Abstract: When measurement by a 1 step sandwich method is performed, a signal corresponding to a quantity of labeled antibodies A is sampled, the labeled antibodies being constrained in the vicinity of a surface of an optical waveguide (D) by an antigen-antibody reaction. A differential value by time at the beginning of the measurement and a signal corresponding to an extent of an immunological reaction at a time at which the signal becomes nearly stable are obtained based upon the sampled signals. The extent of the immunological reaction is then uniquely determined based upon the differential value by time and the signal corresponding to the extent of the immunological reaction.

Abstract: An apparatus for optical measurement is formed as a one-piece molding. The apparatus has a reaction vessel and pre-treatment vessels, at least part of the partitioning wall between the both serves as an optical waveguide body, and a light absorber vessel is formed adjacent the reaction vessel (24). Simplification of the process of manufacture thus is attained. With a light absorber accommodated in the light absorber vessel, (25), reaction components of excitation light and other noise light components that are propagated through the optical waveguide body can be sufficiently attenuated to improve the S/N ratio of the optical measurement.

Abstract: An L-proline derivative represented by: ##STR1## wherein R.sub.2 represents a lower alkyl group is prepared by reacting L-proline with a D-.alpha.-alkyl-.beta.-acylthiopropionic acid halide, ##STR2## wherein R.sub.1 represents an acyl group, X represents a halogen atom and R.sub.2 has the same meaning as defined above. The halide is added to an aqueous medium containing L-proline and a condensation agent for deacidification. The halide and L-proline are reacted while the reaction temperature and pH are maintained at 12.degree. C. or lower and within a range of 10.5-11.5, whereby a compound represented by: ##STR3## wherein R.sub.1 and R.sub.2 have the same meanings as defined above is obtained. The resulting compound is then subjected to deacylation under strong alkaline conditions without being isolated from the reaction mixture, thereby yielding the target L-proline derivative.