Atomic absorption spectroscopy
AAS can be used to determine over 70 different elements in solution, or directly in solid samples via electrothermal vaporization,[1] and is used in pharmacology, biophysics, archaeology and toxicology research.
They were led by Sir Alan Walsh at the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Division of Chemical Physics, in Melbourne, Australia.
By preparing the sample, atomizing the analytes, measuring their absorption of specific light, and applying the Beer-Lambert law, this powerful technique helps us understand the elemental makeup of diverse materials across various scientific and industrial fields.
On top of the spray chamber is a burner head that produces a flame that is laterally long (usually 5–10 cm) and only a few mm deep.
Each of these stages includes the risk of interference in case the degree of phase transfer is different for the analyte in the calibration standard and in the sample.
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.
[citation needed] The major components of this concept are atomization of the sample from a graphite platform inserted into the graphite tube (L’vov platform) instead of from the tube wall in order to delay atomization until the gas phase in the atomizer has reached a stable temperature; use of a chemical modifier in order to stabilize the analyte to a pyrolysis temperature that is sufficient to remove the majority of the matrix components; and integration of the absorbance over the time of the transient absorption signal instead of using peak height absorbance for quantification.
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.
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.
In this atmosphere lies a pair of electrodes applying a DC voltage of 250 to 1000 V to break down the argon gas into positively charged ions and electrons.
When the excited atoms relax back into their ground state, a low-intensity glow is emitted, giving the technique its name.
However, with proper modifications, it can be utilized to analyze liquid samples as well as nonconducting materials by mixing them with a conductor (e.g. graphite).
The technique provides a means of introducing samples containing arsenic, antimony, selenium, bismuth, and lead into an atomizer in the gas phase.
The volatile hydride generated by the reaction that occurs is swept into the atomization chamber by an inert gas, where it undergoes decomposition.
The cold-vapor technique is an atomization method limited only for the determination of mercury, due to it being the only metallic element to have a large vapor pressure at ambient temperature.
The method initiates by converting mercury into Hg2+ by oxidation from nitric and sulfuric acids, followed by a reduction of Hg2+ with tin(II) chloride.
The mercury, is then swept into a long-pass absorption tube by bubbling a stream of inert gas through the reaction mixture.
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.
[citation needed] Inside the sealed lamp, filled with argon or neon gas at low pressure, is a cylindrical metal cathode containing the element of interest and an anode.
The bulb is inserted into a coil that is generating an electromagnetic radio frequency field, resulting in a low-pressure inductively coupled discharge in the lamp.
A special high-pressure xenon short arc lamp, operating in a hot-spot mode has been developed to fulfill these requirements.
The resolution has to be equal to or better than the half-width of an atomic absorption line (about 2 pm) in order to avoid losses of sensitivity and linearity of the calibration graph.
The research with high-resolution (HR) CS AAS was pioneered by the groups of O’Haver and Harnly in the US, who also developed the (up until now) only simultaneous multi-element spectrometer for this technique.
The second monochromator does not have an exit slit; hence the spectral environment at both sides of the analytical line becomes visible at high resolution.
In this case, a separate source (a deuterium lamp) with broad emission is used to measure the background absorption over the entire width of the exit slit of the spectrometer.
This technique (named after their inventors) is based on the line-broadening and self-reversal of emission lines from HCL when high current is applied.
[citation needed] This obviously also includes a reduction of the measured intensity due to radiation scattering or molecular absorption, which is corrected in the same way.
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.
