Separation principles for the various solid phases

Large solid phases (plastic, glass, membranes, paper) retain the attached specific immunoreactant while unbound and/or unreacted molecules are removed by aspiration or decanting. This simple separation procedure is probably responsible to a large degree for the wide application of these solid phases, despite their lower binding capacity. 

Particulate solid phases with a high surface/volume ratio (consequently higher efficiency) give faster reactions since the solid phase is dispersed throughout the reaction mixture, but may suffer from the necessity of more involved separation techniques such as centrifugation, filtration or special procedures (Hunter, 1980). This also makes automation more difficult. 

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