Spectrophotometric determination of lead(II) ion by 96-well microplate electrostatically immobilized porphyrin

A water-soluble 5,10,15,20-tetrakis(4-N-methylpyridyl)porphine (TMPyP) was used as a highly sensitive chromogenic reagent for the lead(II) ion. When this TMPyP was complexed with the lead(II) ion, the absorption spectra of TMPyP significantly changed in the Soret band {H2TMPyP: lambda(max) = 423 nm (epsilon: 2.6 x 10(5) M- cm(-1)), Pb(II)-tmpyp: lambda(max) = 476 nm (epsilon: 1.8 x 10(5) M-1 cm(-1))}. In this study, the spectrophotometric multi-determinations of the lead(II) ion were developed using a microplate electrostatically immobilized TMPyP on the surface of the well. As a result, the lead(II) ion was quantitatively reacted within 15 min with TMPyP at pH 9 and 60degreesC. The determination range of the lead(II) ion was 7.5 x 10(-7) M to 1.0 X 10(-4)M, the relative standard deviation at median was 4.04% (n = 96), and the detection limit (3sigma) was 5.0 x 10(-7) M. Also, the same plate was able to be reused ten times. Furthermore, the determination of the lead(II) ion present in tap water was possible with citric acid as a masking agent.