Method of, and apparatus for, absorbance correction in atomic absorption spectroscopy

• US 5,315,528 A
• Filed: 12/03/1991
• Issued: 05/24/1994
• Est. Priority Date: 12/03/1991
• Status: Expired due to Term

• Current Assignee: Perkinelmer Incorporated
• Original Assignee: Perkinelmer Incorporated
• Inventors: L'vov, Boris V.
• Primary Examiner(s): Black, Thomas G.
• Assistant Examiner(s): NGUYEN, TAN QUANG
• Application Number:
  US07/801,990
• Time in Patent Office: 903 Days
• Field of Search: 364/498, 356/307, 356/312, 356/315, 356/311
• US Class Current: 702/23
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/3103 Atomic absorption analysis

Abstract

In order to provide a linear calibration graph when analysing samples by atomic absorption spectroscopy, a maximum absorbance value is determined conventionally for a given analyte. The individual absorbance values of a sample containing an unknown amount of the analyte are processed as a function of the maximum absorbance value in accordance with the function ##EQU1## The thus obtained corrected individual absorbance values are integrated with respect to time to yield a corrected time-integrated absorbance value which is proportional to the amount of analyte present in the sample. This amount is determined using a calibration factor obtained from the analogously corrected time-integrated absorbance value of a calibration sample containing a known amount of the analyte.

Claims

1. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

electrothermally atomizing a predetermined number of samples containing known amounts of an analyte and integrating with respect to time the respectively obtained transient atomic absorption signals and thereby determining a maximum absorbance value;

electrothermally atomizing the sample containing an unknown amount of said analyte and thereby obtaining a transient atomic absorption signal composed of individual absorbance values as a function of time;

evaluating said individual absorbance values as a function of said maximum absorbance value and thereby obtaining corrected individual absorbance values;

integrating said corrected individual absorbance values with respect to time and thereby producing a corrected time-integrated absorbance value which is proportional to said unknown amount of said analyte contained in said sample, said step of integrating said corrected individual absorbance values and thereby producing said corrected time-integrated absorbance value including producing a time-integrated absorbance value which is substantially corrected for stray light effects;

determining a calibration factor; and

determining said unknown amount of said analyte contained in said sample from said corrected time-integrated absorbance value and said calibration factor.

2. The method according to claim 1, wherein said steps of electrothermally atomizing a predetermined number of samples and determining said maximum absorbance value entails selecting, as said predetermined number of samples, a sample containing an amount of analyte in a range where the absorbance value varies only little with the amount of analyte contained in the sample and using the thus obtained absorbance value as said maximum absorbance value.

3. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

electrothermally atomizing a predetermined number of samples containing known amounts of an analyte and integrating with respect to time the respectively obtained transient atomic absorption signals and thereby determining a maximum absorbance value;

electrothermally atomizing the sample containing an unknown amount of said analyte and thereby obtaining a transient atomic absorption signal composed of individual absorbance values as a function of time;

evaluating said individual absorbance values as a function of said maximum absorbance value and thereby obtaining corrected individual absorbance values, said step of evaluating said individual absorbance values as a function of said maximum absorbance value entailing evaluating said individual absorbance values in accordance with the function ##EQU10## wherein A_o * is corrected individual absorbance value,

A_max is the maximum absorbance value, and

A is the individual absorbance value;

integrating said corrected individual absorbance values with respect to time and thereby producing a corrected time-integrated absorbance value which is proportional to said unknown amount of said analyte contained in said sample;

determining a calibration factor; and

determining said unknown amount of said analyte contained in said sample from said corrected time-integrated absorbance value and said calibration factor.

4. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

electrothermally atomizing a predetermined number of samples containing known amounts of an analyte and integrating with respect to time the respectively obtained transient atomic absorption signals and thereby determining a maximum absorbance value;

electrothermally atomizing the sample containing an unknown amount of said analyte and thereby obtaining a transient atomic absorption signal composed of individual absorbance values as a function of time;

evaluating said individual absorbance values as a function of said maximum absorbance value and thereby obtaining corrected individual absorbance values;

integrating said corrected individual absorbance values with respect to time and thereby producing a corrected time-integrated absorbance value which is proportional to said unknown amount of said analyte contained in said sample,

determining a calibration factor;

said step of determining said calibration factor entailing the following steps;

electrothermally atomizing a calibration sample containing a known amount of said analyte and thereby obtaining a transient atomic absorption signal composed of individual absorbance values as a function of time;

evaluating said individual absorbance values as a function of said maximum absorbance value and thereby obtaining corrected individual absorbance values;

integrating said corrected individual absorbance values with respect to time and thereby producing a corrected time-integrated absorbance value which is proportional to said known amount of said analyte contained in said calibration sample; and

determining said calibration factor from said corrected time-integrated absorbance value and said known amount of analyte contained in said calibration sample; and

determining said unknown amount of said analyte contained in said sample from said corrected time-integrated absorbance value and said calibration factor.

5. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

electrothermally atomizing a predetermined number of samples containing known amounts of an analyte and integrating with respect to time the respectively obtained transient atomic absorption signals and thereby determining a maximum absorbance value;

electrothermally atomizing the sample containing an unknown amount of said analyte and thereby obtaining a transient atomic absorption signal composed of individual absorbance values as a function of time;

evaluating said individual absorbance values as a function of said maximum absorbance value and thereby obtaining corrected individual absorbance values;

said step of evaluating said individual absorbance values as a function of said maximum absorbance value entailing evaluating said individual absorbance values in accordance with the function ##EQU11## wherein A_o * is the corrected individual absorbance value,

A_max is the maximum absorbance value, and

A is the individual absorbance value;

integrating said corrected individual absorbance values with respect to time and thereby producing a corrected time-integrated absorbance value which is proportional to said unknown amount of said analyte contained in said sample;

determining a calibration factor; and

determining said unknown amount of said analyte contained in said sample from said corrected time-integrated absorbance value and said calibration factor.

6. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

atomizing a sample containing a known high amount of an analyte and determining a maximum absorbance value as the peak height of the thus obtained transient atomic absorption signal;

atomizing the sample containing an unknown amount of said analyte and determining a peak height absorbance value as the peak height of the thus obtained transient atomic absorption signal;

evaluating said peak height absorbance value as a function of said maximum absorbance value and thereby obtaining a corrected peak height absorbance value which is proportional to said unknown amount of said analyte contained in said sample, said step of evaluating said peak height absorbance value as a function of said maximum absorbance value and thereby obtaining said corrected peak height absorbance value including producing a peak height absorbance value which is substantially corrected for stray light effects;

determining a calibration factor; and

determining said unknown amount of said analyte contained in said sample from said corrected peak height absorbance value and said calibration factor.

7. The method according to claim 6, wherein said steps of electrothermally atomizing said sample containing said high amount of said analyte and determining said maximum absorbance value entails selecting, as said sample, a sample containing an amount of analyte in a range where the peak height absorbance value varies only little with the amount of analyte contained in the sample and using the thus obtained peak height absorbance value as said maximum absorbance value.

8. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

atomizing a sample containing a known high amount of an analyte and determining a maximum absorbance value as the peak height of the thus obtained transient atomic absorption signal;

atomizing the sample containing an unknown amount of said analyte and determining a peak height absorbance value as the peak height of the thus obtained transient atomic absorption signal;

evaluating said peak height absorbance value as a function of said maximum absorbance value and thereby obtaining a corrected peak height absorbance value which is proportional to said unknown amount of said analyte contained in said sample;

said step of evaluating said peak height absorbance value as a function of said maximum absorbance value entailing evaluating said peak height absorbance value in accordance with the function ##EQU12## wherein A_o * is the corrected peak height absorbance value,

A_max is the maximum absorbance value, and

A is the peak height absorbance value;

determining a calibration factor; and

determining said unknown amount of said analyte contained in said sample from said corrected peak height absorbance value and said calibration factor.

9. A method of determining by atomic absorption the amount of an analyte contained in a sample, comprising the steps of:

atomizing the sample containing a known high amount of an analyte and determining a maximum absorbance value as the peak height of the thus obtained transient atomic absorption signal;

said steps of atomizing said sample containing said high amount of said analyte and determining said maximum absorbance value entailing selecting, as said sample, a sample containing an amount of analyte in a range where the peak height absorbance value varies only little with the amount of analyte contained in the sample and using the thus obtained peak height absorbance value as said maximum absorbance value;

atomizing a sample containing an unknown amount of said analyte and determining a peak height absorbance value as the peak height of the thus obtained transient atomic absorption signal;

evaluating said peak height absorbance value as a function of said maximum absorbance value and thereby obtaining a corrected peak height absorbance value which is proportional to said unknown amount of said analyte contained in said sample;

determining a calibration factor;

said step of determining said calibration factor entailing the following steps;

atomizing a calibration sample containing a known amount of said analyte and determining a peak height absorbance value as the peak height of the thus obtained transient atomic absorption signal;

evaluating said peak height absorbance value as a function of said maximum absorbance value and thereby obtaining a corrected peak height absorbance value which is proportional to said known amount of said analyte contained in said calibration sample; and

determining said calibration factor from said corrected peak height absorbance value and said known amount of analyte contained in said calibration sample; and

determining said unknown amount of said analyte contained in said sample from said corrected peak height absorbance value and said calibration factor.

10. The method as defined in claim 9, wherein said step of evaluating said peak height absorbance value as a function of said maximum absorbance value entails evaluating said peak height absorbance value in accordance with the function ##EQU13## wherein A_o * is the corrected peak height absorbance value,

A_max is the maximum absorbance value, and

A is the peak height absorbance value.

11. An atomic absorption spectrophotometer for determining the amount of an analyte contained in a sample, comprising:

line emitting light source means for emitting a measuring light beam containing a resonance line of an analyte contained in a sample;

electrothermal atomizing means for receiving said sample and atomizing said sample;

said electrothermal atomizing means defining an atomic vapor area for forming the atomized sample;

said atomizing means being arranged for passing said measuring light beam emitted by said line emitting light source means through said atomic vapor area of said electrothermal atomizing means;

detector means arranged for receiving said measuring light beam after passage through said atomic vapor area of said electrothermal atomizing means;

modulating means for alternatingly passing said measuring light beam through said atomic vapor area of said atomizing means to said detector means and to said detector means for producing alternating detector output signals respectively indicative of an attenuated light intensity, which is attenuated due to absorption of the measuring light beam by the atomized sample in said atomic vapor area of said electrothermal atomizing means, and of a reference light intensity;

logarithmating means connected to said detector means for receiving said alternating detector output signals and forming therefrom a logarithmic ratio signal representative of an absorbance value;

said atomized sample being transiently formed in said atomic vapor area of said electrothermal atomizing means and said detector means generating a correspondingly transient atomic absorption signal which is transformed by said logarithmating means into individual absorbance values as a function of time;

integrating means selectively connected to said logarithmating means for receiving therefrom said individual absorbance values and forming a time-integrated absorbance value;

first memory means for storing a maximum absorbance value obtained from a sample containing a predetermined high amount of said analyte;

programmable computing means for computing corrected absorbance values which are proportional to the amount of analyte contained in the sample;

first applying means for selectively connecting said logarithmating means to said integrating means and to said computing means;

said first applying means selectively connecting said logarithmating means to said first memory means for storing therein said maximum absorbance value obtained from said sample containing said predetermined high amount of said analyte;

said first memory means being connected to feed said maximum absorbance value to said programmable computing means and said first applying means selectively connecting said logarithmating means to said programmable computing means during atomization of a sample containing an unknown amount of said analyte;

said programmable computing means being programmed to evaluate said individual absorbance values, which are produced by said sample containing said unknown amount of said analyte, as a function of said maximum absorbance value in order to obtain corrected individual absorbance values as a function of time;

said integrating means being selectively connected to receive said corrected individual absorbance values from said programmable computing means in order to produce therefrom a corrected time-integrated absorbance value which is proportional to the unknown amount of said analyte contained in said sample;

calibrating means for generating a calibration factor; and

said calibrating means being connected to said integrating means for receiving said corrected time-integrated absorbance values and producing, by means of said calibration factor, an output signal indicative of the amount of said analyte contained in said sample.

12. The atomic absorption spectrophotometer according to claim 11, further including:

Zeeman background correction means;

said electrothermal atomizing means receiving a plural number of samples containing said analyte in known amounts in a range in which the absorbance values pass through a maximum as a function of the amounts contained in said plural number of samples;

said first memory storing, as said maximum absorbance value, the maximum value which is selected from said plural number of said absorbance values.

13. The atomic absorption spectrophotometer according to claim 11, wherein said electrothermal atomizing means receives a sample containing an amount of said analyte in a range in which the absorbance value varies only little with the amount of said analyte contained in said sample, for determining and storing in said first memory means said maximum absorbance value.

14. The atomic absorption spectrophotometer according to claim 11, wherein said programmable computing means is programmed to evaluate said individual absorbance values, which are produced by said sample containing said unknown amount of said analyte, as a function of said maximum absorbance value in order to obtain corrected individual absorbance values substantially corrected for stray light effects.

15. The atomic absorption spectrophotometer according to claim 11, wherein said programmable computing means is programmed to evaluate said individual absorbance values, which are produced by said sample containing said unknown amount of said analyte, in accordance with the following function ##EQU14## wherein A_o * is the corrected individual absorbance value,

A_max is the maximum absorbance value, and

A is the individual absorbance value.

16. The atomic absorption spectrophotometer according to claim 11, further including:

second memory means;

second applying means for selectively connecting said integrating means to said calibrating means and said second memory means;

said second applying means connecting said integrating means to said second memory means for storing therein a corrected time-integrated absorbance value produced by a calibration sample which is atomized in said electrothermal atomizing means and which contains a known amount of said analyte; and

said calibrating means generating said calibration factor from said corrected time-integrated absorbance value, which is produced by said calibration sample, and said known amount of said analyte present in said calibration sample.

17. The atomic absorption spectrophotometer according to claim 16, wherein said programmable computing means is programmed to evaluate said individual absorbance values, which are produced by said calibration sample containing said known amount of said analyte, in accordance with the following function ##EQU15## wherein A_o * is the corrected individual absorbance value,

A_max is the maximum absorbance value, and

A is the individual absorbance value.

18. An atomic absorption spectrophotometer for determining the amount of an analyte contained in a sample, comprising:

line emitting light source means for emitting a measuring light beam containing a resonance line of an analyte contained in a sample;

atomizing means for receiving said sample and atomizing said sample;

said atomizing means defining an atomic vapor area for forming the atomized sample;

said atomizing means being arranged for passing said measuring light beam emitted by said line emitting light source means, through said atomic vapor area of said atomizing means;

detector means arranged for receiving said measuring light beam after passage through said atomic vapor area of said atomizing means;

modulating means for alternatingly passing said measuring light beam through said atomic vapor area of said atomizing means to said detector means and to said detector means for producing alternating detector output signals respectively indicative of an attenuated light intensity, which is attenuated due to absorption of the measuring light beam by the atomized sample in said atomic vapor area of said atomizing means, and of a reference light intensity;

logarithmating means connected to said detector means for receiving said alternating detector output signals and forming therefrom a logarithmic ratio signal representative of an absorbance value;

said atomized sample formed in said atomic vapor area of said atomizing means, producing a detector output signal which is transformed by said logarithmating means into a corresponding peak height absorbance value;

first memory means connected to said logarithmating means for storing a maximum absorbance value obtained from a sample containing a predetermined high amount of said analyte;

programmable computing means for computing corrected peak height absorbance values which are proportional to the amount of said analyte contained in the sample;

first applying means for selectively connecting said logarithmating means to said programmable computing means and to said first memory means;

said programmable computing means being programmed to evaluate a peak height absorbance value, which is produced by a sample containing an unknown amount of said analyte, as a function of said maximum absorbance value in order to obtain a corrected peak height absorbance value;

calibrating means for generating a calibration factor; and

said calibrating means being connected to said programmable computing means for receiving said corrected peak height absorbance value and producing, by means of said calibration factor, an output signal indicative of the amount of said analyte contained in said sample.

19. The atomic absorption spectrophotometer according to claim 18, wherein said atomizing means receives a sample containing an amount of said analyte in a range in which the peak height absorbance value varies only little with the amount of said analyte contained in said sample, for determining and storing in said first memory means said maximum absorbance value.

20. The atomic absorption spectrophotometer according to claim 18, wherein said programmable computing means is programmed to evaluate said peak height absorbance value, which is produced by said sample containing said unknown amount of said analyte, as a function of said maximum absorbance value in order to obtain a corrected peak height absorbance value substantially corrected for stray light effects.

21. The atomic absorption spectrophotometer according to claim 18, wherein said programmable computing means is programmed to evaluate said peak height absorbance value, which is produced by said sample containing said unknown amount of said analyte, in accordance with the following function ##EQU16## wherein A_o * is the corrected peak height absorbance value,

A_max is the maximum absorbance value, and

A is the peak height absorbance value.

22. The atomic absorption spectrophotometer according to claim 18, further including:

second memory means;

second applying means for selectively connecting said programmable computing means to said calibrating means and said second memory means;

said second applying means connecting said programmable computing means to said second memory means for storing therein a corrected peak height absorbance value produced by a calibration sample which contains a known amount of said analyte and which is atomized in said atomizing means; and

said calibrating means generating said calibrating factor from said corrected peak height absorbance value, which is produced by said calibration sample, and said known amount of said analyte present in said calibration sample.

23. The atomic absorption spectrophotometer according to claim 22, wherein said programmable computing means is programmed to evaluate said peak height absorbance value, which is produced by said calibration sample, in accordance with the following function ##EQU17## wherein A_o * is the corrected peak height absorbance value,

A_max is the maximum absorbance value, and

A ist the peak height absorbance value.