Restricted access material-ion imprinted polymer-based method for on-line flow preconcentration of Cd2+ prior to flame atomic absorption spectrometry determination

Restricted double access ionic imprinted polymer for online extraction and determination of copper from milk samples via FIA-FAAS system

BACKGROUND

Determining metals in complex biological samples, such as milk, typically involves dry or wet decomposition. However, these techniques have limitations, including low selectivity, risk of contamination, and the use of large reagent volumes. To solve these problems, solid-phase extraction (SPE) using multifunctional sorbents has been extensively explored. In this context, this work proposed synthesizing a new restricted double access ionic imprinted polymer (RAIIP-BSA), for online SPE and determination of Cu2+ from untreated milk samples via flow injection analysis and flame atomic absorption spectrometry (FIA-FASS).

RESULTS

Firstly, the polymer was obtained by bulk polymerization using Cu2+ as a template, 4-vinyl pyridine as a functional monomer, and glycidyl methacrylate as a hydrophilic comonomer. Subsequently, it was covered with bovine serum albumin, creating the restricted double access barrier. The obtained material could exclude 97 % of the proteins from milk samples. RAIIP-BSA was chemically and physically characterized. The main extraction variables were optimized via multivariate optimization. The method showed good figures of merit, such as linearity ranging from 0.05 to 1.0 mg L-1, LoD and LoQ of 0.03 and 0.05 mg L-1, intra- and interday precision ranging from 0.73 to 4.14 % and 0.16-3.68 %, and an intra- and interday accuracy ranging from 97.0 to 115.0 % and 103.0-119.0 %, respectively.

SIGNIFICANCE

The developed method demonstrates the effective extraction of Cu2+ from untreated milk samples, exhibiting selectivity, high extraction capacity, prolonged sorbent (RAIIP-BSA) durability, simplicity, and swift operation. This method holds promise as an alternative to conventional metal analysis approaches in complex matrices.

Cd2+ Detection by an Electrochemical Electrode Based on MWCNT-Orange Peel Activated Carbon

This study reports the development of a new electrochemical sensor based on a carbon paste electrode (CPE) composed of biomass-based orange peel activated carbon (ACOP) and multiwalled carbon nanotubes (MWCNTs), and this composite is used for the electrochemical detection of cadmium ions (Cd2+). The ACOP/MWCNT composite was characterized by FTIR, Raman, and electrochemical impedance spectroscopy. The electrochemical evaluation of Cd2+ was performed using square wave and cyclic voltammetry. The ACOP/MWCNT-CPE electrochemical sensor exhibited a coefficient of determination r2 of 0.9907, a limit of detection of 0.91 ± 0.79 μmol L-1, and a limit of quantification of 3.00 ± 2.60 μmol L-1. In addition, the developed sensor can selectively detect Cd2+ in the presence of different interferents such as Zn2+, Pb2+, Ni2+, Co2+, Cu2+, and Fe2+ with a relative standard deviation (RSD) close to 100%, carried out in triplicate experiments. The ACOP/MWCNT-CPE presented high sensitivity, stability, and reproducibility and was successfully applied for the detection of Cd2+ in river water samples with recovery rate values ranging from 97.33 to 115.6%, demonstrating to be a very promising analytical alternative for the determination of cadmium ions in this matrix.

Direct magnetic sorbent sampling flame atomic absorption spectrometry (DMSS-FAAS) for highly sensitive determination of trace metals

A procedure of direct magnetic sorbent sampling in flame atomic absorption spectrometry (DMSS-FAAS) was developed in this work. Metal-loaded magnetic sorbents were directly inserted in the flame of the FAAS for direct metal desorption/atomization. Magnetic graphene oxide aerogel (M-GOA) particles were synthesized, characterized, and used as a proof-of-concept in the magnetic dispersive solid phase extraction of Pb²⁺ ions from water samples. M-GOA was selected because is a light and porous sorbent, with high adsorption capacity, that is quickly burned by the flame. Magnetic particles were directly inserted in the flame by using a metallic magnetic probe, thereby avoiding the need for a chemical elution step. As all the extracted Pb²⁺ ions arrive to the flame without passing through the nebulization system, a drastic increase in the analytical signal was achieved. The improvement in the sensitivity of the proposed method (DMSS-FAAS) for Pb²⁺ determination was at least 40 times higher than the conventional procedure in which the Pb²⁺ is extracted, eluted, and analyzed by conventional flame atomic absorption spectrometry (FAAS) via the nebulization system. The analytical curve was linear from 5.0 to 180.0 μg L^-1 and the limit of detection was found to be 1.30 μg L^-1. Background measurements were insignificant, and the atomic absorption peaks were narrow and reproducible. Precision assessed as a percentage of the relative standard deviation %RSD was found to be 17.4, 7.1, and 7.8% for 10, 70, and 180 μg L^-1 levels, respectively. The method showed satisfactory results even in the presence of other ions (Al³⁺, Cr³⁺, Co²⁺, Cu²⁺, Fe³⁺, Mn²⁺, Ba²⁺, Mg²⁺, and Li⁺). The performance of the new system was also evaluated for Cd²⁺ ions, as well as by using other magnetic particles available in our lab: magnetic carbon nanotubes (M-CNTs), magnetic restricted access carbon nanotubes (M-RACNT), magnetic poly (methacrylic acid-co-ethylene glycol dimethacrylate) (M-PMA), magnetic nanoparticles coated with orange powder peel (M-OPP), and magnetic nanoparticles covered with SiO₂ (M - SiO₂). Analytical signals increased for both analytes in all sorbents (increases of about 4-37 times), attesting the high potential and applicability of the proposed method. Simplicity, high analytical frequency, high detectability and reproducibility, low cost, and possibility of being totally mechanized are the most relevant advantages.

Development of Micro-Column Preconcentration Method Using a Restricted-Access Poly(protoporphyrin-co-vinyl pyridine) Adsorbent for Copper Determination in Water and Milk Samples by FIA-FAAS

For years, researchers have focused on the determination of metal ions at trace levels in environmental and food samples using analytical methods that employ techniques with low cost acquisition and maintenance and without microwave-assisted acid digestion procedures or aggressive reagents. Therefore, the present study deals with the synthesis and application of a novel, restricted-access poly(protoporphyrin-co-vinyl pyridine) adsorbent to preconcentrate copper in water samples and bovine milk that have only been subjected to pH adjusting (pH 6.0) and filtration using posterior on-line determination by FAAS. Regarding macromolecules, the restricted-access property of the adsorbent was achieved using the hydrophilic compound 2-hydroxyethyl methacrylate (HEMA). This method is based on the preconcentration of Cu2+ ions using a flow-injection system which is buffered with 0.05 mol L−1 of Britton–Robinson (BR) at a pH of 6.0 and has a flow rate of 14.0 mL min−1 through a mini-column packed with 50.0 mg of adsorbent. The elution was carried out using 0.40 mol L−1 of HCl toward the FAAS detector. The developed method provided a preconcentration factor of 44.7-fold, low limits of detection (LOD) (0.90 µg L−1) and quantification (LOQ) (2.90 µg L−1), tolerance to interfering ions (95.0 and 103.0%), and intra-day and inter-day precision assessed as the RSD (percentage of relative standard deviation), which ranged from 3.08 to 4.80%. The restricted-access poly(protoporphyrin-co-vinyl pyridine) adsorbent demonstrated outstanding features to exclude macromolecules, bovine serum albumin (BSA), and humic acid (HA) from an aqueous medium. Lake water and bovine milk samples were analyzed by the proposed preconcentration method with minimal sample pretreatment (which was based mainly on pH adjusting and filtration using an analytical curve with external calibration), yielding recovery values from addition and recovery tests ranging from 91.7 to 101.9%. The developed method shows great advantages over previously published methods, avoiding the time-consuming use of concentrated acids in a microwave-assisted acid digestion procedure.

Analytical perspective and environmental remediation potentials of magnetic composite nanosorbents

The synthesis and application of magnetic nanosorbents to remove emerging pollutants have been considered the best environmental remediation and sustainability option. Incorporating magnetism shortens the treatment time and allows the sorbent to be recovered quickly using external magnetic with many cycles. The implementation of magnetic solid-phase extraction (MSPE) using magnetic materials of different shapes, sizes, and surface morphology can be a valuable tool in applying materials to prepare analytical samples. In MSPE applications, materials with strong magnetic domain can be used as precursors for constructing magnetic composite as a promising sorbent. This article focuses on the most recent and exceptional applications of magnetic adsorbents for preconcentration and removal purposes. Magnetic adsorbents, such as nanoparticles (NPs), foam, sponges, nanocomposites, hydrogels, and beads with multifunctional attributes have been comprehensively studied in terms of preparation procedures, limitations, advantages, and interactions between pollutants and magnetic composites. The role of magnetic sorbents in sample preparation methods, such as simple solid-phase extraction and microextraction, as well as sorptive extraction using a stir bar, was also examined. The use of magnetic adsorbents with analytical techniques, such as solid-phase extraction and solid-phase microextraction improves the method for preparing samples concerning the influential role of magnetic adsorbents. Towards the end, promising features and future outlook are also directed.

Influence of Synthesis Parameters and Polymerization Methods on the Selective and Adsorptive Performance of Bio-Inspired Ion Imprinted Polymers

Ion-imprinted polymers (IIPs) have been widely used in different fields of Analytical Sciences due to their intrinsic selective properties. However, the success of chemical imprinting in terms of selectivity, as well as the stability, specific surface area, and absence of swelling effect depends on fully understanding the preparation process. Therefore, the proposal of this review is to describe the influence of relevant parameters on the production processes of ion-imprinted polymers, including the nature (organic, inorganic, or hybrid materials), structure, properties of the salt (source of the metal ion), ligand, crosslinking agent, porogenic solvent, and initiator. Additionally, different polymerization methods are discussed, the classification of IIPs as well as the applications of these adsorbent materials in the last years (2017–2022).

Vortex-assisted magnetic solid-phase extraction of cadmium in food, medicinal herb, and water samples using silica-coated thiol-functionalized magnetic multiwalled carbon nanotubes as adsorbent

The current work focuses on the facile and effective synthesis of a new nanocomposite based on multiwalled carbon nanotubes (MWCNT) decorated with magnetic core-shell Fe₃O₄@SiO₂ and functionalized with 3-mercaptopropyltrimethoxysilane (3-MPTS) used in the vortex-assisted dispersive magnetic solid-phase extraction (VA-DMSPE) of Cd(II) ions in environmental and food samples. The nanocomposite was characterized and the parameters that influenced the VA-DMSPE were optimized through a fractional factorial design 2^5-1. The proposed method provided a preconcentration factor of 33.14 times, detection and quantification limits of 0.090 μg L^-1 and 0.302 μg L^-1, respectively, and a linearity range of 0.001-40.0 μg L^-1. The developed method was effectively applied to preconcentrate and determine Cd(II) in water, tobacco, green tea leaves, ginkgo biloba, carrots, and rice samples, and its accuracy was evaluated using GF AAS.