Tip# 114: Pressure Drop Across an HPLC Column
Many of you prefer tables of data over equations that you
must work out. So, instead of providing you with another equation, I have done
some basic measurements for you to provide a general overview of how particle
size (porous) effects observed backpressure.
Pore Volume and Flow Resistivity will vary by column type.
Obviously the back pressure will be higher with more viscous solvents (e.g.
EtOH is 1.20 cP) and lower with less viscous solvents (e.g. ACN is 0.34cP). A
Table of HPLC Solvent Viscosity values can be found here [
http://www.hplctools.com/lcsolvent.htm ]. Linear flow rates have been used for
all column I.D.'s to better illustrate the relationship between column
dimensions and flow rate. If you double the flow rate, then the pressure will
approximately double as well.
Note that when run at traditional linear velocities, most
2.5u particles are within the maximum pressure limits of most HPLC systems
(under 400 bars). Only the newer sub 2.0 micron particles used in long columns
exceed the 400 bar limit. The higher maximum pressure limits of many UHPLC
systems allow the use of higher flow rates with these particles. Naturally, you
should optimize both column efficiency and system dwell volume when developing any
UHPLC method. Meeting any/all backpressure requirements to run a method does
not translate to success in sample analysis. Successful ultra-fast separations
require ultra-low system dwell volumes, higher sampling rates and usually
smaller flow cell volumes.
Column I.D. (mm) |
Particle Size (u) |
Column Length (mm) |
Flow Rate (mL/min) |
Back Pressure (Bars) |
4.6 |
5 |
250 |
1.000 |
89 |
4.6 |
5 |
150 |
1.000 |
54 |
4.6 |
5 |
100 |
1.000 |
36 |
4.6 |
5 |
50 |
1.000 |
18 |
4.6 |
3.5 |
250 |
1.000 |
182 |
4.6 |
3.5 |
150 |
1.000 |
109 |
4.6 |
3.5 |
100 |
1.000 |
73 |
4.6 |
3.5 |
50 |
1.000 |
36 |
4.6 |
2.5 |
250 |
1.000 |
357 |
4.6 |
2.5 |
150 |
1.000 |
214 |
4.6 |
2.5 |
100 |
1.000 |
143 |
4.6 |
2.5 |
50 |
1.000 |
71 |
4.6 |
1.9 |
250 |
1.000 |
618 |
4.6 |
1.9 |
150 |
1.000 |
371 |
4.6 |
1.9 |
100 |
1.000 |
247 |
4.6 |
1.9 |
50 |
1.000 |
124 |
|
|
|
|
|
3.0 |
5 |
250 |
0.430 |
90 |
3.0 |
5 |
150 |
0.430 |
54 |
3.0 |
5 |
100 |
0.430 |
36 |
3.0 |
5 |
50 |
0.430 |
18 |
3.0 |
3.5 |
250 |
0.430 |
184 |
3.0 |
3.5 |
150 |
0.430 |
110 |
3.0 |
3.5 |
100 |
0.430 |
74 |
3.0 |
3.5 |
50 |
0.430 |
37 |
3.0 |
2.5 |
250 |
0.430 |
361 |
3.0 |
2.5 |
150 |
0.430 |
217 |
3.0 |
2.5 |
100 |
0.430 |
144 |
3.0 |
2.5 |
50 |
0.430 |
72 |
3.0 |
1.9 |
250 |
0.430 |
625 |
3.0 |
1.9 |
150 |
0.430 |
375 |
3.0 |
1.9 |
100 |
0.430 |
250 |
3.0 |
1.9 |
50 |
0.430 |
125 |
|
|
|
|
|
2.1 |
5 |
250 |
0.210 |
90 |
2.1 |
5 |
150 |
0.210 |
54 |
2.1 |
5 |
100 |
0.210 |
36 |
2.1 |
5 |
50 |
0.210 |
18 |
2.1 |
3.5 |
250 |
0.210 |
184 |
2.1 |
3.5 |
150 |
0.210 |
110 |
2.1 |
3.5 |
100 |
0.210 |
73 |
2.1 |
3.5 |
50 |
0.210 |
37 |
2.1 |
2.5 |
250 |
0.210 |
360 |
2.1 |
2.5 |
150 |
0.210 |
216 |
2.1 |
2.5 |
100 |
0.210 |
144 |
2.1 |
2.5 |
50 |
0.210 |
72 |
2.1 |
1.9 |
250 |
0.210 |
623 |
2.1 |
1.9 |
150 |
0.210 |
374 |
2.1 |
1.9 |
100 |
0.210 |
249 |
2.1 |
1.9 |
50 |
0.210 |
125 |
>
Results obtained on one of our HPLC systems. Your results may vary due
to differences in flow path, tubing ID, column choice and mobile phase
selected.
