Beers Law for a Single Component Sample
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Transcript of Beers Law for a Single Component Sample
Beers Law for a Single Component Sample
11bcAT
I0
A = Absorbance = - log10
I
I / I0
b = Optical path length
c = Solution Concentration (M/L)
ε = Molar Absorptivity (L/M cm)
b
I0 = 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
200250
300 350 400
Typical Molecular absorption band
Continuum source
Molecular band overlap area
Molecular band absorption
200250
300 350 400
Atomic line absorption
Hg 253.7 nm (HCL source)
Hg 253.7 nm (atoms in flame)
Atomic line absorption
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
Method Type of SamplePneumatic nebulization Solution or slurry
Ultrasonic nebulization Solution
Electrothermal vaporization Solid, liquid, solution
Hydride generation Solution of certain elements
Direct insertion Solid, powder
Laser ablation Solid, metal
Spark or arc ablation Conducting solid
Glow discharge sputtering Conducting solid
Methods of Sample Introduction in Atomic Spectroscopy
Types of Atomizers Used for Atomic Spectroscopy
Type of Atomizer Typical Atomization Temperature °C
Flame 1700 – 3150
Electrothermal vaporization 1200 – 3000
Inductively coupled argon plasma
4000 – 6000
Direct current argon plasma 4000 – 6000
Microwave-induced argon plasma
2000 – 3000
Glow discharge plasma Nonthermal
Electric arc 4000 – 6000
Electric spark 40,000 – ?
Laser induced breakdown tba
Processes that occur in flames
)()()( sdesolvate
aerosolnebulize
aq MXMXMX
hMXMXMX gemit
gexcite
gvolatilize )(
*)()(
hMMXM gemit
gexcite
gg )(*
)()()(
hXX gemit
gexcite )(
*)(
hMMM nemitng
exciteng g
)(
*)()(
atomize
ionize
Properties of Flames
Fuel Oxidant Temperatures °C
Methane Air 1700 – 1900
Methane Oxygen 2700 – 2800
Hydrogen Air 2000 – 2100
Hydrogen Oxygen 2550 – 2700
Acetylene Air 2100 – 2400
Acetylene Oxygen 3050 – 3150
Acetylene Nitrous Oxide 2600 – 2800
Degree of Ionization of Metals at Flame Temperatures
Element Ionization Potential, eV
Fraction Ionized at the Indicated Temperature and Pressure
P = 10^-4 atm P = 10^-6 atm
2000 K 3500 K 2000 K 3500 K
Cs 3.893 0.01 0.86 0.11 >0.99
Rb 4.176 0.004 0.74 0.04 >0.99
K 4.339 0.003 0.66 0.03 0.99
Na 5.138 0.0003 0.26 0.003 0.90
Li 5.390 0.0001 0.18 0.001 0.82
Ba 5.210 0.0006 0.41 0.006 0.95
Sr 5.692 0.0001 0.21 0.001 0.87
Ca 6.111 0.00003 0.11 0.0003 0.67
Mg 7.644 0.0000004 0.01 0.000004 0.09