Spectroscopy: Chapter 8 Flashcards
What are the three spectroscopic methods used for quantitative analysis
- Optical Spectrometry
- Mass Spectrometry
- X-Ray Spectrometry
What are the three types of atomic spectroscopy?
- Atomic Absorption spectroscopy
- Atomic Emission Spectroscopy
- Atomic Fluorescence Spectroscopy
What type of atomic spectroscopy has these characteristics:
- Intensity of emitted radiation measured
- concentration of excited atoms are important
- No External EM source is used
- High temperatures used for atomization
Atomic Emission Spectroscopy (AES)
What type of atomic spectroscopy has these characteristics:
- Absorbance values measured
- Determined concentration by **ground state **atoms
- External EM source needed for incident energy
- Must be in a heated environment
Atomic Absorption Spectroscopy (AAS)
What type of atomic spectroscopy has these characteristics:
- Intensity of re-emitted radiation following absorption is measured
- Requires an external EM source
- Spectrum can be measured 90 degrees to light path
Atomic Fluorescence Spectroscopy (AFS)
What type of high temperature conditions can be used with Atomic Absorption Spectroscopy?
Flames, Electrothermal atomizer (graphite furnace)
What type of high temperature conditions can be used with Atomic Emission Spectroscopy?
Flames, electrothermal atomizer (graphte furnace), AND Plasma (inductively coupled plasma)
Why are narrow line widths desirable in an absorption/emission spectra?
They reduce the possibility of interference due to overlapping lines.
Why is effective line width measured at half of an atomic absoption/emission line?
because the measurement can be made more accuratley at half-peak intensity.
what are the four sources (effects) of line broadening?
- the uncertainty effect
- the doppler effect
- Pressure effects
- electric and magnetic field effects
When does a doppler shift occur?
when an atom moves towards or away a photon detector and emits radiation.
when atom is moving towards = higher frequecy
when atom is moving away= lower frequency
When does Pressure broadening occur?
when the emitting/absorbing species collides with other atoms in the heated medium
what are the two classes of atomizers?
Continous and discrete atomizers
Define a continous atomizer and give an example of one
Samples are introduced continuously
Examples: plasmas, flames
Define a discrete atomizer and give examples
introduced in a discontious manner with a device such as a syringe or an autosampler.
Example: electrothermal atomizer
What is the general method for introducing solution samples into plasmas and flames?
Direct Nebulization
How does nebulization work?
the nebulizer introduces sample as an aerosol
what is an aerosol?
Fine spray of droplets
what are the specific methods used for continous atomization of solutions
- Pneumatic nebulization
- Ultrasonic Nebulization
- Electrothermal vaporization
- Hydride generation
what are the specific methods used for continous atomization of solids?
Direct insertion
Laser ablation
Electrothermal vaporization
what are the specific methods used for continous atomization of conducting solids?
Spark or arc ablation
Glow-discharge sputtering
what is the Bernoulli effect?
that fluids in an area moving faster than the the surrounding area possess less pressure. Faster-moving fluid, lower pressure.
How is the Bernulli effect used to introduce a sample into an instrument?
a liquid sample is drawn into a capllary tube by a high pressure stream of gas flowing around the tip of the tube.
Why are smaller droplets preferred in pnematic nebulization?
we want more surface area in our mist because it can transfer heat faster
Hydride generators enhances sensitivity for which elements? and by how much?
As, Sb, Sn, Se, Bi, Pb
10-100x
which method is most effcient for completely dissovled samples?
Pneumatic nebulizer
Ultrasonic Nebulizer
Elecctrothermal vaporizer
Hydride generator
Ultrasonic Nebulizer
which method is most sensitive in general? and why?
Pneumatic nebulizer
Ultrasonic Nebulizer
Elecctrothermal vaporizer
Hydride generator
Electrothermal Nebulizer
because, it uses a **very small **amount of sample and is a discrete nebulizer
Which method is most effcient for As, Sb, Sn, Bi, and Pb?
Pneumatic nebulizer
Ultrasonic Nebulizer
Elecctrothermal vaporizer
Hydride generator
Hydride generator
Define Reasonance Fluorescence.
excited and emitted radiation have the same wavelength (frequency)
Under what conditions can a stokes shift occur in Atomic Spectroscopy?
when fluorescence occurs at a longer wavelength than the excitation wavelength
What is Boltzmann’s Constant?
1.38 x 10-23 J/K
What is the main difference between AAS and AFS?
AFS doesn’t require an External EM source
