Determination of chlortetracycline in body fluids with the complex cation of chlortetracycline¯europium(III)¯trioctylphosphine oxide by total internal reflected fluorescence at a water/tetrachloromethane interface

A highly selective method for determination of chlortetracycline (CTC) is proposed based on the measurements of total internal reflected fluorescence (TIRF) at a water/tetrachloromethane interface. In the pH range 7.5¯8.7, the interaction of the binary complex of Eu(III)¯CTC with trioctylphosphine oxide (TOPO) occurs at the H2O/CCl4 interface, resulting in a greatly enhanced TIRF signal characterized by the emission at 619 nm when excited at 397 nm. The enhanced TIRF intensity is in proportion to the CTC concentration in the range 0.17¯10.0×10-7 mol l-1. The limit of detection (3 sigma) is 2×10-9 mol l-1. It was found that ions in body fluids such as Ca(II), Mn(II), Cu (II), Ni(II), Al(III), Fe(III), Cr(III), Mg(II), Zn(II), Pb(II), and PO43- can be permitted at 1.0×10-4 mol l-1 (tolerance level, 10%). Body fluid samples including human urine, human serum and fresh milk were determined with a recovery of 99.0¯105.2% and R.S.D. of 2.0¯7.7%, respectively.