Atomic Absorption Flashcards
how do atomic absorption and emission wavelengths differ?
Absorption:
what type of lamp is used in atomic absorption spec?
hollow-cathode lamp
how does a hollow-cathode lamp differ from deuterium and tungsten lamps?
atomic absorption experiments require lamps that produce light only at characteristic wave - lengths for the element(s) being analyzed.
what would this lamp need in it to analyze Fe?
Fe
Hollow-cathode - it only produces light at the characteristic wavelengths for Fe, Ni, and Cr
what is the simple schematic of an atomic absorption instrument?
lamp –> atomizer –> monochromator –> detector
what is the role of the atomizer?
breaking the analyte down into gaseous atoms.
how does the location and role of the monochromator differ in an atomic absorption instrument vs a UV/Vis instrument?
Atomic Absorption: removing light from the flame from other wavelengths from reaching detector.
UV/Vis: selecting the wavelengths of light that will go through the sample.
how do molecular and atomic absorption bands differ?
Molecular: uses solutions in a cuvette. (non-destructive)
Atomic: cannot analyze directly in a cuvette. (destructive)
what is the role of the flame in atomic absorption experiments?
flame atomizes samples to produce atoms that are primarily in the ground electronic state.
what is the tole of the flame in a flame atomic emission experiment?
promotes some atoms to excited electron states from which they can emit photons to return to lower energy states
how much of the sample actually gets to the flame? why?
~5% because once the sample becomes an aerosol, the excess liquid is flowed out into waste.
what is signal to noise (S:N) what is it used for?
determines the lower limits of detection and quantitation
determines what can be reported reliably.
what is LLOD and LLOQ?
LLOD (detection): where signal is 3x the noise.
LLOQ (quantitation): where signal is 10x the noise.
how does a furnace differ from the flame?
furnace is like a tube, Ar gas flows through to keep it from igniting, and it uses longitudinal heating, leaving cool spots at the end.
in general, how does the furnace work? - what are the four stages of the heating steps?
- Drying - dries the sample
- Charring - decomposes the sample
- Atomizing - atomizes the sample
- cleaning - cleans out remaining residue
why is transverse more consistent? what sometimes happens with longitudinally heated furnaces?
The transverse is more consistent because it is more evenly heated.
what is the L’vov platform?
small platforms in the furnace
when do we know the furnace needs replacing?
degradation of peak shape
loss of precision
large change of slope of a calibration curve
what do we use a matrix modifier for?
added to matrix to suppress unwanted background signals from matrix
(increases volatility of matrix - vapor at lower temp)
(decreases volatility of anayte - vapor at higher temp)
what is plasma?
a gas hot enough to contain ions and free electrons
how do ICP and MP differ?
ICP: inductively coupled plasma (liquid sample is pumped slowly into nebulizer)
MP: microwaved plasma (uses nitrogen, can look for more than 1 element at a time)
what is the impact of temperature on atomic emission spectroscopy?
the degree to which the a sample breaks down into atoms
the extent to which a given atom is found in its ground, excited, or ionized states
what is the role of monochromator in atomic spectroscopy?
to stop polychromatic light emitted from the flame form burying the signal form lamp (AA) and sample (emission)
how do we perform background correction?
beam chopping and deuterium lamp
how does beam chopping work?
A) when the chopper transmits the hollow-cathode lamp, light from both lamp and flame to reach the detector
B) When it blocks, only flame light can reach the detector
(subtracting signal A from signal B)
how does deuterium lamp correction work?
light from lamp is alternated through the flame
what are four types of interferences??
- spectral: unwanted signals overlapping analyte signal
- physical: viscosity / density of solutions altering nebulation and transport of analyte atoms
- chemical: chemical reactions decreasing the [] of analyte atoms
- ionization: ionization of analyte atoms decreasing the [] of neutral atoms.
why might I pick one technique over the other? Flame, furnace, and plasma
Cost of fuel (acetylene vs argon)
sensitivity needs
desire to analyze multiple compounds simultaneously.
