Patent Grant
8117929
This invention relates generally to sampling means and methods and relates, more particularly, to the means and methods for obtaining samples from areas, or spots, on a surface to be analyzed.
The sampling collection techniques with which this invention is concerned involve the positioning of a collection instrument or other sample collection device in relatively close proximity to a surface to be analyzed, or sampled, for purposes of gathering an amount (e.g. ions) of the surface for analysis. An example of one such collection technique is used in conjunction with desorption electrospray ionization (DESI) mass spectrometry, but other techniques, such as may involve desorption atmospheric pressure chemical ionization (DAPCI) or matrix-assisted laser desorption/ionization (MALDI), are applicable here as well. In any of such techniques, it is desirable that the collection instrument be maintained at a predetermined, or desired, distance from the surface to be sampled for optimum collection results and to reduce the likelihood that the collection results will be misinterpreted when subsequently analyzed.
Furthermore, there exists some sample-collecting processes which involves a self-aspirating emitter through which an agent is delivered to the surface during the sample-collection process in a spray plume. Such an emitter is commonly fixed in position relative to the sample collection instrument, or device, so that the spray plume is directed toward the surface at a predetermined, or fixed, angle of incidence so that the delivered spray plume is intended to strike the surface to be sampled at a predetermined location for effecting the movement of an amount of the surface to be sampled toward the collection instrument. In other words, there is a desirable spatial assignment which exists between the emitter, the collection instrument and the surface to be analyzed so that if the surface is not accurately positioned in a location (e.g. within a predetermined plane) in which the surface is intended to be positioned, poor collection results are likely to be obtained.
To obviate the need for an operator to make manual adjustments to the distance between the sample collection instrument and the surface during the course of a sample collection process, it would be desirable to provide a system and method for accurately controlling the sample collection device-to-surface distance during a sample collection process.
Accordingly, it is an object of the present invention to provide a system and method for automatically controlling the distance between a sample collection instrument, or device, and the surface to be analyzed, or sampled, with the instrument which utilizes a laser sensor for monitoring the actual collection instrument-to-surface distance during the sampling procedure.
Another object of the present invention is to provide such a system and method wherein the collection instrument-to-surface distance is continually monitored throughout the sampling procedure and adjusted, as necessary, so that the collection instrument-to-surface distance is maintained at an optimal spacing.
Yet another object of the present invention is to provide such a system which reduces the likelihood that the results of the sample collection process will be misinterpreted when analyzed.
A further object of the present invention is to provide such a system which, when used in conjunction with sample-collecting operations which utilize an emitter which is directed at a predetermined angle toward the sample helps to maintain the proper spatial assignment between the emitter, the collection instrument and the surface to be analyzed during a sample collecting process.
Yet another object of the present invention is to provide such a system which is uncomplicated in structure, yet effective in operation.
This invention resides in a sampling system and method for collecting samples from a surface to be analyzed.
The sampling system includes a sample collection instrument through which a sample is collected from a surface to be analyzed and means for moving the collection instrument and the surface toward and away from one another and wherein there exists a desired positional relationship between the collection instrument and the surface for sample collecting purposes. The system also includes distance-measuring means including a laser sensor arranged in a fixed positional relationship relative to the collection instrument for generating a signal which corresponds to the actual distance between the laser sensor and the surface and wherein there exists a target distance between the laser sensor and the surface when the collection instrument and the surface are arranged in the desired positional relationship for sample collecting purposes.
In addition, the system includes means for receiving the signal which corresponds to the actual distance between the laser sensor and the surface and comparison means for comparing the actual distance between the laser sensor and the surface to the target distance between the laser sensor and the surface and for initiating the movement of the laser sensor and the surface toward or away from one another when the difference between the actual distance between the laser sensor and the surface and the target distance is outside of a predetermined range so that by moving the surface and the collection instrument toward or away from one another, the actual distance between the laser sensor and the surface approaches the target distance.
The method of the invention includes the steps carried out by the system of the invention. In particular, such steps include the generating of a signal with the distance-measuring means which corresponds to the actual distance between the laser sensor and the surface and determining the actual distance between the laser sensor and the surface from the signal generated by the distance-generating means. Then, the actual distance between the laser sensor and the surface is compared to the target distance, and movement of the surface and the laser sensor toward or away from one another is initiated when the difference between the actual distance between the laser sensor and the surface and the target distance is outside of a predetermined range so that by moving the surface and the laser sensor toward or away from one another, the actual distance approaches the desired target distance.
a is a view illustrating schematically an exemplary positional relationship between the laser sensor, the sample collection instrument and the surface of the
b is a view as seen generally from the right side in
a is a view illustrating schematically an exemplary relationship between the components of the
b is a view similar to that of
c is a view similar to that of
a and 6b are views illustrating schematically the path of the tip of the sample capillary tube relative to the surface of the
Turning now to the drawings in greater detail and considering first
Furthermore and although the depicted system 20 is described herein in connection with desorption electrospray ionization (DESI), the principles of the invention described herein are applicable as well to other surface sampling techniques, such as desorption atmospheric pressure chemical ionization (DAPCI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry.
The system 20 of the depicted example includes a collection instrument in the form of a sampling probe 24 (and an associated DESI emitter 25) comprising a capillary tube 23 which terminates at a tip 26 which is positionable adjacent the surface 22. During a sampling process, for example, a predetermined agent is directed from a syringe pump 37 and onto the surface 22 to be sampled through the emitter 25, and an amount of the sample (e.g. ions of the sample) is conducted by way of a vacuum (and/or an electric field), away from the remainder of the surface 22 through the capillary tube 23 for purposes of analyzing the collected sample.
With reference to
The emitter 25 is fixed in position with respect to the capillary tube 23 and is arranged in a pre-set relationship with respect to the surface 22 so that a jet (gas or liquid) dispensed thereon impinges upon the surface 22 at a predetermined angle of incidence. It therefore follows that there exists a desired relationship, or spatial assignment, between the capillary tube 23, the emitter 25 and the surface 22 for optimum sample collection results.
The support plate 27 is, in turn, supportedly mounted upon the movable support arm 36 of an XYZ stage 28 (
Although a description of the internal components of the XYZ stage 28 is not believed to be necessary, suffice it to say that the X and Y-coordinate position of the support surface 27 (and surface 22) relative to the collection tube tip 26 is controlled through the appropriate actuation of, for example, a pair of reversible servomotors (not shown) mounted internally of the XYZ stage 28, while the Z-coordinate position of the support surface 27 (and surface 22) relative to the collection tube tip 26 is controlled through the appropriate actuation of, for example, a reversible stepping motor (not shown) mounted internally of the XYZ stage 28. Therefore, by appropriately energizing the X and Y-coordinate servomotors, the surface 22 can be positioned so that the tip 26 of the collection tube 23 can be positioned in registry with any spot within the X-Y coordinate plane of the surface 22, and by appropriately energizing the Z-axis stepping motor, the surface 22 can be moved toward or away from the collection tube tip 26.
With reference still to
It is a feature of the depicted system 20 that it includes distance-measuring means, generally indicated 40, for monitoring and controlling the spaced distance (i.e. the distance as measured along the indicated Z-coordinate axis) between the tip 26 of the collection tube 23 and the surface 22. Within the depicted system 20, the distance-measuring means 40 includes a laser sensor 42 supported directly above (i.e. along the Z-coordinate axis) the surface 22. If desired, a closed circuit color camera 44 can be supported above the 22 for collecting images during a sample-collection operation, and a video (e.g. a television) monitor 46 can be connected to the camera 44 for receiving and displaying the images collected by the camera 44. The monitor 46 is, in turn, connected to the first control computer 30 (by way of a video capture device 50) for conducting signals to the computer 30 which correspond to the images taken by the camera 44. These camera-generated images can be used by an operator to visually monitor and record events during the sample collection process.
Furthermore, the system 20 is provided with a webcam 48 having lens which is directed generally toward the collection tube 23 and surface 22 and which is connected to the computer 30 for providing an operator with a wide-angle view of the capillary tube 23 and the surface 22. The images collected by the webcam 48 are viewable upon a display screen, indicated 52, associated with the first control computer 30 by an operator to facilitate the initial positioning of the surface 22 relative to the capillary tube 23 in preparation of a sample-collection operation.
An example of a closed circuit camera suitable for use as the camera 44 is available from Panasonic Matsushita Electric Corporation under the trade designation Panasonic GP-KR222, and the camera 44 is provided with a zoom lens, such as is available from Thales Optem Inc. of Fairport, N.Y. under the trade designation Optem 70 XL. An example of a video capture device suitable for use as the video capture device 50 is available under the trade designation Belkin USB VideoBus II from Belkin Corp. of Compton, Calif., and an example of a webcam which is suitable for use as the webcam 48 is available under the trade designation Creative Notebook Webcam from W. Creative Labs Inc., of Milpitas, Calif.
The operation of the system 20 and its distance measuring means 40 can be better understood through a description of the system operation wherein through its use of the distance-measuring means 40, the system 20 monitors the real-time measurement of the distance between the collection tube 23 and the surface 22 to be sampled and thereafter initiates adjustments, as needed, to the actual capillary tube-to-surface distance by way of the computer 30 and the XYZ stage 28 so that the optimum, or desired, capillary tube-to-surface distance (as measured along the Z-axis) is maintained throughout a sampling process, even though the surface 22 might be shifted along the X or Y coordinate axes for purposes of collecting a sample from other spots along the surface 22 or from along different lanes across the surface 22.
At the outset of one embodiment of a sample-collecting operation performed with the system 20, the tip 26 of the capillary tube 23 is positioned (during a set-up phase of the operation) at a desired capillary tube-to-surface distance which corresponds to an optimal, or desired, distance between the capillary tube 23 and the surface 22 for purposes of collecting a sample therefrom, and this optimal distance is determined (by way of the techniques described herein) and stored within the memory 33 of the first control computer 30. Such a positioning of the surface 22 in such a desired relationship with the capillary tube 23 is effected through appropriate (e.g. manual) manipulation of the joystick control unit 29 of the XYZ stage 28 and is monitored visually by an operator as he watches the TV monitor 46 during this set-up phase of the operation. Once the surface 22 has been positioned in its desired positional relationship with the capillary tube 23, signals which correspond to this initial (and actual) distance between the laser sensor 42 and the surface 22 are generated by the distance-measuring means 40 and sent to the computer 30 for storage (i.e. in its memory) and later use.
It will be understood that the aforementioned manual set-up of the capillary tube tip 26 at such a desired capillary tube-to-surface distance may not be necessary in a fully automated operation. For example, the XYZ stage 28 may not require re-adjustment between sucessive sample-collecting operations. Thus, for a second, or subsequent, sample collecting operation involving a similarly-mounted surface, appropriate commands can be initiated at the computer 30 to initiate a sample collecting operation without the need for a repeated set-up of the capillary tube-to-surface distance at optimal conditions.
As mentioned earlier and as illustrated in
The use of laser sensors, like the laser sensor 42 of the distance-measuring means 40, for measuring the distance from a laser sensor to an object are known so that a detailed description of the operation and structural details of a laser sensor are not believed to be necessary. Suffice it to say that common laser sensors used for measurement purposes emit a laser beam toward an object, and a beam, in turn, is reflected from the object back toward the sensor. The reflected beam is sensed by the laser sensor, and the period required for the laser beam to make the round trip is detected. The distance between the laser sensor and the object is subsequently calculated as being equal to one-half of the time elapsed (during the round trip of the laser beam) multiplied by the velocity of the laser beam.
With reference to
Furthermore, the laser sensor 42 is fixed in relationship to the capillary tube 26. In other words, the Z-coordinate distance as measured between the laser sensor 42 and the capillary tube 23, indicated dSC/LS in
Once the actual distance between the laser sensor 42 and the surface 22 during this set-up stage (i.e. when the capillary tube-to-surface distance is set to its optimum) is determined, this laser source-to-surface distance is stored in the computer 30 and designated, for present purposes, as the target laser sensor-to-surface distance which is desired to be maintained throughout the sample collection process. In other words, once the target laser source-to-surface distance is stored within the computer 30, the sampling process can be initiated by moving the surface 22 relative to the capillary tube 23 along the X-Y plane for the purpose of collecting samples from desired locations on, or along desired lanes across, the surface 22. During the sampling process, the actual distance between the laser sensor 42 and the surface 22 is periodically measured with the distance-measuring means 40, and each measured actual laser sensor-to-surface distance is subsequently compared to the target laser sensor-to-surface distance, and adjustments are made, if necessary, to maintain the actual laser sensor-to-surface distance close to the target laser sensor-to-surface distance.
It will be understood that for comparison purposes, the computer 30 (i.e. the memory 30 thereof) is preprogrammed with information relating to acceptable distance (i.e. tolerance) limits relative to the target distance. In other words, if it is determined that the actual laser sensor-to-surface distance differs from the target laser sensor-to-surface distance by an amount which is outside of these tolerance limits, commands are sent to the XYZ stage 28 to initiate Z-axis adjustments between the capillary tube 23 and the surface 22 to bring the actual distance back in line with (i.e. within the tolerance limits of) the target laser source-to-surface distance. It follows that such preset tolerance limits correspond to a predetermined range within which the actual laser source-to-surface distance can be close enough (e.g. within +3 μm) to the desired target laser source-to-surface distance that no additional movement of the surface 22 toward or away from the capillary tube 23 is necessary.
With reference to
Similarly, in the
It can therefore be seen that in accordance with an embodiment of the present invention, the control of the actual capillary tube-to-surface distance during a sample collecting process is comprised of a series of steps. Firstly and in preparation of a sample collection operation performed with the system 20, an operator adjusts the Z-axis position of the surface 22 until the surface 22 is positioned in relatively close proximity to the tip 26 of the capillary tube 23 so that the capillary tube tip-to-surface distance is optimum for sample collection purposes. During this set-up stage, the relative position between the surface 22 and the capillary tube tip 26 can be visually monitored by the operator who watches the images obtained through the webcam 48 and displayed upon the computer display screen 52. It will be understood, however, and as mentioned earlier, this initial set-up stage can be omitted in a fully automated operation.
Once the surface 22 is moved into a desired positional relationship with the capillary tube tip 26 during this set-up stage, the operator enters appropriate commands into the computer 30 through the keyboard 31 thereof so that the initial (and actual) laser sensor-to-surface distance is determined with the distance-measuring means 40. In this connection, distance-measuring means 40 (by way of the laser sensor 42) is used to measure the actual laser sensor-to-surface distance, and a signal which corresponds to the measured distance is conducted from the distance-measuring means 40 to the computer 30. This initial laser sensor-to-surface distance is stored within the computer memory 30 and designated, for present purposes, as the target laser sensor-to-surface distance to which subsequently-determined actual laser sensor-to-surface distances are ultimately compared.
When a sample collection process is subsequently undertaken, periodic measurements of the actual laser sensor-to-surface distances are taken with the distance-measuring means 40. Electrical signals corresponding to these measured distances are immediately transmitted to the computer 30 for comparison to the target laser sensor-to-surface distance. Such periodic measurements can be taken at preselected and regularly-spaced intervals of time (e.g. every one-half second), and the time interval between which these actual laser sensor-to-surface distances are taken can be preprogrammed into, or selected at, the computer 30.
As far as the analysis of the collected samples are concerned, the samples collected from the surface 22 through the collection tube 23 are conducted to the mass spectrometer 32 and are analyzed thereat in a manner known in the art. If desired, a second control computer 34 (introduced earlier and shown in
It is common that during a sample-collecting operation performed with the system 20, the surface 22 is moved relative to the capillary tube 23 within the X-Y plane so that the tip 26 of the capillary tube 23 samples the surface 22 as the surface 22 sweeps beneath the probe 24. For this purpose and by way of example, the computer 30 can be pre-programmed to either index the surface 22 within the X-Y plane so that alternative locations, or spots, can be positioned in sample-collecting registry with the capillary tube tip 26 for obtaining samples at the alternative locations or to move the surface 22 along an X or Y coordinate axis so that the surface 22 is sampled with the capillary tube 23 along a selected lane (such as the paths 18 of
With reference to
Meanwhile, the dotted lines 64 and 66 depicted in
Each measured actual laser sensor-to-surface distance is then compared, by means of appropriate software 70 (
By comparison and during a sample-collection operation as depicted in
As mentioned earlier, by equating the laser sensor-to-support plate to the laser sensor-to-surface (as is the case when the laser sensor 42 is used to measure the distance to a location on the support plate 27 situated alongside the surface 22, rather than to the surface 22 itself), could be a source for error, especially if the support plate 27 is canted at an appreciable angle with respect to the X-Y plane. However, if in the event that the support plate 27 is canted with respect to the X-Y plane, compensation for such an error can be made. For example, there is shown in
In a system 20 used by applicants, the Y-axis distance between the line of the beam emitted from the laser source 42 and the center of the capillary tube is about 500 μm. Applicants have also found that if, for example, the angle ω (i.e. the angle of tilt of the surface 22) is about one degree (which, in practice, is so small that it is hard to adjust manually), then the product of tan(ω) and 500 μm is only about 9 μm. This 9 μm value is an acceptable error and would not likely have a noticable effect on the signal levels sensed across the surface. If, in the event, that such an error is not acceptable, a system can employ two laser sensors to obtain a more accurate representation of the laser sensor-to-surface distance along the Z-axis distance.
For example, there is depicted in
It follows from the foregoing that a system 20 and associated method has been described for controlling the capillary tube-to-surface distance during a surface sampling process utilizing a sample collection device. In this connection, the system 20 automates the formulation of real-time re-optimization of the sample collection instrument-to-surface distance using distance measurements obtained with a laser sensor 42. The distance measurement analysis includes the periodic measurement of the actual distance between the laser sensor 42 and the surface 22 followed by a comparison of each of the measured actual laser sensor-to-surface distances to a target laser sensor-to-surface distance. By comparing the actual laser sensor-to-surface distance to a target laser sensor-to-surface distance (which corresponds to a desired capillary tube-to-surface distance which can, for example, be established during a set-up phase of the procedure, the system 20 can automatically and continuously re-optimize the capillary tube-to-surface distance during the sample collection procedure by adjusting the spaced laser sensor-to-surface distance, as necessary, along the Z-coordinate axis.
If desired, the surface 22 can be moved along the X-Y plane (and relative to the capillary tube 23) to accommodate the automatic collection of samples with the capillary tube 23 along multiple parallel lanes upon the surface 22 with equal or customized spacing between the lanes. Samples can be collected with the aforedescribed system 20 at constant scan speeds or at customized, or varying, scan speeds.
The principle advantages provided by the system 20 and associated method for controlling the capillary tube-to-surface distance throughout a sample-collection process relate to the obviation of any need for operation intervention and manual control of the capillary tube-to-surface distance (i.e. along the Z-coordinate axis) during a sample-collection process. Accordingly, the precision of a sample-collection operation conducted with the system 20 will not be limited by the skill of an operator required to monitor the sample-collection process. Moreover, the system 20 also provides advantages which bear directly upon the accuracy of samples collected with the capillary tube 23. For example, because the optimum, or desired, capillary tube-to-surface distance is maintained throughout the sample collecting process, the likelihood that the surface 22 would be inaccurately sampled—which could lead to misinterpretation of the collected samples, when analyzed—is substantially reduced.
The aforedescribed system 20 and process provide a further advantage in sample collecting equipment which employs componentry, such as the emitter 25 having a spray tip, which are intended to be positioned in a desired spatial relationship, or assignment, with one another. For example, in a sample collection system in which a spray tip and surface to be sampled are typically arranged in a fixed relationship with respect to one another during a sample collection operation, a change in the spray tip-to-surface distance also results in a change in the sampling capillary-to-surface distance by a corresponding amount. However, because the system 20 and process of the present invention helps to maintain a desired capillary tube-to-surface distance during a sample collecting process, the system 20 and process also help to maintain desired spatial relationship between the emitter, the collection tube and the surface to be sampled.
It will be understood that numerous modifications and substitutions can be had to the aforedescribed embodiment without departing from the spirit of the invention. For example, although the aforedescribed embodiments have been shown and described wherein the capillary tube 23 is supported in a fixed, stationary condition and the surface 22 is moved relative to the capillary tube 23 along either the X, Y or Z-coordinate directions to position a desired spot or development lane in registry with the capillary tube 23, alternative embodiments in accordance with the broader aspects of the present invention can involve a surface which is supported in a fixed, stationary condition and a capillary tube, along with the laser sensor fixed in relationship therewith, which is movable relative to the surface along either the X, Y or Z coordinate directions. Accordingly, the aforedescribed embodiments are intended for the purpose of illustration and not as limitation.
This invention was made with Government support under Contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy to UT-Battelle, LLC, and the Government has certain rights to the invention.
| Number | Name | Date | Kind |
|---|---|---|---|
| 5081353 | Yamada et al. | Jan 1992 | A |
| 5196713 | Marshall | Mar 1993 | A |
| 5200603 | Hackenberg et al. | Apr 1993 | A |
| 6715341 | Bowen et al. | Apr 2004 | B2 |
| 6803566 | Van Berkel | Oct 2004 | B2 |
| 7295026 | Van Berkel et al. | Nov 2007 | B2 |
| 20020070345 | Mizuochi et al. | Jun 2002 | A1 |
| 20060284084 | Morimoto et al. | Dec 2006 | A1 |
| 20080033275 | Blank et al. | Feb 2008 | A1 |
| Number | Date | Country |
|---|---|---|
| 1666866 | Jun 2006 | EP |
| Number | Date | Country | |
|---|---|---|---|
| 20100000338 A1 | Jan 2010 | US |
