Chromatography Forum

I'm a student performing research micropumps and chromatography. I have a few basic questions that I was hoping some of you might be able to help me with. What pumps are used in liquid chromatography? What are the typical flow rates required? Is nanoliter delivery necessary in liquid chromatography?

I appreciate the help. Thanks!

I'm a student performing research micropumps and chromatography. I have a few basic questions that I was hoping some of you might be able to help me with. What pumps are used in liquid chromatography? What are the typical flow rates required? Is nanoliter delivery necessary in liquid chromatography?
I appreciate the help. Thanks!

You can find lots of good information on the web about HPLC pumps. However, the key point to remember is that linear velocity is more an important factor than volumetric flow rate. The conversion is easy. Linear velocity x cross sectional area of the tube = Flow rate. Now imagine, if I have a column which is a 4.6 mm i.d. tube, and an analyte comes out at 2 min, in order to use a narrow bore column, say 2.1 mm i.d., I have to reduce the volumetric flow rate to 0.208 mL/min to maintain the same retention time. For a 1 mm i.d. column, I have to use a flow rate of 0.047 mL/min to maintain the same retention time. You can continue playing with the column i.d. and see at which column i.d. you need nanoliter flow rates. See capillary columns on the web. Narrower the column smaller the flow rates needed. The answer is that nanoliter becomes important in capillary columns. People are already making chip based columns.

M Farooq,

Thanks for your response. I will perform more research on HPLC pumps and capillary columns. I had a couple questions though to just want to make sure I'm understanding this correctly.

First, The speed of the particles over the sensor is more important than the quantity of particles over the sensor? (i.e. Linear Velocity vs. Volumetric Flow Rate)

And second, is it more important to have a steady flow rate vs a pulsing flow rate? (i.e. Syringe Pump Method vs. Peristaltic Pump Method)

M Farooq,

Thanks for your response. I will perform more research on HPLC pumps and capillary columns. I had a couple questions though to just want to make sure I'm understanding this correctly.

First, The speed of the particles over the sensor is more important than the quantity of particles over the sensor? (i.e. Linear Velocity vs. Volumetric Flow Rate)

And second, is it more important to have a steady flow rate vs a pulsing flow rate? (i.e. Syringe Pump Method vs. Peristaltic Pump Method)

1. Most theoretical studies in chromatography use linear velocity. I am not sure what do you mean by the speed of the particles over the sensor.

2. Steady flow rate is more important than pulsing flow rate.

If you are interested in pump designs, think about pumps which can deliver stable low flow rates at high pressures. Imagine, a capillary packed with 600 nm silica particles and you wish to do chromatography on this system.