Potential of porphyrins as chromogenic reagents for determining metals in capillary electrophoresis

Although capillary electrophoresis (CE) with photometric detection is a well-established technique for the determination of various inorganic ions, its limited sensitivity has hindered greater development in this area. In this work, we used a mixture of metals consisting of Co(II), Ni(II), Zn(II) and Mn(II) to demonstrate that the sensitivity of CE with ultraviolet–visible (UV–vis) detection can be improved by using chromogenic reagents such as porphyrins. To this end, the metals were reacted with 5,10,15,20-tetrakis(4-sulphophenyl)-porphine dodecahydrate (TPPS₄) to obtain their respective porphyrinato complexes, which were then separated by CE with a citrate buffer and detected at 410 nm. The ensuing electrophoretic method has a limit of detection (LOD) of 3 × 10⁻⁶ M (180 μg L⁻¹) for Co(II), 2 × 10⁻¹⁰ M (0.012 μg L⁻¹) for Ni(II), 4 × 10⁻⁶ M (260 μg L⁻¹) for Zn(II) and 4 × 10⁻⁹ M (0.219 μg L⁻¹) for Mn(II). The method is a highly promising choice for the ultratrace determination of Ni(II) and Mn(II).