Motorized variable path length cell for spectroscopy

Abstract

Device (100) for measuring an optical property of a sample, comprising the following: a pair of windows (5, 5'); wherein one window (5') of the pair is configured to receive radiation from a source of optical energy (12) via free space, and the other window (5) of the pair is configured with an integrated optical detector (9) used to optically probe a sample positioned between the pair of windows (5, 5'), wherein both windows (5, 5') of the pair are movable with respect to the positioning of the source of optical energy (12); wherein the pair of windows (5, 5') comprises a first window and a second window, each configured with at least one of the following selected surfaces: a flat surface and a conical surface;wherein a flat surface of the window (5'), configured to receive radiation from the optical energy source (12), faces the sample, and a conical surface of the window (5'), configured to receive radiation from the optical energy source (12), faces the optical energy source (12); and ; a processor designed to control a distance between configured surfaces of the pair of windows (5, 5') with a variable distance (P) to pull the arranged sample into a column that is trapped by surface tension or to compress the sample during optical analysis, wherein the processor is additionally configured to automatically collect and store information of different optical path lengths of the pulled and / or compressed sample.

Description

FIELD OF INVENTION

[0001] The present invention relates to the field of spectral analysis and, more particularly, to the identification of the type and quantity of various chemicals present in solid (e.g., soft) and liquid samples by transmitting light of different wavelengths through the sample to provide wavelength information and to provide measured amounts of light absorbed by a respective sample. BACKGROUND OF THE INVENTION Discussion of the related art

[0002] A molecular spectrometer is an instrument in which a solid, liquid, or gas sample is illuminated, often with non-visible light, such as light in the infrared region of the spectrum. The light transmitted through the sample is then detected and analyzed to reveal information regarding the sample's characteristics. For example, a sample can be illuminated with infrared light of a known intensity over a range of wavelengths, and the light transmitted through the sample can then be detected for comparison with the light source. An examination of the detected spectra can then reveal the wavelengths at which the illuminating light was absorbed by the sample.The spectrum, and in particular the locations and amplitudes of the peaks present there, can be compared with libraries of previously obtained reference spectra to obtain information about the sample, such as its composition and characteristics. Essentially, the spectrum serves as a "fingerprint" for the sample and the substances present therein, and by finding a match between the fingerprint and one or more known fingerprints, the identity and quantity of the sample can be determined.

[0003] However, there are numerous cases where the data collected using the methods described above are useless because the transmitted light is substantially absorbed by a path length that is too long, or the light is almost entirely transmitted by a path length that is too short. Both situations can be problematic. With respect to large absorbance (e.g., due to a long path length), uncertainties due to noise (i.e., signal-to-noise ratio) become problematic because the spectral signal of the sample is lost because the light is too weak to be reliably detected within a larger signal. However, if the absorbance signal is too small (e.g., due to a short path length), reliable detection is still a problem, partly due to a lack of absorbance signal strength, even if the overall light level is high.By varying the path length through the sample, both problems can be minimized. Other uncertainties in both situations include natural variations in light intensity caused by dirt, dust particles in the light beam, temperature, vibration variations affecting the measuring equipment, and / or ultimately statistical variation in the light source and detection system.

[0004] Background information on an apparatus and methodology providing for measurement of optimized absorbance properties of a liquid droplet can be found in US Patent No. US 7,365,852 B2 to Schleifer, issued April 29, 2008, entitled "Methods and Systems for Selecting Pathlength in Absorbance Measurements," which states: "Methods and subsystems for substantially optimizing absorbance measurements in optical instruments are provided. One method comprises forming a liquid sample into a droplet extending between opposing surfaces, transmitting a light beam through the sample, and varying the distance between the two opposing surfaces until a distance substantially corresponding to optimal absorbance is obtained."

[0005] Background information on an apparatus and methodology providing measurement of transmission properties of liquids and solids can be found in U.S. Patent No. 7,582,869 B2 to Sting et al., issued September 1, 2009, entitled "System and Method for Optical Analysis," which states: "An optical analysis system using transmission spectroscopy to analyze liquids and solids includes a source of optical energy, a sample, a movable optical energy transmission window, a fixed optical energy transmission window, and a detection system. The fixed optical energy transmission window is fixed relative to the source of optical energy. The sample is selectively positioned between the movable optical energy transmission window and the fixed optical energy transmission window for analysis of the sample.The optical energy is transmitted through one of the windows, the sample, and the other window to obtain encoded optical energy as a result of the transmission of the optical energy through the sample. A detection system receives the encoded optical energy for analysis. The movable optical energy transmission window is selectively movable relative to the fixed optical energy transmission window to repeatedly and precisely align both windows and the sample and make them easily accessible.

[0006] Background information on an apparatus and methodology providing measurement of transmission properties of compressed samples can be found in EP 1 792 653 B1 by Juhl, granted June 6, 2006, entitled: “Apparatus and Method for spectrophotometric analysis”, which states: “an apparatus for spectrophotometric analysis comprises a sample receiving surface configured to receive a sample to be analyzed, and a sample contact surface movable relative to the sample receiving surface so that it can be brought into a first position in which the surfaces are sufficiently spaced apart to allow the sample to be placed on the sample receiving surface, and into a second position in which the sample contact surface contacts the sample and compresses the sample.The apparatus further comprises a sample thickness controller configured to control the distance between the sample receiving surface and the sample contact surface in the second position of the sample contact surface such that a sample thickness between the surfaces can be varied to obtain at least two measurements of the sample at different optical path lengths through the sample."

[0007] US 2010 / 0085571 A1 describes a device in which an optical fiber is mounted in a fiber optic holder that encompasses the non-rotating shaft of a linear actuator. Additionally, an optical path length sensor is used in conjunction with an optimized absorption method to ensure micrometer-level precision of the displacement between the respective receiving and transmitting fibers, enabling absorption measurements of approximately 0.005 to approximately 2.0 absorption units for any path length.

[0008] US 2011 / 0149280 A1 discloses a device for spectrophotometric analysis, comprising a sample receiving surface arranged to receive a sample to be analyzed, and a sample contact surface movable relative to the sample receiving surface so that it can be moved into a first position in which the surfaces are sufficiently far apart to allow the sample to be placed on the sample receiving surface, and into a second position in which the sample contact surface contacts and compresses the sample. The device further comprises a sample thickness controller arranged to control the distance between the sample receiving surface and the sample contact surface in the second position of the sample contact surface so that a sample thickness can be shifted between the surfaces to obtain at least two measurements of the sample at different optical path lengths through the sample. BRIEF DESCRIPTION OF THE INVENTION

[0009] The present invention is directed to an automated system and method for varying the optical path length in a sample through which light from a spectrophotometer must pass. In particular, the presently described embodiments allow the user to easily vary the optical path length over a wide range, typically from about 10 micrometers to about 1000 micrometers, while simultaneously providing the user with an easy way to clean and prepare a transmission cell for optical interrogation. Such varying path lengths can be automatically manipulated by a programmable control system to quickly collect and store data from different path lengths as needed for various spectrographic analyses.

[0010] Thus, one aspect of the present application comprises an apparatus for measuring an optical property of a sample, comprising: a pair of windows; wherein one window of the pair is configured to receive radiation from a source of optical energy via free space, and the other window of the pair is configured with an integrated optical detector used to optically interrogate a sample disposed between the pair of windows, both windows of the pair being movable with respect to the positioning of the source of optical energy; wherein the pair of windows comprises a first window and a second window, each configured with at least one surface selected from: a flat surface and a conical surface;wherein a flat surface of the window configured to receive radiation from the source of optical energy faces toward the sample, and a conical surface of the window configured to receive radiation from the source of optical energy faces toward the source of optical energy; and a processor configured to control a distance between configured surfaces of the pair of windows with a variable distance (P) to pull the arranged sample into a column trapped by surface tension or to compress the sample during optical analysis, wherein the processor is additionally configured to automatically collect and store information of different optical path lengths of the pulled and / or compressed sample.;

[0011] Furthermore, an apparatus for measuring an optical property of a sample is described, comprising: a source of optical energy; first and second windows; wherein the first window is configured to receive directed optical energy from the source via free space, and wherein both the first and second windows are movable with respect to the positioning of the source of optical energy, and wherein the first window is optically coupled to the second window; a processor;and means for adjusting a distance between configured surfaces of the first and second window surfaces with a variable distance (P) to pull a sample into a column to be trapped by surface tension or to compress the sample during optical analysis of the sample, wherein the processor is configured to automatically collect and store multiple sets of data of different optical path lengths of the pulled and / or compressed sample;

[0012] Another aspect of the present application includes a method for measuring an optical property of a sample, comprising: providing a pair of windows; wherein one window of the pair is configured to receive radiation from a source of optical energy via free space, and the other window of the pair is configured with an integrated optical detector used to optically interrogate a sample disposed between the pair of windows, wherein both windows of the pair are movable with respect to the positioning of the source of optical energy; wherein both windows of the pair are movable with respect to the positioning of the source of optical energy;wherein a flat surface of the window configured to receive radiation from the source of optical energy faces toward the sample, and a conical surface of the window configured to receive radiation from the source of optical energy faces toward the source of optical energy; and providing a processor configured to control a distance between configured surfaces of the pair of windows with a variable distance (P) to pull the arranged sample into a column trapped by surface tension or to compress the sample during optical analysis, wherein the processor is additionally configured to automatically collect and store information of different optical path lengths of the pulled and / or compressed sample(s); and collecting spectral data of a sample trapped between windows and provided surfaces for different path lengths; BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows an example infrared (IR) system. Fig. Figure 2 shows an exploded view of the optical mechanical components used to provide IR transmission measurements. DETAILED DESCRIPTION

[0013] In the description of the invention provided herein, it is to be understood that a word appearing in the singular also includes its plural equivalent, and that a word appearing in the plural also includes its singular equivalent, unless otherwise implied or explicitly stated. Further, it is to be understood that for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another, unless otherwise implied or explicitly stated. Furthermore, it is to be understood that the figures presented herein are not necessarily drawn to scale, and some of the elements may be drawn solely for clarity of the invention.Also, reference numerals may be repeated among the various figures to indicate corresponding or analogous elements. In addition, it is to be understood that any list of such candidates or alternatives is merely illustrative and not limiting, unless otherwise implied or stated. In addition, it is to be understood that, unless otherwise indicated, numbers expressing amounts of ingredients, components, reaction conditions, etc., used in the specification and claims are to be understood as modified by the term "about."

[0014] Accordingly, unless otherwise stated, the numerical parameters set forth in the specification and the appended claims are approximations that may vary depending on the desired properties to be achieved by the presently presented subject matter. At a minimum, and not as an attempt to limit the application of the equivalent embodiments teaching to the scope of the claims, each numerical parameter should be interpreted at least in light of the number of significant figures mentioned and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters that set forth the broad scope of the presently presented subject matter are approximations, the numerical values ​​set forth in the specific examples are set forth as precisely as possible.However, all numerical values ​​inherently have certain errors that necessarily arise from the standard deviation found in their respective test measurements. General description

[0015] The presently described embodiments are intended to provide optical interrogation of samples, including, but not limited to, solids, soft solids, and liquids, including oil-based samples. The length of the light transmission path through a particular sample varies over a wide range depending on the particular sample and the type of measurement required. The presently described embodiments are therefore designed to provide the user with a high degree of control, in real time and automatically, over one or more pathlengths. The advantageous result of such a novel aspect is that by collecting and storing many data sets of different pathlengths, later analysis of the stored collected data at many different pathlengths is automatically possible.

[0016] Another advantageous aspect of the presently described embodiments is that the configuration also provides an easy means for a user to place a small sample (typically a drop of sample) onto a scanning window in the light beam for analysis, which of course allows for easy removal of the sample from the sample cell window and cleaning thereof to permit rapid analysis of many samples within a short period of time. Special description

[0017] Now referring to the drawings, the device as shown in Fig. 1 and generally designated by reference numeral 100, a rotating arm configured to be in an "open" position in which a sample of a solid (soft moldable samples (not shown)) or a reference solid sample may be applied, or a drop of the analyte or reference sample (not shown) (e.g., samples of less than about 2 µL, oil-based samples, liquid samples) may be dispensed or aspirated onto a lower surface of a configured window 5'.As discussed in more detail below, such an "open" position allows easy access to the ends of the surfaces, for example, desired surface configurations for the optical windows 5 and 5', to apply any of the respective samples and to allow a user to easily clean such surfaces provided on windows 5 and 5' and to provide a new sample within the device if desired.

[0018] Then, when applying a sample, the arm 4 of the device 100, as shown in Fig. 1, is moved by a user at an angle into the "operating position", i.e., closed position (as often detected by the position sensor (not shown)), resulting in the desired surface of window 5 being brought into contact with a desired sample trapped between surfaces provided by windows 5 and 5'. Such a configuration enables, among other things, a surface tension mode (i.e., pulling a sample into a column) or a mode in which the sample can be "compressed" by means of the configured surfaces of windows 5 and 5'. In both of these exemplary modes, it is understood that the Fig. 1 can then, as described below, automatically collect and store many sets of data of different path lengths and thus provide for later analysis of the stored data at the many different path lengths, if needed.

[0019] Again with reference to Fig. 1 contributes to the closed "operating position" by the mechanical coupling of a hinged rod 6, which is configured through holes in both the pivoting arm 4 and in a hinged spacer block 6', the hinged spacer block 6' being rigidly fixed with respect to the base plate 2. In addition, a detector housing 7, which may include, among other things, but is not limited to, a light detector 9 and a window 5 coupled to the pivoting arm 4, must necessarily rotate about the hinged rod 6 so that a surface of the window 5 comes into contact with a sample provided on an upper surface of the window 5'. However, it must be noted that although samples are often provided on the upper surface of the lower window 5, in some cases the respective sample can of course also be applied to the lower surface of the upper window 5.If this is the desired operating mode, the sample is then rotated at an angle by means of the arm 4 to come into contact with the desired surface of the lower window 5', without deviating from the working embodiments described herein.

[0020] The present embodiments thus allow the user to easily transition from one sample to another by providing a movable pair of windows (5 and 5') that transmit a wide range of light wavelengths. Such windows 5, 5' allow the placement of a wide range of liquids (e.g., oils) and some solids in a light beam for spectral analysis. These windows 5, 5' are arranged opposite one another. Furthermore, the lower window 5' is often adhesively bonded to a large, flat surface (e.g., the sample platform 3) to provide the user with a sufficient area to accommodate samples of various sizes and types.The upper window 5 may be adhesively connected to the aforementioned movable arm 4, which can be raised (e.g., pivoted away) to allow the placement or removal of a sample and then lowered onto the sample to collect spectral data. The sample may, for example, be a thin, malleable solid, but is typically a liquid, since with such a medium the pathlength can be varied, and is therefore a desirable sample type, although the method described in . Fig. 1 and the device described here can of course also treat non-liquid samples.

[0021] As an exemplary design for illustration purposes only, if the field of view of the detector 9, as in Fig. 2, extends approximately 45° to either side of the vertical, the diameter of the lower window 5' is often twice the total distance from the bottom of the lower window 5' to the detector 9 mounted above the upper window 5. In a resulting desired design, this distance would be 1000 µm for the space from the detector to the upper window, plus 200 µm for each window thickness, and 500 µm for the normal maximum distance between the two windows. This adds up to 1900 µm times two, or a minimum lower window size of approximately 4000 µm.

[0022] Using such parameters, a resulting configuration provides two windows measuring at least 4000 µm (4 millimeters (mm)), but preferably 5000 µm (5 mm), to provide sufficient area for adhesive bonding of the windows at their edges and, in addition, to provide dimensions that are easy and inexpensive to manufacture. Smaller windows may also be used, but the use of smaller windows may result in a reduction in the light level reaching detector 9.

[0023] The detector 9 is often, but not necessarily, coupled to the upper window 5 (e.g., integrated, built-in) because it is desirably small and lightweight, allowing the arm to be easily lifted so the user can quickly clean and inspect the windows. Examples of infrared (IR) detectors that can be implemented here include deuterated triglycine sulfate (dTGS), lithium tantalate (LiTaO3), triglycine sulfate (TGS), indium gallium arsenide (InGaAs), germanium (Ge), lead sulfide (PbS), indium antimonide (InSb), mercury cadmium telluride (MCT), and mercury zinc telluride (MZT).

[0024] The arm 4, as in Fig. 1, is designed to be easily lifted and pivoted back (rotated) to a position where the user can easily see the bottom surface of the upper window 15. The arm 4 and the window detector assembly have an upper position (for example, the "open position" as shown in Fig. 1), being held in place by a resilient mechanism (for example, a spring) or a magnetic means (for example, an electromagnetic or permanent magnet) (not shown), allowing the user to use both hands to clean and inspect the upper window. At the same time, the lower window 5' is operatively uncovered, allowing the lower window 5' to also be easily cleaned and inspected.

[0025] The light source 12 can be configured from a number of known designs, such as, but not limited to, an incandescent bulb, an ionizing gas lamp, a laser, a light-emitting diode, etc., to provide the desired electromagnetic radiation. Preferably, the source 12 is adapted to deliver the optical energy via free space to a desired optical window described herein (e.g., a lower window 5'). The optical bandwidth provided by the source 12 can be a desired wide range of wavelengths or narrow bands of wavelengths, but often the source is adapted to provide infrared light from about 1 µm up to about 25 µm. As often desired, such IR light can be modulated for interrogation with Fourier transform infrared spectroscopy (FTIR).Additionally, such IR sources, since they are often larger, and especially when coupled with desired optical focusing means (not shown), are thus designed to be positioned below the lower window 5' and / or to the side of the lower window 5'. Such components may, however, be designed to move, but are often designed to be fixed for practical reasons.

[0026] The sample arm 4 has a repeatable mechanical stop, for example in the form of a pin or joint 11 (not shown), which provides a desired position against which the lower surface of the arm 4 abuts when the arm is rotated, as intended for contact and measurement of a sample. Such a configuration provides a repeatable abutting (active) position relative to the light source optics, which directs upwardly propagating light (see reference numeral 8) toward a repeatable dimensional position (for example, a focal point). This is the same repeatable position that the detector 9 assumes when the scanning arm 4 is in the lower position, as in Fig. 1. As discussed above, a resilient mechanism, e.g., a spring, or a magnetic means, e.g., an electromagnetic or permanent magnet, may be used to provide additional force to hold the scanning arm 4 down in a repeatable position while data collection is performed.

[0027] Fig. Figure 2 shows a more detailed view of the transmission cell piece of the optical assembly, and reference is now made to it to provide clarity on the present embodiments. Thus, Fig. 2 illustrates a disclosed arrangement, generally indicated by reference numeral 200, including a sample platform 3, the respective upper and lower windows 5 and 5', the detector housing 7, and the detector 9. Also generally shown is an optical source 12, often an IR optical source, and more commonly an IR source for providing a modulated IR beam for FTIR, as is known to those of ordinary skill in the art and as briefly discussed above. While FTIR is a desired embodiment to operate in the near-infrared as well as the mid-infrared range, it is to be understood that the present configurations may also be configured with other near-infrared to mid-infrared spectroscopic systems and are not intended to be limited to FTIR systems.

[0028] Again with reference to Fig. 2 shows a resulting transmission cell comprising several (often two) windows 5 and 5', often thin diamond windows, configured with special surfaces (to be discussed below) and an adjustable mechanism 14 (for example motorized (stepper motor)) connected to the sample platform 3 (as in Fig. 1) to adjust the space between the two windows 5 and 5' (ie to adjust the optical path lengths) (also discussed in detail below). From such a configuration, the Fig. 1 provides adjustable lengths over the range from approximately 10 µm up to 1000 µm.

[0029] As an exemplary operating mode runs, again with reference to Fig. 2, the light beam typically travels vertically upwards or downwards through windows 5 and 5', but can also travel at other angles upon request by the user through software or manual control. Since the light detection means (e.g., detector 9) are typically smaller than the light source means (e.g., light source 12), the light is normally directed upwards (see reference numeral 8 and accompanying directional arrows) toward the detection means (e.g., detector 9). The design of the small, lightweight detector 9 allows the upper window 5 to move in the sample arm 4, which moves or pivots upwards, and / or away from the lower window 5', where the light enters the trapped sample. This detector, movable by means of the support arm 4, allows the upper and lower windows 5, 5' to be accessible both for loading new samples and for removing old samples that may be stuck to the upper or lower sample windows 5, 5'.

[0030] The built-in light detector 9 is often designed to be dimensionally substantially small, not only to operate at the sample temperature, but also to advantageously place the detector 9 very close to the upper window 5 in the movable arm 4 and to use near focus as a mode, thus eliminating the need for detector focusing optics. If the detector 9 operates at a different temperature than the sample being interrogated, as an alternative arrangement, the exemplary embodiments provided herein allow for detector transfer optics (not shown) to be incorporated to allow the detector 9 to be located farther from the sample in a known manner. For example, a simple elliptical mirror can be used to allow the detector 9 to be placed farther from the sample, allowing the sample to be heated or cooled to temperatures that the detector 9 cannot otherwise tolerate.

[0031] The light path through the transmission scanning system begins at a light source means 12 (e.g., an IR light source, such as a modulated IR source), which may include one or more light sources and fixed or variable filter means (not shown) to provide a light source 12 containing both light intensity and light wavelength information. The light from source 12 is directed to a focusing means, which may include any known configuration of refractive, reflective components, operative to direct the light through the first sample-bearing window (e.g., lower window 5') and then through the second window (e.g., upper window 5) for collection by a light detection means (e.g., detector 9).It will be appreciated that in some cases it is possible for part or all of the wavelength filtering means (not shown) to be placed in the light path after the sample and the windows 5, 5'. While the above configuration is advantageous, a more desirable optical configuration comprises the light source 12, variable filter / interferometer and focusing means (not shown), which are generally larger than the light detection means, placed near or below the scanning window 5. Thus, the created light is focused in an upward direction through the windows 5, 5' and the sample onto a light detection means 9, which is located in a known standard position relative to the light source 12 and the focusing means, which is known to those skilled in the art (not shown). Furthermore, it will be appreciated that, although in . Fig. 1 the device is coupled with a light source 12 under the platform 3 with the window 5' and the light detection means 9 (for example photometric or spectrophotometric radiation detector) is coupled with the arm 4, it must be emphasized that in other embodiments the arm 4 can be configured with the light source 12 (for example a photometric or spectrophotometric source) and the platform 3 can be arranged with the light detection means 9 (for example photometric or spectrophotometric radiation detector).

[0032] It should be understood, however, that since the light detector 9 is often desirably smaller than the light source 12, as discussed above, it is thus convenient to place the light detector 9 near the upper sample window 5 in the illustrated movable arm 4, which can be raised away from the lower sample window to facilitate user access to the sample position. Thus, the user can inspect both windows, allowing the user to know that the windows are clean and ready to receive a sample.

[0033] As an advantage of the present arrangement, the user can, if desired, move the inspected clean / cleaned upper window 5 and the light detector 9 into the standard known position of the device 100 as shown in Fig. 1, to collect a standard "background spectrum" without a sample present, to verify the entire spectrometer system and save a reference background spectrum for later use. However, it should be understood that, equally with many samples, it is possible to eliminate the background data collection step and simply use Beer's Law and a mathematical model to extrapolate over many different pathlengths to create a background spectrum at virtual zero pathlength, as discussed below. In any event, the user can then raise the upper window 5 and easily place a sample onto the lower window 5'.

[0034] As a further advantageous and new embodiment, the window 5' can be operated by a motor controlled by a computer (processor) (see for example reference numeral 14 of the motor, as in Fig. 1), for example, can be lowered by approximately up to 1 mm to increase the sample path length before the upper window 5 is lowered to its standard scanning position. Thus, the path length can be shortened (e.g., compressed) during data collection. This exemplary "squeezing the sample" process allows highly viscous samples to be examined without concern about air being introduced into the light beam when the windows 5, 5' are separated.

[0035] Maintaining the light detector 9 and window 5 in a known position relative to the light source 12 is important so that a given optical path length between the upper window 5 and the lower window 5' can be determined with confidence in the data obtained and stored with the spectral data. Essentially, the positional placement of the detector 9 and window allows changes in sample type and thickness to be measured without concern that the directed light (e.g., the focus of the light beam) has changed due to changes in the position of the detector 9 relative to the light source optics (e.g., focusing means (not shown)).This is important because relative movement between the light source optics (not shown) and an exemplary light detector 9 can cause a change in the amount of light collected by the detector 9, and if left uncontrolled, will result in an erroneous change in the apparent light absorption of the sample if the detector position changes between different sample and background reference data collection scans.

[0036] Thus, in the present embodiments, the upper sample window 5 and detector 9 are often, but not necessarily, moved to only two repeatable positions. The upper position allows users to remove, inspect, and place samples on the sample windows and clean them, and the lowered position provides a fixed focus and a known optical path length during the collection of background (without a reference sample) and sample scans.

[0037] Again with reference to Fig. 1, a lower sample window 5' is coupled to a flat scanning platform 3 (for example, by means of an adhesive bond). It is understood that a window 5, 5' and / or alternatively the sample platform 3 can be treated with a material (for example, a hydrophobic, a hydrophilic coating) known to those of ordinary skill in the art to prevent excessive spreading of an applied liquid droplet of analyte (for example, oil) or a reference sample (for example, to prevent spreading of an applied sample to the boundaries of the sample platform 3). However, the design of the platform 3 itself is also configured to prevent any liquid sample from running away from the position of the sample windows 5, 5' and dripping over the edge of the scanning platform 3 into the support mechanism and the optics located below the sample windows 5, 5' and the platform 3.Furthermore, a large platform 3 allows various samples to be placed between the windows 5, 5'. To further prevent sample escape (not shown), the sample platform 3 often has a solid construction without perforations (e.g., holes, slots, etc.) through which a desired sample could flow or escape beneath the sample platform 3. As an additional arrangement, the surface of the scanning platform 3 may, but is not necessarily, surrounded by a lip or wall to contain the liquid sample in case large amounts of sample are inadvertently placed within the scanning area.

[0038] As a further feature, the scanning platform 3 can also be supported on a hinge if the hinge is located a great distance (e.g., at least 60 mm) from the window, in order to limit the tilt angle when raising and lowering the window. This fact further allows a single piece of stainless steel to act as the sample platform 3 to support the lower window 5'. This single piece can be rigidly attached to the base of the system, provided it is more than 60 mm from the window. In another arrangement, a thin, flexible surface platform 3 is used. In particular, the natural curvature of a thin piece of metal, such as stainless steel, among others, can act as a hinge, with the advantage that there are no gaps through which liquid samples can escape through the hinge area down into the light source means or another mechanism mounted beneath the same sample platform 3.

[0039] The sample platform 3 can also be attached (i.e., coupled) to the adjustable mechanism 14 (e.g., a computer-controlled elevator, such as a motorized (stepper motor)) to change the sample path length between the two sample windows. Such an adjustable mechanism 14 (e.g., a motor) can be controlled by a manual switch or by a computer program. However, in a preferred embodiment of the invention, the software-controlled motor 14 can automatically change the distance between the sample windows to control the light path length through the sample in a programmed manner to facilitate the measurement of the absorption spectra of many different samples.

[0040] As in Fig. 1, the adjustable mechanism 14 may, as an advantageous configuration, include a linear actuator 16, for example with a motor, configured as the adjustable mechanism 14, which is secured to the base plate 2 by means of fastening means, such as screws, posts, pins, rivets, etc. The use of a motor 14 in such an arrangement thus provides a rotary movement of the linear actuator 16 to raise or lower the sample platform 3. Preferably, the travel distance and / or position of the linear actuator 16 or an integrated raising / lowering means is adjustable during operation of the device 100, as shown in Fig. 1. As an additional arrangement, the movement of the motor 14 and / or the platform 3 may include a reference position sensor (not shown) that establishes a "home" or reference position when the motor control system is initialized upon startup or interrupted, for example, by an opto-interrupt device (not shown).

[0041] Through such a motor / software-controlled arrangement, the entire sample platform 3 can be translated up and down, for example, by approximately 500 micrometers to approximately 1000 micrometers, to change the sample path length as needed. In a desired embodiment, the lower sample window 5' can be programmed via coupling to the sample platform 3 to remain in the lower position, allowing the user to clean, inspect, and collect background data. Only after a sample is loaded and data collection has started will the program move the sample window 5' / platform 3, for example, raise it to reduce the optical path length as needed.

[0042] The sample platform 3 can thus be programmed to always remain in the lowered position until the sample arm 4 is lowered, for example, to protect the configured diamond windows 5, 5' against damage caused if the sample arm 4 is accidentally pushed downwards quickly. In particular, such rapid and unintentional movement, if it cannot be prevented, can result in the stop being hit with sufficient speed and force that the arm 4 and the support systems are sufficiently bent / deflected so that the exemplary configured diamond windows 5, 5' are compressed with enough force to damage them. Thus, a desired method of the present application is to provide that only after the sample arm 4 has been lowered into a scanning position is the motor drive capable of directing the sample platform 3 upwards to produce small optical path lengths.However, as soon as the arm 4 is raised, the drive of the motor 14 is instructed to lower the sample platform 3 sufficiently (for example, lowered to 1000 micrometers) to make damage unlikely.

[0043] It should be noted that for most samples, it is possible to raise and then lower the sample platform 3 multiple times, with the window and surface tension still holding a liquid sample in place. Only highly viscous semi-solid samples are limited to being compressed simply to avoid air bubbles. It should also be noted that the present embodiments described herein are designed to provide surface tension-modifying coatings added to the sample platform 3 to help keep the sample on the window rather than spreading it out on the sample platform 3. These coatings allow the same sample to be scanned at different path lengths over a number of repeated data collection cycles and aid in the use of low-viscosity samples.Different coatings are thus used with different types of samples to help the user place a sample quickly and accurately on the lower window 5'.

[0044] Again with reference to Fig. 2, windows 5 and 5', which may be coated on desired surfaces (e.g., as an anti-reflection coating (AR coating)) to increase light throughput, are mounted one above and below each other. The light 8 travels from the light source via configured optics (not shown) located below the lower window 5' to the detector 9, which is mounted as close as possible to the upper window 5. By placing the detector very close to the upper window (e.g., within micrometers), the need for any optics between the detector and the upper window is eliminated. In one desired arrangement, the upper window 5 is a diamond window approximately 200 micrometers thick, although window 5 is not limited to only one such thickness. The detector 9 is mounted at approximately 1000 micrometers up to over 500 micrometers above the upper window 5.The lower window 5' is often also, but not necessarily, a diamond window of approximately, but not necessarily, 200 micrometers thick. When diamond is used as the material, thin windows are important to reduce costs, reduce diamond phonon absorption, and reduce the distance from the detector to the lower surface of the lower window. However, it should be noted that the present embodiments described herein are not limited to thin windows.

[0045] The preferred windows have one flat side and one side with a conical (e.g. cone-shaped) surface, approximately as in Fig. 2, where the center of the window (e.g., 5) is thicker (at approximately 200 micrometers) than the edge of the window (at approximately 180 micrometers). This feature is desirable so that the center of the window has a minimum path length, even if the window is slightly misaligned (tilted) during manufacture. Such a conical feature also reduces spectral channeling, which is caused by light reflecting off one flat surface of a scanning window to a second flat window surface. These reflections can cause problems if they occur within the window (between the front and back surfaces of a single window), or if they occur between any two different window surfaces if they are flat and adjacent to each other. Thus, each window has one flat and one conical surface.These windows can be used with the upward-facing cone or the downward-facing cone. In the preferred window configuration, the flat surface of the detector window points upward toward the detector, and the cone points downward toward the sample. The lower window has the flat surface facing upward toward the sample, and the lower side of the lower window has a conical surface facing downward toward the light source. Thus, the upward-facing conical surface of the upper window 5 prevents adverse "channel spectral features" from reflections within the upper window surfaces and from the air space between the upper and lower windows where the sample is placed. Additionally, it should be understood that the downward-facing cone of the lower window 5' prevents an adverse channel spectral feature from reflections within the lower window itself.

[0046] As a preferred embodiment, a presently desired application is to provide that only the lower window moves when data is collected to change path lengths. The upper window, detector, and source optics thus preferably, but not necessarily, move with the collection of data to provide the best possible stability in absorption measurements. Thus, moving only the lower window (e.g., moving between approximately 10 to 1000 micrometers) to produce changes in optical path length allows the design of the lower window's motorized drive system to be smaller, stiffer, more repeatable, and less expensive. The motorized drive system (i.e., adjustable mechanism 14) must move the lower window 5' up and down in a repeatable manner with long-term accuracy of only a few micrometers.Obtaining sufficient resolution of the drive system to allow it to move less than 1 micrometer per control step is not that difficult with current systems known to those skilled in the art. However, despite such current systems, there is still a need to calibrate the zero point, where the windows touch and the optical path length in the field has a minimum value, so that the user can trust the measurement. Such a calibration step gives the user confidence that windows 5 and 5', as defined by the closed "operating position" in . Fig. 1 (the minimum optical path length) to account for normal wear, corrosion, and temperature changes in the mechanical stop-and-hinge assembly of the detector arm 4.

[0047] This zero calibration can be performed by several means. One is to place a sample liquid (for example, water or alcohol) into the transmission cell and measure the optical absorbance while the windows are driven toward their minimum optical path length. If absorbance is measured at each step of the travel, the absorbance will change (decrease) with each step until the windows touch, at which point the absorbance changes being monitored will suddenly decrease dramatically. This sudden change in absorbance change per step thus indicates the point at which the minimum path length occurs.

[0048] Another method for calibrating the optical path length is to measure the small amount of optical channel spectra detectable with windows, such as the ones described here, which are designed to ultimately remove the channel spectra with samples but not entirely with air. This optical channel signal is weak by design but is a very accurate measure of the optical path length between the two windows if signals are averaged over a sufficient period of time (e.g., approximately 60 seconds or more). Such a method is advantageous because the procedure can measure path lengths from non-zero up to approximately 50 or more micrometers with excellent accuracy, allowing not only the zero point but also all shorter path lengths to be measured.

[0049] Another advantageous alternative is a good zero calibration procedure designed to be faster than the above-mentioned process, isolating one of the mechanical stops and measuring the sample arm stop contact resistance electronically (i.e., a current measurement system). When the travel length decreases to zero, the windows touch, and the arm is lifted from the stop, causing the stop contact resistance to jump. This can be measured on every sample run with very little or no additional time. Data control system

[0050] It is understood that the method of operation, or various selected steps thereof, may be performed automatically by a system including a computer or other electronic processor and computer program instructions tangibly embodied on a computer-readable medium, such as a floppy disk drive, magnetic tape, disk drive, memory card, etc. The computer-readable medium may act as both an input and output device. If desired, the computer / processor may be further electronically coupled to one or more other output devices, such as display screens, printers, etc., and / or one or more other input devices, such as keyboards, Internet connections, etc.

[0051] In system 100, in one exemplary arrangement, the computer / processor (not shown) provides instructions for setting the path length(s) for the sample between windows 5, 5' to a specific value(s). For example, the computer / processor can automatically send instructions for setting or changing path lengths and for collecting optical information from interrogated samples manipulated to provide different path lengths. If the system of Fig. 1 also includes a position sensor, such position information can be sent back to the computer / processor to provide path length adjustments. The computer / processor (not shown) also receives electronic signal information from the light detector 9 regarding the intensity (e.g., power) of the light detected by the light detector 9 after transmission of such light from the transmission cell section of Fig.1, as described above. The computer / processor may also automatically perform the calculations and evaluate the decisions provided, for example, by software, graphical user input (GUI), etc., to direct steps designed to guide a user. The computer / processor (not shown) may also set the values ​​of variables. The sequence of events performed by the computer / processor may be controlled according to program instructions stored on the computer-readable medium and transferred therefrom to the computer / processor. Results of the measurements may also be transferred from the computer / processor to the computer-readable medium for storage thereon. Output to a user may also be provided via output devices. The user may control program execution by means of input devices known to those skilled in the art.

[0052] A preferred data collection control program procedure may be configured to operate as follows. First, the user can tell the program that a new data collection session is to be initiated. The program will then prompt the user to inspect and clean the windows if necessary. The user can then lower the upper window and detector arm to the standard scanning position, and the arm mechanism would signal the computer program that the arm is in the correct position to begin data collection. The program will then signal the user to automatically collect a background spectrum. This spectrum can then be automatically analyzed to determine whether the collected light has the expected characteristics, indicating that the windows 5, 5' are clean and everything is OK.

[0053] The user can then be prompted to raise the sample window detector arm 4 and place a sample onto the lower sample window 5' (and, if desired, enter a name for the next sample to be run). Upon verification, for example, by a position sensor (not shown) that the arm 4 has been raised and lowered in a pattern indicating that a sample is in place, the control program can then automatically start the data collection cycle.

[0054] Data can be initially collected with a large distance between sample windows (or long optical path lengths). The motor is then instructed (e.g., via software, including graphical user interface (GUI) input by a user, etc.) to raise the lower window 5' to reduce the window spacing and path length, and then collect more data. This process can be repeated a programmed number of times. With the collection of each set of data, data analysis can be started on the previous set of data.

[0055] During the initial analysis, expected reductions in sample absorbance in the transmitted light can be checked. If the absorbance did not occur according to Beer's law, the program can provide a signal to the user that there were likely air bubbles in the light beam and that they should check for a misplaced or too small sample between the sample windows 5, 5'. During the programmed data collections, the program can then provide the data to the user, who can then interpret the data in a number of ways. The user then manually selects the best path length or runs a program that automatically analyzes the data, etc.

[0056] As mentioned above, for many samples, it is also possible to eliminate background data collection and simply use Beer's law and a mathematical model for interpolation over many different pathlengths to construct a background spectrum at a virtually zero pathlength, which is useful in many data analyses. This technique can result in time savings when many samples are analyzed within a short period of time. Such a differential pathlength measurement technique is similar to the techniques described in U.S. Patent Nos. 6,809,826 B2 and 6,628,382 B2.

[0057] The fast-acting contact resistance position sensing system of the present embodiments also enables sample viscosity measurement as an additional feature. The sample window is raised at a constant speed, thereby reducing the sample thickness at a constant rate. At a certain point, the viscosity of the sample flowing out of the decreasing volume will exert sufficient force on the arm to lift it from a configured mechanical stop. This can often be indicated by an increase in contact resistance. The force exerted on the sample arm is known, as are the speed of window movement and the sample thickness. Knowledge of these three things thus allows the viscosity to be determined over a useful range.This information can be used advantageously to prevent air bubbles from being sucked into the scanning light beam, while the path length increases if the speed is too high in later measurements where the path length is increased. Tax software strategy

[0058] The user presses a button to start a data collection cycle. The software can then prompt the user to insert the sample and raise the window to inspect it for cleanliness. After the windows have been cleaned and inspected, the user can then mark the sample as background and then lower the sample arm to start background collection.

[0059] The program can then use background spectra to verify window cleanliness. If this background pass, the user and / or the program can save the background data for later use. The user can also label the sample and then move the sample into position. In most cases, the sample can be a liquid that is placed onto the lower window with a pipette. An example sample placed onto the window includes one of at least 500 µm thickness due to surface tension and viscosity. Thus, in most cases, after the user places the sample onto the lower window and then lowers the arm onto the sample, the sample will then fill the space between the upper and lower windows.

[0060] The user can view from both sides and determine that the sample actually fills the space between the windows, but seeing the sample in position is difficult because the arm blocks most easy viewing angles. Thus, a program can be created to automatically start data collection and check for air bubbles from misplaced samples after the arm is lowered to the standard lower scanning position.

[0061] The software can then detect that the arm has been lowered and proceed with the following illustrative, but non-limiting, example steps: Step 1) Delay for a programmed period of time (approximately 2 to 15 seconds to allow the detector to equilibrate after a light level change). Step 2) Start data collection for approximately 5 to 15 seconds. Step 3) Reduce the distance (optical path length) between the windows by 50% and collect more data. Step 4) Analyze the data to verify that the absorbance has decreased by the expected amount of approximately 50%. If the absorbance is not as expected, the program may signal the user that there appears to be air in the sample or that there is too little sample at the window location.Step 5) If the absorption decrease appears acceptable, the program can decrease the distance (optical path length) by a programmed amount and collect and save a second set of data. Step 6) Analyze the data again for air bubbles and repeat, collecting as many different path lengths as programmed. Step 7) Signal the user that data collection is complete.

[0062] The discussion contained in this application is intended to serve as a basic description. While the present invention is described in accordance with the embodiments shown and described, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments, and those variations would be within the spirit and scope of the present invention. The reader should be aware that the specific discussion may not explicitly describe all possible embodiments; many alternatives are implied. Such modifications and the like are considered simple modifications, well within the ability of one of ordinary skill in the art and within the spirit and scope of the invention. Accordingly, many such modifications can be made by one of ordinary skill in the art without departing from the spirit, scope, and essence of the invention.Neither the description, the drawings nor the terminology are intended to limit the scope of the invention - the invention is defined by the claims.

Claims

[1] Apparatus (100) for measuring an optical property of a sample, comprising: a pair of windows (5, 5'); wherein one window (5') of the pair is configured to receive radiation from a source of optical energy (12) via free space, and the other window (5) of the pair is configured with an integrated optical detector (9) used to optically interrogate a sample disposed between the pair of windows (5, 5'), both windows (5, 5') of the pair being movable with respect to the positioning of the source of optical energy (12); wherein the pair of windows (5, 5') comprises a first window and a second window, each configured with at least one surface selected from the following: a flat surface and a conical surface;wherein a flat surface of the window (5') configured to receive radiation from the source of optical energy (12) faces toward the sample, and a conical surface of the window (5') configured to receive radiation from the source of optical energy (12) faces toward the source of optical energy (12); and; a processor configured to control a distance between configured surfaces of the pair of windows (5, 5') with a variable distance (P) to pull the arranged sample into a column trapped by surface tension or to compress the sample during optical analysis, wherein the processor is additionally configured to automatically collect and store information of different optical path lengths of the pulled and / or compressed sample. [2] The device according to claim 1, wherein a flat surface of the window (5) configured with the integrated optical detector (9) faces toward the optical detector (9), and a conical surface of the window (5) also configured with the integrated optical detector (9) faces toward the sample. [3] The device of claim 1, wherein the pair of windows (5, 5') is configured with a maximum dimension of 0.005 millimeters (mm) up to 5 millimeters (mm). [4] The device of claim 1, wherein the window (5) with the integrated optical detector (9) is additionally coupled to a mechanical stop (11) configured with a contact resistance system that allows the processor to calibrate the point of maximum path length. [5] The apparatus of claim 1, wherein the processor controls the distance between the pair of windows (5, 5') by instructing a motorized mechanism (14) to move a coupled sample platform (3) configured with one of the pair (5'). [6] The apparatus of claim 5, wherein the processor is configured to automatically lower the sample platform (3) to prevent damage to the pair of windows (5, 5') when an arm (4) configured with a window (5) of the pair is lowered. [7] The apparatus of claim 6, wherein the processor is further configured to thereafter instruct the sample platform (3) to lift and compress the sample. [8] The apparatus of claim 6, wherein the processor is further configured to adjust optical path lengths of the sample by moving the coupled sample platform (3). [9] The device according to claim 1, wherein the integrated optical detector (9) is at least one detector selected from the following: dTGS detector (dTGS - deuterated triglycine sulfate), lithium tantalate (LiTaO3), triglycine sulfate (TGS), indium gallium arsenide (InGaAs), germanium (Ge), lead sulfide (PbS), indium antimonide (InSb), mercury cadmium telluride (MCT) and mercury zinc telluride (MZT) detectors. [10] The apparatus of claim 1, wherein the source of optical energy (12) is configured to provide radiation of a wavelength between 0.5 µm up to 100 µm. [11] A method for measuring an optical property of a sample, comprising: Providing a pair of windows (5, 5'); wherein one window (5') of the pair is configured to receive radiation from a source of optical energy (12) via free space, and the other window (5) of the pair is configured with an integrated optical detector (9) used to optically interrogate a sample arranged between the pair of windows (5, 5'), wherein both windows (5, 5') of the pair are movable with respect to the positioning of the source of optical energy (12); wherein a flat surface of the window (5') configured to receive radiation from the source of optical energy (12) faces towards the sample, and a conical surface of the window (5') configured to receive radiation from the source of optical energy (12) faces towards the source of optical energy (12); Providing a processor configured to control a distance between configured surfaces of the pair of windows (5, 5') with a variable distance (P) to pull the arranged sample into a column trapped by surface tension or to compress the sample during optical analysis, wherein the processor is additionally configured to automatically collect and store information of different optical path lengths of the pulled and / or compressed sample; and Collecting spectral data of a sample trapped between surfaces provided by the windows (5, 5') for different path lengths. [12] The method of claim 11, further comprising: eliminating a background spectrum collection step by further configuring the processor with a mathematical model that extrapolates different optical path lengths to allow the generation of a background spectrum of virtually zero path length without the need to separately collect data. [13] The method of claim 11, further comprising: automatically measuring the path length between the pair of windows (5, 5') to comprise the following steps: Manipulating the distance between configured surfaces of the pair of windows (5, 5') to provide one or more path lengths with only air between the pair of windows (5, 5'); Collecting, by means of configured software, a channel spectrum at the one or more path lengths; Enabling the configured software to use the collected channel spectra and a mathematical model to calibrate the one or more path lengths; and Storing the calibrated values at one or more path lengths for use during field operation. [14] The method of claim 11, further comprising: Using the collected information to monitor the expected change in light absorption with changing path length; and Warn a user that the collected data is likely to be erroneous if a measured result deviates from an expected rate of change according to Beer's Law and / or an interpolated rate of change. [15] The method of claim 11, further comprising: Compressing the arranged sample between the pair of windows (5, 5') at a fixed rate by means of a processor-controlled motor (14), wherein as the arranged sample is pressed thinner, a force required to compress the pair of windows (5, 5') increases until the force exerted on the pair of windows (5, 5') is high enough to lift a sample loading arm (4) from a mechanical stop (11); Measuring with a processor the time required for the sample loading arm (4) to lift off the mechanical stop (11); and Calculating the viscosity of the arranged sample using the speed of the motor, the arranged sample thickness and the time to provide the force required to raise the sample loading arm (4).

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