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1. WO2020109746 - METHOD OF TRACE SAMPLING

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

METHOD OF TRACE SAMPLING

Technical Field of the Invention

This invention relates to the field of trace sampling, in particular to a method and apparatus for repeatable trace sampling.

Background to the Invention

Trace sampling refers to the collection of trace substances, such as explosive or narcotic substances, from an item under examination. The sample collected being subsequently analysed by trace substance detection equipment. Trace sampling can be performed using non-contact' methods such as puffer jets, or alternatively using contact methods such as swabbing. The latter is often used in airport security screening of luggage, electronics equipment, and passengers.

Contact sampling or direct sampling will typically be performed by security personnel by manually wiping a swab (a fabric cloth or bud, plastic ticket, or metal mesh) across the device or person being screened. This approach provides a relatively low cost and quick means of sampling, ideally suited to high throughput applications such as airport security. However, the manual nature of this approach renders it prone to inconsistency and ineffective sample collection. For instance security personnel may use different swabbing techniques, or swab different portions of the same type of item, in consecutive screenings.

In an attempt to overcome these issues, research into contact sampling has focussed on optimising the sampling process for different surface types or contaminants, by identifying optimal swab materials, and sampling patterns. However, this understanding has proven difficult to apply in practice due to the challenges of effectively training operators to perform swabbing consistently, and the human error associated with direct sampling.

Therefore it is an aim of the present invention to provide an improved method for repeatable trace sampling.

Summary of the Invention

According to a first aspect of the invention there is provided a method of sampling for trace substances, the method comprising the steps of: locating an item to be sampled in an item holder, wherein the item holder comprises a retention means for holding the item and adjustment means for positioning and orientating the retention means; orientating the retention means to a predetermined orientation using the adjustment means; and then sampling the item using a sampling apparatus; such that a plurality of similar items can be sampled in a repeatable manner

There are a number of factors that affect the repeatability and consistency of trace sampling. These factors include the choice of sampling method (direct or indirect); the sampling apparatus or material; the area of a surface sampled; the type of surface being sampled and the substance being sampled for. Whilst the development of sampling apparatus' and methods has focussed on mitigating these factors, the inventor has identified that an overarching inconsistency is introduced when an item is provided for sampling. This inconsistency arises as a result of the item being arranged randomly when sampled. For instance a plurality of laptops or mobile phones may be swabbed in airport security, but with no consistency in position and orientation of the devices when swabbed. This issue is further amplified during manual sampling processes such as swabbing, owing to the tendency of security personnel to hold an item inconsistently during swabbing. By providing an item holder and orientating the retention means holding an item to be swabbed to a predetermined orientation, control of position and orientation of the item is introduced, improving consistency when sampling successive items, and thereby the repeatability of sampling methods. This degree of control is beneficial whether the method of sampling is implemented using manual or automated means.

The item to be sampled may be an electronic device, a mobile phone, a handbag or another item of luggage, for instance, if the method is being exercised in a high throughput scenario such as airport security screening. The sampling apparatus may comprise non-contact (indirect) sampling apparatus such as puffer jets, or may comprise direct sampling apparatus such as gauze; sponges; swabs; or wipes. Sampling the item comprises automatically or

manually sampling the item to obtain trace substances, for instance manual or automatic wiping of an item.

The item holder is intended to hold an item being sampled such that whilst being sampled the item is held fixed, but thereafter can be separated from the item holder. The 'holding' of the item is performed by retention means (optionally a frame). The retention means may provide an interference fit to the item, or may alternatively provide a mount against which the item is secured (through straps or clips for instance) or another gripping mechanism.

The adjustment means for orientating and positioning the retention means enables the retention means to be rotated to a particular azimuth and elevation angle (the predetermined orientation), and allows a user to locate the item holder in a particular position. A ball and socket (ball joint), a pan and tilt head, or a geared head, may be used for orientating the retention means. A suction cup or similar component may be provided for positioning the retention means at a particular location (for instance on a table). Either the orientation or positioning, or both, may be performed automatically (for instance through use of motorised stages or robotic arms).

The predetermined orientation may be selected for user convenience and then maintained consistently when sampling similar items. For instance all mobile phones may be sampled with the same elevation and azimuth angle applied to the item holder. This will improve consistency of sampling approach. Alternatively the predetermined orientation may be chosen based on the surface type being sampled or the contaminant being sampled for. For instance some trace substances are known to be less potent than others (so a larger sample may be required), whilst other trace elements are more adhering to a surface than others (so a sampling method may be required to 'dig-into' a surface more than for other contaminants).

Some embodiments further comprise the step of translating the item holder to a predetermined position using the adjustment means. This allows items to be consistently sampled when at the same position in addition to orientation. Inconsistency in sampling can be introduced when, for instance, screening staff swab an item at arms-length instead of in closer reach. Alternatively if the sampling is automated, precise location of the item holder is also an important factor in ensuring the desired area of the item is swabbed with appropriate force.

Whilst some embodiments of the method can be implemented or used manually, it is preferable that the adjustment means is automated. The adjustment means may comprise a motorised rotational joint (such as a ball joint) on a translation stage for instance. Alternatively the adjustment means may comprise a robotic arm capable of three axis translation and two degrees of rotational freedom. This allows precise orientation and positioning of the item holder, and may be computer controlled. This improves consistency in the area of an item being sampled, and the force applied during the sampling process.

In some embodiments of the method, the step of sampling the item using the sampling apparatus comprises sampling the item at a predetermined sampling rate. The predetermined sample rate may be selected to mitigate the effects of losing sampled material from a sampling apparatus. For instance wiping a surface for a prolonged period can result in collected material being lost from the wipe itself, and so selecting a specific sampling rate can mitigate this issue. The rate may be varied according to the substance being sampled for, or the surface type of the item being sampled, all of which factor into the collection efficiency. It is known for instance that Teflon is less efficient at collecting a sample than a Muslin material for some surface types. Therefore a slower rate may be chosen for a Teflon wiping material than a Muslin material.

In some embodiments the step of sampling the item comprises sampling the item over a predetermined sampling area. Trace substances present on an item being sampled may not be uniformly distributed across the surface of the item. Therefore sampling in a ra ndom area may not obtain a sufficient sample size. Moreover an inconsistency in sampling occurs when different sampling areas/locations are used for the same item. By adopting a sample method whereby the sampling area is predetermined, the sampling consistency is further improved and can be tailored to particular sampling scenarios (surface type and contaminant type). A predetermined sampling area for a mobile phone may for instance be the edges of the phone where most users will contact the phone in use.

In some embodiments the step of sampling the item comprises sampling the item with a predetermined force. For the same substance type, different forces may be required to remove the substance from different surfaces. Equally different forces may be required to remove different substances from the same surface type. Therefore in these embodiments an intelligent sampling approach is provided where the force exerted on an item by the sampling apparatus can be tailored. Furthermore, and particularly in manual sampling practices, security personnel may have reservations regarding sampling other people. For instance swabbing a hand may be performed with minimal and ineffective force as a result of concern for causing pain or discomfort. Indeed similar concerns may exist when swabbing personal devices which could break under excess force. By specifying that a predetermined force must be used, or provided automatic means for performing the sampling, consistency in swabbing approach can be achieved.

Preferably the method of sampling is a method of direct sampling, for instance swabbing. Human error is most prevalent in direct sampling methods, owing to the tendency for a person performing swabbing to hold an item being swabbed at a random orientation or position. Exercising the method of the invention for direct sampling can lead to improvements in the consistency and repeatability of direct sampling.

In some embodiments of the method the sampling apparatus comprises a swab attached to a means for automatically moving the swab. The means for automatically moving the swab may be a robotic arm. The means for automatically moving the swab may be controlled by a computer system. Automatic motion of the swab further improves upon the consistency and repeatability of sampling, for instance through use of a consistent sampling force, sampling rate, and sampling area.

In preferred embodiments the retention means is a frame. Even more preferable is that the frame comprises means for adjusting the inner dimensions of the frame. The frame inner dimensions may be adjusted in one or more dimensions. This enables one frame to be used with a variety of different sized items. In even more preferred embodiments the means for adjusting the inner dimensions of the frame comprises a resilient material lining an interior surface of the frame. The resilient material may comprise a flexible jacket containing resilient material (such as a high density foam). The flexible jacket may comprise plastic that is washable. The resilient material can be compressed against the interior surface to enable an item to be inserted into the frame. The resilient material then decompresses to provide an interference fit to the item. The use of a resilient material to provide an interference fit allows items with non-planar surfaces to be effectively held within the frame.

In some embodiments the adjustment means comprises a ball joint. A ball joint provides both elevation and azimuth degrees of freedom, enabling the retention means to be rotated to a predetermined orientation. The ball joint may be manually operable or automatically controlled through use of a motor.

Preferably the step of orientating the retention means further comprises the step of locking the adjustment means at the predetermined orientation. This enables the retention means to be positioned in a particular orientation from which it is resistive to further rotation. When an item in the item holder is sampled and consequently a force is applied to the item holder, this ensures the item holder will not move as a result. Motion of the item holder is undesirable because a net reduction in the force applied into the surface of the item being sampled can result, thereby affecting collection efficiency. One or more thumb screws operable by a user of the item holder may be configured such that when operated they apply a pressure to the adjustment means to prevent rotation. Thumb screws provide a user operable means for fixing the orientation of the retention means, but automatically operated latches or similar devices may be used.

According to a second aspect of the invention there is provided trace sampling equipment, comprising an item holder and sampling apparatus, wherein the item holder comprises retention means for holding an item to be sampled, and adjustment means for positioning and orientating the retention means, such that a plurality of similar items can be sampled in a repeatable manner.

Brief Description of the Drawings

Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure la shows an illustration of an embodiment of a method of sampling in which an item is located in an item holder;

Figure lb shows an illustration of the retention means of the item holder in Figure la being orientated;

Figure lc shows an illustration of the item in the item holder of Figure la being swabbed; and

Figure 2 shows an illustration of an alternative embodiment of an automated method of sampling for trace substances.

Detailed Description

Figure la shows an illustration of an item 13 held in an item holder 10. The item to be swabbed 13 is held by a retention means in the form of a frame 11 of item holder 10 by resilient foam pads 12 which are glued to the inner surface of frame 11 and which provide an interference fit to item 13 despite item 13 having non-planar sides. The frame 11 is formed from a plastic that is washable (with respect to removal of trace substance residue). The frame 11 is attached to an adjustment means for orientating and positioning the frame comprising a ball joint 14 and spindle 16. The ball joint 14 also comprises plastic. The frame 11 can be rotated in azimuth and elevation about the ball joint 14 manually. The frame 11 can be further rotated about spindle 16 manually. The ball joint 14 is further attached to a suction cap 15 for providing a means of positioning the item holder 10 to a surface.

Figure lb shows the item holder 10 with frame 11 orientated to a predetermined orientation. The predetermined orientation comprises a convenient angle to vertical axis Ά' for a user wishing to manually swab the item 13. Thumb screws (not visible) are used to fix the predetermined orientation. Figure lc then shows the item 13 (not visible) in frame 11 of item holder 10 being directly sampled using a swab 17.

In use, a user places the item holder 10 on a surface such that suction cup 15 attaches to the surface. This fixes the position of the item holder 10. An item to be swabbed 13 is then placed between resilient foam pads 12. The resilient foam pads 12 having been compressed by the placement of the item 13 between them subsequently expand to provide an interference fit. The item 13 is then held without user support in the frame 11. The user then orientates the frame 11 on the ball joint 14 and spindle attachment 16 to a predetermined orientation. When in the predetermined orientation, the orientation of frame 11 is fixed using thumb screws. The user then manually wipes swab 17 on item 13 with a predetermined sample rate, force, and over a predetermined sample area. The item 13 can be then be removed from holder 10 with the holder 10 remaining in the predetermined orientation and position. The method can then be repeated for other items 13 but with the holder 10 now preconfigured for consistent use.

Alternative embodiments of the invention may comprise alternatives to suction cup 15. For instance a clamping device may be used. If a geared joint instead of a ball joint 14 is used, the geared joint may comprise other means for fixing orientation (other than thumb screws) such as a plurality of holes in a round gear into which a pin can be inserted using a user operated lever, to lock a particular orientation. The frame 11 may be a non-rectangular shape, particularly if using resilient pads 12 to provide an interference fit. Alternatives to resilient pads 12 comprise inserts into frame 11 that can be introduced or removed depending on the size of the item 13, or straps. The frame 11 may comprise a back plate against which an item 13 can rest, to provide further support.

An alternative automated embodiment of a method of sampling for trace sampling is shown in Figure 2. An item holder 20 is shown comprising a retention means in the form of a frame 21 for holding an item to be swabbed, and an adjustment means for orientating and positioning the frame 22. The adjustment means 22 comprises a ball joint 22a rotatable about axis B and separately rotatable about an axis perpendicular to B. Therefore ball joint 22a has two rotational degrees of rotation. The ball joint 22a is motorised. The adjustment means 22 also comprises a first robotic arm 22b attached to the ball joint 22a, the first robotic arm 22b being movable in three linear dimensions 24. A swab 25 is also shown

mounted to a rotational joint 26 itself having two degrees of rotational freedom. The rotational joint 26 is attached on the end of a second robotic arm 27 and is also motorised. The second robotic arm 27 has three linear degrees of freedom 28. The first robotic arm 22b, second robotic arm 27, ball joint 22a and rotational joint 26 are all controlled by a computer system that is not shown in the Figure. In use an item to be swabbed is mounted in frame 21. A swab 25 is mounted in the rotational joint 26. The frame 21 is positioned and orientated automatically under commands issued by a computer system to first robotic arm 22b and ball joint 22a. The swab 25 is moved towards the item in frame 21 using second robotic arm 27 under control of the computer system as well. The rotational joint 26 is rotated under control of the computer system to angle the swab 25 appropriately for the swabbing operation. The second robotic arm 27 is then automatically moved to wipe swab 25 across a predetermined sampling area of the item in frame 21. The movement is performed at a constant rate, and is adjusted to maintain a constant predetermined force on the item surface throughout the sampling operation. The second robotic arm 27 is then withdrawn to allow the swab 25 to be removed and analysed.