Chemistry: analytical and immunological testing – Optical result – Spectrum analysis
Reexamination Certificate
1997-01-21
2002-05-21
Soderquist, Arlen (Department: 1743)
Chemistry: analytical and immunological testing
Optical result
Spectrum analysis
C436S073000, C436S079000, C436S080000, C436S081000, C436S082000, C436S083000, C436S084000, C436S164000, C436S181000, C436S182000, C356S312000, C356S319000
Reexamination Certificate
active
06391647
ABSTRACT:
FIELD OF THE INVENTION
The-present invention refers to a method for atomic absorption spectroscopy of an analyte which is contained in a sample to be analyzed and which is converted into free atoms in an absorption volume of an atomizer, said method comprising the steps of position- and time-dependent measuring of the atomic absorption over the cross-section of the absorption volume, and simultaneous determination of surface temperatures of the atomizer.
Furthermore, the present invention refers to a device for carrying out an atomic absorption spectroscopy, comprising a radiation source, an atomizer enclosing an absorption volume, a position- and time-resolving spectrometer for measuring the light which has been emitted by the radiation source and which has passed through the absorption volume, and a means for determining the surface temperature of the atomizer.
BACKGROUND OF THE INVENTION
Such a method and such a device are known from WO 94/23285.
This known method especially includes the step of first converting an analyte of a sample to be examined in the absorption volume of a graphite furnace into the gaseous phase in the form of free atoms. These free atoms absorb characteristic wavelengths emitted by a primary light source. The extinction of the primary radiation source in these wave-lengths caused by said free atoms is then measured in a temporally resolved manner, i.e. at specific moments of time, in dependence upon the position relative to the cross-section of the furnace.
According to this method, the position- and time-dependent extinctions are first determined for various calibration standards whose concentrations are already known. Accordingly, a connection, i.e. a calibration function, between the extinction and the concentration of the analyte observed is obtained in the sample to be measured.
For determining the concentration of an unknown sample, the position- and time-dependent extinction is, subsequently, determined, and the time-dependent concentration corresponding to the measured extinction is ascertained through the calibration function.
In this connection, non-specific radiation losses (background absorption) can be corrected by background correction methods which are normally used in the field of atomic absorption spectroscopy, such as correction with a continuum radiator, Zeemann effect background correction or correction according to the Smith-Hieftje method. In accordance with the requirements of the correction technique used, data evaluation is temporally controlled in such a way that a distinction can be made between the respective signals (e.g. non-specific absorption, total absorption, emission) coming from the atomizer. In any case, however, also the background absorption is measured in a temporally resolved manner so that correction errors caused by inhomogeneous background absorption, whose distribution can, moreover, be different from that of the atomic absorption, can be avoided, such correction errors being unavoidable in the case of the conventional atomic absorption which is not spatially resolved.
Furthermore, the surface temperature of the atomizer can be measured simultaneously in this method. Additional information on the atomization process can be obtained in this way.
According to WO 94/23285, spatially local deviations, which would result in a non-linearity of the calibration function in their entirety, are taken into account by the use of a spatially-resolving type of atomic absorption spectroscopy. Hence, many calibration measurements must be carried out in this non-linear region so as to obtain a satisfactory, reliable determination of the connection between the measured extinction of the atoms within the absorption volume and the concentration of the analyte in the sample to be measured. These spatially local deviations include, for example, the inhomogeneous distribution of the atoms in the absorption volume, the inhomogeneous distribution of the radiation intensity in the absorption volume and the temperature gradients in the absorption volume.
The method and the device according to WO 94/23285 are, however, disadvantageous insofar as spectral effects, such as Doppler broadening and pressure broadening effects, which depend on the temperature, are not taken into account.
SUMMARY OF THE INVENTION
Hence, it is the object of the present invention to improve the known method and the known device.
According to the present invention, this object is achieved by a method of the type mentioned at the beginning which is characterized by the steps of reconstructing the temperature field in said absorption volume on the basis of the surface temperatures determined, determining position- and time-dependent numbers of particles of the absorbing atoms of the analyte on the basis of the measurements of the position- and time-dependent atomic absorption and the absorption profile that has been determined with due regard to effects influencing the line profile of the analyte and with due regard to the reconstructed temperature field, and determining the time-dependent total number of the absorbing atoms of the analyte on the basis of the position- and time-dependent numbers of particles.
It follows that the method according to the present invention first reconstructs, for each predetermined time step, the temperature field over the cross-section of the absorption volume on the basis of the surface temperatures of the atomizer which are determined at the support points or support values. Accordingly, the temperature is known at any point over the cross-section of the absorption volume. With the aid of this position-dependent temperature, position-dependent absorption profiles are determined in which spectral effects, such as Doppler broadening and pressure broadening effects, have already been taken into account. These position-dependent absorption profiles can then be used for determining with the aid of absorption measurements position-dependent numbers of particles on the basis of which the total number of the absorbing atoms of the analyte can then be determined for each predetermined time step.
Due to the fact that spectral effects, such as Doppler broadening and pressure broadening effects, are directly taken into account upon determining the position-dependent numbers of particles, said position-dependent numbers of particles and, consequently, also the total number of absorbing atoms can be determined with a degree of accuracy which is much higher than that obtained by methods according to the prior art. This direct taking into account has especially the effect that systematic deviations, which are caused by the above-mentioned effects, are reduced significantly.
A further advantage of the method according to the present invention results from the fact that the experimental set-up used for carrying out the measurement only has to be taken into account upon reconstructing the temperature field in the absorption volume on the basis of the surfaces temperatures determined. When the manner in which the temperature field is to be reconstructed on the basis of the surface temperatures has been determined for a specific experimental set-up, any type of analytes can be examined by means of this set-up without any necessity of measuring calibration standards. This results in a certain degree of independence of the measurements from the set-up used in the device in question.
It follows that, in addition to an improvement of the measuring accuracy, the method according to the present invention also makes the execution of these measurements much simpler.
Measurements of the position- and time-dependent absorption are corrected in an advantageous manner with regard to the above-mentioned background absorption.
According to a special embodiment of the present method, the the position- and time-dependent particle number N(X,t) can be determined from
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Gilmutdinov Albert
Sperling Michael
PerkinElmer Instruments LLC
Soderquist Arlen
St. Onge Steward Johnston & Reens LLC
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