Atomic Absorption and Emission

1. The characteristic wavelengths of metals

1. Atomic Absorption Spectroscopy (AAS)
   1. Single light source, single beam
   2. Usually ______________________ at a time
   3. Components of AAS

• 1. Light source – Hollow cathode lamp

i. High voltage to cause buffer gas to ionize – _______________ ii. Ionized buffer gas knocking off atoms from the cathode

• 1. The burner system

i. Sample aspiration ii. Nebulizer turns sample into tiny droplets iii. What happens in the flame? – 2000 °C

• 1. Monochromator and detector

i. _____________________________ – the fingerprint wavelength ii. Detector is usually a ___________

• 1. Double beam AAS

i. _______________ parses light into inconsecutive slices

1. Flameless Atomic Absorption – Graphite furnace atomic absorption spectroscopy (GFAA)
   1. The furnace allows for gradual heating of the sample aliquot in several stages.

i. _____________ of sample ii. Ashing of organic matter iii. ______________________ of analyte atoms

• 1. Allows removal of unwanted components by using temperature programming
  2. Affords extremely ____________ detection limits.

1. Cold Vapor Atomic Absorption (CVAA) Spectroscopy for Hg
   1. Free Hg atoms exist at room temperature
   2. Hg is reduced to the free atomic state by a strong reducing agent, like stannous chloride

(SnCl₂) or sodium borohydride (NaBH₄)

• 1. Closed system

1. Hydride-generation atomic absorption (HGAA) spectroscopy
   1. Chemical reduction to create ___________________________ (AsH₃ and SeH₂)
   2. Must be heated
   3. Can also be used for other metals (e.g., Bi, Ge, Pb, Sb, Sn, and Te)

1. Atomic Emission Spectroscopy (AES)
   1. Usually coupled with Inductively Coupled Plasma – ICP-AES
   2. Sometimes referred to as Inductively coupled plasma optical emission spectrometry

ICP torch

(ICP-OES)

• 1. Can measure ___________ metals at once
  2. More widely used than AAS
  3. Generation of ICP

i. Plasma gas (e.g., Ar) flow to induction coil ii. Switch on radio frequency power

iii. Spark from Tesla Coil causes ionization of Ar iv. Resistance of e- to move with the circular magnetic field causes intense heat –

10,000 °C

• 1. Radial and Axial ICP-AES

i. The axial ICP-AES has a ____________ detection limit than the radial ICP-AES – by as much as a factor of 10.

• 1. Detectors

i. Multiple detectors all set at the _____________________________ for each metal ii. No movement in the system iii. Very accurate

• • 1. Calibration curve is used for quantification
    2. Usually ___________ points ii. Calibration blank
       • • Every ___________ samples
         • Make sure you have stable baseline, no carry over

1. Detection limit comparison

1. Interferences
   • 1. Spectral: When another emission line (e.g., from other elements in the sample) is __________________ the emitted line of the test element and is not resolved by the monochromator
     2. Chemical: Formation of undesired species during atomization
     3. Physical: Variation of ______________________ parameters such as uptake in the burner and atomization efficiency (gas flow rate, sample volume etc.)

1. Sample throughput comparison

1. Equipment cost

1. Analysis cost comparison

1. Sample preparation
   1. If only interested in dissolved metals

i. Filtration

• 1. If interested in both particulates and dissolved metals

i. ____________________________ ii. Break up the ________________________ iii. Acids, heat, sonic system, etc.

• 1. Sequential digestion

i. Extract different types of metals sequentially