API Aerosizer

Comparison tests between the PSS Accusizer 770 (light blockage), API Aerosizer (time of flight) and MALLS instruments (Malvern Mastersizer and Coulter LS) indicated that the MALLS instruments gave results that differ from each other and from microscopy whereas the other two instruments gave results in agreement with each other and with microscopy [167]. The choice of the Fraunhofer or Mie theory model affected the calculated size distribution in an unpredictable manner and the use of Mie... 

The Malvern API Aerosizer (Malvern Instruments Ltd., Southborough, MA) operates on the principle of supersonic flow in a jet, followed by laser Doppler velocimetry to measure the aerodynamic diameter of particles in the size range from 0.5 to 200 pm using 50 channels. The operating flowrate is 6 L/min. The Atcor Net-2000 is a similar device for determining aerodynamic diameter, except that it is capable of sizing particles up to only 5.0 pm in diameter at a flowrate of 0.1 ft3/min (2.83 L/min). 

Fig. 11.8 are photographs of two instruments offered by Amherst Process Instruments (API). Fig. 11.8a is the API aerosizer, a high resolution particle size analyzer for fine powders (range 0.2 - 700 pm), which is based on aerodynamics. A gas containing the entrained particles expands through a nozzle at supersonic velocities into a partial vacuum which is contained within a barrel shock envelope. The exit velocity of a particle depends on its density and size. Two laser beams, separated by a defined distance, and two photomultipliers form the measurement zone. From the velocity and the known density of the particulate solid, the aerosizer determines size, one by one, with a speed of up to 100,000 particles per second and an accuracy of better than 1 % which make this instrument rather unique. The system uses interchangeable dispersers for different types of particles and, in total (refer to Fig. 11.8a), consists of particle dispersers (A), sensor unit (B), vacuum system (not shown), and computer (C). 

Fig. 11.8 Photographs of (a) the API aerosizer and (b) the API aero-flow, (a) also includes a schematic presentation of the measuring principle (courtesy API, Amherst, MA, USA),...

Mitchell IP, Nagel MW, Archer AD. Size analysis of a pressurized metered dose in-haler-dehvered suspension formulation by API aerosizer particle size analyzer. J... 

There are to my knowledge two instruments on the market which use this principle, firstly the APS 33 of TSI, St. Paul, Min. and secondly, to my knowledge since 1989, the API Aerosizer of Malvern Instr. Ltd, Worcestershire, U.K. Fig. 4 shows the main part of the principle set up of the APS 33, as given in the TSI advertising leaflet. 

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