An approach to quantitation in rhodamine isothiocyanate labeling

A survey of commercially available TMRI and RBI products revealed that many are of unsatisfactory quality. Optimum dye/IgG ratios were obtained in conjugates with TMRI of about 65% purity by labeling them with reaction mixture ratios of 10 and 20 mug dye/mg IgG. Optimum labeling with RBI of comparable purity required reaction mixture ratios of at least 20 mug dye/mg IgG. Although specific storage stability studies of TMRI or RBI products were not performed, one TMRI product underwent appreciable degradation during a 2-year period of storage in a desiccator over Drierite. The importance of evaluating the protein labeling capacity of TMRI or RBI products before making immune conjugate preparations is evident.