Immobilization of chromogenic reagent for the determination of trace cobalt by lab-on-valve bead injection spectroscopy

Abstract

An approach for the immobilization of a chromogenic reagent on solid phase micro-beads is performed via a sulfonation reaction. The product as an optical sensor is applied in lab-on-valve bead injection spectroscopy. The benzene ring structure exists in various chromogenic reagents, which facilitates the introduction of a sulfonic acid group via sulfonation. Chromogenic reagents ranging from neutral to anionic can be immobilized on anion exchanger micro-beads. As a model of application, micro-beads of Sephadex QAE A-25 loaded with the chromogenic reagent 1-(2-pyridylazo)-2-naphthol-sulfonic acid (PAN-S) are employed for the determination of trace cobalt by lab-on-valve bead injection spectroscopy. The characteristics of the micro-beads and some important parameters governing the performance of the method are investigated. With a sample volume of 1.0 mL, a detection limit of 8 μg L⁻¹ and a linear range of 20–500 μg L⁻¹ are obtained for cobalt, along with a RSD value of 2.8% (at the 200 μg L⁻¹ level). The accuracy and practical applicability of the present method are validated by analysing a certified reference material of soil GBW07404, vitamin B₁₂ injection and mecobalamin tablets, and further demonstrated by spiking recovery of cobalt in two water samples.