Cesium chloride density gradient centrifugation is commonly

Cesium chloride density gradient centrifugation is commonly used for the separation of DNA molecules. The buoyant density, ρ, of a double stranded Cs⁺ DNA is given by the equation ρ = 1.66 + 0.098X_{G + C} where X_{G + C} denotes

1. total number of G and C
2. mole fraction of G + C
3. number of GC repeats
4. ratio of G + C to A + T content

The density of DNA (g/mol or g/cm3) as a function of its G : C content is given by following equation.
ρ =1.66 + 0.098 X_{G + C}

∴ X_{G + C} =	ρ - 1.66
	0.098

as G + C is the mole fraction of G + C in DNA.
So it can be expressed in terms of mole % G + C as falls

% X_{G + C} =	ρ - 1.66	× 100
	0.098