Atomic absorption spectrometer

Details Atomic absorption spectrometer Atomic absorption spectrometer

1998-08-28

2001-04-24

Evans, F L. (Department: 2877)

Optics: measuring and testing

By dispersed light spectroscopy

With background radiation comparison

C356S319000, C356S312000, C356S315000

Reexamination Certificate

active

06222626

ABSTRACT:

TECHNICAL FIELD
The invention relates to an atomic absorption spectrometer, comprising a measuring light path, leading from at least one light source emitting a line radiation corresponding to at least one element to be detected, through an atomization means for atomizing a sample containing the at least one element to be detected, to a detection means and a reference light path from each light source to the detection means.
Further, the invention relates to a method comprising the steps of coupling radiation of at least one light source emitting line radiation of at least one element to be detected into a measuring light path, leading from each light source through an atomization means for atomizing a sample containing the element to be detected, to a detecting means, coupling of radiation of each light source into a reference light path, leading from each light source to the detection means, measuring the intensity of the radiation passed through the measuring light path, measuring the intensity of the radiation passed through the reference light path, determining the radiation absorbed by the atomized sample from the intensity of the radiation passed through the measuring light path and the intensity of the radiation passed through the reference light path.
BACKGROUND ART
Such atomic absorption spectrometer and such method are known in the prior art.
FIG. 5
schematically shows an atomic absorption spectrometer
500
in accordance with the prior art. The atomic absorption spectrometer
500
comprises a measuring light path
510
and a reference light path
520
. Further, the atomic absorption spectrometer
500
is provided with a light source
550
emitting a line radiation corresponding to an element to be detected, said element being contained in a sample to be examined.
The light emitted by the light source is coupled, by a chopper means
590
, into either the measuring light path
510
of the reference light path
520
. The coupling is in accordance with the position of the elements being provided in the chopper means (not shown).
In
FIG. 5
a
, the light path is shown for a first position of the elements of the chopper means
590
. In this position, the light emitted from the light source is coupled into the measuring light path
510
. Accordingly, the reference light path
520
is represented by a dashed line.
The light emitted from the light source travels on the measuring light path
510
through an atomization means
560
in which the sample to be examined is atomized. In
FIG. 5
, the atomization means
560
is only shown schematically. In dependency on the sample matrix and the element contained in the sample, all atomization means known in the field of atomic absorption spectroscopy, as for example atomization furnace, flame, cold vapor cell and the like, can be used.
After passing through the atomization means
560
, the radiation impinges on a detector device
530
, for measuring the intensity of the radiation.
In
FIG. 5
b
, the light path is shown for a second position of the elements of the chopper means
590
. In this position, the light emitted from the light source is coupled into the reference light path
520
. In accordance with
FIG. 5
a
, the measuring light path
510
is shown in dashed line in
FIG. 5
b.
Using the reference light path
510
, the line radiation emitted from the light source impinges directly onto the detector
530
for measuring the intensity of the radiation.
Beside the above described components, the atomic absorption spectrometer
500
comprises optical elements
511
and
521
, for example, mirrors and/or lenses. These optical elements are, if need be, for focusing and redirecting the light paths.
In the following, a method for performing a double-beam atomic absorption spectroscopy with the atomic absorption spectrometer of
FIG. 5
will be described. With this, reference is made to
FIG. 14
, representing a time sequence of the method.
After the sample has been atomized in the atomization means
560
, line radiation from the light source is coupled in accordance with the respective position of the elements of the chopper means (see FIG.
5
A), into the measuring light path
510
for a predetermined time T
T
during a first phase P of a measuring cycle C, and the intensity of the radiation passed through the measuring light path
510
is measured in the detector device
530
.
After completion of this measurement, radiation emitted by the light source is coupled for a predetermined time T
R
into the reference light path due to the respective position of the chopper means (see
FIG. 5
b
). The intensity of the radiation path through the reference light path is detected in the detector device
430
.
Finally, the radiation absorbed by the atomized sample is determined from the intensity of the radiation passed through the measuring light path and the intensity passed through the reference light path.
The measuring cycle shown in
FIG. 14
is repeatedly performed in order to improve the statistics, in particular, if the atomic absorption is constant over a range which is larger compared to the measuring time. The case of these slowly running processes is particularly seen in the absorption with a flame or a cold vapor cell.
For fast running processes, as for example the atomization in an atomization furnace, the measurements can be, instead of averaging, time dependently recorded. Thus, with the above described spectrometer and respective methods, it is possible to perform an atomic absorption spectroscopy with time resolution.
The disadvantage of the above described spectrometer and the method is the loss of measuring time due to performing the reference measurement, i.e. the second phase R of the measuring cycle T. This is particularly critical in an atomization with an atomization furnace, since the available measuring time is generally very short.
SUMMARY OF THE INVENTION
In view of this, it is the objective problem underlying the invention to improve the prior art spectrometer and the prior art method for performing a doublebeam atomic absorption.
This objective problem is achieved by an atomic absorption spectrometer of the above mentioned kind, which is distinguished in that a beam splitting means is provided such that a first component of the line radiation of each light source is guidable via the measuring light and a second component of the line radiation of each light source is simultaneously guidable via the reference light path.
Via the beam dividing means, the line radiation from the light source can be divided, and thus, coupled simultaneously into both the measuring light path and the reference light path. Therefore, it is possible to simultaneously perform the sample measurement and the reference measurement. As a consequence, the available measuring time can be considerably increased. For the case that the time T
T
and T
R
for the sample measurement and the reference measurement are set equal, a doubling of the available measuring time results.
For the case that the time T
T
and T
R
are set differently, the increase of additional measuring time is given by the smaller of the two time intervals.
With this, the detection means may comprise a first detector device for detecting the first component of the line radiation (measuring light) and a second detector for detecting the second component of the line radiation (reference light).
This embodiment has the advantage, that a known atomic absorption spectrometer, as for example shown in
FIG. 5
, can be easily modernized.
In accordance with a preferred embodiment, the atomic absorption spectrometer in accordance with the invention comprises a detection means having a single detector, being provided with at least two sections, the first section being for detecting the first component of the line radiation and the second section being for detecting the second component of the line radiation. It is an advantage of this embodiment that only one detector has to be provided, and therefore, the detector means can be formed considerably smaller and with less costs.
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