Unit 5 Flashcards
What is the state of stationary phase in column chromatography
Solid
What is the state of mobile phase in column chromatography
Liquid
What is chromatography
Technique used to separate compounds in mixture
What does partition coefficient tell (K=mobile/stationary)
Which state A1 or A2 the analyte prefers to be in
What is liquid-liquid extraction dependent on
Ionic strength, pH, solvent etc..
What is a method of measuring the progression of a reaction
Thin Layer Chromatography
Partition vs Adsorption Chromatography
Partition is when the solute is absorbed into the other face while Adsorbance is when it sticks to the surface of the other phase
Examples of Adsorption Chromatography
TLC or Column Chromatography
Examples of Partition Chromatography
HPLC
What is the stationary phase in TLC or column chromatography made of
silica or alumina
In normal HPLC what is the polarity of the column
Polar
In reversed HPLC what is the polarity of the column
Non-Polar
Effect of polarity on elution in normal HPLC
Non-Polar elutes first and Polar elutes last
Effect of polarity on elution in reversed HPLC
Polar elutes first and Non-Polar elutes last
What is dead time in HPLC
Time spent in mobile phase
(tm)
What is retention time in HPLC
Time for analyte to elute (tr)
What is retention factor
time in stationary/ time in mobile (t’r/tm)
What is t’r
retention time after being corrected for tm (tr-tm=t’r)
What is the equation for efficiency of separation with good resolution
R= (2|trb-tra|)/ (Δtb+Δta)
What is tr(x)
the time of elution of compound X
what is Δtr(x)
the amount of time that compound X was being eluted
What is (FWHM)x
The full width (Δtr(x)) at half of the max signal for compound X
Is a high or low number of plates for efficient and why
More plates is more efficient because it gives a narrower peak/ better resolution
What does N=L/H show
Relationship between # of theoretical plates and length/height of column
What does N=(16(tr)^2)/(w)^2 show
Relationship between # of theoretical plates and time of elution and how long it took for the compound to be eluted (width of peak/resolution)
Why are later eluted compounds more poorly resolved, Longitudinal Diffusion
From, N=(16(tr)^2)/(w)^2, if N in constant later eluting compounds (higher tr) will result in larger w (width of peak)
What is Eddy Diffusion
Diffusion due to particles being different shapes and sizes, they’ll take different pathways, poorer resolution
What is Mass Transfer
Equilibrium between the stationary and mobile phase, flow rate effects this
What is Longitudinal Diffusion
Diffusion due to the solute going from high to low concentration, wider peaks because later elution
Van Deemter Equation
H = A + B/v + Cv
What does A in Van Deemter Equation mean
Eddy Diffusion
What does B in Van Deemter Equation mean
Longitudinal Diffusion
What does C in Van Deemter Equation mean
Mass Transfer
Why does Van Deemter Equation contradict itself
B wants a high flow rate, faster elution but C wants a smaller flow rate, more time to reach equilibrium
What does H in Van Deemter Equation mean
Plate Height (WE WANT TO MINIMIZE)
What does v in Van Deemter Equation mean
flow rate
What are the axes on Van Deemter graph
Y= Plate Height X=Flow rate
What is effected before optimum flow rate
B, longitudinal diffusion
What is effected after optimum flow rate
C, mass transfer
Isocratic Elution
When the mobile phase is kept constant
Gradient Elution
When the mobile phase changes
Why is Gradient Elution beneficial
by changing the polarity of the mobile phase the elution time can be decreased thus resolution can be increased
Van Deemeter Equation in GC
H = B/v + Cv…No A because no packing of column
What predicts elution in GC?
Boiling point, lower=first
What is split injection for GC
Some of sample goes to waste to prevent overloading the column
Does GC or LC have better resolution and why?
GC because there is smaller plate height thus more theoretical plates
Effect of particle size on separation efficiency
Smaller=better
HPLC Instrumentation order
Pump, Injector, Column, Detector, Computer
GC Instrumentation order
Mobile Phase (gas), Flow Regulator, Injector, Column (w/oven), detector, computer
What does pump do in HPLC
Forces mobile phase through column
What does Injector do
introduces sample to columns
What does column do
separates compounds
What does detector do in chromatography
produces signal upon elution
In reversed phase gradient HPLC what do you want the properties of the mobile to be
Polar -> Non-Polar
In normal phase gradient HPLC what do you want the properties of the mobile to be
Non-Polar -> Polar
Benefits of superficially porous particles
Allows for shorter diffusion lengths, Improves mass transfer because the inside is solid and thus the particles are pushed closer to the outside of the column
What is the gradient elution equivalent for GC
temperature programming
What is the purpose of the Z-shaped flow cell in liquid HPLC?
Higher path length which will increase sensitivity because it will increase the slope of calibration curve
