Modern solutions in magnetic analytical extractions of metals: A review

Ultrasonic assisted magnetic solid phase extraction of ultra-trace mercury with ionic liquid functionalized materials

Due to the agglomeration between particles, the inherent adsorption characteristics of magnetic powder materials are usually difficult to fully display. Taking ionic liquid functional materials as an example, the enrichment behavior of these adsorbents for trace mercury (Hg²⁺) in ultrasonic (US) assisted dispersion mode was systematically studied. The dissociation of protonic ionic liquids (IL) occur in the process of dispersion and the strong electrostatic attraction can improve the diffusion and adhesion of mercury on the adsorbent surface. Spectral measurement data showed that with the help of US, the more uniform dispersion of magnetic materials accelerated the adsorption of trace Hg²⁺. Ultrasonic intrinsic parameters such as frequency, power and radiation duration significantly affect the dispersion and apparent adsorption properties of magnetic functional materials. In the range of experimental parameters, the dye/paper image experimental results documents that there is a positive correlation between cavitation effect and ultrasonic frequency/power. The enrichment degree of fixed adsorbate (0.1 μg L^-1) under high frequency (59 kHz) or high-power input (100%) is 1-2 times higher than that under low frequency (40 kHz) or low power (60%) input. This is a valuable conclusion for the subsequent study of US dispersion of magnetic and even non-magnetic powder materials. In addition, the in-situ desorption and accurate measurement of adsorbed mercury were realized by combining slurry vapor generation atomic fluorescence spectroscopy (SVG-AFS). The constructed US assisted magnetic solid phase extraction (US-MSPE) method has the characteristics of low detection limit (0.36 ng L^-1), high recovery (>90%), sustainable utilization (>3) and reasonable measurement deviation (<5%), which can meet the requirements of ultra-trace Hg²⁺ (0.01-1.0 μg L^-1).

Ultrasound-assisted dispersive solid phase extraction for promoting enrichment of ng L-1 level Hg2+ on ionic liquid coated magnetic materials

Herein, we investigated the enrichment behavior of inorganic mercury (Hg²⁺) on magnetic adsorbent with different ultrasound (US) energy field input. The enrichment rate of 0.10 μg L^-1 mercury is increased by 4.5 times after US instead of stirring as dispersion mode. The input of higher frequency and power ultrasound can accelerate the enrichment of magnetic ionic liquid adsorbent and reduce the Hg²⁺ residue, importantly, which has not been reported. The positive correlation between cavitation effect and acoustic frequency and power in imaging experiments documents that US parameters are the key factors affecting the magnetic solid phase extraction. In addition, in-situ desorption and detection of adsorbate and recovery of adsorbent can be realized by slurry vapor generation (SVG) technology. The recovery of Hg²⁺ in four cycles is more than 90%, which indicates that the structure and properties of the material are not affected by the application of US. Hence, the degradation of adsorption properties caused by agglomeration of magnetic materials can be improved by introducing dispersion methods such as US. At the same time, 95% enrichment efficiency and 0.01-1.0 μg L^-1 linear calibration range corresponding to 150 mL sample documents that magnetic ionic liquid adsorbent combined with US and sensitive spectral detector can meet the needs of ng L^-1 level Hg²⁺ analysis in natural water samples.

Greenness of magnetic nanomaterials in miniaturized extraction techniques: A review

Green analytical chemistry principles should be followed, as much as possible, and particularly during the development of analytical sample preparation methods. In the past few years, outstanding materials such as ionic liquids, metal-organic frameworks, carbonaceous materials, molecularly imprinted materials, and many others, have been introduced in a wide variety of miniaturized techniques in order to reduce the amount of solvents and sorbents required during the analytical sample preparation step while pursuing more efficient extraction methods. Among them, magnetic nanomaterials (MNMs) have gained special attention due to their versatile properties. Mainly, their ability to be separated from the sample matrix using an external magnetic field (thus enormously simplifying the entire process) and their easy combination with other materials, which implies the inclusion of a countless number of different functionalities, highly specific in some cases. Therefore, MNMs can be used as sorbents or as magnetic support for other materials which do not have magnetic properties, the latter permiting their combination with novel materials. The greenness of these magnetic sorbents in miniaturized extractions techniques is generally demonstrated in terms of their ease of separation and amount of sorbent required, while the nature of the material itself is left unnoticed. However, the synthesis of MNMs is not always as green as their applications, and the resulting MNMs are not always as safe as desired. Is the analytical sample preparation field ready for using green magnetic nanomaterials? This review offers an overview, from a green analytical chemistry perspective, of the current state of the use of MNMs as sorbents in microextraction strategies, their preparation, and the analytical performance offered, together with a critical discussion on where efforts should go.

Recent progress in the LC-MS/MS analysis of oxidative stress biomarkers

The presence of a dynamic and balanced equilibrium between the production of reactive oxygen (ROS) and nitrogen (RNS) species and the in-house antioxidant defense mechanisms is characteristic for a healthy body. During oxidative stress (OS), this balance is switched to increased production of ROS and RNS, exceeding the capacity of physiological antioxidant systems. This can cause damage to biological molecules, leading to loss of function and even cell death. Nowadays, there is increasing scientific and clinical interest in OS and the associated parameters to measure the degree of OS in biofluids. An increasing number of reports using LC-MS/MS methods for the analysis of OS biomarkers can be found. Since bioanalysis is usually complicated by matrix effects, various types of cleanup procedures are used to effectively separate the biomarkers from the matrix. This is an essential part of the analysis to prepare a reproducible and homogenous solution suitable for injection onto the column. The present review gives a summary of the chromatographic methods used for the determination of OS biomarkers in both urine and plasma, serum, and whole blood samples. The first part mainly describes the biological background of the different OS biomarkers, while the second part reports examples of chromatographic methods for the analysis of different metabolites connected with OS in biofluids, covering a period from 2015 till early 2020. The selected examples mainly include LC-MS/MS methods for isoprostanes, oxidized proteins, oxidized lipoproteins, and DNA/RNA biomarkers. The last part explains the clinical relevance of this review.

Microextraction Techniques with Deep Eutectic Solvents

In this review, the ever-increasing use of deep eutectic solvents (DES) in microextraction techniques will be discussed, focusing on the reasons needed to replace conventional extraction techniques with greener approaches that follow the principles of green analytical chemistry. The properties of DES will be discussed, pinpointing their exceptional performance and analytical parameters, justifying their current extensive scientific interest. Finally, a variety of applications for commonly used microextraction techniques will be reported.