Atomic Absorption and Emission
- The characteristic wavelengths of metals
- Atomic Absorption Spectroscopy (AAS)
- Single light source, single beam
- Usually ______________________ at a time
- Components of AAS
- Light source – Hollow cathode lamp
i. High voltage to cause buffer gas to ionize – _______________ ii. Ionized buffer gas knocking off atoms from the cathode
- The burner system
i. Sample aspiration ii. Nebulizer turns sample into tiny droplets iii. What happens in the flame? – 2000 °C
- Monochromator and detector
i. _____________________________ – the fingerprint wavelength ii. Detector is usually a ___________
- Double beam AAS
i. _______________ parses light into inconsecutive slices
- Flameless Atomic Absorption – Graphite furnace atomic absorption spectroscopy (GFAA)
- 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
- Allows removal of unwanted components by using temperature programming
- Affords extremely ____________ detection limits.
- Cold Vapor Atomic Absorption (CVAA) Spectroscopy for Hg
- Free Hg atoms exist at room temperature
- Hg is reduced to the free atomic state by a strong reducing agent, like stannous chloride
(SnCl2) or sodium borohydride (NaBH4)
- Closed system
- Hydride-generation atomic absorption (HGAA) spectroscopy
- Chemical reduction to create ___________________________ (AsH3 and SeH2)
- Must be heated
- Can also be used for other metals (e.g., Bi, Ge, Pb, Sb, Sn, and Te)
- Atomic Emission Spectroscopy (AES)
- Usually coupled with Inductively Coupled Plasma – ICP-AES
- Sometimes referred to as Inductively coupled plasma optical emission spectrometry
ICP torch
(ICP-OES)
- Can measure ___________ metals at once
- More widely used than AAS
- 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
- 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.
- Detectors
i. Multiple detectors all set at the _____________________________ for each metal ii. No movement in the system iii. Very accurate
- Calibration curve is used for quantification
- Usually ___________ points ii. Calibration blank
- Every ___________ samples
- Make sure you have stable baseline, no carry over
- Detection limit comparison
- Interferences
- 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
- Chemical: Formation of undesired species during atomization
- Physical: Variation of ______________________ parameters such as uptake in the burner and atomization efficiency (gas flow rate, sample volume etc.)
- Sample throughput comparison
- Equipment cost
- Analysis cost comparison
- Sample preparation
- If only interested in dissolved metals
i. Filtration
- If interested in both particulates and dissolved metals
i. ____________________________ ii. Break up the ________________________ iii. Acids, heat, sonic system, etc.
- Sequential digestion
i. Extract different types of metals sequentially