Determination of copper at ng ml−1-levels based on quenching of the europium chelate luminescence

The work describes a novel assay for copper at trace levels. Aqueous Cu2+ ions efficiently quench the luminescence of a europium–terpyridine-polyaminopolycarboxylate chelate. Both static and dynamic quenchings were identified and separated by time-resolved luminescence spectroscopy. Single exponential decay was observed throughout, with decay times ranging from 1261 μs, in the absence of copper, to 750 μs at 300 ng ml−1 copper, reflecting strong dynamic quenching. The calibration graph obeys the Stern–Volmer equation and is given for the 0–300 ng ml−1 range. The quenching constant was determined at 1.39×105 l mol−1 and the 3SD limit of detection was 7 ng ml−1. Time-resolved luminescence spectroscopy provided additional selectivity for copper by discriminating static quenching by other heavy metals. Thus, solely static quenchers Zn2+, Cd2+, Hg2+ and Pb2+ did not interfere, whereas the relative interference by dynamic quenchers was 0.16% (Fe3+), 1.15% (Co2+), 0.38% (Ni2+), 3.81% (Cr3+) and 3.03% (Mn2+). The quenching mechanism is discussed. The method appears suitable for industrial and environmental applications.