Atomic Absorption Spectroscopy (AAS)I Mentor : Prof. Kuniyuki KITAGAWA Assistant: Dr. Eng.NelfaDesmira
Uv-Vis Spectrometer Double Beam Light Source UV (Deuterium/D2) Diffraction Grating 1a 2 Mirror 1 Slit 1 1b Light Source Vis (Tungsten) Slit 2 3 Detector-2 Filter I0 Reference Cuvette Mirror 4 7a Reference Beam 6a Lens 1 Half Mirror 5 4 Detector-1 Mirror 2 Sample Cuvette 6b 7b Sample Beam I Mirror 3 Lens 2
Uv-Vis Spectrometer Double Beam • No 1a and 1 b • The UV-Visible spectrophotometer uses two light sources, a deuterium (D2) lamp for ultraviolet light and a tungsten (W) lamp for visible light. Two light sources hit Mirror 1 one pass through slit 1 go to diffraction grating (no.2) • No 2 • The grating is able to rotated so a specific wavelength is selectable. From diffraction grating goes to slit 2 and filter (No. 3) • No 3 • A filter is used to remove unwanted higher orders of diffraction. • No 4 • The light beam hits a second mirror • No 5 • splited by a half mirror to 6a and 6b • No 6a and 6b • Half of the light is reflected (6a), the other half passes through (6b) • No 7a • One of the beams is allowed to pass through a reference cuvette. • No 7b • the other passes through the sample cuvette. The intensities of the light beams are then measured at the end
Beer-Lambert Law • The Beer-Lambert law is the linear relationship between absorbance and concentration of an absorbing species. • Experimental measurements are usually made in terms of transmittance (T), which is defined as:T = I / Iowhere I is the light intensity after it passes through the sample and Io is the initial light intensity. • The relation between A and T is:A = -log T = - log (I / Io) where A is the measured absorbance
Transmittance The relationship between absorbance and transmittance is illustrated in the following diagram:
Assignment • Calculate the transmission for absorbance A 0.6 and 0.06 • How to make correction for background absorption caused by sample matrices using a one-beam spectrophotometer? • Explain the system of single beam Uv-Vis Spectrometer
Atomic Absorption Spectroscopy(AAS) II Mentor : Prof. Kuniyuki Kitagawa Assistant : Dr. Eng. NelfaDesmira
Atomic Spectroscopy • A method to analyze the elemental composition using atomic absorption or emission • Energy transition electrons of atoms Absorption Emission E1 E1 1 2 3 1 v1 Excited State Excited State E2 E2 v2 2 E3 E3 3 v3 E0 Ej Ground State Ground State h = Ei– E0 i = 1.2 and 3 h = Ej – Ei i = 1.2 and 3
Atomic Absorption Spectroscopy Ej Beer Lambert Law : I I0 E0 Where : A = absorbance/Emission T = Transmitance Atomic Absorption Spectroscopy : The term used when the radiation absorbed by atoms is measured E0 and Ej : energy levels where Ej higher than E0. Arrow line: Absorption
Atomic Absorption Spectrometry Atomized Sample (Flame) Lens Radiation Source Lens Monochromator Detector Flame Atomic Absorption Spectrometry AAS consist of two type: Flame AAS and Graphite-furnace AAS. Please open this link : http://www.cee.vt.edu/ewr/environmental/teach/smprimer/aa/aadiag.gif Output
Atomic Absorption Spectrometry • Radiation Source • Hollow-Cathode Lamp • AtomizationSample • AAS analyzes atoms in gas phase so atoms in a sample must heated/vaporized in a high-temperature source such as a flame or graphite furnace. Flame AA is suitable to analyze solutions, while graphite furnace AA is able to analyze solutions, slurries, or solid samples.
Atomic Absorption Spectrometry • Monochromator and Detector • AA spectrometers use monochromators and detectors for UV and visible light. • Monochromator is used to isolate the absorption line from background light due to interferences.
Assignment • Explain the detail of flame atomization absorption spectrometry (FAAS) • Explain the detail of graphite furnace atomization absorption spectrometry (GAAS) • Compare the detection limits of FAAS and GAAS and mention their applications respectively