Solvent Strength Parameter:
Table: Solvent Strength Parameter, εo and the Physical Properties of Selected Solvents Used in HPLC
|
Solvent
|
εo(SiO2)
|
εo (Al2O3)
|
Viscosity,
20ºC (mN
sec m-2)
|
Refractive index, 20ºC
|
|
Pentane Hexane Cyclohexane Carbon disulphide
Carbon tetrachloride
1-Chlorobutane
Di-isopropyl ether
2-Chloropropane
Benzene Diethyl ether Chloroform Methylene dichloride Tetrahydrofuran Acetone
1,4-Dioxane
Ethyl acetate
1-Pentanol Acetonitrile Methanol Water
|
0.00
-0.05
0.14
0.14
0.25
0.38
0.26
0.47
0.49
0.38
0.50
|
0.00
0.00
0.04
0.15
0.18
0.26
0.28
0.29
0.32
0.38
0.40
0.42
0.45
0.56
0.56
0.58
0.61
0.65
0.95
Large
|
0.23
0.313
0.980
0.363
0.965
0.47
0.379
0.335
0.65
0.23
0.57
0.44
0.55
0.32
1.54
0.45
4.1
0.375
0.60
1.00
|
1.358
1.375
1.426
1.628
1.460
1.402
1.368
1.378
1.501
1.353
1.443
1.425
1.407
1.359
1.422
1.370
1.410
1.344
1.329
1.333
|
As the column flow rate is proportional to the product of the linear velocity and the cross sectional area of the column, a solvent consumption is considerably decreased as illustrated in Table.
Table : Solvent Consumption for Different Diameter HPLC Columns
|
ID (mm)
|
Flow rate for linear velocity of 0.14 cm/sec (mL/min)
|
Volume in a
8 hr day (mL)
|
|
0.51
0.71
1.02
1.29
1.59
4.6
|
0.02
0.027
0.044
0.079
0.12
1.00
|
6.9
13
24
38
57
480
|
When two more solvents with a fixed composition are used, it is called isocratic elution. This, however, is a very cumbersome process and instead gradient elution is used.