exam 3 Flashcards
MS
mass spectrometry
GC
gas chromatography
HPLC
high performance liquid chromatography
TIC
total ion current
SIC
select ion current
WCOT
wall-coated open tubular
HETP
height equal to theoretical plate
FID
flame ionization detector
TCD
thermal conductivity detector
ECD
electron capture detector
ion exchange
analytes are electrostatically attached to permanently charged groups bonded to a resin head
analytes are electrostatically attached to permanently charged groups bonded to a resin head
ion exchange
adsorption
analytes stick to the surface of a solid stationary phase
analytes stick to the surface of a solid stationary phase
adsorption
partition
analytes dissolve in a liquid stationary phase or in a liquid bonded to or coated on a solid stationary phase
analytes dissolve in a liquid stationary phase or in a liquid bonded to or coated on a solid stationary phase
partition
gel exclusion
analytes are separated by size/shape
analytes are separated by size/shape
gel exclusion
affinity
analytes adhere to groups attached to the stationary phase via very specific molecular mechanisms
analytes adhere to groups attached to the stationary phase via very specific molecular mechanisms
affinity
Van Deemter equation: A
A = multiple path lengths (unaffected by U)
Van Deemter equation: B
B = longitudinal diffusion, constant rate (minimizes with increase in flow)
Van Deemter equation: C
C = finite mass transfer rate, equilibration time (minimizes with decrease in flow)
Who discovered chromatography?
Tswett
In order to analyze a sample by GC, what properties must the analytes possess?
boiling point less than 350 C
thermally stable up to 350 C
HPLC columns have lengths in which range?
5 to 30 cm
Open tubular GC columns typically have lengths in which range?
30 to 100 m
Which of the following detectors is most commonly used for HPLC?
UV
Which of the following detectors is considered a universal detector for GC?
TCD
Which detector would be best for the trace analysis of halogenated pesticides by GC?
ECD
What are advantages of an MS detector in GC or HPLC?
responds to all analytes
mass spectrum is strong proof of identity
TIC is proportional to concentration
In size-exclusion chromatography when would a high molecular weight protein elite relative to a small molecular weight molecule?
earlier in the chromatogram
Which is the best choice for mobile phase GC?
He
octanoic, benzoic, and 1-aminooctane separated in reverse phase HPLC. which elutes first?
1-aminooctane
nonpolar, reverse phase, separated with 65% methanol in water
90% methanol in water?
molecules would elute faster
polar, normal phase, 40% 2-propanol in MTBE
60% 2-propanol in MTBE?
molecules would elute faster
AES
atomic emissions spectroscopy
UV
ultra-violet
A
absorbance
IR
infrared
ICP
inductively-coupled plasma
T
transmittance
lambda
wavelength
weird V
frequency
weird E
molar absorptivity
PDA
photo diode array
molar spectra are called
bands
atomic spectra are called
lines
doubling the frequency does what to energy?
doubles the energy
doubling the wavelength does what to the energy?
halves the energy
tripling the wave number will do what to the energy?
triples the energy
absorption spectrums plots consist of
absorbance, wavelength, and molar absorptivity
which radiation is highest in energy?
ultra-violet
which radiation has the longest wavelength?
microwaves
when an atom/molecule absorbs visible light, what transition does the electron undergo?
electronic
when an atom/molecule absorbs infrared light, what transition does it undergo?
rotational-vibrational
Beer’s Law requires
monochromatic light
dilute solutions (<0.01 M)
steady temperature
standard source of UV light
deuterium lamp
hollow cathode lamp
frequency tuner for sources of light (lasers)
provide characteristic wavelengths
provide band of wavelengths more narrow than absorption bands
globar
thermal light source for IR spectroscopy
best precision for absorbance readings?
0.3 - 2.0
when a molecule absorbs a photon
the energy is released as heat
what is true of fluorescence?
fast with lifetimes of 10-8 to 10-4 sec
typically from rigid molecules
what is true of phosphorescence?
slower with lifetimes of 10-4 to 10+2 sec
typically from rigid molecules (solids)
triplet to singlet transition
what technique has the lowest detection limit?
fluorescence
intersystem crossing is
an electron moving from a singlet excited state to a triplet excited state
what is true about atomic spectroscopy?
form of elemental analysis
most useful for metals
analytes are in the gas phase
Which technique is most sensitive to variations in flame/plasma temps?
flame AES
typical plasma temp range for ICP
6,000 to 10,000 K
advantages of ICP over flame AAS an AES
lower detection limits
broader linear range
advantages of ICP MS over ICP AES
lower detection range
broader linear range