Simultaneous detection of three drugs labeled by cationic metal complexes at a nafion-loaded carbon paste electrode

The synthesis of the pentaammine ruthenium(II) complex of N-isonicotinoyl-n ortriptyline (NORPy-Ru2+) was performed and its electrochemical properties at a nafion-loaded carbon paste electrode were examined. The anodic oxidati on of the positively charged labeled antidepressant proceeded at -0.06 V (v ersus Ag/AgCl, 0.05 M Cl-). A detection limit of 0.075 mu M (S/N = 3) was a chieved at physiological pH by square-wave voltammetry after a 5-min precon centration step, with a linear response over the range 0.075-5.0 mu M. With a view to a future triple-analyte immunoassay, the detection of NORPy-Ru2 was also examined in the presence of two labeled antiepileptics previously synthesised, i.e. phenytoin labeled by a ferroceneammonium salt (oxidation potential at 0.26 V) and phenobarbital labeled by a cobaltocenium salt (re duction potential at -1.05 V). The simultaneous detection of the three labe led drugs proceeded with analytical performances similar to those correspon ding to the separate accumulation of each tracer. However it was observed t hat the pentaammine ruthenium(II) complexes of pyridine and its derivatives were not stable in the presence of serum, which does not allow for their u se as redox cationic labels in a multi-analyte immunoassay to be envisaged. (C) 1999 Elsevier Science B.V. All rights reserved.