Patent Application
20130258341
Near infra-red (NIR) spectroscopy is used for food, pharmaceutical, petroleum, and agricultural industries for identification and quantification of chemical compounds. Until now, the technique has been limited to traditional lab based instruments due to the required stability, accuracy and data processing power. In recent years, handheld microelectromechanical (MEMS)-based NIR Hadamard transform spectrometers have been introduced that exhibit lab instrument accuracy and precision. With the advent of this type of instrumentation combined with the sampling technology described by this patent, the restriction of such measurements to a lab only environment has been eliminated. Food, feed and agricultural sample analysis can now be performed successfully in the field with such portable instrumentation.
For food, feed, and agricultural products, it is practically impossible to analyze the entire batch. A representative sample of the total product is taken, from which the appropriate analysis can be made. For samples that will be analyzed in the lab environment, a representative sample is obtained by taking several primary samples. Once they have been gathered and mixed together in a clean receptacle, they constitute a global sample on which the necessary test will be made. Analysis often occurs by placing the material in a sample cup designed to be compatible with the benchtop laboratory instrumentation.
A sampling accessory coupled to a hand-held reflectance Hadamard transform spectrometer provides expanded sampling area which in turn provides better signal averaging from agricultural products which are often inhomogeneous.
The sampling accessory includes a sample site repositioning means and a “sample cup” having a base that is transparent to near IR wavelengths. The hand-held reflectance spectrometer includes a shutter responsive to control signals from the control circuitry.
When the shutter is dosed, a baseline measurement, e.g. reference measurement, may be made. When the shutter is open, a sample measurement is taken.
Sample repositioning and data acquisition within the cup may be performed by several means. Fresh sample regions may be exposed through either manual or motor driven sample cup movement. Alternatively, the sample may be vibrated to induce fresh sample exposure at the window. A further embodiment includes illumination and/or detection paths that may be altered through electrically driven steering optics.
The sample accessory 14 consists of a sample site repositioner, e.g. cup rotator 12, and a sample cup 30. The attachment flange 28 houses the shutter 22 and the flange window 32. The attachment flange 28 is contoured to receive the sample accessory 14 with positive “snap in” for reproducible positioning. The shutter 22 interposes the flange window 32 and the detection optics 24 that lead to the spectrometer engine 16. The shutter 22 is responsive to control signals provided by the control circuitry 16 through activation of a mechanically coupled shutter motor 20. In this illustrative example, the shutter 22 has a diffuse gold surface designed to reflect light at all angles regardless of the incidence angle, e.g. Lambertian reflectance. Other suitable materials include but are not limited to diffuse gold, PTFE materials such as SpectraIon and Fluorilon, and aluminum. Other materials may also be used as long as the reflectance is stable with time, temperature, and humidity.
The hand-held instrument 10 may be a hand-held near IR Hadamard transform spectrometer such as that disclosed in by McAllister, et al. in U.S. Pat. No. 7,791,027, “Apparatus and Method Providing a Hand-Held Spectrometer,” assigned to Polychromix Corporation, a wholly owned subsidiary of Thermo Fisher Scientific. In this context, a “hand-held” spectrometer instrument weighs less than 10 kg, and more typically less than 5, 2, 1, or even less than 0.5 or 0.2 kg, and may have dimensions of less than 50 cm or 30 cm in each dimension, and one of the dimensions (the thickness) may even be less than 10 cm or 5 or 3 cm. A “hand-held” spectrometer will often be battery powered with the battery typically fitting within the foregoing dimensions and included in the foregoing weights, although a separate power supply could be provided and connected to the spectrometer.
To be a practical “hand-held” instrument, the IR spectrometer should meet generally accepted ergonomic standards for such tools. Eastman Kodak's publication [Eastman Kodak Co. 1983, Ergonomic Design for People at Work, Lifetime Learning Pub., Belmont, Calif.] describes requirements for hand-held tools generally and includes a recommended maximum weight of five pounds for hand-held tools. Further, the size/volume of the tool should be small enough so that the tool is not cumbersome and unwieldy. The above-recommended maximum weight may also limit the power capacity of the tool, and consequently, the amount of time that the tool can operate. That is, the weight of a power source generally increases as its power rating increases, and in particular, the weight of battery power sources becomes quite large relative to the overall weight of the tool when large amounts of power are required for the tool's operation. As a result, the power consumption of the tool should be controlled to allow the tool to be used over an extended period of time (e.g., hours) with a relatively lightweight power source, for example, a battery power source that is light enough to be employed in a hand-held tool.
In practice, to be hand held and portable, a spectrometer should contain its own light source. Light sources, however, consume a considerable amount of power. Thus, the power consumption of both the spectrometer electronics and the light source are important considerations when developing a hand held IR spectrometer.
The analyzer attachment flange 28 may be in direct contact with a sample. Alternatively, an optional sample accessory 14 is used to contain the sample. The base of the sample accessory 14 is a window 32 that is transparent to the light source 18. In this illustrative example, the window is transparent to near IR frequencies.
The sample site repositioning may be performed automatically or manually. Repositioning may be done by moving the sample, sample accessory, or beam steering optics (shown in
The sample accessory 14 may be integrated into the housing of the handheld instrument 10 or a detachable cup. The analyzer 8 may be in direct contact with the sample. Alternatively, the detachable sample cup 30 is used to contain the sample.
The sample site may also be repositioned on the sample by a beam steering mechanism. The mechanism may move the illumination source and detection optics, or it may redirect the illumination and detection path via optical deflection (mirrors or lenses).
