Beers Law for a Single Component Sample I0I0 A = Absorbance = - log 10 I I / I 0 b = Optical path length c = Solution Concentration (M/L) ε = Molar Absorptivity (L/M cm) b I 0 = Incident beam intensity I = Transmitted beam intensity

Atomic Absorption Spectrometry Advantages over solution U.V./Vis spectrometry 1.More selective – narrow atomic lines, compared with broad molecular bands Only 5 spectral overlaps known 2.Lock-and-key match with HCL source and atoms in flame cell 3.Working ranges from 0.1 – 1,000 ppm

Wavelength (nm) Typical Molecular absorption band Continuum source Molecular band overlap area Molecular band absorption

Atomic line absorption Hg nm (HCL source) Hg nm (atoms in flame)

Atomic line absorption

Helium Arc Lamp spectrum Mercury Arc Lamp spectrum

Typical Atomic Absorption Spectrometer

Electrothermal Vaporization AAS Electrothermal Vaporizer (ETV) Graphite Tube Electrode Terminals

MethodType of Sample Pneumatic nebulizationSolution or slurry Ultrasonic nebulizationSolution Electrothermal vaporizationSolid, liquid, solution Hydride generationSolution of certain elements Direct insertionSolid, powder Laser ablationSolid, metal Spark or arc ablationConducting solid Glow discharge sputteringConducting solid Methods of Sample Introduction in Atomic Spectroscopy

Types of Atomizers Used for Atomic Spectroscopy Type of AtomizerTypical Atomization Temperature °C Flame1700 – 3150 Electrothermal vaporization1200 – 3000 Inductively coupled argon plasma 4000 – 6000 Direct current argon plasma4000 – 6000 Microwave-induced argon plasma 2000 – 3000 Glow discharge plasmaNonthermal Electric arc4000 – 6000 Electric spark40,000 – ? Laser induced breakdowntba

Processes that occur in flames atomize ionize

Properties of Flames FuelOxidantTemperatures °C MethaneAir1700 – 1900 MethaneOxygen2700 – 2800 HydrogenAir2000 – 2100 HydrogenOxygen2550 – 2700 AcetyleneAir2100 – 2400 AcetyleneOxygen3050 – 3150 AcetyleneNitrous Oxide2600 – 2800

Degree of Ionization of Metals at Flame Temperatures ElementIonization Potential, eV Fraction Ionized at the Indicated Temperature and Pressure P = 10^-4 atmP = 10^-6 atm 2000 K3500 K2000 K3500 K Cs >0.99 Rb >0.99 K Na Li Ba Sr Ca Mg