Chromatography Forum

I have method developed for analytical column using flow rate of 0.9ml/min (4.6x150 mm ,5un,C18)

what should be ideal flow rate for prep col: C18, 10x150 mm, 5 micron

I appreciate your help

Hi Mk12,

Assuming you’ve determined the ideal flow rate on the analytical column (you haven’t stated it) to be 0.9 mL/min, then the ideal flow rate for the preparative column you intend to use is 4.2 mL/min - with high probability.

Best Regards

Danko's right (4.2 mL/min), and here's why:


Your analytical column - 0.46 cm x 15 cm

0.46 cm diameter = 0.23 cm radius

Column volume calculation is pi r^2 H (volume of a cylinder)

0.23 * 0.23 * pi * 15 cm = 2.5 cm^3 (2.5 mL column volume)

2.5 mL / 0.9 mL min-1 = 2.8 min to get 1 column volume of mobile phase


Scaling up... 1.0 cm x 15 cm

0.5*0.5*3.14*15 = 11.8 mL (column volume)

11.8 mL / 2.8 min (from analytical calculations) = 4.2 mL/min to keep mobile phase velocity constant.

Ouch my brain hurts...

For quick and dirty work, if columns are identical ( same length, packing, particle size etc. ), I use the following flow rate multipliers ( derived from X-section of 16.62 mm2 for 4.6 mm ID column ).

4.6 mm ID = 1.0
10 mm ID = 4.73
21.2 mm ID = 21.2 ( my brain likes this fairly common column size )
30mm ID = 42.5
50mm ID= 118

Please keep having fun,

Bruce Hamilton

I found this simple formula to calculate and calculated 4.25 ml/min for 10mm if using0.9ml/min for 4.6 mm. which matches your calculation...thanks

v1/v2=r1square/r2square


V1=flow of column 1
V2=flow of column 2
r1 =radius of column 1
r2= radius of column 2