Long Exam 1 Flashcards
Process involving the emission of light from any substance in the excited states
fluorescence
What is a flurophore
any type of material that fluoresces
what are the two types of fluorophore
1.) endogenous — naturally occurring (amino acids such as tryptophan, tyrosine, phenylalanine)
2.) exogenous — synthesized such as organic dyes or fluorescent tags (fluorescein)
what is a fluorescein?
it acts like a chromophoric reagent and used to be attached on compounds that do not fluoresce
TRUE OR FALSE: Not all compounds fluoresce
False. All compounds fluoresce but not all are evident because some only have insignificant amounts of fluorescing components.
TRUE OR FALSE: Fluorescence is an emission energy
TRUE
TRUE OR FALSE: fluorophore can absorb/emit light
TRUE
explain the Jablonski energy diagram
.
duration of excitation (absorption)
10^-16 seconds
duration of internal conversion and vibrational relaxation
10^-14 to 10^-11
duration of fluorescence
10^-9 to 10^7 sec
what is excited triplet state
- also called as forbidden state
-slightly lower than the excited state
compounds that are most likely to fluoresce
-containing aromatic rings (most intense and most useful for molecular fluorescence emission)
-some aliphatic and alicyclic compounds
- compounds that are highly conjugated
equation of fluorescence spectroscopy and define the parameters
F = 2.303K Io ebc
F = fluorescence intensity
K = constant based on instrument geometry
Io = intensity of the excitation light
a = fluorophore’s molar absorptivity
b = pathlength
c = concentration
differentiate different types of spectroscopy
absorption (UV-Vis, AAS)
-linear (source to wavelength selector)
-has light source
emission (AES)
-linear
-no light source
emission (fluorescence)
-90 degree angle (source-sample-wavelength selector)
-has light source
give some light source/lamps for fluorescence spectrometer
Mercury arc lamp (366, 405, 436, 546, 578 nm)
Xenon arc lamp ( 250-1000 nm)
Tungsten-halogen lamp (350-1000 nm)
Blue diode laser/LED (4xx nm)
Helium-cadmium laser (325, 442 nm)
Argon ion laser (457, 488, 514 nm)
YAG Laser (532 nm
Helium-neon laser (633 nm)
Yellow diode laser/LED (5XX nm)
Krypton ion laser (568, 647 nm)
Red diode laser (6xx nm)
what are some metals that can be analyzed via AAS?
Alkali Metals (Li, Na, K, Rb, Cs)
Alkaline Earth Metals (Be, Mg, Ca, Sr, Ba)
Sc, Y, Ti, Zr, V, Nb, Ta, Cr, Mb, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Hg
Triels (B, Al, Ga, In, Tl)
Tetrels (Si, Ge, Sn, Pb)
Pnictogens (As, Sb, Bi)
Chalcogen (As, Sb, Bi)
Can nonmetals be analyzed using AAS?
Yes. As long as atoms can be converted into gas phase
differentiate the atomic absorption techniques
1.) Flame Atomic Absorption (FAAS)
-air (oxidizer)
-acetylene (fuel)
-samples in the form of LIQUID ONLY
-2360 up to 2600K
-you need enough amount of sample
2.) Electrothermal AAS
-no more flame
-you can place your sample in a an electrically graphite tube
-consistent temp profile
-up to 3000K
-better accuracy
-requires less sample
-LOD to 100 ppb
- samples can be in the form of solution, slurries, solid samples
best analyzed by AES only
elements
Na, K, Rb, Sr, Co, Th, Eu, P, S
Requires N2O/C2H2 flame. Better analyzed by inductively coupled plasma (ICP) only
elements
Ba, Sc, Ti, V, Zr, Nb, Mo, Si, Ge, Hf, Ta, W, Os, Ir, Nd, Dy, Ho, Er
can be analyzed via both ICP and AES
elements
Ba, Pr, Y, La, U, Sm, Gd, Tb, B, Al
Enumerate the components of the AAS
Light source
Flame
Nebulizer
Monochromator
Detector
Computer
part of the AAS that provides analytical light for the element of interest and provides constant and intense beam
Light Source
Light source of the AAS can be composed of
-hollow cathode la,p
electrodeless discharge lamp
-lasers
part of the AAS that aspirates liquid aerosol at control rate, forms fine aerosol, and mix aerosol, fuel, and oxidant
what are its specific parts?
nebulizer
specific parts:
-capillary tubing
-glass bead adjuster
-venturi
-oxidant
-glass bead
-spray chamber
-drain
part of the AAS that destroy analyte ions and breakdown complexes
it creates atoms (the elemental form) of the element of interest
Flame
Fuels and their corresponding oxidants for the AAS flame
Fuel: Acetylene
Oxidant: Air
Temp: 2400 to 2700 K
Fuel: Acetylene
Oxidant: Nitrous oxide
Temp:2900-3100 K
Fuel: Acetylene
Oxidant: Oxygen
Temp: 3300-3400
Fuel: Hydrogen
Oxidant: Air
Temp: 2300-2400
Fuel: Hydrogen
Oxidant:Oxygen
Temp: 2800-3000
Fuel: Cyanogen
Oxidant: Oxygen
Temp: 4800 K
used in electrothermal AAS that is more sensitive than a flame
this is used to introduce the sample in the AAS
Graphite Furnace
Typical fuel for electrothermal
Argon gas
purpose of matrix modifier
-changes the behavior of the analyte element or matrix in solution wrt temperature
-increases the volatility of the matrix
everything in a sample other than the analyte. it decomposes and vaporizes during the charring
Matrix
it isolates the wavelength of the maximum absorbance
monochromator
what is/are the purpose of monochrometer in the AAS?
-isolate analytical lines’ photons passing through the flame
-remove scattered light of other wavelengths from the flame so that only a narrow spectral line impinges on the photomultiplier tubes
-allows only light not absorbed by sample to reach the pm tubes
it determines the intensity of photons of the analytical line exiting the monochromator
detector
types of detectors for AAS
-photomultiplier tubes
-solid state detector
what are differrent types of interferences
-spectral interferences
-chemical interferences
-ionization interference
-matrix effect
-broadening of spectral lines
it is the type of interference where there is an overlap of the analyte signal with signals due to other elements or molecules in the sample or with signals due to the flame or furnace
how can we resolve this type of interference?
spectral interference
1.) do background correctiom
2.) choose different wavelength for the analysis
a type of interference wherein any component of the sample decreases the atomization of the analyte
how to resolve this interference?
chemical interference
use of releasing agent to release the analyte (breaks the possible bonds with the other components)
a type of interference wherein the ionization of analyte atoms decreases the concentration of neutral atoms
how to resolve this?
Ionization Interference
use of ionization suppressor (decreases the extent of ionization of analyte)
a type of interference where it can either suppress or enhance the absorbance signal of the analyte. it occurs when components of sample matrix other than the analyte react to form molecular species and sample background
matrix effect
broadening of spectral lines can be caused by
-doppler effect
-lorentz effect
-quenching effect
-self absorption or self reversal effect
this happens due to atoms having different components of velocity along the line of observation
Doppler effect
in the doppler effect, atoms moving towards the source absorb ________ whereas atoms moving away the source absorb ______
lower frequency (longer wavelength), higher frequency
result of the concentration of foreign atoms present in the environment of the emitting or absorbing atoms
Lorentz effect
presence of foreign gas molecules that affects the flame/same spectral lines or resonance with the analyte
quenching effect
atom emits instead of absorbing
self absorption/self reversal
conversion of analyte to gas phase atoms
atomization
provide sufficient energy to promote valence electrons of an atom from ground state to excited state
excitation
emission
excited electron relaxed back to ground state giving back their energy as atomic emission
compare/contrast AES and AAS
AAS
-has light source
-uses flame for atomization
AES
-no light source
-uses inductively-coupled plasma (icp) instead of flame
compare/contrast flame and icp
FLAME
Temp: 1700-3150 K
Spectroscopy: AAS/AES
Boltzmann Distribution: 8.75 x 10e-4
ICP
Temp: 4000-6000K
Spectroscopy: ICP-AES, ICP-MS
Boltzmann Distribution: 512 x 10e-4
according to Boltzmann distribution equation, the higher distribution means that?
the are more population in the excited state
there will be more atoms that will emit energy
how is icp initiated?
spark from a Tesla coil
fuel for ICP
Argon gas
what does the induction coil do?
creates an alternating radio frequency and create a fluctuating magnetic field that induces the argon ions and the analyte to move in a circular path
the production of light can be measured in what orientation?
which is more accurate?
1.) radial
2.)axis
radial view is much preferred because it has higher LOD and precision
How do we analyze AES? Explain the method used.
Standard Addition method
-we prepare a standard
-dilute them to obtain at least 5 standards with different known concentrations
-we measure their absorbances
-we get the x-intercept. that is the concentration of the sample without any of the standards.
this type of analysis is used to analyze colored samples. it is also used to monitor titrations
UV-Vis spectrophotometer
species that strongly absorb to UV raidiation
double bonds
what is a chromophore?
anything that is pigmented
give some examples of chromophore
-alkene
-conjugated alkene
-alkyne
-carbonyl
-carboxyl
-amido
-azo
-nitro
-nitroso
-nitrate
-aromatic
give an example of solvent
n-heptane
n-hexane
ethanol
water
isooctane
dioxane
how to conduct UV-Vis experiment?
1.) wavelength scan - we determine the maximum wavelength
2.)set the instrument at the maximum wavelength and determine the absorbance of the prepared samples with different concentrations but run the blank first
for inorganic compounds, how does absorption take place?
when electrons make transitions between filled and unfilled d orbitals with energies that depend on the ligands bonded to the metal ions.
what if we want to analyze colorless samples via UV Vis?
we react the colorless sample to a chromophoric reagent
it is a complex that consists of an electron donor group bonded to an electron acceptor
charge-transfer complex
what happens when the charge-transfer complex after being subjected to the UV Vis spectrophotometer?
the electron from the donor is transferred to an orbital that is associated with the acceptor
the excited state is thus the product o a kind of redox process
Give some solvents and their LOWER wavelength limit in nm
water - 180 nm
ethanol - 220 nm
hexane - 200 nm
cyclohexane 200 nm
carbon tetrachloride - 260 nm
diethyl ether - 210 nm
cetone - 330 nm
dioxane - 320 nm
cellosolve - 320 nm
criteria for UV Vis spectrophotometry
1.) sample solutions must be diluted
2.) the solvent must be transparent in the region of the spectrum where the sample absorbs
3.)the analyte must be sufficiently soluble in the solvent
some metals do not absorb/absorb at lower wavelengths which makes the analysis impossible/difficult. however, if they are reacted to species such as diethyldithiocarbamate and diphenylthiocarbazobne, analysis via UV Vis spectrophotometer is possible. how is this so?
the formation of the metal-ligand complexes produces color. the color is caused by the excitation of electrons in the d orbital
differentiate:
spectrophotometer, spectrometer, and photometer.
1.) spectrophotometer - kind of spectrometer
-gets the ratio of the radiant powers of two beams
-has monochromator for wavelength selection
2.)spectrometer - converts electrical intensities into electrical signals
-uses monochromator or polyhromator
3.) photometer - uses a filter for wavelength selection
-much simpler
a type of UV Vis spectrophotometer where radiation from the filter passes through either the reference or sample cell before striking the photodetector
-this type of UV Vis spectrophotometer is where you add your sample and your black — taking it out and taking it back every after analysis
single beam instrument
a type of UV Vis instrument where radiation from the filter split into two beams that simultaneously pass through reference and sample cells before striking 2 matched photodetectors
-you don’t have to remove and return your sample and your solvent.
-gets the ratio of the absorbance of the sample and the solvent
-has two photodetectors
Double beam instrument
a type of instrument where the beam is alternately sent through reference and sample cells, striking a single photodetector. a period of only a few milliseconds separates the beams as they pass through the two cells.
double-beam in time
what is EM radiation?
emission and transmission of energy in the form of electromagnetic waves
-radiation that reacts with the analyte
TRUE or FALSE: higher energy means higher frequency
TRUE. energy is directly proportional to frequency but inversely proportional to wavelength
EM radiation that can be seen by our naked eye
visible light
380-420 nm
Color absorbed?
Color observed?
CA: Violet
CO: Green-yellow
420-440 nm
color absorbed?
color observed?
CA: Violet-blue
CO: Yellow
440-470 nm
color absorbed?
color observed?
CA: Blue
CO: Orange
recite the electromagnetic spectrum
.
5 basic parts of spectrophotometer
light source
monochromator
cuvette
detector
digital display or meter
Criteria for light source
1.) sufficient power ready for detection and measurement
2.) sufficient electromagnetic radiation
3.) constant beam with high intensity output
characteristics of a good detector
1.) high sensitivity
2.) high signal to noise ratio
3.) constant response over a considerable range of wavelengths
4.) fast response time
5.) minimal output signal in the absence of illumination
