Apparatus and Method for Measuring Components in Fluidic Samples Sealed in a Bag

Abstract

The present invention discloses an apparatus and a method for measuring components in fluidic samples in a non-invasive fashion using Infrared (IR) transmission spectroscopy. Fluidic samples are sealed in flexible IR-transparent bags that are then fixed on a supporting bed. The supporting bed is then mounted between the front and back plates of the apparatus so that the bag is squeezed by two IR transparent windows from opposite directions until the windows contact the spacer sheet mounted on the back plate. The thickness of the spacer sets the gap distance between the two windows and thereby sets the optical path for the measurement in the transmissive mode.

Claims

1. An apparatus for analyzing fluid samples using the transmission spectroscopy of electromagnetic radiations, comprising: (a) A supporting bed for holding a sample bag to a fixed position on said supporting bed so as to prevent said bag from slipping or deforming; (b) A back plate for holding said supporting bed at the fixed position; (c) A front plate for holding said supporting bed at the fixed position;

2. Said apparatus of claim 1 in which said supporting bed is sandwiched between said front plate and said back plate. Said front plate and said back plate are fastened so that said supporting bed is squeezed by said front plate and said back plate from two opposite directions.

3. Said apparatus of claim 2 employs means for fastening said front plate and said back plate. Said means of fastening includes bolts, spring-loaded wires, spring-loaded clip, glue, friction force, and magnetic force.

4. Said apparatus of claim 1 in which said supporting bed has a void in the center so that the beam of electromagnetic radiations can pass. Said supporting bed also has four holes in four corners for aligning said supporting bed with said back plate.

5. Said apparatus of claim 1 in which said back plate comprises a back chassis, a window holder, and a piece of window.

6. Said window of claim 5 is made of materials with low absorption of said electromagnetic radiations.

7. Said window holder of claim 5 is made of elastomer. Said window of claim 5 is mounted in said window holder.

8. Said back chassis of claim 5 has a void in the center so that said windows holder in claim 5 is mounted in said void.

9. Said back chassis of claim 5 has four posts perpendicular to said back chassis surface. Said posts align to said holes of claim 4 when said supporting bed in claim 1 is pushed toward said back plate of claim 1 so that said supporting bed is held in a fixed position.

10. Said apparatus of claim 1 in which said front plate comprises a front chassis, a window holder, and a piece of window.

11. Said window of claim 10 is made of materials with low absorption of said electromagnetic radiations.

12. Said window holder of claim 10 is made of elastomer. Said window of claim 10 is mounted in said window holder.

13. Said front chassis of claim 10 has a void in the center so that said windows holder in claim 10 is mounted in said void.

14. Said apparatus of claim 1 employs a pair of sheet spacers to set the optical path before obtaining the transmission spectroscopy of said electromagnetic radiations. Said sheet spacers are flat sheet with pre-determined thickness. Said sheet spacer in each pair has identical thickness. Said pair of spacers is placed on the upper and lower section of said void of claim 4, respectively. In operation, said back plate, said supporting bed, and said front plate are fastened against each other. Said pair of sheet spacers is sandwiched between said window of claim 5 and said window of claim 10. Therefore, the distance between said window of claim 5 and said window of claim 10 is the thickness of said sheet spacer, which sets the optical path. A series of sheet spacer pairs with different thickness is available to set the optical path to different values. Therefore, said apparatus of claim 1 sets optical path to a series of pre-determined values with no need for adjustment and calibration.

15. Said sheet spacers of claim 14 can be cut into a plural of pieces or joined together to form a one-piece sheet spacer.

16. A bag for holding fluidic sample in the transmission measurement of electromagnetic radiations.

17. Said bag of claim 16 is made of a flexible film that has a low absorption in one or a plural of bands of said electromagnetic radiations.

18. Said bag of claim 16 has four holes in its four corners. Said poles of claim 9 are inserted into said holes, so that said bag is fixed on said apparatus.

19. Said bag of claim 16 comprises one or a plural of port sections, one or a plural of neck sections, and one cell section. Said port is a wide mouth that receives the fluid sample. Said neck provides a narrow channel that leads fluid to cell section. Said cell holds fluid. Said electromagnetic radiation passes through said cell, interacts with the fluid holding inside said bag before it reaches the detector.

20. A method for rapid loading and unloading fluid samples in a spectrometer that operates in transmission mode of electromagnetic radiation, comprising steps of: a. Fluid sample is injected into said bag of claim 17, via said port of said bag so that said fluid is accumulated in said cell section. b. Bag walls of said cell are squeezed from opposite directions so that fluid level in said cell reaches to said neck section. c. Said bag is closed at the jointing section between said cell and said neck by means of sealing, which includes thermos-fusing, glue, clip-holding, stitching with wires, tie with wires, bending, or combination of heretofore means. Next, said bag is closed again at the jointing section between said neck and said port. d. Said sealed bag is placed on said support bed of claim 1. e. Said pair of sheet spacers is positioned on said support bed to set optical path. f. Said back plate of claim 1, said supporting bed of claim 1, said sealed bag, said front plate of claim 1 are fastened together. g. Said apparatus of claim 1 is mounted in a spectrometer for measurement. h. After measurement, said apparatus of claim 1 is un-fastened and said bag is removed.

Description

5. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG. 1 is the exploded view of the apparatus.

[0045] FIG. 2a. The exploded view of the back plate, from right side

[0046] FIG. 2b. The exploded view of the back plate, from left side

[0047] FIG. 3 The exploded view of the supporting bed

[0048] FIG. 4. The exploded view of the front plate, from left side

[0049] FIG. 5 The layout of the sample bag

[0050] FIG. 6 The scheme for loading and sealing liquid sample into the bag [0051] a) Inject fluid sample into the bag via the port section; b) After fluid is accumulated in the cell section, squeeze the bag; c) The bag is squeezed until the liquid reaches the neck section; d) and e) The bag is then sealed.

[0052] FIG. 7 The scheme illustrating the process of installing a sample bag onto the apparatus [0053] a. Select the correct pair of spacer sheet to set the optical path, and then mount the supporting bed to the back plate through the guiding posts. [0054] b. Mount the bag onto the supporting bed through the guiding posts [0055] c. Install the front plate [0056] d. The apparatus with the sample installed, ready to be measured.

[0057] FIG. 8 The process of inserting the apparatus into a generic sample holder inside a spectrometer [0058] a. Slide the apparatus down [0059] b. The apparatus in position for measurement inside the spectrometer

[0060] FIG. 9 IR peak area of a series of sucrose solutions and their linear relationship with concentration [0061] (a) IR transmission spectra of sucrose solutions with different concentrations (spectral range 1300-1000 cm.sup.1), the samples were in polyethylene bags with a constant OP of 25 m. (b) Sucrose concentration vs. Absorbance for the band area at 1050 cm.sup.1.

[0062] FIG. 10 IR spectra of toluene with different optical path and the relationship between the peak area and corresponding optical path

(a) IR transmission spectra of Toluene (spectral range 2200-1650 cm.sup.1)), the samples were in polyethylene bags and tested with different OP (i.e. various thick spacers) (b) Absorbance vs. Optical path curve for the band area at 1952 cm.sup.1. A least-square fitting line is plotted, and the coefficient of determination (R.sup.2=0.996) is displayed as well.

[0063] For a better understanding of the invention, reference is made to the following detailed description of the preferred embodiments which should be referenced to the herein before described drawings.

6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0064] Various aspects of the present invention will evolve from the following detailed description of the preferred embodiments thereof which should be taken in conjunction with the hereinbefore described drawings.

[0065] The invention as a whole is depicted in the drawings by reference character 10. The invention is composed of an apparatus 20 and a bag 12, which can be mounted and dismounted from 20. The apparatus 20 is shown in the drawings as including three embodiments, a front plate 22, a supporting bed 24, and a back plate 26. Referring to FIG. 1, during measurement, the flexible bag 12 is mounted on the supporting bed 24. The back plate 26, the supporting bed 24 with the mounted bag 12 and the front plate 22 are held against each other by means of fasteners, spring-loaded hinges, spring-loaded clips, clamps, magnets or friction.

[0066] FIG. 2a shows the layout of the back plate 26, which is viewed from right side. The back plate 26 is composed of a back chassis 28, a window holder 30, and a window 42. The drawing in FIG. 2b shows that the back chassis has a rectangular shape from the left viewpoint. The back chassis has two wings 34, 36 in the left and right sides of the back chassis. Wings 34, 36 are used to guide the apparatus 20 to slide into the alignment slots of standard sample holders of a spectrometer. A round hole 38 in the center of the back chassis 28 is designed for mounting windows on the back chassis 28. The window holder 30 is made of elastomer. The shape of the window holder 30 can be depicted as three fused co-axial tubes 40, 41, 44. The outside diameter of the smallest tube 40 is the same as the diameter of hole 38. Tube 40 is inserted into hole 38. Thereby the window holder 30 is mounted on the back chassis 28. Tubes 40 and 41 have the same inside diameter. The outside diameter of tube 41 and 44 are the same, which is larger than the diameter of the window 42. The inside diameter of tube 44 is same as the diameter of the window 42, but it is larger than the inside diameter of the smaller tube 40. Window 42 is held by tube 44 when it is mounted on window holder 30. Window 42 is made of materials that have a low Mid-IR absorbance such as KBr, NaCl, ZnSe, Si, CaF.sub.2 or Ge. On the back chassis 28, four posts 46, 48, 50, 52 are located around hole 30. Posts 46, 48, 50, 52 are symmetric with respect to the center of hole 30 and they are arranged in a rectangle shape. The border lines of this rectangle formed by posts 46, 48, 50, 52 are parallel to the borderlines of the back chassis 28. Posts 46, 48, 50, 52 are perpendicular to the flat surface of window 42. Posts 46, 48, 50, 52 function as the alignment guiding rods for hooking up supporting bed 24, which has four holes in the corresponding positions. Two spacer bars 54, 56 are located along the borders of the back chassis 28. Spacer bars 54 and 56 are perpendicular to the wings 34, 36. Spacer bar washers 55, 57 are on top of spacer bar 54, 56, respectively. Spacer bar washers 55, 57 are made of elastomer. There are four tapped holes 58, 60, 62, 64 on the spacer bars 54, 56. Each bar has two holes. There are four through holes 59, 61, 63, 65 on the spacer bar washer 55, 57. Each bar washer has two holes. Bolts are inserted into holes 58, 60, 62, 64 to assemble back plate 26, supporting bed 24 and front plate 22.

[0067] FIG. 3 shows the layout of supporting bed 24. Supporting bed 24 is a thin sheet with a large round cavity 66 in the center. The diameter of cavity 66 is larger than the diameter of window 42, 44. The center of cavity 66 and center of window 42 are on the same axis as tubes 40, 41, 44. Four holes 68, 70, 72, 74 are located on supporting bed 24. The distances from the centers of holes 68, 70, 72, 74 to the center of cavity 66 are the same. Lines connecting the centers of holes 68, 70, 72, 74 form a rectangle. The diameter of holes 68, 70, 72, 74 is the same as the diameter of posts 46, 48, 50, 52. The distance between the centers of holes 68, 70, 72, 74 are the same as the distance between the centers of posts 46, 48, 50, 52. Two sheet spacers 76, 78 are attached along the border lines of supporting bed 24. Sheet spacers 76, 78 adopt the same shape as spacer bars 54, 56 and are aligned in the same directions as spacer bars 54, 56. The width of sheet spacers 76, 78 determines the gap between sheet spacer 76, 78. This gap is designed to be smaller than the diameter of window 42. Sheet spacers 76, 78 are designed to set the optical path, which have exactly the same thickness and their thickness determines the distance between windows 42, 84 when they are pushed against each other from opposite directions. Sheet spacers 76, 78 are made of ultra-flat sheet with a series of standard thickness such as 10 m, 20 m, 30 m, 50 m, 100 m, 200 m and so on. By choosing a pair of sheet spacers 76, 78 with designated thickness, the optical path is set accordingly.

[0068] The front plate 22 is composed of a front chassis 80, a window holder 82, and a window 84. The drawing of 80 in FIG. 4 shows that the front chassis has a rectangular shape. Window holder 82 is the same as window holder 30. Window 84 is identical to window 42. Front chassis 80, window holder 82, and window 84 are mounted in the same way as the assembly of back chassis 28, window holder 30, and window 42. Four through holes 86, 88, 90, 92 are located at the four corners of front chassis 80. The diameter of holes 86, 88, 90, 92 is the same as the diameter of holes 58, 60, 62, 64. Four bolts are inserted into holes 86, 88, 90, 92, and are fastened in holes 58, 60, 62, 64, respectively.

[0069] The shape of bag 12 is illustrated in FIG. 5. The bag is formed by fusing two pieces of thin film together. The means of fusing includes thermos-fusing, press-fusing, adhesive glue, or stitching by wires. Four holes 94, 96, 98, 100 are located on the four corners of the bag. The diameter of holes 94, 96, 98, 100 is the same as the diameter of posts 46, 48, 50, 52. The liquid-holding section of bag 12 is composed of a port 102, a neck 104 and a cell 106.

7. DESCRIPTION OF OPERATION

[0070] Loading Liquid into the Bag

[0071] The loading process is illustrated in FIG. 6. Bag 12 is placed in the direction that port 102 is up, and cell 106 is down. A pre-determined amount of liquid sample is injected into bag 12 through the opening port 102. Next, cell 106 is squeezed gently from the two window areas so that the liquid meniscus inside bag 12 reaches to neck 104. Then a means of sealing, such as thin plastic film thermal sealer, clamps, clip, magnate, glue or stitch, is used to close the bag at port 102 section. The sealing can be conducted once or multiple times at different positions in port 102 section so that no air is remained in the sealed bag. The volume of bag 12 is zero before liquid is injected and the flexible thin film is fully extended with no tension. After liquid injection, because of the volume of liquid sealed in bag 12, bag 12 forms a positive curvature over cell 106.

Mounting the Sealed Bag on Back Plate 26

[0072] Four posts 46, 48, 50, 52 on the back chassis 28, four holes 68, 70, 74, 72 on supporting bed 24, and holes 96, 100, 98, 94 on bag 12 are aligned according to FIG. 7. Next, supporting bed 24 is pushed to let posts 46, 48, 50, 52 inserted into corresponding holes 68, 70, 74, 72 so that supporting bed 24 is fixed on back chassis 28. Next, bag 12 is pushed to let posts 46, 48, 50, 52 inserted into corresponding holes so that bag 12 is fixed to avoid bag slippage and bag collapse.

Assembling the Apparatus 20

[0073] Front plate 22 is pushed against back plate 26. A typical means of pushing is to use four long bolts to fasten front plate 22 and back plate 26. Four threaded bolts are inserted into through holes 86, 88, 90, 92 on front plate 22, then into four through holes 61, 59, 65, 63 on spacer bar washers 55, 57 and ended in tapped holes 60, 58, 64, 62 on back plate 26.

[0074] Because front plate 22 is pushed against back plate 26, window 42 and window 84 are moved against each other until window 42 and window 84 contact sheet spacers 76, 78. Sheet spacers 76, 78 are sandwiched between windows 42 and 84. A further pushing of windows 42 and 84 causes the elastomer window holders 30, 82 to deform. The elastic deformation of windows holders 30, 82 maintains the distance between windows 42 and 84 and prevents the window from cracking due to excessive pushing forces.

Installing the Apparatus into Spectrometer

[0075] FIG. 8 shows that apparatus 20 is inserted into the standard sample holder in a generic spectrometer by aligning wings 34, 36 of apparatus 20 with the slots in the sample holder and then slide the apparatus into the sample holder. A beam of electromagnetic radiation then passes through the sample loaded inside bag 12 and reaches the detector.

[0076] It will be understood by those skilled in the art that while an embodiment of the invention was disclosed in considerable detail for purposes of illustration, many of these details may be varied without departing from the spirit and scope of the invention.

8. EXAMPLES OF APPLICATION

Example 1

Determine the Sucrose Concentration of Regular Coca-Cola.

[0077] Six standard solutions containing 0%, 2%, 5%, 10%, 15% and 20% w/w sucrose in distilled water are prepared. These solutions are sealed in the bag and loaded on the apparatus, respectively. The optical path is set to 25 m and the Mid-IR transmission spectra are acquired for each sample, which are shown in FIG. 9a. The band near 1050 cm.sup.1 reflects the O-C stretching in sucrose molecules, and its peak area is used to assay the concentration of sucrose. [ref. Duarte, I. F. et al Journal of Agriculture and Food Chemistry, 2002, 50, 3104-3111.] The peak area versus concentration is plotted in FIG. 9b. The fitting shows that the concentration and the corresponding peak area demonstrate a linear relationship, which follows the Lambert-Beer's law. The least square fitting of the data points in FIG. 9b yields that the coefficient of determination (R.sup.2) is 0.991, the slope is 2.230.02 and the intercept is 0.120.06. Next, a sample coca-cola with unknown sucrose content is also analyzed in the IR spectrometer using the same setup. Its peak area at 1050 cm.sup.1 is 29.5. Using the standard calibration curve plotted in FIG. 9b, we determine that the sucrose concentration in the sample coca-cola is 13.170.12% w/w.

Example 2

[0078] Demonstrate that the Absorbance of Toluene is Linearly Dependent on the Set Optical Path of the Apparatus

[0079] The Lambert-Beer's law states that the absorbance is a linear function of the optical path. In this experiment, [0080] 1. We set the optical path of the apparatus to 13 m, 75 m, 125 m, 200 m, 300 m, and 400 m; [0081] 2. We loaded toluene in sealed bag into the apparatus; [0082] 3. We measured the corresponding absorbance of toluene sealed in a bag.

[0083] The obtained toluene mid-IR spectra in the 1650 cm.sup.1-2200 cm.sup.1 range are plotted in FIG. 10a. The area of the peak at 1952 cm.sup.1 is used to represent the absorbance of toluene. We then plotted the peak area as a function of the set optical paths in FIG. 10b. The least square fitting of data points in FIG. 10b yields the coefficient of determination (R.sup.2) to be 0.996, which indicates the good linearity. Such excellent linearity of the plot demonstrates the accuracy and precision of the optical path setting mechanism of this invention.