(122a) Optical Single Particle Detection with Wide Dynamic Range for Nano- and Microparticle Sizing and Counting

Dispersions, suspensions, and emulsions are used in different industrial branches and consist of various materials. Two important parameters to characterize such products are particle size distribution and particle concentration. Typical methods used in industry to characterize suspensions are photon correlation spectroscopy also named dynamic light scattering and laser diffraction. But, these methods cannot measure the particle concentration directly and have limited capability of detection of subpopulations in polydisperse systems. Especially small subpopulations and size differences are not detected properly.

To address this issue, we are developing a particle counter for particle sizing and counting with a wide dynamic detection range. The instrument is designed to detect nano- and microparticles in aqueous suspension with simultaneous concentration determination. Particle detection is based on light scattering measured in two directions and hydrodynamic focusing for particle separation. The detection of single particles has the advantage of very good sizing resolution enabling for example determination of particle agglomerates for stability analysis or growth of shell for core shell particle production. Concentration determination is important e.g. for product stability where particle suspensions are stabilized using detergents and for pharmaceutical products where particle concentration must be certified.

We present results for detection of polydisperse particle suspensions in a size range of approximately 100 nm to 3 µm and monodisperse particles made of different materials. The current lower detection limit for polystyrene particles is approximately 65 nm in side scatter and 100 nm for forward scatter. Additionally, the data show a very good resolution in signal intensity enabling accurate particle sizing. The particle concentration can be determined with a measurement uncertainty of less than 1%. However, according to the applied theory of Mie scattering and Rayleigh-Debye-Gans approximation, the lower detection limit for detectable particle size by light scattering strongly depends on the index of refraction of the material which the particles consist of.

ACKNOWLEDGEMENTS

The work is supported by the funding program 'Messen, Normen, Prüfen und Qualitätssicherung' (MNPQ) of the Federal Ministry for Economic Affairs and Energy (BMWi) in Germany