Quantitative estimation of diphtheria and tetanus toxoids. 2. Single radial immuno-diffusion tests (Mancini) and rocket immuno-electrophoresis test in comparison with the flocculation test.

The concentration in Lf units, of an unknown diphtheria or tetanus toxoid preparation is estimated in the flocculation test relative to reference preparations of tetanus and diphtheria antitoxins, respectively. By replacing the antitoxin reference preparations with toxoid reference preparations it should be possible to use immunological methods other than the flocculation test for the quantitative estimation of toxoids in Lf units. A number of diphtheria and tetanus toxoids were tested by rocket immuno-electrophoresis and single radial immuno-diffusion (Mancini test). The concentrations of the unknown toxoids were expressed relative to a diphtheria toxoid calibrated in Lf units (DIFT) and a tetanus toxoid calibrated in Lf units (TEFT), respectively. These two toxoid preparations are regarded as candidates for establishment as international standard preparations. The results obtained in the two tests were compared with those obtained in the flocculation test. In most cases the differences between the results did not exceed 10%. It is concluded, therefore, that the rocket electrophoresis or the radial immuno-diffusion tests can be used as alternatives to the flocculation test.