what is the chemical coposition of loading buffer in agerose gel electrophoresis?

Answer 1

For the running buffer, it's normally either TBE or TAE (1st link below). Tris-borate-EDTA or Tris-Acetate-EDTA. The TBE is supposed to make smaller fragments sharper and more distinguishable, but I've always seen taht with TAE, though.

For the actual loading dye, its usually bromophenol blue and/or xylene cyanol, with glycerol (2nd link below)

Answer 2

There are a variety of compositions. The basic idea is three-fold: a buffer similar to the runnning/gel buffer, either TAE or TBE; one or more dyes to indicate approximate position of fragments or the leading edge of the sample; and a thickener to get the sample to sink down into the well rather than just disperse in the buffer. The major choices for thickener are glycerol and sugar variants. Standard references like Maniatis will give you several recipes to choose from.