In-syringe dispersive μ-SPE of estrogens using magnetic carbon microparticles obtained from zeolitic imidazolate frameworks

Herein, we propose for the first time the use of magnetic porous carbons (MPCs) derived from zeolitic imidazolate frameworks (ZIFs) for the automated in-syringe magnetic dispersive micro-solid phase extraction (D-μ-SPE) of environmental pollutants prior to their analysis using GC-MS. MPCs with dual porosity are obtained from the direct combustion of the ZIF-67, obtaining robust and magnetic porous carbons on the micrometer scale. As proof of concept, this material has been applied for the automated D-μ-SPE of estrogens (estrone, 17β-estradiol, and 17α-ethynylestradiol) cataloged as Contaminants of Emergent Concern by the Environmental Protection Agency of the United States (US-EPA). The automation of the system provided a good precision given the low relative standard deviations (RSDs) obtained, ranging from 2.70 to 5.90 % for intra-day precision and from 4.6 to 9.55 % for inter-day precision. Furthermore, the clean-up and preconcentration of the sample is easy and quick, as the in-syringe magnetic D-μ-SPE is carried out in less than 20 min. The high porosity, magnetism, and good stability of the MPCs facilitated the automation of the SPE in dispersive mode enabling the analysis of samples with a complex matrix without backpressure or problems related with the clogging of the instrumentation conduits. The applicability of the method to wastewater samples has been demonstrated given the good recoveries attained ranging from 86 to 115 %.