Complexing porous polymer monoliths for online solid-phase extraction of metals in sequential injection analysis with electrochemical detection

Effect of crosslinker/porogen ratio on sponge-nested polymer monoliths for solid-phase extraction

Polymer monoliths can be polymerised within different molds, but limited options are available for the preparation of free-standing polymer monoliths for analytical sample preparation, and in particular, solid-phase extraction (SPE). Commercial melamine-formaldehyde sponges can be used as supports for the preparation of polymer monoliths, due its flexibility, giving various shapes to monoliths. Herein, the crosslinker/porogen ratio of highly porous sponge-nested divinylbenzene (DVB) polymer monoliths has been evaluated. Monoliths prepared using different crosslinker/porogen ratios were applied to the extraction of bisphenol F, bisphenol A, bisphenol AF, and bisphenol B. Monoliths containing 50 wt % DVB and 50 wt % porogens presented the highest recovery of bisphenols. Under the optimised conditions, the developed method showed a linear range between 2.5 µg L-1 and 150 µg L-1 for BPA and BPAF, and between 5 µg L-1 and 150 µg L-1 for BPB and BPF. The limits of detection (LOD, S/N = 3) and limits of quantification (LOQ, S/N = 10) ranged from 0.36 µg L-1 to 1.09 µg L-1, and from 1.20 µg L-1 to 3.65 µg L-1, respectively. The recoveries for spiked bisphenols (10 µg L-1) in tap water and water contained in a polycarbonate containers were between 82 % and 114 %.

Development of salt-induced homogeneous liquid-liquid extraction using a deep eutectic solvent performed in a narrow-bore tube for the extraction of Zn(II), Cu(II), and Cd(II) ions from honey samples

In this study, a sample preparation procedure based on salt-induced homogeneous liquid-liquid extraction performed in a narrow-bore tube was used for the preconcentration and extraction of Zn(II), Cu(II), and Cd(II) ions from honey samples. To perform the procedure, a mixture of working solution containing sodium chloride, acetonitrile, and a synthesized deep eutectic solvent (as an extraction solvent) was transferred into a narrow tube filled with solid sodium chloride up to a specific level. As the solution flowed through the tube, tiny droplets of the extraction solvent were formed at the boundary between the solution and salt layer. The droplets moved upwards in the tube and eventually collected as a distinct layer on the top of the solution. The separated phase was removed and dispersed into ionized water. After centrifugation, tiny droplets of the extraction solvent containing the analytes were sedimented at the bottom of the tube. The concentrated analytes were measured using flame atomic absorption spectrophotometry. The linear ranges and extraction recoveries were obtained in the ranges of 1.5-100 μg kg-1 and 89.6-94.8%, respectively. The detection limits ranged from 0.35 to 0.48 μg kg-1. Low relative standard deviations (C = 10 μg L-1, n = 6) of 3.1, 2.8, and 3.4% for Zn(II), Cu(II), and Cd(II), respectively, were obtained. Finally, the optimized method was successfully used in determination of concentration of the selected heavy metal ions in various honey samples.

Polymer monoliths for the concentration of viruses from environmental waters: A review

Even at low concentrations in environmental waters, some viruses are highly infective, making them a threat to human health. They are the leading cause of waterborne enteric diseases. In agriculture, plant viruses in irrigation and runoff water threat the crops. The low concentrations pose a challenge to early contamination detection. Thus, concentrating the virus particles into a small volume may be mandatory to achieve reliable detection in molecular techniques. This paper reviews the organic monoliths developments and their applications to concentrate virus particles from waters (waste, surface, tap, sea, and irrigation waters). Free-radical polymerization and polyaddition reactions are the most common strategies to prepare the monoliths currently used for virus concentration. Here, the routes for preparing and functionalizing both methacrylate and epoxy-based monoliths will be shortly described, following a revision of their retention mechanisms and applications in the concentration of enteric and plant viruses in several kinds of waters.

Evolution of Environmentally Friendly Strategies for Metal Extraction

The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed.

Evaluation of the tubing material and physical dimensions on the performance of extraction columns for on-line sample preparation-LC-MS/MS

Nowadays, high analytical throughputs are required considering an increasing demand for faster, simple and improved methods to analyze contaminants in a considerable number of samples. Generally, these compounds are present in complex matrices in contact with a high number of interferents becoming their determination difficult at low concentration. In this context, on-line extraction techniques arose to improve the extraction as well as separation power, while minimizing errors related to human sample manipulation. This paper describes a study regarding the development and optimization of columns used as an extraction device in multidimensional liquid chromatography. The main goals were the evaluation of the material used as column body as well as the investigation of the tube dimensions (internal diameter and length) in the extraction performance. Firstly, several tube materials were tested (steel, fused silica, PEEK, among others) being steel whose reported the best performance and was consequently chose for further studies. The investigation about the effects of the columns physical dimensions revealed a linear relationship between performance and the amount of sorbent utilized as extractive phase. However, when different columns with same amount of sorbent were tested results suggests that both i.d. and lengths play an important role in extraction efficiency. The longest columns with lower internal diameter showed the best results favoring the radial as well as axial analytes diffusion into the extraction column. After evaluation of these column variables, applications were carried out employing several different analytes belonging to various chemical classes and practical utilization, in order to reinforce the versatility as well as the robustness of this proposed study.

A rapid on-site analysis method for the simultaneous extraction and determination of Pb2+ and Cd2+ in cereals

In order to achieve rapid on-site screening and solve the problem of rapid pretreatment for the determination of lead (Pb²⁺) and cadmium (Cd²⁺) in cereals by a portable electrochemical analyzer with disposable screen-printed electrodes (SPEs), a new reliable and simple extraction method for Pb²⁺ and Cd²⁺ in cereals was developed. The Pb²⁺ and Cd²⁺ in cereals were purified by a mixed solution of 1 mol L⁻¹ potassium iodide (KI)/5% vitamin C (VC)/ethyl acetate after being extracted by 10% HNO₃, which transfers the Pb²⁺ and Cd²⁺ into ethyl acetate after a reaction with KI–VC. Then, the Pb²⁺ and Cd²⁺ were eluted from ethyl acetate with 5% HNO₃ and were determined by an electrochemical analyzer with screen printed electrodes. Under the optimized conditions, the matrix calibration curves of Pb²⁺ and Cd²⁺ in rice and wheat showed good linear relationships with R² > 0.996. The method shows a detection limit (LOD) for Cd²⁺ in rice and wheat of 6.7 μg kg⁻¹ and 11.5 μg kg⁻¹, and the corresponding values for Pb²⁺ were 34.9 and 31.1 μg kg⁻¹, respectively. The relative standard deviation (RSD) was less than 8.7% for Cd²⁺ and Pb²⁺. In addition, the recoveries of the tested reference materials using this method were between 80% and 120%. From sample pretreatment to testing results, the whole process took no more than 25 min, and the operation was simple for operators, green to the environment, cheap in terms of instruments, and above all suitable for on-site detection. The results implied that this portable electrochemical method with new pretreatment may be a good choice for screening Pb²⁺ and Cd²⁺ in cereal samples on-site.

To achieve rapid on-site screening rapid pretreatment for the determination of Pb²⁺ and Cd²⁺ in cereals by a portable electrochemical analyzer with disposable screen-printed electrodes, a new reliable and simple extraction method for Pb²⁺ and Cd²⁺ was developed.

Rapid monitoring of plant growth regulators in bean sprouts via automated on-line polymeric monolith solid-phase extraction coupled with liquid chromatography tandem mass spectrometry

An automated on-line solid-phase extraction (SPE) following liquid chromatography tandem mass spectrometry was established for the fast determination of plant growth regulator residues in soybean sprout and mung bean sprout. The crude extracted specimens were directly purified on a poly (2-(dimethylamino) ethyl methacrylate-co-ethylene dimethacrylate) monolithic column which was well-defined as the on-line SPE adsorbent. Under the optimized conditions, the developed method gave the linear range of 0.3-50 ng/mL for gibberellin and 2,4-dichlorophenoxyacetic acid, 0.2-50 ng/mL for 4-chlorophenoxyacetic acid, and 0.5-50 ng/mL for 1-naphthaleneacetic acid (r ≥ 0.998). The detection limits (S/N = 3) ranged from 1.0 to 2.5 μg/kg and the recoveries for spiked soybean sprout samples were in the range of 75.0-93.3%. Besides, the total time for one analysis was 16 min. The reusability of the monolith was up to 600 extractions. The proposed process facilitated fully automated SPE and accurate determination in one step with rapidity, simplicity, and reliability. Graphical abstract ᅟ.

Current status and future trends on automated multidimensional separation techniques employing sorbent-based extraction columns

Determination of target analytes present in complex matrices requires a suitable sample preparation approach to efficiently remove the analytes of interest from a medium containing several interferers while at the same time preconcentrating them aiming to improve the output signal detection. Online multidimensional solid-phase separation techniques have been widely used for the analysis of different contaminants in complex matrices such as food, environmental, and biological samples, among others. These online techniques usually consist of two steps performed in two different columns (extraction and analytical column), the first being employed to extract the analytes of interest from the original medium and the latter to separate them from the interferers. The extraction column in multidimensional techniques presents a relevant role since their variations as building material (usually a tube), sorbent material, modes of application, and so on can significantly influence the extraction success. The main features of such columns are subject of constant research aiming improvements directly related to the performance of the separation techniques that utilize multidimensional analysis. The present review highlights the main features of extraction columns online coupled to chromatographic techniques, inclusive for in-tube solid-phase microextraction, online solid phase and turbulent flow, aiming the determination of analytes present at very low concentrations in complex matrices. It will critically describe and discuss some of the most common instrumental set up as well as comments on recent applications of these multidimensional techniques. Besides that, the authors have described some properties and enhancements of the extraction columns that are used as first dimension on these systems, such as type of column material (poly (ether ether ketone), fused silica, stainless steel, and other materials) and the way that the extractive phase is accommodated inside the tubing (filled and open tubular). Practical applications of this approach in fields such as environment, food, and bioanalysis are also presented and discussed.