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ATOMIC ABSORPTION SPECTROSCOPY

PRESENTED BY: ANSHUL SHARMAM.PHARM ANALYSIS

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Introduction History Principle Instrumentation Applications

CONTENTS

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Atomic absorption is a very common for

detecting metals and metalloids in a samples.

It is very reliable and simple to use. It can analyse over 62 elements. It also measure the concentration of

metals in the sample.

INTRODUCTION

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The first atomic absorption spectrometer

was built by the CSIRO (Commonwealth Scientific and Industrial Research Organisation) scientist Alan Walsh in 1954.

HISTORY

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The technique uses basically the principle

that free atoms generated in an atomizer can absorb radiation at specific frequency.

AAS quantifies the absorption of ground state atoms in the gaseous state.

The atoms absorb ultraviolet or visible light and make transition to higher electronic energy levels. The analyte concentration is determined from the amount of absorption.

PRINCIPLE

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Concentration measurement are usually

from a working curve after calibrating the instrument with standards of known concentration.

Atomic absorption is a very common technique for detecting metals and metalloids in environmental samples.

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OPERATIONAL PRINCIPLE OF AAS

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Source of light Chopper Nebulizer Atomizer Monochromator Detectors Readout

INSTRUMENTATION

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Hollow Cathode Lamp (HCL) Electrodeless Discharge Lamps

SOURCE OF LIGHT

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HOLLOW CATHODE LAMP

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HCL is the most common radiation

source in AAS. It contains a tungsten anode and a

hollow cylindrical cathode made of the element to be determined.

These are sealed in a glass tube filled with an inert gas (neon, argon).

Each element has its own unique lamp which must be used for that analysis.

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A small amount of the metal or salt of the

element for which the source is to be used is sealed inside a quartz bulb.

This bulb is placed inside a small, self-contained RF generator or “driver”. When power is applied to the driver, an RF field is created.

The coupled energy will vaporize and excite the atom inside the bulb causing them to emit their characteristic spectrum.

ELECTRODELESS DISCHARGE LAMP

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They are typically much more intense and, in

some cases, more sensitive than comparable HCL. Hence better precision and lower detection limits where an analysis is intensity limited.

EDL are available for a wide variety of elements, including Sb, As, Bi, Cd, Cs, Ge, Pb, Hg, P, K, Rb, Se, Te, Th, Sn and Zn.

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CONSTRUCTION OF ELECTRODELESS

DISCHARGE LAMP

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NEBULIZER

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FUEL AND OXIDANT USED FOR

FLAME COMBUSTION

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There is no nebulization, etc. The sample is

introduced as a drop (usually 10-50 uL)

The furnace goes through several steps:a- Drying (usually just above 110 deg. C.)b- Ashing (up to 1000 deg. C)c- Atomization (Up to 2000-3000 C)d- Cleanout (up to 3500 C or so). Waste is

blown out with a blast of Ar.

ELECTROTHERMAL EVAPORATOR

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Samples are reacted in an external

system with a reducing agent, usually NaBH4.

Gaseous reaction products(volatile hydrides) are then carried to a sampling cell in the light path of the AA spectrometer.

To dissociate the hydride gas into free atoms, the sample cell must be heated.

The cell is either heated by an air-acetylene flame or by electricity.

HYDRIDE GENERATION TECHNIQUE

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FLAME ATOMIZERS ELECTROTHERMAL ATOMIZERS

ATOMIZER

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Flame is used to atomize the sample. Sample when heated is broken into its atoms. High temperature of flame causes excitation. Electrons of the atomized sample are

promoted to higher orbitals, by absorbing certain amount of energy.

FLAME ATOMIZER

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Graphite furnace atomic

absorption spectrometry (GFAAS) (also known as Electro thermal Atomic Absorption spectrometry (ETAAS)) is a type of spectrometry that uses a graphite-coated furnace to vaporize the sample.

Instead of employing the high temperature of a flame to bring about the production of atoms from the sample and it is non-flame methods involving electrically heated graphite tubes or rods.

ELECTROTHERMAL ATOMIZERS

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SIMPLE SCHEMATIC

DIAGRAM

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• Aqueous samples should be acidified (typically with nitric acid,

HNO3) to a pH of 2.0 or less. Discoloration in a sample may indicate that metals are present in the sample. For example, a greenish color may indicate a high nickel content, or a bluish color may indicate a high copper content. A good rule to follow is to analyze clear (relatively dilute) samples first, and then analyze colored (relatively concentrated) samples. It may be necessary to dilute highly colored samples before they are analyzed.

• After the instrument has warmed up and been calibrated, a small aliquot (usually less than 100 microliters (µL) and typically 20 µL) is placed, either manually or through an automated sampler, into the opening in the graphite tube.

WORKING

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The graphite furnace is an electrothermal atomizer

system that can produce temperatures as high as 3,000°C. The heated graphite furnace provides the thermal energy to break chemical bonds within the sample and produce free ground-state atoms. Ground-state atoms then are capable of absorbing energy, in the form of light, and are elevated to an excited state.

WORKING

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Sample holder: Graphite tube: Samples are placed directly in the

graphite furnace which is then electrically heated. Beam of light passes through the tube

GFAAS

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Three stages: 1. drying of sample 2. ashing of organic matter (to burn off organic

species that would interfere with the elemental analysis. 3. vaporization of analyte atoms

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Greater sensitivity and detection limits (hundred- or

thousand fold improvements in the detection limit compared with flame AAS) than other methods.

Direct analysis of some types of liquid samples. Some solid sample do not require prior dissolution. Low spectral interference. Very small sample size (as low as 0.5µL).

ADVANTAGES OF GFAAS

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Expensive. low precision. low sample throughput. requires high level of operator skill

DISADVANTAGES OF GFAAS

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GFAA has been used primarily for analysis of low

concentrations of metals in samples of water. The more sophisticated GFAAs have a number of lamps and therefore are capable of simultaneous and automatic determinations for more than one element.

for the quantification of beryllium in blood and serum.

APPLICATIONS OF GFAAS

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MONOCHROMATOR

- Wavelength selectors- Produces monochromatic light

Consists of:1) Entrance slit2) Diffraction grating3) Exit slitDiffraction gratings are mostly used rather than prisms

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GRATINGS AND PRISM

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The intensity of the light is fairly low, so a

photomultiplier tube (PMT) is used to boost the signal intensity

A detector (a special type of transducer) is used to generate voltage from the impingement of electrons generated by the photomultiplier tube

DETECTOR

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INTERFERENCE

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INTERFERENCES & CONTROL MEASURES

NON SPECTRAL

Matrix

Method of Standard Additions

Chemical

add an excess of another

element or compound

whichwill form a thermally

stablecompound with the

interferent

using a hotter flame.

Ionization

adding an

excess of an

element whichis very easily

ionized

SPECTRAL

Background Absorption

Continuum Source

Background

Correction

Zeeman Backgroun

d Correction

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This may be caused by direct overlap of the

analytical line with the absorption line of the matrix element.

HOW TO OVERCOME ? By choosing an alternate analytical

wavelength By removing the interfering element

from the sample.

SPECTRAL INTERFERENCE

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Formation of compound of low volatility

Decrease in calcium absorbance is observed with increasing concentration of sulfate or phosphate. HOW TO OVERCOME

By increasing flame temperature Use of releasing agents (La 3+ ) Cations react with the interferent releasing the

analyte Use of protective agents: They form stable but volatile compounds with

analyte.

CHEMICAL INTERFERENCE

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Ionization of ground state gaseous atom with in a

flame will reduce extent of absorption in AAS. M ↔ M+ + e

HOW TO MINIMIZE:Low temperature of the flame Addition of an excess of ionization suppressant

e.g. the alkali metals (K, Na, Rb, and Cs)

IONIZATION INTERFERENCE

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Advantages1. High selectivity and sensitivity2. Fast and simple working3. Doesn’t need metals separation4. Specific because the atom of a particular element can only

absorb radiation of their own characteristic wavelength

Disadvantages5. Analysis doesn’t simultaneous6. Can’t used for elements that give rise to oxides in flames7. Limit types of cathode lamp (expensive).

ADVANTAGES AND DIADVANTAGES

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Quantitative analysis. Qualitative analysis. Simultaneous multicomponent analysis. Determination of metallic element in biological

materials. Determination of metallic element in food

industry. Determination of Ca, Mg, Na, K in blood.

APPLICATIONS

THANK YOU

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