Lecture7-9 Flashcards
What is spectrometry?
Method used to acquire a quantitative measurement of the spectrum.
Practical application.
What is spectroscopy?
Science of studying interaction between matter and radiated energy.
Theoretical approach.
What is light?
Light is electromagnetic radiation which can be understood as an electromagnetic wave that travels through vacuum at the speed of light c and can be characterized by either its wavelength lenda or its frequency v.
Any material that can _____ light of a certain _____ will also _____ light of that _____
emit
wavelength
absorb
wavelength
What is atomic absorption?
Atomic absorption is the measurement of the absorption of optical radiation by atoms in the gaseous state.
3 forms of atomic spectroscopy?
- Atomic emission signal (–>monochromator–>detector)
- Atomic absorption, Hollow-cathode lamp
- Atomic fluorescence signal, Laser
What does the atomic emission transitions look like?
two arrows pointing downward.
How does atomic absorption transitions look like?
two arrows pointing upward.
How does atomic fluorescence transitions look like?
one arrow pointing up, two blue arrows pointing down (emission), one black arrow pointing down at excited states (nonradiative).
How does atomic absorption signal work?
Hollow cathode lamp - P0 - Flame - P - Monochromator - Detector - Amplifier - Computer
Formula to calculate Absorption A
Absorption A = log(Io/It) = kcd
AFS
Atomic Fluorescence Spectroscopy
Why AFS use more often than AAS?
AFS is often more sensitive than AAS because weak fluorescence signal can be observed above a dark background; not widely use.
AAS
Atomic Absorption Spectroscopy
Atomization
- flame (____)
- electrically heated ____ ____ (GFAAS) }
- ____ ____ ____ (ICP) } of most practical relevance
- heated quartz cell (____ ____)
FAAS
graphite furnace
inductively coupled plasma
hydride technique
Name of the tube that inject liquid to glass bead?
pneumatic nebulizer
Minimum amount of sample that is needed for FAAS?
1-2mL
Most common fuel oxidizer: ____/__
30 so-called ____ that from stable oxides -> need ____ flame to prevent this. Height in flame at which ___ atomic absorption/emission observed must be manually optimized and depends on:____, ____, ____
acetylene/air
“refractory elements” hotter maximum
element, fuel / oxidizer flow rate / nebulization speed
Graphite furnaces: electrically heated ____ can also be used to generate atoms from sample analyte.
Advantages? (2 of them)
hollow graphite tube
- less sample needed (5-100uL)
- more sensitive than flame
How long do atoms in the ground state reside in optical path? also called ____?
flame < 1s
furnace: several seconds b/c atomic “cloud” confined by tube
How are atoms generated? What must be carefully optimized? What should be carefully for first step and second step?
dry - ash - atomize - clean - cool
temperature
avoid splatter
no analyte loss
Ar gas passed through graphite tube, typical temperature program:
dry: 60C for 20s (remove solvent)
ash: 1400C for 60s (destroy organic matter)
atomize: (2300C for 6s)
clean: 2700C for 3s + cool (60s)
For elements that form _____ with carbon from the tube, use ____
carbides
pyrolytically deposited carbon tubes
Additional advantages of furnace:
- pre-concentration
- analyze solid samples
(impossible with flame)
Everything other than analyte in sample = _____, ideally _____ decomposes and vaporizes during ashing if ____ constitutes a problem -> need to add a _________, to increase volatility of ____ and decrease volatility of _____.
matrix matrix matrix
matrix modifier
matrix analyte
NaCl + NH4NO3 = NaNO3 + NH4Cl, it’s called ____
sublime (at 400C)
Other matrix modifiers: Pd(NO3)2, added to seawater to ____ volatility of Sb: without modifier 90% of Sb lost during ____ step at 1250C; with the ______ seawater matrix can be evaporated at 1400C without loss of Sb.
decrease
matrix modifier
Other matrix modifiers: Mg(NO3)2, raise ____ temperature of Al at high temperature of Al ____ by MgO (g). 3MgO(g) + 2Al(s) -> 3Mg(g) + Al2O3(s) when all MgO(g) evaporated reaction no longer occurs and Al2O3 decomposes.
atomization
retarded
______ increases boiling point of ____ -> higher ____ temperature can be used without losing analyte.
matrix modifier
analyte
ashing
Inductively coupled plasma: induction coil connected to a high ____ current generator -> generates ____ magnetic fields ____ oriented inside coil -> Tesla discharge ______ ionizes Ar -> free e- accelerated by _____ collide with ____ and ____ + transfer energy to entire gas (6000-10000K)
frequency oscillating
axially ignition
radio frequency field
atoms ions
Advantage of ICP: high temperature, _____ + _____ inert Ar environment, this eliminates _____ (flame), allows _____ multielement analysis.
stability relatively
interferences
simultaneous
Heated quartz cell (hydride technique) advantage: _____ and _____ of analyte and complete _____ of interferences.
separation enrichment
elimination
How temperature affects atomic spectroscopy: temperature determines: 1. ____ to which sample breaks down (FAAS/GFAAS) 2. ____ to which atom found in ____/____/____
degree
extent
ground/excited/ionized state
Boltzmann distribution describes _______ of different states at _______.
If _____ exists, _________ (N*/N) of any two states is _________.
k (Boltzmann’s constant) = _____
relative populations thermal equilibrium equilibrium relative population N*/No = g*/go *e^(-delta E/kT) k = 1.381*10^(-23) J/K
Critical in atomic emission spectroscopy that ____ is very stable or _______ will vary significantly.
flame
emission intensity
Instrumentation: atomic line widths. Beer’s Law requires that _____ of _______ must be narrower than _____ in atomic sample vapor, otherwise measured _____ not be _____ to sample concentration.
linewidth radiation
linewidth absorbance
proportional
Linewidth governed by ______
Heisenberg uncertainty principle
Hollow cathode lamp: _____ cannot isolate lines narrower than _____-> produce narrow lines with correct lenda, we use hollow cathode lamps.
monochromators
10^(-3) - 10^(-2)
Hollow cathode lamp made of element we want to analyze for:1. when 500V applied -> gas ____ and + ions accelerated toward ____2. lamp maintained at ____ 3. ____ strike cathode -> metal ____ into gas phase -> gaseous atoms collide with high energy electrons to ____ protons 4. atoms in lamp lamp emission narrower
ionized cathode
2-30mA cations
sputtered emit
flame
multi-element detection with inductively coupled plasma: an ______ does not require any ____ and can measure as many as ___ elements simultaneously.
ICP-AES
lamps
70
two types of configurations
- color plate
2. box purged with Ar to exclude O2 to observe lenda 100-200nm halogens + S,P,C and N
Standard solutions for FAAS not necessarily suitable for _____ techniques and GFAAS: need extremely pure water and ___ to avoid contamination (_____, ____); clear room conditions (no dust). Standard solutions have limited ____ and _____ will change the _____ over time.
ICP-based aids trace metal grade acids, Teflon vessels
shelf life evaporation concentration
Definition of interference?
any effect that changes signal while analyte concentration remains unchanged.
_____ interference: _____ reactions decreasing [ ] of analyte atoms.
_____ interference: _____ of analyte atoms dereasing [ ] of neutral atoms. Desired signal is ____.
Chemical chemical
Ionization ionization decreased
Virtues of inductively coupled plasma: eliminates many common ____: two times as hot as flame, _____ more complete and intense and no formation of ______.
interferences
atomization
refractory oxides/hydroxides
____ remarkably free of background radiation. _____ is a problem in FAAS, but not in ____ because _____ more uniform.
plasma
self-absorption
ICP
temperature
ICP-AES: atomization at > ____, dominant form today. In contrast to AAS and AFS _____ is needed. ______ proportional to analyte [ ] in sample.
6000K
no lamp
emission intensity
ICP-MS: ionization energy of Ar: ___, ___ than that of all elements except He, Ne and F. Ar plasma: analyte elements ionized by ____ with Ar+ excited Ar atoms or energetic e-, direct plasma at MS, can measure ___ and ___ at very low [ ].
15.8eV greater collisions
metals metalloids
matrix can have ____ effect on yield of ions generated in plasma: ___________ in same matrix as unknown -> ______
profound
calibration standards
standard addition
_____ interference: interference by ___ of similar mass-to-charge ratio.
Use a high resolution _____ to resolve species.
isobaric
ions
ICP-MS
What’s normal mass?
integer mass of most abundant isotope of each of the constituent atoms.
MS = a technique for studying masses of ___/___/______: desorb ____ species; ____ them; ____ ions; separate ions according to ___/___ ratio; ____. If all species have a charge of +1, m/z is ___ to mass; if an ion has a charge of +2, m/z is ___ of mass.
atoms/ molecules/ fragments of molecules
gaseous ionize accelerate mass/charge (m/z) detection
equal half
magnetic sector mass spectrometer formula:
m/z = eB^2r^2/2V
EI stands for? e- emitted from a hot ____ accelerated, ___ electrons interact with incoming (neutral) molecules. ____ of molecules (M) absorb ____, enough for ionization.
electron ionization
filament 70eV
0.01% 12-15eV
If we lower E in ______, _____ yield of ions + less ______, higher chance to observe M+. 70eV customarily used because it gives reproducible _____ that can be compared with spectra in a library. Most intense peak = _____. ____ of all other peaks expressed as % of _____
ionization source lower fragmentation
fragmentation base peak
intensities base peak intensity
Resolving power: each mass spectral peak has ____, _____ how closely 2 peaks could be spaced and still be resolved the _____ the resolving power of a ___, better able to separate 2 peaks of similar mass.
width
limits
higher
MS
