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trace elements
small quantities of elements present in products and natural materials (concentrations less than 1%)
provide invisible markers
may establish the source of a material or provide additional points for comparison
primary techniques for determining the elemental composition of inorganic materials
wet chemical analysis
atomic spectroscopy
neuron activation analysis
x-ray diffraction
inorganics
often encountered as physical evidence
metals and nonmetals
analyze tools, coins, weapons, explosives, poisons, and metal scrapings, and trace components in paints and dyes
wet chemical analyses
gravimetric analysis
titrimetric analysis
colorimetric analysis
gravimetric analysis
especially useful for the analysis of metals
ex: how much copper is in a penny
titrimetric analysis
most useful for acids and bases, can be used for metals
colorimetric analysis
can be performed with a simple color change in a solution that’s measured using a UV-Vis spectrometer
ex: can test for led-based paint
absorption spectroscopy
measures the amount of light energy absorbed by an atom when exciting electrons
emission spectroscopy
collects and measures the various light energies given off by the atom
Stoke’s shift
energy levels
each element has its own set of ______
each will emit its own set of frequencies (unique fingerprint)
atomic absorption spectroscopy (AAS)
sputter a liquid sample with analyte into a vapor
an acetylene flame burns the vapor
absorbs certain wavelengths from a light source specific to the analyte (different bulbs for different metals)
great for most metals
graphite furnace AAS
sample is atomized in a graphite tube at very high electric current and temperature
much higher sensitivity than flame
Atomic Emission Spectroscopy (AES)
atomic emission spectrophotometer heats samples so that the atoms in the material achieve an “excited” state
under these circumstances the excited atoms will emit light
if the light is separated into components, one observes a line spectrum (each element in the spectrum can by identified by its characteristic line frequencies—can be matched line for line in a comparison between samples)
Inductively coupled Argon Plasma (ICAP/ICP)
uses ionized argon at very high temperatures (10,000K)
sample is atomized in Ar plasma and the resulting emission lines are measured
much higher sensitivity than AAS
x-ray diffraction
applied to the study of solid, crystalline materials
as the x-rays penetrate the crystal, a portion of the beam is reflected by each of the atomic planes
diffraction pattern
a unique series of light and dark bands formed as the reflected beams leave the crystal’s planes and combine with one another in x-ray diffraction
every compound has a unique diffraction pattern (a way to fingerprint inorganic compounds)
