Methods and apparatus for analysis of complex mixtures

• US 5,668,373 A
• Filed: 04/26/1996
• Issued: 09/16/1997
• Est. Priority Date: 04/26/1996
• Status: Expired due to Fees

• Current Assignee: Tufts University
• Original Assignee: Trustees of Tufts College
• Inventors: Gankin, Yuriy V., Robbat, Albert Jr.
• Primary Examiner(s): Porta, David P.
• Assistant Examiner(s): Bruce, David Vernon
• Application Number:
  US08/639,183
• Time in Patent Office: 508 Days
• Field of Search: 250/338.5, 250/339.07, 250/339.12, 250/339.08, 364/498, 364/499
• US Class Current: 250/339.12
• CPC Class Codes: G01N 1/405 by adsorption or absorption
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 30/8668 using retention times
• CPC Class Codes: H01J 49/0027 Methods for using particle spectrometers
• CPC Class Codes: H01J 49/049 with means for applying heat to desorb the sample; Evaporation

Abstract

This invention provides methods and apparatus for determining the presence or absence of a specific constituent in a mixture. The method includes the steps of (a) applying energy to the mixture to cause constituents in the mixture to produce characteristic patterns of spectral lines and detecting quantity values at the spectral lines, wherein a quantity value may represent a contribution of two or more constituents; (b) comparing detected quantity values for a number N of spectral lines from a pattern of spectral lines characteristic of the specific constituent with known quantity values for the N spectral lines; (c) determining whether the detected quantity values for the N spectral lines fall within a predetermined error range, and; (d) determining the presence of the constituent in the mixture when detected quantity values of a number of spectral lines less than N fall within the predetermined error range.

Claims

1. An apparatus for determining the presence or absence of a specific constituent in a mixture, said apparatus comprising

(a) an energy source arranged to apply energy to the mixture to cause constituents in the mixture to absorb, emit, or fluoresce particles of energy;

(b) a spectral separation unit arranged to separate said particles of energy into patterns of spectral lines, wherein each line represents one particle, the size of each line represents the quantity of each type of particle, and each pattern of spectral lines is characteristic for one constituent, and wherein a quantity value may represent a contribution of two or more constituents;

(c) a detector arranged to detect the particles and produce data representing said patterns of spectral lines;

(d) a memory arranged to store the data, a library containing a known set of ratios for spectral lines of a pattern characteristic of said constituent, and predetermined error ranges; and

(e) a processor arranged to analyze the data, wherein the processor is programmed to;

(f)(i) calculate a set of relationships R_N of detected quantity values for a number N of spectral lines within a pattern characteristic of said specific constituent;

(f)(ii) compare relationships R_N with a known set of relationships for said N spectral lines of said constituent in a library, wherein correspondence of said relationships R_N to said known library relationships within a predetermined error range is taken to indicate that said constituent is present in the mixture;

wherein if said relationships R_N do not correspond to said known library relationships within said error range,

(g)(i) select a first subset N_s of N spectral lines wherein N_s is less than N;

(g)(ii) calculate a set of relationships R_S of detected quantity values for said N_s spectral lines in said first subset;

(g)(iii) compare said first subset relationships to said library relationships and record a first subset variation value based on variations between the first subset relationships and said library relationships;

(g)(iv) repeat said selecting, calculating, and comparing steps (i-iii) for different subsets N_s of N spectral lines, and record a variation value for each subset; and

(g)(v) determine if a subset has a variation value within a predetermined error range and if so, using said subset to indicate that said specific constituent is present in the mixture.

2. An apparatus of claim 1, wherein said relationships are ratios between detected quantity values of spectral lines.

3. A method for determining the presence or absence of a specific constituent in a mixture, said method comprising

(a) applying energy to the mixture to cause constituents in the mixture to produce characteristic patterns of spectral lines and detecting quantity values at said spectral lines, wherein a quantity value may represent a contribution of two or more constituents;

(b) calculating a set of relationships R_N of detected quantity values for a number N of spectral lines within a pattern characteristic of said specific constituent;

(c) comparing relationships R_N with a known set of relationships for said N spectral lines of said constituent in a library, wherein correspondence of said relationships R_N to said known library relationships within a predetermined error range is taken to indicate that said constituent is present in the mixture;

wherein if said relationships R_N do not correspond to said known library relationships within said error range,

(d)(i) selecting a first subset N_s of N spectral lines wherein N_s is less than N;

(d)(ii) calculating a set of relationships R_S of detected quantity values for said N_s spectral lines in said first subset;

(d)(iii) comparing said first subset relationships to said library relationships and recording a first subset variation value based on variations between the first subset relationships and said library relationships;

(d)(iv) repeating said selecting, calculating, and comparing steps (i-iii) for different subsets N_s of N spectral lines, and recording a variation value for each subset; and

(d)(v) determining if a subset has a variation value within a predetermined error range and if so, using said subset to indicate that said specific constituent is present in the mixture.

4. A method of claim 3, wherein step (d)(v) is achieved by determining the subset with the minimum variation values, wherein a minimum variation value within said predetermined error range is taken to indicate that said specific constituent is present in the mixture.

5. A method of claim 3, wherein in step (c), the constituent is indicated to be present in the mixture if sets of relationships of less than N spectral lines correspond to said known library relationships within a predetermined error range.

6. A method of claim 3, wherein in step (c), the constituent is indicated to be present in the mixture if sets of relationships of less than N but greater than N/2 spectral lines correspond to said known library relationships within a predetermined error range.

7. A method of claim 3, wherein said relationships are ratios between detected quantity values of spectral lines.

8. A method of claim 3, further comprising determining the concentration of said constituent in the mixture, said method comprising selecting a spectral line having the highest quantity value of said N spectral lines used to indicate the presence of said constituent, and using said quantity value as an indication of the concentration of the constituent in the mixture.

9. A method of claim 3, wherein, if a spectral line having the highest quantity value of said N spectral lines does not form a subset having a variation value within a predetermined error range, taking a spectral line having the second highest quantity value of said N spectral lines, and using said second highest quantity value as an indication of the concentration of the constituent in the mixture.

10. A method of claim 3, wherein, if a spectral line having the highest quantity value of said N spectral lines does not form a subset having a first variation value within a predetermined error range, and other of said N spectral lines form subsets having a variation value within a predetermined error range, correcting said highest quantity value based on said first variation value to provide a corrected quantity value, and using said corrected quantity value as an indication of the concentration of the constituent in the mixture.

11. A method of claim 3, including, prior to said comparison step (c), subtracting a background value from each detected spectral line quantity value.

12. A method of claim 3, wherein the spectral lines represent fragment ions of a constituent separated by a mass spectrometer, and the quantity value is abundance.

13. A method of claim 12, wherein said mixture is passed through a separation unit before entering a mass spectrometer, said constituent eluting from said column characteristically within a predetermined time range, and said analysis steps (b) through (d) are performed substantially only at times in which the constituent characteristically elutes from said column.

14. A method of claim 12, wherein, for a given peak in total ion current produced by a mixture input to the mass spectrometer through a separation unit, repeating said analysis at one or more different points in the peak and determining that said constituent is present in the mixture only if more than one of said analyses indicates the presence of said constituent.

15. A method of claim 14, wherein said constituent is determined to be present when the analyses indicate that the constituent is present in at least 2 of 4 different analyses of the peak.

16. A method for determining the presence or absence of a specific constituent in a mixture, said method comprising

(a) applying energy to the mixture to cause constituents in the mixture to produce characteristic patterns of spectral lines and detecting quantity values at said spectral lines, wherein a quantity value may represent a contribution of two or more constituents;

(b) comparing detected quantity values for a number N of spectral lines from a pattern of spectral lines characteristic of said specific constituent with known quantity values for said N spectral lines;

(c) determining whether the detected quantity values for said N spectral lines fall within a predetermined error range, and;

(d) determining the presence of said constituent in the mixture when detected quantity values of a number of spectral lines less than N fall within said predetermined error range.

17. A method of claim 16, wherein the spectral lines represent fragment ions of a constituent separated by a mass spectrometer, and the quantity value is abundance.

18. A method of claim 16, wherein said mixture is a solid, liquid, or gas.

19. A method of claim 18, wherein, without prior sample clean-up, the mixture is introduced into a mass spectrometer by the technique of programmed thermal desorption.

20. A method of claim 18, wherein, without prior separation, the mixture is introduced into a mass spectrometer by the technique of programmed thermal desorption.

21. A computer program for analyzing data representing patterns of spectral lines of a constituent in a mixture, wherein each line represents one particle from the constituent, the size of each line represents the quantity of each type of particle in the mixture, and each pattern of spectral lines is characteristic for one constituent, said program residing on a computer-readable medium and comprising instructions for causing a processor to:

(a) select a number N of spectral lines from a pattern characteristic of said specific constituent;

(b) calculate a set of relationships R_N of detected quantity values for said N spectral lines; and

(c) compare relationships R_N with a known set of relationships for N spectral lines of a pattern characteristic of said constituent in a library, wherein correspondence of said relationships R_N to said known library relationships within predetermined error ranges is taken to indicate that said constituent is present in the mixture;

wherein if said relationships R_N do not correspond to said known library relationships within said error ranges,

(d)(i) select a first subset N_s of N spectral lines wherein N_s is less than N;

(d)(ii) calculate a set of relationships R_S of detected quantity values for said N_s spectral lines in said first subset;

(d)(iii) compare said first subset relationships to said library relationships and record first subset variation values based on variations between the first subset relationships and said library relationships;

(d)(iv) repeat said selecting, calculating, and comparing steps (d)(i-iii) for different subsets N_s of N spectral lines, and record variation values for each subset; and

(d)(v) determine if a subset has variation values within predetermined error ranges, and if so, use said subset to indicate that said specific constituent is present in the mixture.

22. A computer program of claim 21, wherein said relationships are ratios between detected quantity values of spectral lines.

23. A spectrometer including the computer program of claim 21.

24. A mass spectrometer including the computer program of claim 21.