ABSTRACT

The electrical zone sensing method, or ‘Coulter counter’ is a well-established technique for the size analysis of particles in suspension. It was originally devised for counting of blood cells (Coulter 1956), and later developed into one of the most popular and widely used size analysis techniques. It is now sufficiently well established to be used as a standard method in many ASTM specifications, and is the subject of a British Standard (BS3405 part 5, 1983). The original instrument (the Coulter model ‘A’) is now a much soughtafter antique by those interested in particle technology, and has been replaced by a series of more advanced models. The best-known of these are the TA and TAII, which sort particles into 16 size bands. Currently the top-of-the-range instrument is the Multisizer, which provides up to 256 size bands and is under full computer control. The model ZM is essentially a particle counter, which can perform size analysis over a limited size range with the addition of a multichannel analyser (‘Channelyser’); a range expander is also available. Despite the electronic sophistication, some users still prefer the earlier models!