embodiments of the disclosure aim to direct the flow of fluid with a flow director that varies this spatial distribution of particulates. This provides a volume of the flow passage, downstream of the flow director, in which the spatial distribution of particulates is depleted. The sampling inlet can be arranged to obtain samples from this depleted sampling volume to reduce the risk of contaminating the detector with unwanted particulate material, or simply blocking the sampling inlet.

This modification of the distribution of particulates may be achieved, for example, by speeding up, slowing down, or changing the direction of at least a part of the fluid flow along the flow passage.

FIG. 1shows a detector1comprising a detector inlet2, coupled to an analytical apparatus6by a sampling inlet14, such as a pinhole, capillary or membrane inlet, and a sampler10arranged to obtain samples of the fluid via the sampling inlet14from a sampling volume16around the sampling inlet14.

The detector inlet2shown inFIG. 1comprises a flow passage for carrying a flow of fluid8past the sampling inlet14. As illustrated the detector inlet2ofFIG. 1comprises a flow provider18arranged to flow the fluid into the flow passage, past the sampling inlet14, and along the flow passage20to an outlet. The detector inlet2may also comprise a heater4which may be arranged to heat the flow of fluid8upstream of the sampling inlet14.

The flow passage20comprises a flow director21which, in the example ofFIG. 1, is provided by a bend in the flow passage20arranged to change the direction of the fluid flow upstream from the sampling inlet14.

The sampling inlet can be coupled to the flow passage20and adapted for collecting samples of the fluid from a sampling volume16in the flow passage20around the sampling inlet14. The sampler10is configured to draw a selected volume of fluid, smaller than the sampling volume16, through the inlet to provide a sample to the analytical apparatus. The sampler10may comprise an electromechanical actuator, for example a solenoid driven actuator, and/or a mechanical pump arranged to transfer vapour from the sampling volume16, through the sampling inlet14and into the analytical apparatus.

The analytical apparatus6shown inFIG. 1comprises a mass spectrometer. A mass spectrometer may comprise an ioniser, an ion accelerator, a beam focusser, a magnet, and a faraday collector arranged to perform mass spectrometry analysis on samples of vapour. As illustrated, a controller12is coupled to control the analytical apparatus, the flow provider, the heater, and the sampler. The controller12may comprise a processor and a memory storing instructions for operation of the detector1.

In operation of the embodiment illustrated inFIG. 1, the flow provider18flows fluid along the flow passage, and the bend in the flow passage20changes the direction of the fluid flow upstream from the sampling inlet14. By directing the flow in this way, the spatial distribution of particulates across the fluid flow can be changed to increase a proportion of the particulates which flow past the sampling inlet14without entering a volume around the sampling inlet14. In the example shown inFIG. 1this occurs because the inlet is arranged on the inside of the bend, and particulates carried by the flow tend to flow along the outside of the bend, away from the sampling inlet14. This change in distribution is illustrated in Inset A ofFIG. 1. Inset A illustrates a plot100of a spatial distribution of particulates along the line A, the horizontal axis indicates position across the direction of flow of the fluid. The plot100shown in Inset A ofFIG. 1corresponds to a spatial distribution of particulates upstream from the flow director21. Inset B illustrates a plot102of a spatial distribution of particulates along the line B, across the direction of flow of the fluid in the region of the sampling volume16. From a comparison of Inset A and Inset B, it can be seen that the spatial distribution of particulates across the flow of fluid8is changed to increase the relative proportion of the particulates carried past the sampling inlet14along the flow passage20without entering the sampling volume16.

The controller12can control the sampler10to draw a sample from the sampling volume16and to provide the sample to the analytical apparatus6. The analytical apparatus6illustrated inFIG. 1can then analyse the sample by performing mass spectrometry on the sample.

As will be appreciated, the detector inlet2of the present disclosure may also be used in other kinds of detectors such as, detectors comprising ion mobility spectrometers, time of flight ion mobility spectrometers, chromatography apparatus and other kinds of analysers for detecting substances of interest.

FIG. 2shows a detector1in which the analytical apparatus comprises an ion mobility spectrometer6′ but which is otherwise identical to the apparatus shown inFIG. 1. The ion mobility spectrometer ofFIG. 2is coupled to a detector inlet2by a sampling inlet14. A sampler10is arranged to obtain samples of the fluid through the sampling inlet14and to provide them to the ion mobility spectrometer6′. As in the example ofFIG. 1, the controller12may comprise a processor and a memory storing instructions for operation of the detector1. Also as inFIG. 1, the sampler10may comprise an electromechanical actuator, for example a solenoid driven actuator, and/or a mechanical pump arranged to transfer vapour from the sampling volume16through the sampling inlet14into the analytical apparatus.

InFIG. 2, the ion mobility spectrometer6′ may comprise a reaction region36in which a sample can be ionised by an ioniser34. The sampler10can be operated to obtain a sample from the sampling volume16through the sampling inlet14, and to provide the sample to the reaction region36. Some examples of sampling inlets14include ‘pinhole’ inlets, which may be approximately 0.7 mm in diameter, for example the diameter may be at least 0.4 mm, for example at least 0.6 mm, for example less than 1.0 mm, for example less than 0.8 mm.

A gate electrode30may separate the reaction region36from a drift chamber38. The gate electrode30may comprise an assembly of at least two electrodes, which may be arranged to provide a Bradbury-Nielsen gate. The drift chamber38can comprise a collector32toward the opposite end of the drift chamber38from the gate electrode30for detecting ions. The drift chamber also comprises a drift gas inlet44, and a drift gas outlet46arranged to provide a flow of drift gas along the drift chamber38from the ion collector32towards the gate30. The sampler10can be operated by the controller12to obtain fluid from sampling volume16through the sampling inlet14. The sampler10can also be operated to provide an obtained sample into the reaction region36of the spectrometer6′. The reaction region shown inFIG. 2comprises an ioniser34for ionising a sample. The ioniser34may comprise a corona discharge ioniser. The drift chamber38may comprise drift electrodes40,42for applying an electric field along the drift chamber38to move ions towards the collector32against the flow of the drift gas. Although the apparatus ofFIG. 2is illustrated as comprising two drift electrodes40,42, some embodiments may comprise more than two drift electrodes.

In operation, the flow provider18can be operated to direct a flow of fluid8past the flow director21in the flow passage20and then past the sampling inlet14. As the fluid flows past the flow director21the change in direction it provides varies the distribution of particulates transverse to the direction of flow of the fluid relative to the shape of said distribution upstream of that bend. This may provide a depleted region of the cross section of the flow passage20through which relatively few particulates flow, the majority of the particulates being carried through other parts of the cross section of the flow passage. This depleted region may persist for a distance along the flow passage20thereby defining a sampling volume16in which the number (e.g. count per unit volume) of particulates is relatively lower than in other regions of the flow passage.

The sampler10can be operated to obtain a sample of fluid from this sampling volume16via the sampling inlet14. The obtained sample of fluid can then be provided to an analytical apparatus. In the example ofFIG. 2the analytical apparatus comprises an ion mobility spectrometer6′.

As explained above, detector inlets of the present disclosure find particular application in portable devices which may be used in hostile environments where dust and contaminants are prevalent. These detector inlets may be used with a variety of analytical apparatus, such as the mass spectrometer ofFIG. 1and the ion mobility spectrometer ofFIG. 2, other kinds of analysers, spectrometers and/or chromatography apparatus. In addition, the detector inlet2may have different configurations.

As shown inFIG. 3,FIG. 4, andFIG. 5, a detector inlet2may comprise flow directors having different structural forms. Each of these flow directors may vary the distribution of particulates in the flow of fluid8to provide a sampling volume16having a relatively lower concentration of particulates (e.g. a lower mass per unit volume, or particulate count per unit volume). In some embodiments the flow director21may provide a sampling volume16where fluid flow is slow compared to the flow of fluid8past the sampling volume16along the flow passage. This may be achieved by providing a region of slow flow, and/or by accelerating part of the flow.

Accelerating may comprise changing the direction of at least a part of the flow of fluid8or increasing its speed, or both. Providing a region of slow flow may comprise providing a culvert or recess or other sheltered region as inFIG. 5.

FIG. 3shows an example of a detector inlet2comprising a flow director, a sampling inlet14, and a flow passage.FIG. 3comprises three views of the detector inlet2,FIGS. 3A, 3B and 3C.FIG. 3Ashows a section view of the detector inlet2from the line indicated as X-X inFIG. 3C.FIG. 3Bshows a section view of the detector inlet2from the line indicated as Y-Y inFIG. 3A.FIG. 3Cshows a section view of the detector inlet2from the line indicated as Z-Z inFIG. 3B.

As can be seen inFIG. 3AandFIG. 3B, in the embodiment illustrated inFIG. 3the flow director21protrudes into the flow passage20from a wall of the flow passage. The flow director21can direct the flow of fluid to flow only to one side of the flow director. The flow director21may protrude further into the flow passage20toward the flow director's downstream end than towards its upstream end. For example, the flow director21may have a sloped surface, which may be straight, curved or graduated, to provide a ramp. As illustrated inFIG. 3A, the sampling inlet14may be disposed downstream of the flow director21to obtain samples from a sheltered sampling volume16. The speed of the fluid flow in the sampling volume16may be lower than the speed of fluid flow past the sampling volume16. The speed of the fluid flow past the sampling volume16may be higher than the speed of the fluid flow upstream from the flow director.

FIG. 3Dillustrates one example of a spatial distribution of particulates across the flow passage20upstream from the flow director. As can be seen inFIG. 3D, upstream from the flow director, particulates carried by the fluid flow may be distributed relatively evenly across the width of the flow. As will be appreciated in the context of the present disclosure, the distribution shown inFIG. 3Dis merely exemplary and may be different in different conditions, for example, gravity may skew the distribution in one direction or another depending on the orientation of the device. As illustrated inFIG. 3E, downstream from the flow director, the spatial distribution of particulates across the direction of flow of the fluid may be modified by the flow director. For example, as illustrated inFIG. 3Ethe spatial distribution of particulates may be more uneven downstream from the flow director21than upstream from it. As shown inFIG. 3E, downstream from the flow director the particulates are more concentrated outside the sampling volume than within it. As a result of this unevenness in the distribution, particulates may be more likely to flow past the inlet without entering the sampling volume16.

FIG. 4shows another example of a flow director.FIG. 4comprises three views of a detector inlet2,FIGS. 4A, 4B and 4C.FIG. 4Ashows a section view of the detector inlet from the line indicated as X-X inFIG. 4C.FIG. 4Bshows a section view of the detector inlet2from the line indicated as Y-Y inFIG. 4A.FIG. 4Cshows a section view of the detector inlet2from the line indicated as Z-Z inFIG. 4B.

As can be seen fromFIG. 4AandFIG. 4B, the flow director21may be arranged to separate the fluid flow into at least two separate flow paths, separated by the flow director. For example the flow director21ofFIG. 3Bmay be arranged mid-flow, spanning across the flow passage, and coupled to two walls of the flow passage. The flow director21shown inFIG. 4Bmay be tapered so that it is narrower towards its upstream end than it is towards its downstream end. As shown inFIG. 4AandFIG. 4C, the flow director21provides a sheltered sampling volume16at its downstream end, and the sampling inlet14may be arranged on the downstream end of the flow director. The passage of fluid flow on both sides of this flow director21may reduce the tendency of particles to accumulate around the sampling inlet14.

FIG. 4Dillustrates one example of a spatial distribution of particulates across the flow passage20upstream from the flow director. The description ofFIG. 3D, above, also applies toFIG. 4D.FIG. 4Eillustrates a shape of a distribution of particulates across the direction of the fluid flow in the region of the sampling volume16. It can be seen fromFIG. 4Ethat the flow director21can increase the probability that particulates will flow around the sampling volume16, rather than flowing through it.

FIG. 5illustrates another example of a detector inlet.FIG. 5comprises three views of a detector inlet,FIGS. 5A, 5B and 5C.FIG. 5Ashows a section view of the detector inlet2from the line indicated as X-X inFIG. 5C.FIG. 5Bshows a section view of the detector inlet2from the line indicated as Y-Y inFIG. 5A.FIG. 5Cshows a section view of the detector inlet2from the line indicated as Z-Z inFIG. 5B.

InFIG. 5, the flow director21is provided by a variation in cross section of the flow passage. In this embodiment, the flow director21comprises a recess in a wall of the flow passage, and the sampling inlet14is arranged in the recess. For example, the sampling inlet14may be arranged in the upstream wall of the recess, so the flow can be directed away from the sampling inlet14. Accordingly, the fluid flow can be directed past the recess (and the sampling volume), thereby reducing the probability that particulates carried by the flow of fluid will enter the sampling volume16.

FIG. 5Dillustrates one example of a spatial distribution of particulates across the flow passage20upstream from the flow director. The description ofFIG. 3D, above, also applies toFIG. 5D.FIG. 5Eillustrates the spatial distribution of particulates across the direction of the flow downstream of the flow director21where the flow passes the recess.FIG. 5Eillustrates a lower number of particulates in the recess than in the fluid flowing past it, thereby illustrating one way in which the shape of the spatial distribution of particulates may be changed by a flow director. It can be seen inFIG. 5Ethat, where the flow director21comprises a recess, and in some other examples, total width and/or shape of the flow passage20may be changed by a flow director, so although part of the distribution of particulates may be relatively unchanged the shape of the distribution is still different from its shape upstream of the flow director.

FIG. 6Ashows another example of a flow director. In the example ofFIG. 6Athe flow director21comprises a series of foils50,52,54,56,58,60,62. The foils,50-62, may be ring shaped and may be arranged on a common axis. Each foil50-62, may have an aerofoil type profile, or be otherwise configured, for example by being shaped, profiled and/or angled, to funnel particulates inside the foils in preference to fluid. In an embodiment the foils50-62may be configured, for example by being shaped, profiled and/or angled, to preferentially direct fluid flow outside of the foils.

The foils50-62may be spaced apart in the direction of flow of the fluid. At the upstream end of this flow director21, one of the foils50may span most or all of the width of the flow passage. The span of the downstream foils52,54,56,58,60,62may become successively smaller, to provide a tapered structure. Each of the foils may be pitched (e.g. at an acute angle) relative to the direction of flow of the fluid along the flow passage20. The foils may all have the same pitch, or the pitch may be varied. The foil62at the downstream end of the flow director may be smaller than the other foils. The sampling inlet14illustrated inFIG. 6is arranged to obtain samples of fluid from a sampling volume16downstream from this last, most downstream, foil in the series of foils. The foils may be heated to inhibit the accumulation of substances on the foils, and/or to vapourise aerosols carried by the flow of air along the detector inlet.

Although they are described as being rings, the foils of course need not be circular rings and may be non-circular, for example oval, tapered, rectangular, square or any other shape. The foils may be arranged to be symmetrical about a common axis, for example an axis aligned with the direction of flow of fluid along the flow passage. For example, one or more of the foils may be helical, or all of the circular foils may be replaced by a single helical foil. For example a helical foil may spiral inward along the flow passage so that it has a greater diameter at its upstream end than at its downstream end.

FIG. 6Billustrates one example of a spatial distribution of particulates across the flow passage20upstream from the flow director foils50-62ofFIG. 6A. The description ofFIG. 3D, above, also applies toFIG. 6B.FIG. 6Cillustrates the spatial distribution of particulates across the direction of the flow downstream of the flow director foils50-62where the flow passes the inlet14. As shown inFIG. 6C, in this region, downstream from the foils50-62, the particulates are concentrated into a narrow region of the flow passage.

Some flow directors (e.g. for example those shown inFIG. 3,FIG. 4, andFIG. 6A) may provide a reduction in the cross section of the flow passage20through which the fluid can flow. In some embodiments, the flow director may cause a change in direction of the fluid flow which could cause undesirable concentration and/or deposition of particulates in a region of the flow passage.

FIG. 7illustrates some embodiments of detector inlets in which the flow passage20comprises variations60in the shape and/or area of its cross section to accommodate changes in flow caused by the flow director21. These variations60in cross section may be arranged at least partially downstream of the flow director21, for example at least part of the variation60in cross section may be arranged downstream from the upstream end of the flow director21. For example these variations in cross section may be configured to promote laminar flow of fluid past the flow director. In some embodiments the variations comprise a bulge in at least one wall of the flow passage. The bulge may comprise curved, sloped or graduated portions arranged to accommodate variations in fluid flow caused by the flow director.

The disclosure above has made reference to particular types of apparatus, but features of the embodiments described may be substituted for functionally equivalent elements. For example, the controller12of the apparatus may be provided by any appropriate processing means such as an FPGA, an ASIC, a general purpose processor, or an appropriate arrangement of logic gates. In addition, the flow provider18may comprise pump or a fan or any other device capable of inhaling a flow of fluid along the flow passage. As another example, the heater4described with reference toFIG. 1may be arranged in any of the other detector inlets described above to heat the flow of fluid upstream from the sampling inlet14. Such heaters4may comprise a resistive heater, such as a tape or membrane heater, or it may be provided by a source of radiative heat such as an infrared light source, for example a laser. In some examples the heater may comprise a jet of heated air. Particular examples of analytical apparatus have been described, such as mass spectrometers and ion mobility spectrometers, but other kinds of analytical apparatus may also be used. Other examples and variations will be apparent to the skilled addressee in the context of the present disclosure. It will also be apparent that features of each of the embodiments described with reference to each of the drawings may be combined, individually or otherwise, with some or all or the features of any of the other embodiments. Method features may be implemented by suitably configured apparatus, and the methods of operation described with reference to particular types of apparatus are intended as an independent disclosure of the methods themselves