Atomic absorption spectrometer

Details Atomic absorption spectrometer Atomic absorption spectrometer

1990-10-10

1993-01-19

Evans, F. L.

Optics: measuring and testing

By dispersed light spectroscopy

With background radiation comparison

356312, G01J 310, G01N 2131, G01N 2174

Patent

active

051810778

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an atomic absorption spectrometer comprising
(a) a line emitting first light source,
(b) an optical system for generating a measuring light beam, this measuring light beam passing through a sample cavity and impinging on a photo-electrical detector,
(c) an atomizing device arranged in the sample cavity for atomizing a sample such that the components of the sample are present in atomic state in an atomizing area passed-through by the measuring light beam,
(d) a second light source emitting a continuum, from which light source a light beam originates,
(e) a beam splitter optionally removable from the path of rays, which beam splitter is arranged to reflect the light beam from the second light source into the path of rays of the measuring light beam as reference light beam, and
(f) switching means which are arranged to switch on the two light sources alternately.
Atomic absorption spectrometers serve for determining the amount or concentration of an element looked for in a sample. For this purpose a measuring light beam from a line-emitting light source, a hollow cathode lamp for example, is directed to a photo-electrical detector. An atomizing device is arranged in the path of rays of this measuring light beam. The sample to be analyzed is atomized in this atomizing device such that the components of the sample are present in atomic state. The measuring light beam contains the resonant lines of the element looked for. These resonant lines of the measuring light beam are absorbed by the atoms of the element looked-for in the cloud of atoms, while ideally the other elements contained in the sample do not influence the measuring light beam. Therefore the measuring light beam is subjected to an attenuation which is a measure of the number of the atoms looked-for in the path of the measuring light beam and thus a measure of the concentration or the amount of the looked-for element in the sample, depending on the method of atomization applied. The absorption to which the measuring light beam is subjected is not only effected by the atoms of the element looked for. There is a "background absorption" due to the absorption of the light by molecules, for example. This background absorption has to be compensated for particularly highly sensitive measurements.
A flame may serve as atomizing device into which a sample is sparyed in as a solution. For highly sensitive measurements the electrothermal atomization is preferably used: The sample is introduced into a furnace which is heated to high temperature by passing electrical current therethrough. Thereby the sample is dried, at first, then charred and, eventually, atomized. Then a "cloud of atoms" is generated in the furnace in which cloud the element looked-for is present in atomic state. The measuring light beam is passed through this furnace. These furnaces can have different shapes. Conventionally they are made of graphite.
The invention relates to the background compensation with such an atomic absorption spectrometer.


BACKGROUND ART

Substantially two methods are used determining and compensating for background absorption. With one method, a reference light beam originating from a light source emitting a continuum with a relatively large bandwidth as compared to the line width is directed through the flame or cloud of atoms alternately with the measuring light beam, the absorption due to the atomic absorption plus background absorption, while the absorption of the reference light beam virtually is determined only by the background absorption (DE-A-1,911,048).
Atomic absorption spectrometers are known wherein a measuring light beam originates from a line emitting light source and is directed through a flame or a furnace for the electrothermal atomization to a detector and wherein a reference light beam originating from a light source emitting a continuum becomes effective alternately with this measuring light beam containing a line spectrum of an element looked for. This reference light beam is reflected into the path of rays of the measu

REFERENCES:
Liddell et al., Analytical Chemistry, vol. 52, No. 8, Jul. 1980, pp. 1256-1260.
Perkin-Elmer Advertisement, Analytical Chemistry, vol. 53, No. 3 Mar. 1981, p. 415A.
Applied Spectroscopy, vol. 27, No. 6, Nov.-Dec. 1973, D. L. Dick et al.: "Modification of an Atomic Absorption Unit for Dual Beam, Background Correction Measurements", pp. 467-470, see p. 467, left hand column, line 18--right hand column, line 35; Fig. 1.
Patent Abstracts of Japan, vol. 4, No. 100 (P-19) (582), Jul. 18, 1980 and JP, A, 5558419 (Hitachi Seisakusho K.K.) May 1, 1980, see abstract; Figs. 3,4.
TRAC. Trends in Analytical Chemistry, vol. 1, No. 9, May 1982, Elsevier Scientific Publishing Company (Cambridge, Great Britain), L. de Galan: "Zeeman Atomic Absorption Spectrometry", pp. 203-205, see Fig. 2; p. 204, left hand column, lines 24-35.
International Laboratory, vol. 17, No. 3, Apr. 1987 (Fairfield, Conn., U.S.) R. P. Liddell et al.: "The Effect of Background Correction Speed on the Accuracy of AA Measurements", pp. 82-87, see Fig. 1; p. 82, middle column, line 10--right hand column, line 13.

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