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In LS AAS background absorption can only be corrected using instrumental techniques, and all of them are based on two sequential measurements, firstly, total absorption ( atomic plus background ), secondly, background absorption only, and the difference of the two measurements gives the net atomic absorption.

It should also be pointed out that in LS AAS there is no way to correct for ( the rare case of ) a direct overlap of two atomic lines.

The same algorithm can actually also be used to correct for direct line overlap of two atomic absorption lines, making HR-CS AAS the only AAS technique that can correct for this kind of spectral interference.

Congruence of triangles is determined by specifying two sides and the angle between them ( SAS ), two angles and the side between them ( ASA ) or two angles and a corresponding adjacent side ( AAS ).

The shape of a triangle is determined up to congruence by specifying two sides and the angle between them ( SAS ), two angles and the side between them ( ASA ) or two angles and a corresponding adjacent side ( AAS ).

( In British usage, ASA and AAS are usually combined into a single condition AAcorrS-any two angles and a corresponding side.

In 1840 divisions between Garrisonians and the more political wing of the anti-slavery movement split the AAS and correspondingly the BFASS into two opposing factions.

In 1863, but for a passing interest in the AAS, Chapman retired from public life and for the next two decades, until her death in 1885, she “ savored the perceived success of her cause and, equally, her own role in the victory .”

* two AAS Flight Achievement Awards

He has been awarded three Defense Superior Service Medals, the Legion of Merit, the National Intelligence Medal of Achievement, the National Defense Service Medal, two Navy Meritorious Unit Commendations, two Navy Battle Efficiency Awards, the Sea Service Deployment Ribbon, the AAS Flight Achievement Award and Victor A. Prather Award for 1993, three NASA Space Flight Medals, two NASA Exceptional Service Medals, and seven NASA Group Achievement Awards.

The oldest and most commonly used atomizers in AAS are flames, principally the air-acetylene flame with a temperature of about 2300 ° C and the nitrous oxide ( N2O )- acetylene flame with a temperature of about 2700 ° C.

In classical LS AAS, as it has been proposed by Alan Walsh, the high spectral resolution required for AAS measurements is provided by the radiation source itself that emits the spectrum of the analyte in the form of lines that are narrower than the absorption lines.

Hollow cathode lamps ( HCL ) are the most common radiation source in LS AAS.

Deuterium HCL or even hydrogen HCL and deuterium discharge lamps are used in LS AAS for background correction purposes.

As already pointed out above, we have to distinguish between medium-resolution spectrometers that are used for LS AAS and high-resolution spectrometers that are designed for CS AAS.

Simple monochromators of the Littrow or ( better ) the Czerny-Turner design are typically used for LS AAS.

Photomultiplier tubes are the most frequently used detectors in LS AAS, although solid state detectors might be preferred because of their better signal-to-noise ratio.

Another source of background absorption, particularly in ET AAS, is scattering of the primary radiation at particles that are generated in the atomization stage, when the matrix could not be removed sufficiently in the pyrolysis stage.

There are several techniques available to correct for background absorption, and they are significantly different for LS AAS and HR-CS AAS.

In essence there are three techniques used for background correction in LS AAS:

In HR-CS AAS background correction is carried out mathematically in the software using information from detector pixels that are not used for measuring atomic absorption ; hence, in contrast to LS AAS, no additional components are required for background correction.

As measurement of total and background absorption, and correction for the latter, are strictly simultaneous ( in contrast to LS AAS ), even the fastest changes of background absorption, as they may be observed in ET AAS, do not cause any problem.

In this case HR-CS AAS is offering the possibility to measure correction spectra of the molecule ( s ) that is ( are ) responsible for the background and store them in the computer.

In LS AAS the high resolution that is required for the measurement of atomic absorption is provided by the narrow line emission of the radiation source, and the monochromator simply has to resolve the analytical line from other radiation emitted by the lamp.

When a continuum radiation source is used for AAS measurement it is indispensable to work with a high-resolution monochromator.

The acid droplets, condensed on the surface, are then analyzed using AAS.

Atomic absorption spectroscopy ( AAS ) is a spectroanalytical procedure for the quantitative determination of chemical elements employing the absorption of optical radiation ( light ) by free atoms in the gaseous state.

AAS can be used to determine over 70 different elements in solution or directly in solid samples employed in pharmacology, biophysics and toxicology research.

The modern form of AAS was largely developed during the 1950s by a team of Australian chemists.

In flame AAS a steady-state signal is generated during the time period when the sample is aspirated.

Electrothermal AAS ( ET AAS ) using graphite tube atomizers was pioneered by Boris V. L ’ vov at the Saint Petersburg Polytechnical Institute, Russia, since the late 1950s, and further investigated by Hans Massmann at the Institute of Spectrochemistry and Applied Spectroscopy ( ISAS ) in Dortmund, Germany.

The so-called Stabilized Temperature Platform Furnace ( STPF ) concept, proposed by Walter Slavin, based on research of Boris L ’ vov, makes ET AAS essentially free from interference.

In ET AAS a transient signal is generated, the area of which is directly proportional to the mass of analyte ( not its concentration ) introduced into the graphite tube.

Its sensitivity is 2 – 3 orders of magnitude higher than that of flame AAS, so that determinations in the low μg L-1 range ( for a typical sample volume of 20µL ) and ng g-1 range ( for a typical sample mass of 1 mg ) can be carried out.

It shows a very high degree of freedom from interferences, so that ET AAS might be considered the most robust technique available nowadays for the determination of trace elements in complex matrices.

The advantage of this technique is that only a medium-resolution monochromator is necessary for measuring AAS ; however, it has the disadvantage that usually a separate lamp is required for each element that has to be determined.

In CS AAS, in contrast, a single lamp, emitting a continuum spectrum over the entire spectral range of interest is used for all elements.

When a continuum radiation source is used for AAS, it is necessary to use a high-resolution monochromator, as will be discussed later.

Another feature to make LS AAS element-specific is modulation of the primary radiation and the use of a selective amplifier that is tuned to the same modulation frequency, as already postulated by Alan Walsh.

This way any ( unmodulated ) radiation emitted for example by the atomizer can be excluded, which is imperative for LS AAS.