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The coefficient of variation (CV) typically refers to the size variation of a bead population. The CV relates the measure of dispersion to the average about which it is measured in percentage. The CV is obtained by dividing the standard deviation by the mean particle diameter, i.e.: % CV = 100 % x Standard deviation / Mean diameter.
Our micromer^® particles with diameters between 2 and 10 µm have CV values ≤ 5%.

In general the size of particles with diameters < < 2 µm is measured by Dynamic Light Scattering (DLS) with the Zetasizer Nano ZS 90 (Malvern Instr. Ltd.). DLS is also known as Photon Correlation Spectroscopy (PCS).
The Zetasizer determines the size by first measuring the Brownian motion of the particles in a sample using Dynamic Light Scattering (DLS) and then interpreting a size from this using established theories.

There are four different types of data analysis of the PCS measurement:
– the cumulants analysis
– the multi exponential analysis,
– the CONTIN analysis and
– the non negative least squares analysis.

The Z-average Size is the most important and stable number produced by the technique. This is the size to use if a number is required for quality control purposes.
The Z-average Size is obtained by the cumulants analysis. This analysis gives only two values, a mean value for the size and a width parameter known as Polydispersity Index (PDI). This mean size is an intensity mean and directly calculated from the signal intensity.
According to our experiences we use different types of analysis for the evaluation of our nanoparticles. Especially the different scattering properties of fluorescent or magnetic nanoparticles require on optimal adjustment of the analytical methods.

The size distribution of our nanoparticles is measured by photon correlation spectroscopy (PCS). The quality of size distribution is given by the polydispersity index (PDI). This value is calculated as deviation between the measured autocorrelation function and the mathematically adapted correlation function. This value is below 0.2 for nanoparticles with a small size distribution and between 0.2 and 0.5 for broad size distributions. PDI values higher than 0.5 show that the measurement can not be analyzed.

We measure the Zeta Potential of our particles with the Zetasizer Nano ZS 90 (Malvern Instr. Ltd.). The Zeta Potential is measured using a combination of the measurement techniques: Electrophoresis and Laser Doppler Velocimetry, sometimes called Laser Doppler Electrophoresis. This method measures how fast a particle moves in a liquid when an electrical field is applied – i.e. its velocity.

We recommend the SEPMAG Q1L (www.sepmag.eu) for volumes up to 1L. For example, our nanomag-D, 500 nm particles (V = 600 ml, c = 10 mg/ml, product code: 09-00-502) were separated with the SEPMAG Q1L within ~ 30 min.

The amino functionalization of silica particles is performed by polycondensation of the Si-OH groups on the surface of plain silica particles with 3-(aminopropyl)triethoxysilane. Beside the NH2 groups there are numerous acidic Si-OH groups on the particle surface available that are responsible for the overall negative zeta potential of the amino-functionalized silica particles. The comparison of the zeta potential-pH functions of plain and amino functionalized silica particles with a diameter of 1 µm demonstrates the shift of the zeta potential of plain silica particles into positive direction for amino functionalized silica particles. The amino functionalized silica particles have a positive zeta potential at pH < 4 and a negative zeta potential at pH > 4.