A "normal" centrifuge = piece of laboratory equipment, driven by a motor, which spins liquid samples at high speed to allow centripetal acceleration to separate substances of greater and lesser density.
Without further information regarding the method you read, a "vacuum" centrifuge might be a reference to one of the following:
- a centrifuge optimized for spinning a rotor at very high speeds.
The vacuum ultracentrifuge was invented by Edward Greydon Pickels in the Physics Department at the University of Virginia. It was his contribution of the vacuum which allowed a reduction in friction generated at high speeds. Vacuum systems also enabled the maintenance of constant temperature across the sample, eliminating convection currents that interfered with the interpretation of sedimentation results
- device used in chemical and biochemical laboratories for the efficient and gentle evaporation of solvents from many samples at the same time.
The system works by lowering the pressure in the centrifuge system [via a vacuum pump] - as the pressure drops so does the boiling point of the solvent(s) in the system.
The centrifugal force generated by spinning the centrifuge rotor creates a pressure gradient within the solvent contained in the tubes or vials, this means that the samples boil from the top down, helping to prevent "bumping".
Use a combination of centrifugal force, vacuum and heat to speed evaporation of multiple small samples. They offer maximum throughput required by biology, microbiology, biochemistry, pharmaceutical research and analytical chemistry laboratories
UPDATE: Based on updated info from the OP quoting the method of the paper, it sounds like they're most likely talking about using a centrifugal evaporator to remove solvent.