REALLY important NEED to know Flashcards
Matrix Matching
Used in analysis to compensate for matrix effects that influence analytical response.
4 processes of laser
- Pumping, a process by molecules in ground state of a laser is excited to E3 by means of an electrical discharge, passage of an electrical current, or
exposure to an intense radiant source. - Spontaneous Emission, a species in an excited electronic state may lose all or part of its excess energy by spontaneous emission of radiation.
- Stimulated emission, the excited
laser species are struck by photons that have precisely the same energies. Collisions of this type cause the excited species to relax to the lower energy state and to simultaneously emit a photon. The stimulated emission is totally coherent with the incoming radiation. - Absorption, two photons with energies exactly equal are absorbed
XRF
- An incoming x-ray knocks out an electron from an inner atomic orbital
- An unstable electron configuration is produced
- An electron from a higher energy orbital fills the hole and excess energy is emitted as a fluorescence x-rays which can be measured
ICP torch
very very hot and makes ions to use in MS. Analyte must be separated before entering ICP. Laser adsorption to produce ions. Plasma detected through cooling cone. Extraction lens attracts positive ions from plasma. Ions enter collision cell (with H2 or He). Ions guided to mass spec
ESI
used for large molecules where fragmentation is avoided.
Dispersal of fine spray charges droplets followed by solvent evaporation and ion ejection. Sample is injected into high voltage capillary and comes out as a highly charges mist. Solvent evaporated with N2. Molecular ions then repel each other and charged analyte is ejected into mass analyzer.
Matrix Assisted Laser Desorption ionization (MALDI)
Analyte is mixed in matrix solvent and applied to metal plate. A laser light hits causing energy absorption. The analyte is ionized and ejected into gas phase and is then accelerated into chosen MS.
Very expensive but has HIGHEST m/z ratio
Multiple reaction monitoring (MRM) vs Selected “” (SRM) vs product ion scan (PIS
MRM/SRM monitors each precursor ion/product ion transition at a time.
SRM is monitoring only a single fixed mass window
MRM scans rapidly over multiple mass windows and thus acquires traces of multiple fragment ion masses
PIS used for qualitative applications to obtain structural information.
Q1 is set to allow only the transmission of one m/z. The parent ion collides with Argon gas in Q2 to create fragment or product ions. Product ions are scanned through Q3
All allow relative and absolute quantification of proteins, peptides and metabolites.
Adsorption
Solute equilibrates between mobile phase and surface of stationary phase. Adsorbed on surface of stationary phase
Ion- exchange
Ions in mobile phase are attracted to counterions covalently attached to stationary phase. Anion exchange resin
Partition
Solute equilibrates between mobile phase and film of liquid attached to stationary phase. Bonded to surface of column
Affinity
Solute in mobile phase is attracted to specific groups covalently attached to stationary phase. All other molecules wash through
Van deemter equation!!
KNOW
Used to find the optimal flow rate for the best resolution!
H of Van deemter equation
Plate height
A of Van deemter equation
Multiple Flow Paths
The residence time in the column for molecules of the same species is variable. Some flow paths are longer than others.
B/Ux of Van deemter equation
Longitudinal Diffusion
Diffusional broadening of a band. Takes place along axis of column and while band is moving along column by flow of solvent. Species migrate from a more concentrated part of medium to a more dilute. The faster the less diffusional broadening.
Cux of Van deemter equation
Mass Transfer Coefficients
The finite time required for solute to equilibrate between mobile and stationary phases. Cs Rate of mas transfer through stationary phase. Cm is “ “ mobile phase
Chromatography applications
Qualitative and Quantitative
Qualitative: gives either retention time or position on the stationary phase
Quantitative: Peak height (amount of analyte present), Peak area (Shows concentration
Gas vs Liquid chromatography
what is it
mobile phase
stationary phase
cost
analytes
Separation
Van D
Detectors
Look at Image
Open Tubular Column
Advantages and Disadvantages
Common in GC. Made of fused silica and plymides or support and protection.
Offers high resolution, short analysis time and greater sensitivity then packed columns.
has a less sample capacity
Three types of open tubular columns?
Wall Coated: Has a thick film of stationary liquid on inner walls
Support coated: Has solid particles coated with stationary liquid. Can handle larger samples but performance isn’t as good
Porous Layer: Solid particles are the active stationary phase
Making Liquid Stationary phase
The choice is base on “like dissolves like” non-polar columns are the best for non-polar solutes (strong for strong ect..). Surface silanol groups are exposed and strongly retain polar compounds by adsorption. To prevent stationary phase bleed silanol is bonded to silica surface.
Column surface deactivated by silanization.
Column Bleeding?
Occurs at high temperatures where the stationary phase decomposes and the products elevate background signal and increase interference.
How to reduce column bleeding?
To reduce this use the thinnest stationary phase on the narrowest and shortest column
Temperature programming?
Temperature of column is raised during separation to increase analyte vapour pressure and decrease retention time.
white powder?
test to see if the compound is organic or inorganic
1) Burn it → if it burns it is organic, it it doesn’t it is inorganic
2) Do an XRF → if the result is mainly silica it is organic, but if significant amounts of metals are present, it is inorganic
inorganic:
o Do an acid digestion to dissolve the insoluble powder
o Perform atomic absorption spectroscopy to test for metals (ex. Fe, Mn, etc.) and their percent by weight
organic:
o Perform an FT-IR (ATR since insoluble)
o The vibrational spectra gives a very good detailed fingerprint region which will tell us very quickly what the unknown white powder is once compared to reference spectra
priceless painting?
o XRF - X-ray Fluorescence
it is non-destructive and therefore will not ruin or alter this priceless painting
Through XRF, I would obtain a good idea of the sorts of metals present in the pigments the artist used
However, for this information to even mean anything, a known authentic painting from this artist would also need to be analyzed under XRF to obtain a “standard reference” of how much metals are present in the pigments this author is known for using
o FT-IR (ATR)
Can provide information on the bonds in the pigments, canvas/leather/paper used for the painting. Once again, a known authentic painting from this author would need to be analyzed under FT-IR as well to compare to the suspected forgery
o ICP-MS (AAS)
Because ICP-MS requires very little to no sample, a little thread from the canvas or even a small amount of pigment shaved off the edge is enough to test for the 13C/12C isotope ratios
For this to be of use, we must be certain of what kind of canvas or pigment the artist used for his/her work
