Transcript Slide 1

Lecture 15
Chromatography
Introduction and Plumbing
Harris Ch. 23
t
Time = m
“Dead time”
t
Time = m
“Dead time”
No separation!
time
Mobile phase
Stationary phase
Time for solvent molecule is the same as before:
tm
Time for analyte molecule is different: tr
Retention time
tr  tm
Adjusted retention time:
tr  tm  t 'r
tm
t’r
tr
time
Retention factor:
Time in stationary phase
t 'r
k
tm
Time in mobile phase
Distribution coefficient
If you have many molecules
Cs
K
Cm
num ber_ of _ m olecules_ in _ stationary_ phase
k
num ber_ of _ m olecules_ in _ m obile_ phase
or
k
CstationaryVstationary
CmobileVmobile
Vs
K
Vm
Mobile phase
Stationary phase
Time for solvent molecule is the same as before:
tm
Time for analyte molecules is different: tr(1) and tr(2)
t ' r (1)

t ' r ( 2)
Selectivity factor
Separation factor
Relative retention
tm
t’r(1)
tr
t’r(2)
time
Retention factor k:
Cs
K
Cm
k
t 'r
k
tm
Distribution coefficient
CstationaryVstationary
CmobileVmobile
Vs
K
Vm
t 'r  k  tm
Separation factor:
t 'r (1) K (1)


t ' r ( 2) K ( 2)
tr (1)  tr (2)
peak _ separation
Resolution RS 

1
average
_
peak
_
width
(W1  W2 )
2
tr (1)  tr (2)
peak _ separation
Resolution RS 

1
average
_
peak
_
width
(W1  W2 )
2
Number of theoretical plates:
Plate Number
W = 4
L - length of column
Height of theoretical plate is:
Plate Height
N
t
2
r
2

2
r
2
t
N  16 
W
H = L / N = L  2 / tr2
Zone broadening:
The van Deemter equation
B
H  A C u
u
H - plate height
u - flow rate
A=0
 x  2Dt
x
2
L
 2 Dt  2 D
u
B
van Deemter plot