The Archimedes RMM system is complementary to NTA, covering the nanoscale to single micron range. RMM detects particle buoyant mass by measuring the change in frequency of a resonator as individual particles interact with it. This technique is a true orthogonal technique to MFI and LO since it does not rely on refractive index changes or blockage of light, but instead on the volume of solution displaced by individual particles. The method is capable of detecting femtogram differences of masses of particles flowing through the channel.
Archimedes is recommended for detection of particles in the 0.5 – 5 µm size range when solutions have the presence of particles that differ in density (i.e. silicone oil droplets, etc.). MFI is unable to classify particles below 5 micron with image parameters. Therefore, the combination of RMM and MFI allows for the full characterization of particles in the 1 – 10 µm size range, which has been of interest lately. This method is limited to particles below 5 micron, therefore filtration or centrifugation is performed prior to analysis if larger particles are present to keep from blocking flow channels.
KBI recommends Archimedes as a tool to evaluate if populations of different densities are present in samples. The optimal concentration range for Archimedes is 104 to 109 particles/mL.