Particle and Surface Sciences has introduced the Ankersmid Eyetech particle characterisation analyser, which offers size and image/shape analysis, in Australia and New Zealand.
The Ankersmid Eyetech combines a laser-based particle size analyser with advanced image/shape analysis software to provide a complete particle characterisation system in a single compact, PC-controlled bench-top unit.
Unlike other laser-based particle size analysers based on light scattering or diffraction techniques, the Ankersmid Eyetech employs the principle of time-of-transition analysis to measure particle size directly over the dynamic range of 0.1 to 2,000um.
Allowing measurement of particles in liquids, gases and even on solid surfaces, the mode of operation is based on a focused laser beam scanning circularly in space at a constant high frequency.
This scanning operation sets up a photo-defined zone, essentially toroidal in shape, in which any particle passing through produces interaction pulses of light detected by a PIN photodiode.
The time width of these pulses is directly proportional to particle diameter - the larger the particles scanned, the longer the time of interaction with the laser beam.
By rotating the beam in a circle at high frequencies, the instrument minimises the effect of any motion of the particles relative to the beam.
Laser obscuration time (LOT) analysis avoids many of the factors which complicate other optical laser methods.
Inconsistencies of light scattering or diffraction theories are eliminated, as well as Brownian motion, refractive index, viscosity and thermal effects.
Having recorded the interaction pulses, the Ankersmid Eyetech system then has to analyse them to convert them directly into particle size data.
This is done with software that performs the size analysis and, by pulse-shape analysis, produces the photo-defined measurement zone.
By selectively rejecting pulses whose shape is outside previously defined criteria, the problem of particles interacting with the laser beam outside the focus point is avoided.
Since the diameter of the laser beam varies along its length, any interaction of a particle outside the focus point would produce an erroneous pulse width and therefore particle size.
The open architecture of the system - made possible by the optically defined measurement zone, with no need for orifices - has enabled a video monitoring system to be easily added.
The Eyetech incorporates a CCD (close-coupled device) microscopic TV camera, placed at right angles to the laser beam, to produce real-time images of the particles as they pass through the measurement zone.
Particle shape analysis software gives a wide variety of particle information, including Ferret's diameter, Martin's radius, area, perimeter, shape factor and aspect ratio.
Since the laser size analysis system, in common with most others, operates on the assumption of spherical particles, this second image analysis channel in the same instrument provides important additional shape information when analysing aggregates and non-spherical particles.
Besides being fed into the system's computer for the shape, grain and other geometric analyses, the visual image of the particles in the measurement volume is displayed on a separate video.
Essentially, there are two separate analysers in one unit, which use different detection principles, allowing a direct cross reference.
A further advantage of the instrument's open architecture is the variety of cell types that can be employed to introduce particles to the measurement zone.
Available modules include mechanically stirred, magnetically stirred, microscope slide, flow-through and Peltier heated/cooled cells, and an aerosol generator.
Applications for the Ankersmid Eyetech include assessing microbial contamination in drug solutions, carbon, ceramics, food processing, geology, industrial areas, microbiological work such as monitoring membrane filtration, paint, paper; particulate contamination in parenteral solutions, pharmaceutical applications and plastics production.
