Evaluation of the anthropogenic input of caffeine in surface waters of the north and center of Portugal by ELISA.

This study comprises the development of an enzyme-linked immunosorbent assay (ELISA) for the quantification of caffeine in complex aqueous matrices without any sample clean-up procedure. Salinity and dissolved organic matter were selected as potential interfering agents. The addition of a sample buffer containing bovine serum albumin (BSA) prior to the sample was found to decrease the influence of those interfering agents. The working range of the developed method was 0.1-100 μg L(-1). Quantification of caffeine was possible in 43 out of 51 real aqueous samples, at values between <LOD and 15 μg L(-1). Results correlate well with those obtained by LC-MS/MS. To the best of our knowledge this is the first study dealing with the quantification of caffeine in Portugal's surface waters.