Atomic absorption spectrometer

Details Atomic absorption spectrometer Atomic absorption spectrometer

1989-11-07

1992-03-10

Evans, F. L.

Optics: measuring and testing

By dispersed light spectroscopy

With background radiation comparison

356312, G01N 2174

Patent

active

050945300

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to an atomic absorption spectrometer with electrothermal atomization of the sample and background compensation by use of the Zeeman effect.
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 which is 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 caused 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 high sensitive measurements.
A flame may serve as atomizing device into which a sample is sprayed in as a solution. For high 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 ashed and at last atomized. Then a "cloud of atomes" is generated in the furnace in which cloud the atom 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 "Zeeman effect" is used for background compensation. When a magnetic field is applied to the absorbing atoms in the atomized sample a splitting and shifting of the resonant lines of these atoms is effected. Then the resonant lines of the atoms coincident no longer with the spectral lines of the measuring light beam and no atomic absorption takes place in the borderline case. This permits discrimination between non-atomic background absorption which is also present when the magnetic field is applied, and real atomic absorption which is superposed to the background absorption when the magnetic field is not applied.
The present invention relates to an atomic absorption spectrometer in which the atomization of a sample is effected by the electrothermal atomization described and in which the Zeeman effect is used for background compensation in the way described also.


BACKGROUND ART

From German Patent Application 1,964,469 an atomic absorption spectrometer is known wherein the radiation originates from a single light source designed as a line emitter, the radiation of which passing through the sample is frequency modulated by use of the longitudinal Zeeman effect. In this prior atomic absorption spectrometer a hollow cathode lamp is arranged between the pole pieces of a solenoid. One of the pole pieces has a bore through which the measuring light beam passes. Then the measuring light beam is directed through a flame serving as atomizing device and a monochromator and impinges upon a photo-electrical detector. The solenoid is arranged to be switched on and off, whereby the atomic absorption of the sample atoms compensated with respect to the background absorption can be determined from the difference of the signals with the solenoid switched off and switched on. The windings of the solenoid are provided on the pole pieces.
In this pri

REFERENCES:
patent: 3825344 (1974-07-01), Bonne
Liddel et al., Analytical Chemistry, vol. 52, No. 8, Jul. 1980, pp. 1256-1260.

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