Chromatography Forum

Hello,

I need to cleanly remove ~5 cm of stationary phases from inside out of DB-1 0.53 mm column. Would like to keep the outside polyimide coating. Any hints are greatly appreciated. Thanks!

Don't know how you would do this.
Some manufacturers produce columns with about 5M uncoated at one end, I think Restek is one.

Just buy a retention gap and some press-connect fittings.
Retention gap is imide coated glass w/o any stationary phase on the inside. Cut to length, install in injector end as you would any column and join to regular column w/ a press connector.

If the coating is not crosslinked or bonded then you just suck pentane 5 cm into the column and squirt it out again a few dozen times.

Trouble is that almost all columns have crosslinked bonded phases these days. You could try swelling the portion to be removed by filling the end with pentane - this will soften the phase enough that you might be able to scrape it loose with a thin wire (such as come with syringes for cleaning the needles). Hot acid or base will eat the phase off but will probably weaken the silica so much that the newly uncoated portion will just fall off. If you want to get elaborate soak the phase in octane to swell it, insert a wire into the octane filled section, freeze the octane and pull the wire out, hopefully with the octane and stationary phase stuck to it.

All in all this is going to be fiddly enough that I would want to be very sure that the benefits were worth it before I even tried.

Peter

BTW - for what reason do you need 5CM phase free column?