Minimizing Gradient Delay volume - Static or Dynamic mixing?

[entropiclabs]

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.

[dhobbs]

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%).

[LiVD]

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...

[Andy Alpert]

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.

[entropiclabs]

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?