Hello, I synthesize gold nanorods in CTAB following the classical El-Sayed protocol. To separate other forms of nanoparticles and then remove excess CTAB, I perform centrifugation (8000 rpm, 30 min). However, during centrifugation, the nanorods (maximum absorbance = 750 nm) remain in the supernatant, while the spheres (absorbance at 540 nm) form the precipitated pellet. Does anyone know what could be going on here?
Diogo Pellosi
Formula for calculating centrifugal force
F= m x angular velocity squared х r
m- mass of nanoparticle
r- distance from nanoparticle to center of centrifuge (center of test tube)
The greater the centrifugal force, the better the sedimentation. Therefore, the mass of your spherical particles is greater than the mass of your nanorods.
1. Do you know the particle sizes, or can you estimate them? Looks like the spheres have more mass.
2. rpm is not a useful unit. If you have a very small rotor, you should not have any pellet; for a large rotor, this is ultracentrifugation and you would certainly precipitate everything but small molecules. So please provide either rotor, or better the g value.
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