Particle size analysis counting

The Zeiss AxioHOME (Highly Optimized Microscope Environment) was developed by pathologists to count, measure and analyze cell structure in biological thin sections. The AxioHOME is a light microscope coupled to a personal computer that allows the microscopist to make measurements on particles whilst still observing the real image. It is highly suited to particle size analysis because the measurements can be exported directly to a spreadsheet [103]. 

During particle size analysis, in addition to screening, sifting, and counting, sedimentation techniques are often used which produce unequivocal results only if the individual particles can move without influencing each other. For that reason, very dilute suspensions are used. Nevertheless, it is possible that agglomerates form or already... 

Originally applied to the counting of blood cells, the technique has become fairly popular for particle size analysis of ceramic powders. 

If dilution and counting were fully automated, the flow ultramicroscope might well provide rapid, on-line particle size analysis. To the author s knowledge, commercial units are not available, and construction of a prototype is admittedly difficult. 

A wide variety of particle size measurement methods have evolved to meet the almost endless variabiUty of iadustrial needs. For iastance, distinct technologies are requited if in situ analysis is requited, as opposed to sampling and performing the measurement at a later time and/or in a different location. In certain cases, it is necessary to perform the measurement in real time, such as in an on-line appHcation when size information is used for process control (qv), and in other cases, analysis following the completion of the finished product is satisfactory. Some methods rapidly count and measure particles individually other methods measure numerous particles simultaneously. Some methods have been developed or adapted to measure the size distribution of dry or airborne particles, or particles dispersed inhquids. 

Two general methods have evolved. One uses a stirred tank system, while the other depends on the measurement of particle size or surface area change via particle counting or image analysis techniques. 

HPLC systems have recently become commercially available, which allow the use of pressures up to 1000 bar. Columns of particle size around 1.7 p,m and up to approximately 10-cm long can be operated at their optimum flow rate within the pressure capability of the system. The main advantage of these columns is that they can generate the same plate count as longer columns of larger particles but in a shorter analysis... 

From Equations 2 and 3 it can be seen that wider particle size distributions need to be corrected as shown. In the present study, an additional sensitive volume check was made using an electron microscope count of the particles on a millipore filter placed in the delivery tube for a fixed time. Results indicated that the analysis and observations were consistent. This also applies to calibration measurements with silicon oil mists. 

Fairs [79] used a projection microscope for training purposes. This technique can also be used for size analysis [80] but is not recommended for particles smaller than 2 pm. Hamilton et. al. [81 c/7.82] demonstrated the need to train operators and showed that gross count differences on the same samples at different laboratories were much reduced after interlaboratory checks. 

Sieves may also be calibrated by a counting and weighing technique applied to the fraction of particles passing the sieve immediately prior to the end of an analysis. These will have a very narrow size range and the average particle size may be taken as the cut size of the sieve. A minimum number ( ) of particles need to be weighed to obtain accurate volume diameters let this weight be m and the particle density be / then ... 

Micromeretics Elzone 5380 has one analysis station features complete sizing and counting capability and reports particle size distribution as a function of number, area or volume. 

The instrument has also been used for size analysis of sugar crystals from 40 pm to several mm in size. By means of a vibratory feeder, the sugar is fed in free fall, past a vision camera and sized every 5s. The final result of the measurement is available after 100-300 frames and documented via an interface with a database and printer. Measured data includes particle count and size or projected area. 

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