Application of ZIF-8–graphene oxide sponge to a solid phase extraction method for the analysis of sex hormones in milk and milk products by high-performance liquid chromatography

Abstract

A zeolitic imidazolate framework-8 (ZIF-8) incorporating a graphene oxide sponge (GOS) nanocomposite (ZIF-8–GOS) was synthesized successfully by a simple one-pot preparation method. Compared with the raw materials (ZIF-8 and GOS), the ZIF-8–GOS nanocomposite has a very large surface area (1660 m² g⁻¹), and super-high pore size (14.95 nm) and pore volume (6.21 cm³ g⁻¹). Based on this, a method using ZIF-8–GOS for solid phase extraction (SPE)-high performance liquid chromatography (HPLC) was established for the analysis of five sex hormones in milk and milk products. The main experimental parameters that can affect the solid extraction process were optimized in detail. From a comparison of ZIF-8, GOS and commercial C18 SPE cartridges, the ZIF-8–GOS adsorbents showed the best compromise between selectivity and efficiency for target analytes. The analytical performance showed low limits of detection (0.52–2.11 µg L⁻¹) and limits of quantification (1.75–6.97 µg L⁻¹), as well as good linear ranges (10.0–3000 µg L⁻¹ for most sex hormones except nandrolone, where the range was 5.0–3000 µg L⁻¹) with remarkable linear correlation coefficients (r > 0.9998). Excellent repeatability was also achieved through intra-day (RSD < 0.39%) and inter-day (RSD < 3.86%) experiments. When the proposed analytical approach was applied to milk and milk products, the results revealed satisfactory recoveries and sensitivities at trace level, with detection of some of the target compounds, which demonstrates the good application potential of the ZIF-8–GOS adsorbent in the trace analysis of organic contaminants.