Atomic spectroscopy

Atomic absorption

Requires external light souce

Measures light absorbed by ground state atoms

Atomic emission

No external light source

Measures light emmited by excited atoms

Atomic fluorescence

Ppt

Requires external light source

Measures fluorescense emission from excited atoms

Flame atomizer (AAS)

Ppb

Liquid sample nebulizes to aerosol - nebulizer not efficient only ~5% of sample usuable

Aerosol gets evaported to dry aerosol

Dry aerosol gets vaporated to gas molecule

Gaf molecule decomposes to gas atom

Increase efficiency in flame AAS

Premix burners increase optical pathlength

Fuel rich flame has reduced oxides and hydroxides

Fuel lean flame is hotter

Graphite furnace AAS advantages

Better sensitivity

More efficient ~100% sample usuable

Requires lower sample volume

Increases sample in optical pathlength

Easier preconcentration

Graphite furnace (AAS)

100’s Ppt

Inert gas Argon protects graphite against oxidation stopped before atomization

Drying

Charring

Atomization - peak

Cleaning

Matrix modifiers for GFAAS

Reduces loss of sample during charring

By decreasing volatility of analyte and increasing volatility of matrix

Eliminates smoke interference

Light source line broadening

Causes

1) Doppler effect - closer sees higher frequency, lower frequency longer wavelength absorbed

2) Pressure - atoms collide, shorten excited state time

Hollow cathode lamp

Filled with Ne or Ar

Voltage causes gas to be ionized

Positive ions causes atoms to collide and be excited to emit light

impractical white light source

Too broad range

Background correction

Beam chopping - corrects for flame emission

Deuterium lamp (flame) - corrects for scattering and nonspecific absorption detected by D2

Smith - Hieftje - high (nonspecific absorption only) vs low current signals

Zeeman correction (GFAAS) - magentic field on (background only)

Effect of temperature (AES)

Signal increases by 4% when temperature increases by 10K

Flame source (AES)

Low temp

For alkali and alkali earth metals

Poor sensitivity

Inductively coupled plasma (ICP)

Ppt

Argon electrons excited by radio frequency magnetic field

Transfer energy to gas

High temp produced - stable and uniform

Microwave plasma

Ppb

Nitrogen gas excited by microwave magentic field

Laser induced breakdown spectroscopy

Ppb

Laser ablation

• Explosion of solid sample sending atoms into gas phase

• Emission of vaporized atoms measured

Mercury analyzers (atomic fluorescence)

Mercury to mercury(0) sample

Mercury and oxygen free argon gas into sample

Mercury(0) sample trapped

Sample heated to release mercury for detection

Xray fluorescence

% to ppm

Sample absorbs xrays then emission of xrays

Xray knocks out electron in K or L shell, electron in higher shell takes it place

L-K Ka

M-K Kb

M-L La

N-L Lb