Atomic Absorption Spectrometry.ppt

Atomic Absorption Spectrometry.ppt - Atomic Absorption...

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Unformatted text preview: Atomic Absorption Spectrometry Dr AKM Shafiqul Islam University Malaysia Perlis An atomic absorption spectrophotometer consists of a light source, a sample compartment and a detector. Atomic spectroscopy is one of the major tools for trace (ppm and ppb) metallic elements in industrial and environmental laboratories. In these methods the solution sample is aspirated into a flame that is hot enough to break the molecules into their atomic states. The concentration of the analyte in the flame may be measured by either its absorption or emission of the radiation. The absorption mode is known as atomic absorption spectroscopy (AAS) whereas emission mode as atomic emission Spectroscopy (AES) Sensitivity Atomic spectroscopy is very sensitive for most elements. Concentrations at the ppm level may be routinely determined using flame atomisation. Using electrothermal atomisation, concentrations at the ppb may be determined. – 1 ppm = 10-6g/g or 1g/g – The density of dilute aqueous solutions is approximately 1.00 so that: – 1 g/g of aqueous solution = 1g/ml = 1 ppm 1 ppm Fe = 1 x 10-6 g Fe/ml = 1.79 x 10-5 mol dm-3 Both methods are used to determine the concentration of an element in solution. Both methods use a standard curve. Difference between UV and IR spectroscopy is that sample must be atomised. Sample may be atomised by: (1) A flame (2) Electrically heated furnace (3) A Plasma Instrumentation for an Atomic Absorption Spectrometer. The flowing fuel and air mixture provides the aspiration action drawing the solution sample into the flame. Atomic Absorption Spectroscopy In atomic absorption spectroscopy the radiation of the lines of the analyte are produced by the lamp; the presence of the atomic state of the analyte in the flame attenuates or reduces the intensity of the radiation. The absorbance is proportional to the concentration of the analyte, similar to optical spectroscopy. Upper Diagram is AES and the lower one is AAS. In FES the flame provides the excitation, but in Hollow Cathode Lamp The light source in AAS is the hollow cathode lamp (HCL). The cathode is constructed of the metal or metals of the analysis. Passage of a dc voltage through the lamp produces the specific lines of those elements. Atomic Absorption Spectroscopy The signal from the detector is transferred to the computer, and the output registers on the monitor in a manner specified by the user. Spectra output of the multi-element steel hollow cathode lamp. Note the extremely sharp spectral lines. Atomic Absorption Spectrometry Most widely used method for determination of single elements in analytical chemistry Quantification of energy absorbed from an incident radiation source from the promotion of elemental electrons from the ground state Technique relies on a source of free elemental atoms electronically excited by monochromatic light Sample Introduction in AAS Flame – Method of supplying atom source – Utilizes a nebulizer in conjunction with air/acetylene flame – Solvent evaporates – Metal salt vaporizes and is reduced to complete the atomization process Radiation source is a hollow cathode lamp ...
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