A new luminescent europium probe is presented for the determination of phosphate (P) in microliter plate format. The assay is based on the quenching of the luminescence of the europium-tetracycline (EuTc) 1:1 complex by phosphate using a reagent concentration of 20.8 mu mol/L. The probe is excited at 400 nm and displays a large Stokes' shift of 210 nm. The emission maximum is located at 616 nm. The system works best at neutral pH 7 and is therefore suitable for phosphate determination in biological and biochemical systems. The linear range of the calibration plot is from 5 x 10(-6) mol/L to 7.5 x 10(-4) mol/L of phosphate, and the limit of detection is 3 mu mol/L. (c) 2005 Elsevier B.V. All rights reserved.