Monitoring of the conjugation reaction between human serum transferrin and fluorescein isothiocyanate by capillary electrophoresis

Labeling of iron-free human serum transferrin by an amine-reactive probe, fluorescein isothiocyanate (FITC) was monitored with different dye to protein ratios. The degree of labeling was followed and determined by capillary electrophoresis. Depending on the number of the bound FITC, a shift in the electropherogram was observed, but the conjugated-transferrin forms were resolved from the unbound FITC in zone electrophoresis. The lowest protein concentration that resulted in detectable transferrin conjugate was 0.13 μM, and the limit of detection of the conjugated protein was 0.13 nM (10 ng/ml) with a signal to noise ratio of one to three.