Lab-In-Syringe automation of dispersive micro-solid phase extraction based on in situ formation of Ni/Fe-layered double hydroxides for the determination of angiotensin receptor blockers in environmental waters

Pharmaceutical residues in environmental waters continue to raise significant public and ecological concerns, necessitating advanced analytical methodologies for their monitoring. In this work, a novel Lab-In-Syringe automated dispersive micro solid-phase extraction (LIS-DMSPE) method was developed to determine three angiotensin receptor blockers in water samples. The approach was based on the in situ synthesis of Ni/Fe-layered double hydroxides within the void of an automatic syringe pump through controlled pH adjustment following the aspiration of precursor solutions. This enabled the rapid formation of the adsorbent and eliminated the need for pre-synthesized or magnetized sorbents. Enhanced sedimentation speed, achieved by increasing ionic strength with NaNO₃, allowed isolating the sedimented sorbent from the sample matrix without centrifugation and filtration. The instrumental setup was successfully coupled online with HPLC-DAD. After in-syringe washing and dissolving the sediment, the low organic solvent content of the extract enabled large-volume injection (200 μL), thereby boosting sensitivity. Parameters including type and volume of precursor solution, NaNO₃ addition, buffer volume and pH, stirring rate and time, and the composition of elution/destruction solution were carefully optimized. Recoveries and enrichment factors were in the ranges of 62.0–88.7 % and 13.3–25.8, respectively. The method was linear over a 5–200 μg L⁻¹ concentration range for all analytes. Accuracies ranged from 88.7 % to 105.8 % for real samples spiked at two concentrations with RSDs less than 3.5 %. To our knowledge, this is the first report on a LIS-DMSPE method that does not require pre-synthesis or magnetization of the sorbent for extraction and uses accelerated sedimentation for adsorbent isolation.