Validity of Method

Accuracy

How accurately can particle size be determined?

For samples in which an adequate number of particles are present in the sample (typically >10⁹/ml), the determination of particles size can be as accurate as that of equivalent dynamic light scattering techniques such as Photon Correlation Spectroscopy. For samples in which solvent viscosity and temperature is correctly entered, the diameter of a well prepared, monodisperse, calibration polystyrene micro-sphere can, for instance, be accurately measured to within 1-2 percent of nominal. Increasing analysis time (e.g. 1 to 2 minutes) will increase accuracy of measurement.

Polydispersity

How accurately can particle size be determined?

For polydisperse samples, the NanoSight system exhibits significant advantages over PCS in that the size distribution profile obtained is based on the separate but simultaneous analysis of each and every particle seen during the analysis period. This is in stark contrast to the data obtained by PCS in which a large ensemble of particles are measured and from which an intensity weighted (z-average) is obtained.

The NanoSight system can distinguish between a bimodal system if the particles are 50% different in size (for example 80 nm and 120 nm particles).

Reproducibility

How reproducible is the result?

Given the statistical nature of analysis of a population of particles, reproducibility is a function of the numbers of particles measured over the period of analysis. For optimum concentrations of monodisperse samples containing no contaminating aggregates, results reproducible to within approx 2-3% can be achieved in a comparatively short time (e.g. 10-20 seconds). Clearly, for low concentrations of particles exhibiting a range of particle sizes, extended analysis periods will be required to obtain reproducibility of results. Note that analysis times need to be increased for larger particle diameters to achieve similar reproducibilities.