Microtrac Nanotrac - Status: Up
||The Nanotrac measures the particle size distribution of small particles (0.8-6500 nm) by dynamic liqht scattering (DLS). It has a fiber optic probe which allows direct measurement and measurement of small amounts (<0.5 mL) of sample.Latest Status Log EntrySep 13, 2017 - Resource Status Up - Recovered after storm shutdown|
The NanoTrac measures light scattering intensities as a function of Doppler shifted frequency, by heterodyning the light scattered from particles moving by Brownian motion with the reference beam reflected internally from the sapphire probe window. The frequency spectrum of Doppler shifted light is fitted to a sum of Lorentzian curves, whose widths are proportional to the particle’s diameter, and height proportional to the relative number of particles of each diameter. A fixed set of diameters is used to fit the data; the instrument does NOT measure particle diameters!!
Size range is given as 0.8 nm to 6.54 microns. However, the equations used to relate scattering intensity to particle size distribution assume particles are moving by Brownian motion, in still fluid. If the samples are stirred, the derived particle size distribution may not accurately represent the actual size distribution, especially if the flow is turbulent. Since the sample volume is within 100 microns of the end of the probe tip, if particles settle 100 microns in less than a few seconds, you will not get sizing data on them.
Sample size can be as little as ~ ½ mL, with concentrations as low as 100 ng/mL or as high as 40 vol% particles. The probe diameter is 8 mm, so any sample cell that is greater than 8 mm can fit the probe. Typical minimal sample cells are the small Eppendorf centrifuge ampules and 4 mL cuvettes. However, it is recommended, that the probe be inserted into the sample at least 1/4 of an inch, to eliminate surface effects.
Data needed are the real refractive index of the particles at 780 nm, and the viscosity of the fluid at the temperature of the sample. When using the probe externally to the body of the instrument, as is the usual case, you must measure the room temperature and apply the appropriate viscosity for best results. The product of particle diameter times viscosity is treated as constant in fitting the data, so small/ large values of viscosity result in oversizing/ under sizing the particles.