Reliability of Pumps at Low Flow Rates

Discussions about HPLC, CE, TLC, SFC, and other "liquid phase" separation techniques.

10 posts Page 1 of 1
Hello All

In our lab we are now trying to move from 4.6 and 3 mm ID columns to the use of 2 mm ID columns (in order to minimize solvent use and waste generation). Now, of course, the flow rate that one must use is lower with these narrower ID columns. A typical flow rate for a 0.2 mm ID column would be something like 0.2 or 0.25 mL/min.

So I wanted to get some opinions on this question: With modern HPLC systems, how low can you go in flow rate, and still be confident that the flow rate will be delivered reliably?

Thanks in advance for any feedback!
Hi Adam,

With Waters Acquity-H, Agilent 1260/1290 series and Shimadzu Nexera instruments, the flow rate is reliable to the 10s of nanoliters per minute. These are LCs I've demo-ed or use routinely.
MattM
Here's the calculations that you need to make in order to determine if your HPLC system is up to the task. Let's say that you're running at a flow rate of 200 µl/min. At the start of your gradient, there will be a point when your system is pumping 99% A/1 % B. That 1% B will be at a flow rate of 2 µl/min. Same goes at the end of the gradient, when you're at 1% A/ 99% B. Look up the specs for the HPLC system. If it can deliver 2 µl/min or less reliably, then it can generate and deliver your gradient reliably. If the lowest flow rate that it can address is 5 or 10 µl/min, though, then it will not generate the beginning and end of gradients reliably at this flow rate.

In addition to making sure that you have a pump system that can deliver the mobile phases with the necessary precision, it's very important to minimize dead volume in the system, including detector flow cells. Running at 0.2 ml/min on a system that's plumbed for 1 ml/min will result in significant fronting of all peaks due to diffusion in the extracolumn dead volume.
PolyLC Inc.
(410) 992-5400
aalpert@polylc.com
@ Andy Alpert,

Your response way outclasses mine--I greatly appreciate that!!
MattM
adam wrote:
In our lab we are now trying to move from 4.6 and 3 mm ID columns to the use of 2 mm ID columns (in order to minimize solvent use and waste generation). Now, of course, the flow rate that one must use is lower with these narrower ID columns. A typical flow rate for a 0.2 mm ID column would be something like 0.2 or 0.25 mL/min.

So I wanted to get some opinions on this question: With modern HPLC systems, how low can you go in flow rate, and still be confident that the flow rate will be delivered reliably?


Adam - I did the same - OVER 20 YEARS AGO - for almost all of our commonly-used methods. I used Agilent 1050 HPLCs then, no cGMP/USP issues using flow rates of 0.2 - 0.25 ml/min.

You'll save a fortune in solvent purchases and solvent disposal costs too.

We generally used an injection volume of 5 µl, so you might need to reduce your injection volume.
@mattmullaney:

Hey, we all do what we can on this forum!
PolyLC Inc.

(410) 992-5400

aalpert@polylc.com
@ Andy Alpert,

My thanks!
MattM
Most any research grade analytical scale HPLC system (0.100 - 10 ml) should be fine. Look at the Pump's formal manufacturer's rating to determine if it is capable of operating in the range you wish to use. IOW: Read the manual.

To insure nice quiet flows at lower ranges such as 200 ul/min include: (1) Make sure your HPLC is working perfectly and is not in need of any services or repairs; (2) Make sure you use either an inline degassing or continuous sparging with helium gas to remove the bulk of the dissolved gasses inside the mobile phase solutions (it will make a big difference in allowing your pumps to function well); (3) Insure that there is enough system back pressure on the system during the entire time it is running. Most HPLC systems are rated for % pulsation based on backpressure (that is what helps keep the pump heads primed and the valves working without getting stuck). For a typical analytical HPLC, this is usually 60 Bars or higher; (4) Use fresh, filtered, high quality HPLC grade solvents and Water; (5) Keep the system well flushed, primed and cleaned.
Hi Adam,

Looks to me that You're in good shape. I think I may try out Andy's experiment on our LCs when I get the chance to do so. Rigorous evaluation of the LC pump, for sure!
MattM
Thanks guys, that is helpful feedback.

We appreciate the help.
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