how do increase the packing density of DAC column

[moon704520]

hi,
I meet a trouble!each time I pack my DAC column 50*250 packed with RP C4 silica 300A! but because of this silica is very fragile, 750psi was used during packing !every time , the column efficiency is not well!including the plates and tailing factor!when I unpack the column ,I find that the column bed was not solidity at all ?how can I improve?

thank you!

[tom jupille]

What happens when you try packing at a higher pressure?

[moon704520]

hi all:

once higher packing pressure(850pis) was used but higher column pressure drop arised ,the column efficiency was not improved at all ,not as well as 750pis'!and the end of column bed is still rather soft !I guess
that the low column efficiency was because of soft column bed?but I really want to make the column bed more solid but how?every time ,I unpack the column ,I found that the head of the column is rather solid ,but the end of the column is rather soft!how can I change all of this ?

thank you !

[philippem]

Hi moon 704520 ,

Do you have instructions ,which should be provided by the supplier.
These instructions should guide you through the packing process.

I was familiar with packing analytical columsn and next to the applied pressure , also the solvent in which the silica matrial is dispersed, does have an influence on the quality of the packing bed. I can believe that also for these columns it has influence.


Philippe

[moon704520]

do you have some recommendations on the slurry solvent?is there any pricipals on slurry solvent choosing?thanks!the silica I use is C4,partical size is 10-15um,pore size is 300A!
many thanks

[philippem]

you have to check, if you make a slurry , that the material does not sink immediatley to the bottom. You should obtain a stable slurry ( depands on nature of solvent ).

In the time we used CCl4 or related products, but later on we moved to aceton

but please keep in mind, i amtalking about analytical clolumns packe da high pressure (up to 1000 bar)

[Mark Tracy]

Several other folks have asked similar questions about prep columns. The advice is similar: budget yourself a significant amount of time and resources to learn how this is done. First, talk to the manufacturer of the column hardware. Next, spend time optimizing your conditions. The important variables are slurry solvent, solvent/silica ratio, compression rate, final pressure. Take good notes. You have a lot of variables to explore. When you figure it out, write it down and stick to your protocol.

There are many solvents that have been used over the years, but acetone, isopropanol and methanol are popular these days. Some people have their own secret sauce.

It takes a lot more than 850 psi to crush the silica particles. What is probably happening is the packed bed is not sufficiently compressed, and is in a metastable state. After a while it shifts and settles. Don't be afraid to raise the packing pressure. At minimum, use 1.5x the highest operating pressure you will ever use.

Commercial column vendors spend a lot of time working out the conditions, and don't give away that knowledge.

[moon704520]

dear tracy:

thanks for your advice!it it really useful !and everytime I am in trouble ,it is always you give me some confidence!thank you!here I have some questions!

(1)why people choose IPA ,methonal ,acetone rather than some other solvent as slurry solvent?as I know ,the desity and visisity ,polarity of ACN,EtOH was much similar with methanol why not ACN,EtOH ?

(2)once after slurry preparation,I pour the slury into the column ,and let it settle for 48hours ,finally I got a solid column bed ,but low column efficiency,can you help to explain?

[Mark Tracy]

I have to admit that the art of selecting solvents is largely empirical, and most of the reasons given for choosing one over another don't convince me. We have our "secret sauces" for packing various types of columns and sometimes the details need to be tuned for different column geometries. So, pick something relatively cheap, pure and easy to handle for your starting point.

The closer you can get to the theoretical 68% (spherical) particle volume in the tube, the more stable the bed will be. The small particles tend to stick to each other and not settle into the most well-packed configuration without a some force, and gravity just is not enough. One cause of poor symmetry is nonuniform packing density across the width of the column, and compression helps to level out the density.

Column efficiency versus packing parameters is highly empirical. (Forgive me for being evasive. Trade secrets.) After a while you develop an intuition that can get you headed in the right direction, most of the time. Fortunately, there are more than one set of conditions that will produce a good column. You just need to find one set that works for you.

[Uwe Neue]

Column packing is not an easy exercise. However, if you want to learn a lot more about column packing, I suggest to read Chapter 5, Column Packing and Testing, in my book "HPLC Columns", Wiley-VCH.