I’m looking at my copy of Terrance Cooper’s ‘The Tools of Biochemistry’ (Wiley, 1977). It identifies two approaches to fractionating gradients. The first is the one Michael describes (allowing the liquid to drip out of the bottom). The other is to pierce the bottom of the tube, and then pump a very dense solution into the tube from the bottom. This forces the liquid out from the top (into some tubing that is connected to the fraction collector). This way you wind up collecting fractions from low density to high density. I’m not sure which method is preferred; I dimly recall using the latter approach, owing to an argument that it leads to less turbulent mixing (but I may be talking through my hat).
In any case, it’s important to minimize the length of tubing between the sample and the destination tubes, so as to reduce mixing. For CsCl gradients, we used to simply irradiate the tube to light up the band of interest (there was EtBr in there, obviously), and then stick a needle into the side of the tube immediately below the band (bevel up). Then you pierce the top of the tube to relieve the vacuum, and your band starts to drip out though the needle. If you want to get fancy you can put a little Luer valve on the needle. Pat > On 3 Feb 2017, at 3:01 PM, R. Michael Garavito <rmgarav...@gmail.com> wrote: > > Reza, > > Almost any fraction collector will do. If you have a pack rat colleague > around NY City, find an unused, but working Gilson fraction collector, with a > rack (which I surprising number of people use without knowing what the rack > is for). In our teaching lab we have about 7 of them we occasionally use for > the students. Although it does a serpentine collection on 60 tubes, which is > OK, more importantly, it has a drop counter, as well as timed advance. > > To me, my biggest dilemma was trying to get the samples out. We used > thin-walled tubes that allowed the bottom to be punctured. So you needed that > whole setup to puncture the tube and drain it into the fraction collector to > get fractions from highest to lowest density. Clunky, but it works. Do you > have that? > > Michael > > **************************************************************** > R. Michael Garavito, Ph.D. > Professor of Biochemistry & Molecular Biology > 603 Wilson Rd., Rm. 513 > Michigan State University > East Lansing, MI 48824-1319 > Office: (517) 355-9724 Lab: (517) 353-9125 > FAX: (517) 353-9334 Email: rmgarav...@gmail.com > **************************************************************** > > > > >> On Feb 3, 2017, at 12:04 PM, Reza Khayat <rkha...@ccny.cuny.edu> wrote: >> >> Hi, >> >> Sorry for another non crystallography question. Can someone suggest a >> fraction collector to collect fractions from a CsCl/glycerol/sucrose/... >> gradient from an ultracentrifugation run? Thanks. >> >> Best wishes, >> Reza >> >> Reza Khayat, PhD >> Assistant Professor >> City College of New York >> Department of Chemistry >> New York, NY 10031 >
