Unit 7 Flashcards
(27 cards)
define chromatographic detector
a device that measures the change of composition of the effluent
gives you the retention time
what is the qualitative and quantitative information pertinent to chromatography?
what is each defined by?
qualitative: identity of chemicals in the sample
- retention time of chemical entering detector
- detector specific (ie. absorbance wavelength, m/z in mass spectrum)
quantitative: mass or concentration of chemicals entering the detector
- signal intensity vs amount of chemical
detectors are coupled w/ what?
liquid chromatography
ion chromatography
capillary electrophoresis
what wavelength is used for UV-Vis?
190-600nm
what is an important law for UV-vis?
beers law
how is the wavelength for UV-Vis selected?
it is wavelength that provides max absorbance
what is the equation of beer’s law?
what are each of the variables?
A=E.L.c
A= absorbance e= molar extinction coefficient K= path length of cell C= molar sample concentration
what are systems used for UV-Vis?
- one fixed wavelength
- one variable wavelength
- multiple variable wavelengths (DAD or PDA)
what is UV-vis coupled to usually?
HPLC
IC
CE
what is DAD?
diode array detector
what is PDA?
photodiode array PDA
define fluorescence
measures optical emission of light by molecules after they have been excited at a higher energy wavelength
what does the conductivity detector measure?
what is it common for?
what are disadvantages?
electric conductivity (presence of ions) of the solution eluting out from the column
common for analysis of inorganic ions and small organic substances (organic acids and amines)
disadvantages: limited working range, low sensitivity and specificity, strong dependence on temperature
what does TCD stand for?
what does TCD do?
what does it detect?
thermal conductivity detector
compares the thermal conductivities of 2 gas flows: the pure reference gas and the mobile phase coming from the GC
in the presence o the sample, the power required to keep the wire temp constant changes
it is a universal detector
what does FID stand for? what does it detect? how is the signal produced?
flame ionization detector
detects carbon:
signal production:
- the combustion of organic molecules in the flame generates ions
- the current produced by collecting ions is proportional to the number of carbons in the molecule
what does ECD stand for?
what does it detect?
how is the signal produced?
advantageS?
electron capture detector
detects: electronegative halogen-containing organis SO2
signal prod:
- e emitted by beta source (63Ni) ionizes the gas
- the presence of electronegative functional group reduces the current
adv
- insensitive to amines, alcohols, hydrocarbons
- relatively cheap
what does GC olfactometry (GC-O) detect?
how is the signal produced?
detects odours
signal is produced from using human assessors as a sensitive and selective detector for odour-active compounds
what do you do if a peak valley is <25-50% of the peak height of the smaller peak?
separate the two peaks with a line drawn from the valley bottom to the projected baseline
what is the valley criterion?
25% or 50%
in a chromatogram, how many points per peak is needed for identification? and for quantification?
identification: 10 points
quantification: 15-20 points
what is IDL? what is it also known as?
define it.
instrument detection limit
also known as sensitivity
smallest amount of material detectable in a matrix relative to the amount of material analyzed. Given in atomic mole or wt fractions
what equation is associated with IDL?
S/N=3
what is the dynamic range?
the ratio between the maximum usable indication and the minimum usable indication (detection limit)
what is the equation to determine linear dynamic range?
response = response factor * concentration
