Selective extraction and determination of trace metals by magnetic covalent organic frameworks with abundant thione and secondary amine groups coupled with ICP-MS

Abstract

A core-shell magnetic covalent organic frameworks (MCOF-SN) nanocomposite with high adsorption capacity was prepared by simply and directly coating covalent organic frameworks with abundant thione and secondary amine groups on the surface of magnetic nanoparticles, which were used to selectively extract copper (Cu²⁺), cadmium (Cd²⁺), lead (Pb²⁺), cobalt (Co²⁺) and nickel (Ni²⁺) ions prior to the detection by ICP-MS. The prepared magnetic covalent organic frameworks have high adsorption capacity of 52, 65, 162, 34 and 42 mg g⁻¹ for Cu²⁺, Cd²⁺, Pb²⁺, Co²⁺ and Ni²⁺ ions, respectively. The analytical parameters affecting magnetic solid-phase extraction (MSPE) of metal ions were optimized. They were pH of sample, 4–5; eluent, 1 mL of 1 % (v/v) HNO₃; amount of adsorbent, 15 mg; and sample volume, 200 mL. Under optimal experimental conditions, the limits of detection (LODs) of Cu²⁺, Cd²⁺, Pb²⁺, Co²⁺ and Ni²⁺ ions for water are 0.26, 0.16, 0.25, 0.08 and 0.17 ng L⁻¹ with enrichment factors of 192, 191, 196, 188 and 190, and their relative standard deviations (RSD) were less than 5 % (20 ng L⁻¹, n = 3), respectively. The LODs for Chinese herbal medicine samples were 0.52, 0.32, 0.50, 0.16 and 0.34 μg kg⁻¹ based on 0.100 g sample, respectively. The proposed MSPE-inductively coupled plasma mass spectrometry (MSPE-ICP-MS) method with simple operation, high sensitivity and high anti-matrix interference ability has been successfully applied to the samples with complicated matrices, such as water and Chinese herbal medicine.