Spectrochemical Analysis

Electromagnetic Radiation

Energy propagated by an electromagnetic field, having both particle and wave nature.

E h

hc h 6.626 10 34 J s

Photon

A “packet” of energy released when a single atom or molecule relaxes from an excited energy state to a lower lying state via a radiative transition.

Spectrum

A display of the intensity of radiation emitted. Absorbed, or scattered by a sample, versus a quantity related to photon energy (such as wavelength or frequency).

Spectrum

Wavelength (nm)

494.5 495.0 495.5 496.0

c(Fe + Fe)

CrFeFeFeNi

494.5 495.0 495.5 496.0

Wavelegnth (nm)

Fe

Fe

CrFe

Fe

Fe

Ni

Why Dark Lines in the Solar Spectrum?

The discovery of atomic spectra

Spectroscopy

The branch of physical science treating the theory and interpretation of spectra.

Spectrometry

The quantitative measurement of the intensity of radiation at one or more wavelengths using a photoelectric detector.

Spectrochemical Analysis

A spectrum, or some aspect of a spectrum, is used to ascertain the identity and/or concentration of the components of a sample.

Spectrochemical Phenomena(how light interacts with matter)

1. Emission:

The release of a photon during a transition between energy states (regardless of the means of excitation). Number of photons tells how many transition. Energy of photons tell which transitions.

Emission (neon sign)

Types of Emission

A. Atomic Emission: excited by collisions

B. Chemiluminescence: excited by reaction

C. Triboluminescence: excited by friction

D. Photoluminescence: excited by photons

Photoluminescence

Fluorescence: Transition between two singlet states.

Phosphorescence: transition between am excited triplet state and a singlet ground state.

Jablonski Diagram

Absorption

Absorption

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1

Concentration (mM)

Tra

nsm

itta

nce

or

Ab

sorb

ance

Beer’s Law

A = -log T = εbc

where:

A = Absorbance (no units)

T = Transmittance (no units)

ε = molar absorptivity (L cm-1 mole-1)

b = sample path length (cm)

c = concentration (M)

Miscellaneous Interactions