Abstract:
A photometer for analyzing a plurality of samples. The photometer comprises a light source and a detector. An optical assembly defines two or more light paths, each light path arranged to carry light from the light source, through a separate sample location, and to the detector.

Description:
BACKGROUND  
       [0001]     Spectrophotometry operates on the principle that certain compounds will absorb certain wavelengths (i.e., colors) of light. Light having known intensity at a variety of wavelengths is projected into one side of a sample vessel of known thickness that contains a sample such as a liquid, mixture, solution, reacting mixture, or the like. The light is detected after it exits the other side of the sample vessel. The detected light is analyzed for the absence, or reduced intensity levels, of certain wavelengths of light. This information, along with the sample thickness, is used to identify and measure the concentration of compounds in the sample.  
         [0002]     One difficulty with spectrophotometers (i.e., the instrument used for spectrophotometry) is that they have limited throughput because they can analyze a sample in only one vessel at a time. If there are multiple vessels, a user must individually load and test each sample, which can take significant amounts of time, especially if there are a large number of samples that must be analyzed.  
       SUMMARY  
       [0003]     In general terms the present disclosure and claims relate to a photometer having two or more light paths arranged to carry light to separate sample locations.  
         [0004]     One aspect is a photometer for analyzing a plurality of samples. The photometer comprises a light source and a detector. An optical assembly defines two or more light paths, each light path arranged to carry light from the light source, through a separate sample location, and to the detector.  
         [0005]     Another aspect is a photometer for analyzing a plurality of samples. The photometer comprises a light source and a two-dimensional photo-detector array (2D-PDA). An optical assembly defines two or more light paths. Each light path includes at least one input optical fiber arranged between the light source and a sample location. A lens is positioned between the input optical fiber and the sample location, and is configured to substantially collimate light radiated from the input optical fiber. At least one output optical fiber is arranged between the sample location and the 2D-PDA. The output optical fiber has a first end positioned to receive light passing through the sample location and a second end positioned to direct light to the 2D-PDA. The second end is positioned to substantially eliminate crosstalk between light directed to the 2D-PDA from the two or more light paths.  
         [0006]     Another aspect is a method of analyzing a plurality of samples. The method comprises conducting light along two or more light paths; passing the light from each of the two or more light paths through separate samples; and conducting the light from each of the separate samples to a detector. 
     
    
     DESCIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a schematic drawing illustrating one possible embodiment of a spectrophotometer.  
         [0008]      FIG. 2  illustrates a possible arrangement of a portion of the optical fibers taken along line  2 - 2  in  FIG. 1 .  
         [0009]      FIG. 3  is an axiometric view of the spectrometer and a portion of the optical fibers shown in  FIG. 1 .  
         [0010]      FIG. 4  illustrates the detector shown in  FIG. 3 .  
         [0011]      FIG. 5  illustrates sample output from the detector shown in  FIGS. 1 and 2 .  
         [0012]      FIG. 6  illustrates an alternative embodiment of a bracket shown in  FIG. 3 . 
     
    
     DETAILED DESCRIPTION  
       [0013]     Various embodiments will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed subject matter.  
         [0014]      FIG. 1  illustrates a spectrophotometer, generally shown as  100 . The spectrophotometer  100  includes a plurality of light paths  104   1 - 104   n  that form signal paths or channels and extend between a light source  102  and a spectrometer  105 . In the exemplary embodiment, the light paths  104   1 - 104   n  are substantially similar to one another, and for purposes of explanation light path  104   n  is described herein in more detail with the understanding that the reference n could apply to any of the light paths  104   1 - 104   n . Other embodiments, however, might provide different structures for each of the light paths  104   1 - 104   n  and different numbers of light paths  104   n .  
         [0015]     The light path  104   n  includes an input optical fiber  108   n  and an output optical fiber  116   n . The input optical fiber  108   n  has first and second ends  110   n  and  112   n  extending between the light source  102  and a first optical coupling arrangement  114   n , and the output optical fiber  116   n  has first and second ends  124   n  and  126   n  extending between a second optical coupling arrangement  118   n  and a position proximal to a spectrometer  105 .  
         [0016]     The light source  102  includes a lamp for generating light and appropriate conventional input optics arranged to couple light from the lamp into the first end  110   n  of the optical fiber  108   n . Additionally, the first ends  110   1 - 110   n  of the input optical fibers  108   1 -l 08   n  are tightly bundled in the exemplary embodiment as illustrated in  FIG. 2  (which illustrates exemplary bundling for seven input optical fibers  108   1 - 108   7 ) so that all of the input optical fibers  104   1 - 104   n  collect light from the light source  102  for travel along the light paths  104   1 - 104   n .  
         [0017]     In the exemplary embodiment, the light source  102  includes a broadband light source such as a Xenon flash lamp providing light in the ultraviolet, visible, and near infrared spectrum or in the range of about 200 to about 1000 nm. Although the exemplary embodiment of the light source  102  is a single lamp with appropriate conventional optics to couple light into the input optical fibers  108   1 - 108   n , alternative embodiments include separate lamps, each separate lamp arranged to direct light into a separate, individual input optical fiber  108   1 - 108   n  or into small groups of fibers that are within the main group of input optical fibers  108   1 - 108   n . Additionally, the light source  102  can output light having various ranges of wavelengths other than the exemplary embodiment and also can include other types of devices for generating light such as incandescent lamps, light emitting diodes (LEDs), as well as dual sources such as separate deuterium and tungsten lamps.  
         [0018]     The first and second optical coupling arrangements  114   n  and  118   n  oppose each other and are spaced to form a sample location  120   n  in which a sample vessel (not shown) can be positioned between the first and second optical coupling arrangements  114   n  and  118   n . The sample location  120   n  is sized to receive a sample vessel. Although the first and second optical coupling arrangements  114   n  and  118   n  of the exemplary embodiment are arranged to project light through opposite sides of the sample location  120   n , other embodiments are possible.  
         [0019]     An example of a sample vessel includes cuvettes, capillaries, and standard spectrophotometer cells. A possible embodiment uses sample vessels having a volume of about 5 μl or less. Another possible embodiment utilizes sample vessels having a volume of about 2 μl or less, and yet another possible embodiment utilizes sample vessels having a volume of about 1 μl or less. Other embodiments utilize sample vessels having different volumes as well. Still other embodiments simultaneously utilize sample vessels of different volumes. For example, during use of the spectrophotometer  100  a sample vessel of a first volume might be in sample location  120   1 , while a sample vessel of a second, different volume might be in sample location  120   2 .  
         [0020]     The first optical coupling arrangement  114   n  includes at least one lens, which collimates light  121   n  output from the input optical fiber  108   n . The collimated light  122   n  travels through the sample location  120   n  and to the second optical coupling arrangement  118   n . The second optical coupling arrangement  118   n  also includes at least one lens and focuses  123   n  the collimated light  122   n  into the output optical fiber  116   n . The diameter of the collimated light  122   n  and the dimensions of the sample vessel are sized so that substantially all of the collimated light  122   n  traveling between the first and second optical coupling arrangements  114   n  and  118   n  travels through the sample vessel and through the sample contained in the sample vessel. A possible embodiment for the first and second optical coupling arrangements  114   n  and  118   n  is disclosed in more detail within U.S. patent application Ser. No. 10/963,865, filed on Oct. 12, 2004, the entire disclosure of which is hereby incorporated by reference.  
         [0021]      FIGS. 3 and 4  illustrate an exemplary embodiment of the spectrometer  105  configured to receive input from seven signal paths or channels  104   1 - 104   7 , although other embodiments can receive inputs from more or less than seven signal paths  104   1 - 104   7 . The spectrometer  105  includes an elongated input slit  130  and a detector  106 . One will appreciate that the spectrometer  105  also includes internal components (not shown) for processing the light traveling between the input slit  130  and the detector  106 . Examples of such internal components include diffraction gratings, collimating mirrors or lenses, other mirrors or lenses, prisms, and the like. As with conventional spectrometers, the internal components process light traveling between the entrance slit  130  and the detector  106  to disperse the light into its component wavelengths and image it onto the detector plane.  
         [0022]     The second end  126   n  of the output optical fiber  116   n  is positioned proximal to and opposing the input slit  130  of the spectrometer  105  so that light output from the output optical fiber  116   n  travels through the input slit  130  and to a detector  106 , which resides at the imaging plane  107  for the spectrometer  105 . The width of the input slit  130  is chosen to obtain the desired wavelength resolution of the spectrometer  105 , and the spectrometer input numerical aperture is chosen to match the numerical aperture of the fiber  116   n .  
         [0023]     The detector  106  is a two-dimensional photo-detector array (2D-PDA) that has rows of light sensitive photo-detectors that are sensitive to the part of the spectrum (i.e., light wavelengths) used to analyze various compounds of interest. An example of a detector  106  includes a charge-coupled device (CCD) having rows of photodiodes formed in a semiconductor material such as a complimentary metal-oxide semiconductor (CMOS). One possible detector  106  is a two-dimensional charge coupled device (CCD) such as the S8667-1010 2D-CCD detector, which is commercially available from Hamamatsu Corp. of Bridgewater, N.J.  
         [0024]     The imaging plane  107  of the detector  106  defines a Cartesian coordinate system having an x-axis  140  and a y-axis  142 . The light-sensitive photo-detectors in each row form the first dimension of the photo-detector array and extend along the x-axis  140 . The x-axis  140  corresponds to the wavelength of light in the spectra detected by the light-sensitive photo-detectors in the row.  
         [0025]     Additionally, the second end  126   1 - 126   n  of the output optical fibers  116   1 - 116   n  are arranged in a one-dimensional array that is substantially parallel to and opposing the input slit  130 . The array of fiber ends  126   1 - 126   n  and the input slit  130  extend along the y-axis  142  so that they are orthogonal to the rows of photo-detectors in the detector  106 .  
         [0026]     The rows form the second dimension of the array and are arranged along the y-axis  142 . The spectrometer  105  projects light received from each separate signal path or channel  104   1 - 104   7  onto separate groups  152   1 - 152   7  of light-sensitive photo-detector rows in the detector  106 . The y-axis  142  corresponds to the signal path channels  104   1 - 104   7 . In this embodiment, the detector  106  simultaneously images spectra  154   1 - 154   n  (i.e., light at a particular wavelength) received from each of the sample locations  120   1 - 120   n , respectively, and thereby simultaneously detects and records the intensity of light as a function of wavelengths for light that is received from all n-samples.  
         [0027]     The detector  106  outputs image data representative of the light intensity as a function of wavelength for each imaged spectra  154   1 - 154   n  and hence each separate light signal output from the output optical fibers  161   1 - 116   n . The output data is processed by a data acquisition device, which is a device that gathers, displays, and records the image data.  FIG. 5  illustrates an example of the output from the detector  106  and the data acquisition device. In this example, output from the first output optical fiber  116   1  is illustrated as a plot of wavelength versus light intensity for light detected from each signal path or channel  104   1 - 104   7 . Outputs from other output optical fibers  116   1 - 116   n  are illustrated as plots  144   1 - 144   n .  
         [0028]     Returning to  FIGS. 3 and 4 , adjacent second ends  126   1 - 126   7  of the output fibers  116   1 - 116   n  in the exemplary embodiment are spaced to eliminate or reduce cross talk between light output from the signal bearing fibers  118   1 - 118   7 . In this embodiment, there are one or more rows  146   x  of light-sensitive photo-detectors that are not exposed to light positioned between each adjacent group  152   1 - 152   7  of light-sensitive photo-detector rows that received light from one of the signal channels or paths  104   1 - 104   7 . In another possible embodiment, there is no dead spot  146   x  between adjacent sets of light-sensitive transducer rows that image the diffracted light. In yet another embodiment, there is some cross talk between adjacent diffracted light signals, although it is desirable to minimize such cross talk.  
         [0029]     The second ends  126   1 - 126   7  of the output optical fibers  116   1 - 116   7  are secured in place by a bracket  138 . In the exemplary embodiment, one or more spacer fibers  134   x  are inserted between adjacent signal bearing output fibers  116   1 - 116   7  to provide accurate spacing between the adjacent signal bearing output fibers  116   1 - 116   7 . At least one end of each the spacer fiber  134   x  is opaquely sealed so that no light will pass from the spacer fiber  134   x  into the spectrometer  105 . In an alternative embodiment, as illustrated in  FIG. 6 , a bracket  156  a series of v-shaped grooves  158   n  forming a saw-tooth pattern. Each signal-bearing output fiber  116   1 - 116   7  is positioned in a v-shaped groove  158   n  with center-to-center spacing between adjacent fibers  161   1 - 116   7  chosen to minimize cross talk between adjacent fibers  116   1 - 116   7 . The v-shaped grooves  158   n  locate and space the fibers  116   n  without the need for spacer fibers  134   x .  
         [0030]     Many other possible embodiments are possible. In other embodiments, for example, there are only two light paths  104   1  and  104   2  having two samples locations  120   1  and  120   2 , respectively. In this embodiment, one sample location  120   1  contains the sample to be examined and the second sample location  120   2  contains a reference sample that is used to normalize the signal from the first light path. In this embodiment, the second end  126   1  of the first output optical fiber  116   1  is adjacent to a first slit, and the second end  126   2  of the second output optical fiber  116   2  is adjacent to a second slit. The second ends  126   1  and  126   2  of the output optical fibers  116   1  and  116   2  are equidistant from the x-axis. A one-dimensional photo-detector array (1D-PDA) is used to record images from the spectra output from the two output optical fibers  116   1  and  116   2 , with one image formed on one half of the 1D-PDA and the other image formed on the other half of the 1D-PDA. An example of a spectrometer with a 1D-PDA capable of simultaneously recording two images is the model MD5 spectrometer manufactured by Headwall Photonics, Inc. of Fitchburg, Mass.  
         [0031]     The various embodiments described above are provided by way of illustration only and should not be construed to limit the following claims. Those skilled in the art will readily recognize various modifications and changes that may be made without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the disclosure and the following claims.