ABOUT 025 AND 087 UVVIS SPECTROMETER SINGLE BEAM THIS

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FAAS:

About 0.25 and 0.87


Uv-Vis spectrometer single beam:

This is the schematic of Uv-Vis spectrometer single beam:(simple schematic)


Light sourceDiffraction GratingSlitSample Cuvette(Lens)DetectorI



FAAS:


Flame atomic absorption (FAAS) is a very common technique for detecting metals and metalloids in environmental samples. It is very reliable and simple to use. which. The technique is based on the fact that ground state metals absorb light at specific wavelenths. Metal ions in a solution are converted to atomic state by means of a flame. Light of the appropriate wavelength is supplied and the amount of light absorbed can be measured against a standard curve.

The technique of flame atomic absorption spectroscopy (FAAS) requires a liquid sample to be aspirated, aerosolized, and mixed with combustible gases, such as acetylene and air or acetylene and nitrous oxide. The mixture is ignited in a flame whose temperature ranges from 2100 to 2800 oC.

During combustion, atoms of the element of interest in the sample are reduced to free, unexcited ground state atoms, which absorb light at characteristic wavelengths.

The characteristic wavelengths are element specific and accurate to 0.01-0.1nm. To provide element specific wavelengths, a light beam from a lamp whose cathode is made of the element being determined is passed through the flame. A device such as photonmultiplier can detect the amount of reduction of the light intensity due to absorption by the analyte, and this can be directly related to the amount of the element in the sample.


GFAAS:

Graphite furnace atomic absorption spectrometry (GFAAS) (also known as Electrothermal Atomic Absorption Spectrometry ETAAS) is a type of spectrometry that uses a graphite-coated furnace to vaporize the sample. Briefly, the technique is based on the fact that free atoms will absorb light at frequencies or wavelengths characteristic of the element of interest (hence the name atomic absorption spectrometry). Within certain limits, the amount of light absorbed can be linearly correlated to the concentration of analyte present. Free atoms of most elements can be produced from samples by the application of high temperatures. In GFAAS, samples are deposited in a small graphite or pyrolytic carbon coated graphite tube, which can then be heated to vaporize and atomize the analyte. The atoms absorb ultraviolet or visible light and make transitions to higher electronic energy levels. Applying the Beer-Lambert law directly in AA spectroscopy is difficult due to variations in the atomization efficiency from the sample matrix, and nonuniformity of concentration and path length of analyte atoms (in graphite furnace AA). Concentration measurements are usually determined from a working curve after calibrating the instrument with standards of known concentration.

GFAA spectrometry instruments have basic features: a source of light (lamp) that emits resonance line radiation; an atomization chamber (graphite tube) in which the sample is vaporized; a monochromator for selecting only one of the characteristic wavelengths (visible or ultraviolet) of the element of interest; a detector, generally a photomultiplier tube (light detectors that are useful in low-intensity aapplications), that measures the amount of absorption; and a signal processor-computer system (strip chart recorder, digital display, meter, or printer).



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