1. AAS Atomic Absorption Spectrophotometry

2. AAS – Widely in clinical laboratories to measure elements such as aluminum, calcium, copper, lead, lithium, magnesium, zinc, & other metals.

3. Atomic Unexcited or ground state (neutral atom) at a low energy level Absorption – Capable of absorbing radiation at a very narrow bandwidth corresponding to its own line spectrum Photometry – Original light, enters the flame, some of it is absorbed, net decrease in the intensity of the beam

4. COMPONENTS OF AAS Essentials of an atomic absorption spectrophotometer

6. Kinds of burners Total consumption burner – Disadvantage large droplets are produced in the flame – Scatter light and thus cause signal noise Acoustical noise produced – Advantage the flame is more concentrated, and it can be made hotter – Molecular dissociation » Desirable for some chemical systems

8. Premix burner – The sample is aspirated, volatilized, and burned – Advantage Larger droplets go to waste – Producing a less noisy signal Pathlength through the flame of the burner is longer – Increase the sensitivity of the measurement – Disadvantage Flame is usually not as hot as that of the total consumption burner – Cannot sufficiently dissociate certain metal complexes

10. When light leaves the flame, it is composed of – Pulsed unabsorbed light from the lamp – a small amount of unpulsed flame spectrum – Sample emission Detector senses all light Tuned amplifier accept only pulsed signals

11. Flameless atomic absorption Sample cup – Sample is placed in a depression on a carbon rod in an enclosed chamber – Dry, char, and finally atomize the sample into the chamber – atomized element then absorbs energy from the corresponding hollow cathode lamp Advantage – More sensitive permits determination of trace metals in small samples of blood or tissue

12. Flameless atomic absorption Zeeman effect (Background correction) – In an intense magnetic field – the energy levels in the atom are shifted slightly – The magnetic field can be pulsed alternately on and off – The difference between the two signals is background-corrected absorbance

13. INTERFERENCE IN AAS Chemical Ionization Matrix effects

14. Chemical interference – The flame cannot dissociate the sample into free atoms – Example Phosphate interference in the determination of calcium – Being solved, by Using a special high-temperature burner Adding a cation that competes with calcium for the phosphate

15. Ionization interference – When atoms in the flame become excited – Overcome by Adding an excess of a more easily ionized substance – absorb most of the flame energy Reducing the flame temperature

16. Matrix interference – Enhancement of light absorption by organic solvents – Formation of solids from sample droplets Concentrations greater than 0.1 mol/L – Refractory oxides of metals

17. Summary AAS – Advantages Sensitive Accurate Precise Highly specific – Disadvantage the problem of interferences

18. Does not require excitation of the element – Less affected by Temperature variations in the flame Transfer of energy from one atom to another High specificity – Light used has an extremely narrow bandwidth (0.01 nm) Selectively absorbed by the atoms being measured