A rate nephelometer for measuring specific proteins by immunoprecipitin reactions

A kinetic nephelometric method and instrument have been developed for the rapid determination of specific serum proteins by means of immunoprecipitin reactions. The maximum rate of change of scattered light intensity in an antigen-antibody reaction can be made to occur within 60 s after initiation of the reaction and provides a measure of the antigen concentration under antibody excess conditions. A mathematical relationship has been found for the conversion of the nonlinear maximum rate data directly into a linear concentration read-out, making possible the use of single-point calibration. Instrument operating parameters and computations are programmed for a particular analysis by means of machine-readable cards. Antigen-excess samples are detected rapidly by injection of calibrator into the reaction mixture after the rate signal has dropped to a pre-selected level. The method correlates well with both radial immunodiffusion and end-point nephelometric methods.