Bioequivalence and Bioavailability Forum

Dear Mr Kaushik panigrahi,

Centrifugation parameters are calculated based on

1. Sedimenting force on particle
2. Flotation force
3. Frictional resistance &
4. Diffusion

Sedimenting force will depends on angular velocity of Rotor.
Sedimenting force on particle
= Mass × centrifugal field
= mω²r
where ω = angular velocity of rotor (radians/sec)
r = radius (ie distance of particle from axis of rotation)
Relative Centrifugal Force (RCF)
RCF = 1.119 × 10^-5 × (rpm)² × r
RCF value reported as "No. × g" (ie multiples of earth's gravitational (force).

Interacting Forces in Centrifugation are Flotation Force, Frictional resistance and Diffusion. Sedimenting force, mω²r, is opposed by

1. Flotation Force (Archimedes)
= mω²rνρ
where: ν = partial specific volume
(volume displaced by 1g of sedimenting particles)
ρ = density of solution
NET SEDIMENTING FORCE on particle, after allowing for flotation
= mω²r(1-νρ)

2. Frictional Resistance
against particle moving through fluid.
= fv
where: f = frictional coefficient
v = particle velocity

3. Diffusion
- acting to counter uneven concentration distributions set up when dissolved molecules sediment.

Reference