Hello, all:

Anybody here have experience with running a cesium chloride gradient? I am trying to identify a particular protein and DNA from a cell culture.

Here's what I did: I took some media and cellular extract, added CsCl to a final concentration of 0.4 g/ml, and then spun this down at 50,000 rpm for 16 h. I took fractions from the gradient and measured the refractive index of the fractions with an Olympus refractometer.

My question is this - I was expecting some of the fractions to have a refractive index of somewhere between 1.30 and 1.35. Instead, all of the fractions were between 1.37 and 1.355. Did I do something wrong, was the CsCl gradient not separated enough, or was the RI numbers shifted because I used media from cells and extract rather than a more "pure" solution?

Please let me know. Thank you.