The CaptureSelect LambdaFabSelect Leakage ELISA is designed to detect possible leached ligand of human Fab fragments or Ig's with a lambda light chain that have been purified using LambdaFabSelect affinity resin (Cytiva). Even when covalently attached, small amounts of the LambdaFabSelect affinity ligand can leach off of the chromatography support and co-elute with the antibody. This ELISA provides typical sensitivity and accurate quantitation of possible leached ligand greater than or equal to 1 ng/mL. The CaptureSelect LambdaFabSelect Leakage ELISA can be used as a tool to aid in optimal purification process development and in routine quality control of in-process streams as well as final product.