The effectiveness of aromatic o-diamines as chromogenic reagents for PtII determination in aqueous micellar solutions

reagents for PtII determination in aqueous micellar solutions has been reported.1 It is believed that complexation of the PtII ion with these ligands is accompanied by a unique redox reaction of the PtII complexes (Scheme 1). These complexes exhibit peculiar and huge absorption having a molar absorptivity (ε >104 to 105 l mol–1 cm–1) in the near-infrared (NIR) region of 700 to 900 nm when they are incorporated into a hydrophobic environment, for example, surfactant micelles. Since in the NIR region background noise is minimized, this spectrally transparent region is favorable for spectroscopic use. The NIRabsorbing PtII-diamine complexes are neutral species having a bi-radical quinonediimine structure,1 which is responsible for a low-energy intraligand π-π* transition speculated based on molecular-orbital calculations.2,3 A few studies on PtII determination with 1,2-diaminobenzene derivatives have been reported,1,4–6 while no reports for the naphthalene derivatives have been presented. On the other hand, it is well known that 2,3diaminonaphthalene (DAN, Fig. 1) specifically reacts only with the SeIV ion (not SeVI) to form a fluorescent compound, socalled “piazselenol”, in acidic aqueous solutions.7 A large number of studies with DAN have been performed to optimize the separation–concentration extraction methods with various organic solvents after piazselenol derivatization to bring the concentration of the fluorescent species within the working range of the method. If reactions of DAN with PtII and SeIV ions can be carried out in a surfactant micellar solution, successive detections of both ions are achievable by NIR spectrophotometry and fluorometry. The fact that DAN has two active amino groups sensitive to air and light has restricted the practicability. To minimize this disadvantage, 1,4-dibromo-2,3-diaminonaphthalene (Br2DAN, Fig. 1) having electron-withdrawing substituents (bromo groups) has been prepared. 859 ANALYTICAL SCIENCES JULY 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry