Translator for HPLC HINTS and TIPS for Chromatographers

Friday, August 26, 2011

Pressure Drop Across an HPLC / UHPLC 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 backpressure.

For simplicity, let us start with a few parameters. Pore Volume = 0.70; Linear Velocity = 1.44 mm/sec; Solvent Viscosity = 0.89 cP at 25C (Water). 

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