Method for calibrating spectrophotometric apparatus

• US 6,611,777 B2
• Filed: 06/07/2001
• Issued: 08/26/2003
• Est. Priority Date: 11/23/1999
• Status: Expired due to Term

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Spectromedical Inc.
• Inventors: Samsoondar, James
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): BHAT, ADITYA S
• Application Number:
  US09/875,227
• Publication Number:
  US 20030078746A1
• Time in Patent Office: 810 Days
• Field of Search: 702/104, 702/30, 702/22-28, 600/310, 356/39, 356/40, 356/42, 356/432, 356/433, 356/436, 356/437, 356/244, 435/7.1, 436/22, 436/66, 436/171
• US Class Current: 702/104
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/4785 Standardising light scatter apparatus; Standards therefor

Abstract

Described is a method for calibrating a spectrophometric apparatus and determining the concentration of an analyte in a sample. This method involves incorporating at least one primary calibration algorithm that uses an order of derivative of absorbance obtained for at least one of a standard set of wavelengths, on a second apparatus. The absorbance values of the sample are measured on the second apparatus at three or more wavelengths from a wavelength calibration table. Interpolated absorbance values are derived from the measured absorbance values for wavelengths from a standard set of wavelengths. A derivative of the interpolated absorbance values is obtained, using the same order of derivative used by the first apparatus. Followed by calculating a concentration of the Analyte in the sample, by applying the Primary Calibration Algorithm to the derivative. The present invention also provides for a medium storing instructions adapted to be executed by a processor to determine analyte concentration within a sample, as defined by the above method.

Claims

1. A method of determining the concentration of an Analyte in a Sample in a second apparatus comprising:

(i) incorporating at least one primary calibration algorithm that uses an order of derivative of absorbance obtained for at least one of a standard set of wavelengths, on said second apparatus;

(ii) measuring absorbance values of said sample at three or more wavelengths from a wavelength calibration table on said second apparatus;

(iii) determining interpolated absorbance values from said absorbance values for wavelengths from a standard set of wavelengths;

(iv) obtaining a derivative of said interpolated absorbance values, using said order of derivative; and

(v) calculating a concentration of said Analyte in said sample, by applying said Primary Calibration Algorithm to said derivative.

2. The method of claim 1, wherein in said step of incorporating (step (i)), and wherein in said step of measuring (step (ii)), said standard set of wavelengths is a set of approximate wavelengths derived from a wavelength calibration table of a first apparatus, said second apparatus, or both a first and said second apparatus.

3. The method according to claim 2, wherein said wavelength calibration table for a first apparatus, or said second apparatus is obtained by:

(i) projecting a first electromagnetic radiation of known wavelength, onto a first pixel of a first linear diode array of a first apparatus, or a second linear diode array of said second apparatus;

(ii) using a second electromagnetic radiation of known wavelength, said second electromagnetic radiation having a different wavelength than said first electromagnetic radiation, projecting said second electromagnetic radiation onto a second pixel of said first or said second linear diode array;

(iii) identifying said first and second pixels within said first or said second linear diode array;

(iv) calculating a pixeldispersion for said first or said second linear diode array; and

(v) assigning a wavelength to each pixel within said first or said second linear diode array to produce said wavelength calibration table using said pixeldispersion and either said first electromagnetic radiation of known wavelength, and said first pixel, or said second electromagnetic radiation of known wavelength and said second pixel.

4. The method according to claim 2 wherein said wavelength calibration table for a first apparatus or a second apparatus is obtained by:

(a) projecting a known wavelength of electromagnetic radiation, onto a pixel in a linear diode array;

(b) identifying pixel number of said pixel;

(c) assigning a wavelength to each pixel within said linear diode array to produce said wavelength calibration table using a predetermined pixeldispersion, said known wavelength of electromagnetic radiation, and said pixel number.

5. The method according to claim 4, wherein said steps of projecting (step (a)), identifying (step (b)) and assigning (step (c)) are repeated on said second apparatus, and wherein said electromagnetic radiation of known wavelength is projected onto a pixel of a second linear diode array of said second apparatus having said pixel number, whereby said first apparatus and said second apparatus produce said wavelength calibration table, and said wavelength calibration table is used as a standard set of wavelengths.

6. The method according to claim 4, wherein said steps of projecting (step (a)), identifying (step (b)), and assigning (step (c)) are repeated on said second apparatus, and wherein said electromagnetic radiation of known wavelength is projected onto a pixel of a second linear diode array of said second apparatus, having a different pixel number.

7. The method according to claim 6, wherein said standard set of wavelengths is obtained by:

(A) establishing a set of wavelengths common to said wavelength calibration table of both said first and said second apparatus; and

(B) selecting a range of wavelengths of said set of wavelengths, said range of wavelengths having wavelengths belonging to said standard set of wavelengths.

8. The method according to claim 4, wherein in said step of identifying (step (b)), an incorrect pixel is identified, said incorrect pixel is within less than or equal to about ±

N pixel, where, N is a number of pixels that encompass a range of wavelengths of no more than about 20 nm.

9. The method of claim 8 wherein said range of wavelengths is about ±

10 nm.

10. The method of claim 8 wherein said range of wavelengths is about ±

5 nm.

11. The method of claim 8 wherein said range of wavelengths is about ±

2 nm.

12. The method according to claim 2, wherein in said step of incorporating (step (i)), the at least one of a standard set of wavelengths is an optimized primary calibration wavelength, and derived from at least two or more apparatus.

13. The method according to claim 12, wherein said optimized primary calibration wavelength is selected by visual examination of a derivative of absorbance spectra, and one or more wavelength(s) that exhibits changes in the derivative absorbance as a function of analyte concentration and which also exhibits a low variability in the derivative of absorbance between apparatus for a given analyte concentration, is selected for each said optimized calibration wavelength.

14. The method according to claim 12, wherein said optimized primary calibration wavelength is selected by the steps comprising:

(A) obtaining a first set of interpolated absorbance measurements of a set of primary calibration samples from a first apparatus and one or more second apparatus; and

(B) including said set of interpolated absorbance measurements (step (i)) in a primary calibration set used to select one or more optimal wavelength(s) for use in developing said at least one primary calibration algorithm, by a process of step-wise multiple linear regression to derive said optimized primary calibration wavelength.

15. The method according to claim 14 wherein in said step of obtaining (step A)), only the data from said First Apparatus is used to develop the primary calibration algorithm at said optimized wavelength(s).

16. The method according to claim 15, wherein said absorbance data and variability in said selected wavelengths of said more than one apparatus is included in said primary calibration algorithm.

17. A medium storing instructions adapted to be executed by a processor to determine analyte concentration within a sample, as defined by the method of claim 1, said instructions comprising

i) said at least one primary calibration algorithm;

ii) identity of first apparatus used to obtain said at least one primary calibration algorithm.

32. The method of claim 1, wherein said second apparatus comprises a second linear diode array comprising the same number of pixels as a first linear diode array in a first apparatus.

64. The method of claim 1, wherein in said step of incorporating (step (i)), and in said step of obtaining (step (iv)), said order of derivative of absorbance is of a first, second, or third order.

65. The method of claim 64, wherein a statistical technique selected from the group consisting of simple linear regression, multiple linear regression, partial least squares, and principal component analysis, is used to process absorbance measurements for the determination of said at least one primary calibration algorithm.

66. The method of claim 1, wherein said standard set of wavelengths comprises wavelengths from about 300 nm to about 2500 nm.

67. The method of claim 1, wherein said standard set of wavelengths comprises wavelengths from about 500 nm to about 1100 nm.

68. The method according to claim 1, wherein said sample is placed in a like vessel having optical properties substantially similar to that used for the primary calibration.

69. The method according to claim 68, wherein said vessel is selected from the group consisting of a pipette tip, a labeled test tube, an unlabeled test tube, blood bag tubing, a transparent sample container, and a translucent sample container.

70. The method according to claim 1, wherein said sample is any biological or non-biological fluid, and said analyte is any substance in said sample for which an absorbance measurement can be obtained.

71. The method according to claim 1, wherein said sample is a solid, and said analyte is any substance in said sample for which an absorbance measurement can be obtained.

72. The method of claim 1, wherein in said step of determining (step (iii)), photometric correction is performed.

73. The method according to claim 1, wherein, in said step of incorporating (step (i)), a wavelength calibration table for a first apparatus or said wavelength calibration table for said second apparatus is obtained by:

(i) projecting a first electromagnetic radiation of known wavelength, onto a first pixel of a first linear diode array of a first apparatus, or a second linear diode array of said second apparatus;

(ii) using a second electromagnetic radiation of known wavelength, said second electromagnetic radiation having a different wavelength than said first electromagnetic radiation, projecting said second electromagnetic radiation onto a second pixel of said first or said second linear diode array;

(iii) identifying said first and second pixels within said first or said second linear diode array;

(iv) calculating a pixeldispersion for said first or said second linear diode array; and

(v) assigning a wavelength to each pixel within said first or said second linear diode array to produce said wavelength calibration table using said pixeldispersion and either said first electromagnetic radiation of known wavelength, and said first pixel, or said second electromagnetic radiation of known wavelength and said second pixel.

74. The method according to claim 1, wherein, in said step of incorporating (step (i)), a wavelength calibration table for a first apparatus or said wavelength calibration table for said second apparatus is obtained by:

(a) projecting a known wavelength of electromagnetic radiation, onto a pixel in a linear diode array of a first apparatus, or said second apparatus;

(b) identifying pixel number of said pixel;

(c) assigning a wavelength to each pixel within said linear diode array to produce said first, second, or both said first and said second wavelength calibration table using a predetermined pixeldispersion, said known wavelength of electromagnetic radiation, and said pixel number.

18. A method of determining the concentration of an Analyte in a Sample in a second apparatus comprising:

(i) incorporating at least one primary calibration algorithm that uses an order of derivative of absorbance obtained for at least one of a standard set of wavelengths, on said second apparatus, where wavelengths of said standard set of wavelengths are the same as wavelengths of a wavelength calibration table on said second apparatus;

(ii) measuring absorbance values of said sample at two or more wavelengths from the wavelength calibration table on said second apparatus;

(iii) obtaining a derivative of said absorbance values, using said order of derivative; and

(iv) calculating a concentration of said Analyte in said sample, by applying said Primary Calibration Algorithm to said derivative.

19. A method of determining concentration of one or more Analytes in a Sample in a second apparatus having a second linear diode array detector that contains the same number of pixels as a first linear diode array in a first apparatus, said method comprising,

(i) incorporating at least one primary calibration algorithm from said first apparatus, that uses an order of derivative of absorbance obtained for at least one of a standard set of wavelengths, onto said second apparatus;

(ii) measuring absorbance values of said sample at two or more wavelengths on said second apparatus;

(iii) obtaining a derivative of said absorbance values, using said order of derivative; and

(iv) calculating a concentration of said one or more Analyte in said sample, by applying said one or more Primary Calibration Algorithms to said derivative.

20. A method according to claim 19, wherein at least one pixel on said first linear diode array is aligned within ±

20 nm of a same pixel on said second linear diode array, said first and said second linear diode array having a similar pixeldispersion.

21. A method according to claim 19, wherein at least one pixel on said first linear diode array is aligned within ±

10 nm of a same pixel on said second linear diode array, said first and said second linear diode array having a similar pixeldispersion.

22. A method according to claim 19, wherein at least one pixel on said first linear diode array is aligned within ±

5 nm of a same pixel on said second linear diode array, said first and said second linear diode array having a similar pixeldispersion.

23. A method according to claim 19, wherein at least one pixel on said first linear diode array is aligned within ±

2 nm of a same pixel on said second linear diode array, said first and said second linear diode array having a similar pixeldispersion.

24. The method according to claim 19, wherein in said step of incorporating (step (i)), and in said step of obtaining (step (iii)), said order of derivative, is of a first, second, or third order.

25. The method according to claim 19, wherein a statistical technique selected from the group consisting of simple linear regression, multiple linear regression, partial least squares, and principal component analysis, is used to process absorbance measurements for the determination of said at least one primary calibration algorithm.

26. The method according to claim 19, wherein, in said step of measuring (step (ii)), Photometric Correction is performed.

27. A method of determining the concentration of an Analyte in a Sample in a second apparatus comprising:

(i) incorporating at least one primary calibration algorithm that uses an order of derivative of absorbance obtained for at least one of a standard set of wavelengths, on said second apparatus;

(ii) measuring absorbance values of said sample at two or more wavelengths from said standard set of wavelengths on said second apparatus;

(iii) obtaining a derivative of said absorbance values, using said order of derivative; and

(iv) calculating a concentration of said Analyte in said sample, by applying said Primary Calibration Algorithm to said derivative.

28. The method according to claim 27, wherein in said step of incorporating (step (i)), said standard set of wavelengths comprises wavelengths that are common to a wavelength calibration table of both a first apparatus used to obtain said primary calibration algorithm, and said second apparatus.

29. The method according to claim 27, wherein in said step of incorporating (step (i)), and in said step of obtaining (step (iii)), said order of derivative, is of a first, second, or third order.

30. The method according to claim 29, wherein a statistical technique selected from the group consisting of simple linear regression, multiple linear regression, partial least squares, and principal component analysis, is used to process absorbance measurements for the determination of said at least one primary calibration algorithm.

31. The method according to claim 27, wherein, in said step of measuring (step (ii)), Photometric Correction is performed.

33. A method of determining the concentration of an Analyte in a Sample in a second apparatus comprising:

(i) incorporating at least one primary calibration algorithm on said second apparatus, said at least one primary calibration algorithm developed using a primary calibration set on a first apparatus, for at least one of a standard set of wavelengths;

(ii) measuring an absorbance of said sample for at least one wavelength from said standard set of wavelengths on said second apparatus;

(iii) calculating a concentration of said Analyte in said sample, by applying said Primary Calibration Algorithm to said absorbance obtained in step (ii).

34. The method of claim 33, wherein in said step of incorporating (step (i)), a statistical technique selected from the group consisting of simple linear regression, multiple linear regression, partial least squares, and principal component analysis, is used to process absorbance measurements of said primary calibration set for the determination of said at least one primary calibration algorithm.

35. The method of claim 34, wherein said statistical technique includes data preprocessing of smoothing of absorbance, or obtaining an order of derivative of absorbance, or a combination of smoothing and obtaining an order of derivative of absorbance.

36. The method of claim 35, wherein said order of derivative of absorbance is of a first, second, or third order.

37. The method of claim 33, wherein said standard set of wavelengths comprises wavelengths from about 300 nm to about 2500 nm.

38. The method of claim 33, wherein said standard set of wavelengths comprises wavelengths from about 500 nm to about 1100 nm.

39. The method according to claim 33, wherein said sample is placed in a like vessel having optical properties substantially similar to that used for the primary calibration.

40. The method according to claim 39, wherein said vessel is selected from the group consisting of a pipette tip, a labeled test tube, an unlabeled test tube, blood bag tubing, a transparent sample container, and a translucent sample container.

41. The method according to claim 33, wherein said sample is any biological or non-biological fluid, and said analyte is any substance in said sample for which an absorbance measurement can be obtained.

42. The method according to claim 33, wherein said sample is a solid, and said analyte is any substance in said sample for which an absorbance measurement can be obtained.

43. The method of claim 33, wherein in said step of measuring (step (ii)), photometric correction is performed.

44. The method according to claim 33, wherein in said steps of incorporating (step (i)), and measuring (step (ii)), said standard set of wavelengths is obtained by creating a table of approximate wavelengths derived from a first, a second or both said first and said second wavelength calibration table, wherein a pixel number of a linear diode array of said first apparatus and a pixel number of a second linear diode array of said second apparatus must be within less than or equal to about ±

N pixel of a reference pixel number of said first apparatus, where, N is a number of pixels that encompass a range of wavelengths of no more than about ±

20 nm, wherein said reference pixel number of said first apparatus is associated with a known wavelength of electromagnetic radiation.

45. The method according to claim 44, wherein said wavelength calibration table for said first apparatus or said second apparatus is obtained by:

(i) projecting a first electromagnetic radiation of known wavelength, onto a first pixel of a first linear diode array of said first apparatus, or a second linear diode array of said second apparatus;

(ii) using a second electromagnetic radiation of known wavelength, said second electromagnetic radiation having a different wavelength than said first electromagnetic radiation, projecting said second electromagnetic radiation onto a second pixel of said first or said second linear diode array;

(iii) identifying said first and second pixels within said first or said second linear diode array;

(iv) calculating a pixeldispersion for said first or said second linear diode array; and

(v) assigning a wavelength to each pixel within said first or said second linear diode array to produce said wavelength calibration table using said pixeldispersion and either said first electromagnetic radiation of known wavelength, and said first pixel, or said second electromagnetic radiation of known wavelength and said second pixel.

46. The method according to claim 44, wherein said wavelength calibration table for said first or said second apparatus is obtained by:

(a) projecting a known wavelength of electromagnetic radiation, onto a pixel in a linear diode array of said first apparatus, or said second apparatus;

(b) identifying pixel number of said pixel; and

(c) assigning a wavelength to each pixel within said linear diode array to produce said first, second, or both said first and said second wavelength calibration table using a predetermined pixeldispersion, said known wavelength of electromagnetic radiation, and said pixel number.

47. The method according to claim 44, wherein said range of wavelengths is about ±

20 nm.

48. The method according to claim 44, wherein said range of wavelengths is about ±

10 nm.

49. The method according to claim 44, wherein said range of wavelengths is about ±

5 nm.

50. The method according to claim 44, wherein said range of wavelengths is about ±

2 nm.

51. A method of determining the concentration of an Analyte in a Sample in a second apparatus comprising:

(i) incorporating at least one primary calibration algorithm on said second apparatus, said at least one primary calibration algorithm developed using a primary calibration set on a first apparatus, for at least one of a standard set of wavelengths;

(ii) measuring an absorbance of said sample for two or more wavelengths from a wavelength calibration table on said second apparatus;

(iii) determining interpolated absorbance values from said second absorbance obtained in (step (ii)), for wavelengths from said standard set of wavelengths; and

(iv) calculating a concentration of said Analyte in said sample, by applying said Primary Calibration Algorithm to said interpolated absorbance.

52. The method of claim 51, wherein in said step of incorporating (step (i)), a statistical technique selected from the group consisting of simple linear regression, multiple linear regression, partial least squares, and principal component analysis, is used to process absorbance measurements of said primary calibration set for the determination of said at least one primary calibration algorithm.

53. The method of claim 52, wherein said statistical technique includes data preprocessing of smoothing of absorbance, or obtaining an order of derivative of absorbance, or a combination of smoothing and obtaining an order of derivative of absorbance.

54. The method of claim 53, wherein said order of derivative of absorbance is of a first, second, or third order.

55. The method of claim 51, wherein said standard set of wavelengths comprises wavelengths from about 300 nm to about 2500 nm.

56. The method of claim 51, wherein said standard set of wavelengths comprises wavelengths from about 500 nm to about 1100 nm.

57. The method according to claim 51, wherein said sample is placed in a like vessel having optical properties substantially similar to that used for the primary calibration.

58. The method according to claim 57, wherein said vessel is selected from the group consisting of a pipette tip, a labeled test tube, an unlabeled test tube, blood bag tubing, a transparent sample container, and a translucent sample container.

59. The method according to claim 51, wherein said sample is any biological or non-biological fluid, and said analyte is any substance in said sample for which an absorbance measurement can be obtained.

60. The method according to claim 51, wherein said sample is a solid, and said analyte is any substance in said sample for which an absorbance measurement can be obtained.

61. The method of claim 51, wherein in said step of determining (step (iii)), photometric correction is performed.

62. The method according to claim 51, wherein, in said step of incorporating (step (i)), a wavelength calibration table for said first apparatus or said wavelength calibration table for said second apparatus is obtained by:

(i) projecting a first electromagnetic radiation of known wavelength, onto a first pixel of a first linear diode array of said first apparatus, or a second linear diode array of said second apparatus;

(ii) using a second electromagnetic radiation of known wavelength, said second electromagnetic radiation having a different wavelength than said first electromagnetic radiation, projecting said second electromagnetic radiation onto a second pixel of said first or said second linear diode array;

(iii) identifying said first and second pixels within said first or said second linear diode array;

(iv) calculating a pixeldispersion for said first or said second linear diode array; and

(v) assigning a wavelength to each pixel within said first or said second linear diode array to produce said wavelength calibration table using said pixeldispersion and either said first electromagnetic radiation of known wavelength, and said first pixel, or said second electromagnetic radiation of known wavelength and said second pixel.

63. The method according to claim 51, wherein, in said step of incorporating (step (i)), a wavelength calibration table for said first apparatus or said wavelength calibration table for said second apparatus is obtained by:

(a) projecting a known wavelength of electromagnetic radiation, onto a pixel in a linear diode array of said first apparatus, or said second apparatus;

(b) identifying pixel number of said pixel; and

(c) assigning a wavelength to each pixel within said linear diode array to produce said first, second, or both said first and said second wavelength calibration table using a predetermined pixeldispersion, said known wavelength of electromagnetic radiation, and said pixel number.