Chromatography Forum

I am hoping I can get some advice from some more experienced people regarding minimizing delay volume in a dual pump high pressure gradient mixing system. The current system I am using is from Varian, using two 210 solvent pumps (these are simple single piston pumps with a pulse dampener/pressure module)

The dynamic mixer included with the system has a volume of 1.2ml!!! Thus, when I run flowrates at 0.2ml/min, it takes nearly 6-7mins for the beginning of the gradient to reach the column... so I'm essentially running an isocratic system when I use a narrowbore column.

To solve the problem, in one instance, I've used a static mixing tee...

http://chromatography.hplcsupply.com/vi ... ing-tees-2

The mixing noise from this tee was nearly 1mAu! In another instance I've used a tee to connect the solvent lines, and a 75ul Perkin Elmer series 200 dynamic mixer. The mixing noise is about 250uAu end-to-end, way higher than I would like it, but better than the mixing tee.



Here at 15min, you can see the moment where I turn on the dynamic mixer and mixing noise decreases.

I have not tried a static mixer cartridge yet, but plan to try a 50-150ul next. Can anyone furnish any advice? Dionex proposes using a dynamic mixer and static mixer in series for best mixing and minimal noise.

Can anyone suggest a low-volume mixer or mixing system for this problem? I'm looking to attain a delay volume of 150uL or less.

I'm not familiar with those pumps or mixers, but you may be able to reduce the noise of the static mixer by partially pre-mixing your mobile phases (e.g., if your gradient ramp is 10-50% organic, mix 10% organic in one reservoir, 50% organic in the other, and program the gradient to run 0-100%).

I'm not familiar with your equipment, but wouldn't it be easier (if your software allows it) to delay your injection? If time is not an issue of course...

A low dead-volume static mixer that's easy to make is an empty HPLC column that you fill with nonporous glass beads in the 25-50 um range. These sell by the pound. Backpressure is nominal.

I'm not familiar with your equipment, but wouldn't it be easier (if your software allows it) to delay your injection? If time is not an issue of course...

I guess that is an option. I'll have to carefully calculate the delay time using acetone, but that's no problem. For each run I will have to program a 5-6min delay before injection, and then another 5-6min delay afterwards to return to initial conditions. So essentially 10-12min downtime between injections - kind of sucks but do-able.

People who run narrowbore - what do you use as a mixer on your system?