Abstract: Apparatus are provided which automatically add diluent/quench reagent in such a manner as to enable adequate mixing as well as a short period for further mixing in automated immunoassay techniques. The probes for adding the diluent/quench reagents are offset from the optics module probe so that reagents are being added to a second row while the optics probe aspirates solutions from a first row.

Abstract: An apparatus for centering the open end of tubes prior to the insertion of a probe is described. The tube aligning means has a frustoconical inner surface to gather the tube mouth held loosely in a tube rack. The tube is centered relative to the probe. The aligning means is caused to move along the probe shaft axis by cooperation of an outer probe surface and an inner female surface for receiving the probe. In the preferred embodiment, a spool-like cylindrical member is positioned within the arms of a U-shaped bracket which limits the vertical and restricts the rotational movement of the aligning member.

Abstract: Variations in the intensity of a light source and the sensitivity of a fluorescence detector photo-multiplier tube are simultaneously compensated by measuring the intensity (I.sub.LS1) of the light source at the sample excitation frequency with a silicon detector, measuring the intensity (I.sub.LS2) of the light source at the emission frequency with another silicon detector, measuring with the photo-multiplier detector the intensity (I.sub.S) of the sample's fluorescence and the intensity (I.sub.

Abstract: A reproducible mounting for use in conjunction with prealigned optional assemblies. The mounting comprises a base member and a mating member attached thereto by fastening means cooperating with first, second and third noncollinerly disposed mounting holes whereby all six degrees of freedom between the base and the mating member are eliminating.