Direct immersion single-drop microextraction of semi-volatile organic compounds in environmental samples: A review

Self-generated single-drop microextraction enhanced aggregation-induced emission strategy based on magnetic metal-organic framework for microRNA-21 detection

Lung cancer is one of the most common malignancies with low prevention efficiency and high mortality, so prevention and early detection are very important. In this work, we propose a magnetic metal-organic skeleton nanomaterial bound to biological nucleic acid chains in a spatially confined magnetic single-drop microextraction (SDME) system to enhance the aggregation-induced emission (AIE) effect for fluorescence detection of miRNA-21 associated with lung cancer. DNA/MOF network structure was formed, and loaded with an AIE material, 4',4''',4''''',4'''''''-(ethene-1,1,2,2-tetrayl) tetrakis-([1,1-biphenyl]-3-carboxylic acid) (H4ETTC), by DNA amplification reaction. From a serum sample, the structure was then spontaneously collected, forming a single drop at the end of a magnetic rod in less than 10 s by utilizing a magnetic SDME process. In this self-generated single drop, the structure was aggregated and the fluorescence signal of H4ETTC was enhanced. Direct detection by fluorescence spectrophotometry was enabled. The limit of detection of miRNA-21 was 0.194 fM, and the linear range of miRNA-21 was 1 fM to 100 nM, respectively. The method was applied to the fluorescence detection of miRNA in human serum samples. The relative recoveries were 98.4 %-104.5 %.

An exploratory study of volatile and semi-volatile organic compounds in PM2.5 atmospheric particles from an outdoor environment in Brazil

The development of methods for determining volatile and semi-volatile organic compounds in public spaces has become necessary to identify potential health and environmental risks. This study presents a practical methodology for sampling, extracting, detecting, and identifying these compounds in a vehicular traffic region in Belo Horizonte, Brazil. The methodology uses direct-immersion solid phase microextraction (DI-SPME) and static headspace (SHS) to extract SVOCs/VOCs. Comprehensive time-of-flight gas chromatography mass spectrometry (GC×GC/Q-TOFMS) and gas chromatography coupled to mass spectrometry (GC/MS) were used to detect and identify compounds. The analysed samples, collected with a high-volume sampler (Hi-Vol) with quartz filters and in which particulate matter (PM2.5) was retained, showed the presence of more than 200 compounds, both biogenic (natural origin) and anthropogenic (human origin). Regarding the distribution of chemical classes, aromatic compounds were predominantly found at 29.2%, followed by esters at 20.8%, non-aromatic hydrocarbons at 5.6%, and carboxylic acids at 9.4%. Static headspace gas chromatography (HS-GC) enabled the identification and quantification of 21 volatile compounds, including BETX, dichloromethane, chloroform, and naphthalene, which are currently regulated by the US Environmental Protection Agency (EPA).

Recent advances in solid phase microextraction with various geometries in environmental analysis

Solid phase microextraction (SPME) has emerged as a versatile sample preparation technique for the preconcentration of a broad range of compounds with various polarities, especially in environmental studies. SPME has demonstrated its eco-friendly credentials, significantly reducing the reliance on solvents. The use of biocompatible materials as a coating recipe facilitates the acceptance of SPME devices in analytical chemistry, primarily in the monitoring of environmental pollutants such as persistent organic pollutants (POPs), volatile organic compounds (VOCs), and pesticides from the various environmental matrices. During the last few years, investigators have reported an improvement in the SPME enrichment technique after changing the coating recipe, geometries, and sampling procedure from the complex matrices. Furthermore, the development of various geometries of SPME with large surface areas has enhanced the extraction efficiency of environmental pollutants. As a miniaturized sample preparation technique, SPME significantly reduces the solvent usage, suggesting a potential platform for green chemistry-based research for water, air, and soil analysis. This review article summarizes the evolution of SPME, its various modes, the application of SPME, recent innovations, and prospects for the determination of water, air, and soil pollution. The advantages and disadvantages of SPME in comparison to other extraction techniques have been discussed here. This review serves as a valuable resource for investigators working in sustainable environmental research.

Deep eutectic solvents for the determination of endocrine disrupting chemicals

The harmful effects of endocrine disrupting chemicals (EDCs) to humans and other organisms in the environment have been well established over the years, and more studies are ongoing to classify other chemicals that have the potential to alter or disrupt the regular function of the endocrine system. In addition to toxicological studies, analytical detection systems are progressively being improved to facilitate accurate determination of EDCs in biological, environmental and food samples. Recent microextraction methods have focused on the use of green chemicals that are safe for analytical applications, and present very low or no toxicity upon disposal. Deep eutectic solvents (DESs) have emerged as one of the viable alternatives to the conventional hazardous solvents, and their unique properties make them very useful in different applications. Notably, the use of renewable sources to prepare DESs leads to highly biodegradable products that mitigate negative ecological impacts. This review presents an overview of both organic and inorganic EDCs and their ramifications on human health. It also presents the fundamental principles of liquid phase and solid phase microextraction methods, and gives a comprehensive account of the use of DESs for the determination of EDCs in various samples.

Unpacking Phthalates from Obscurity in the Environment

Phthalates (PAEs) are a group of synthetic esters of phthalic acid compounds mostly used as plasticizers in plastic materials but are widely applied in most industries and products. As plasticizers in plastic materials, they are not chemically bound to the polymeric matrix and easily leach out. Logically, PAEs should be prevalent in the environment, but their prevalence, transport, fate, and effects have been largely unknown until recently. This has been attributed, inter alia, to a lack of standardized analytical procedures for identifying them in complex matrices. Nevertheless, current advancements in analytical techniques facilitate the understanding of PAEs in the environment. It is now known that they can potentially impact ecological and human health adversely, leading to their categorization as endocrine-disrupting chemicals, carcinogenic, and liver- and kidney-failure-causing agents, which has landed them among contaminants of emerging concern (CECs). Thus, this review article reports and discusses the developments and advancements in PAEs' standard analytical methods, facilitating their emergence from obscurity. It further explores the opportunities, challenges, and limits of their advancements.

Development and validation of an improved QuEChERS method for the extraction of semi-volatile organic compounds (SVOCs) from complex soils

In order to achieve rapid, sensitive, and high-throughput determination of typical semi-volatile organic compounds (SVOCs) in soil samples, a method for the rapid determination of 63 SVOCs in soil was developed by optimizing and improving the QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) extraction technique in conjunction with gas chromatography-mass spectrometry (GC-MS) analysis. A small amount of soil sample (5.0 g) was vortexed with 10 mL of a mixture of acetone and n-hexane (V/V = 1 : 1) for 2 min, followed by rapid vortex purification and centrifugation using a mixture of copper powder and octadecylsilane (C18) dispersant. The resulting supernatant was then purified through a 0.22 μm filter membrane. The results showed that the 63 SVOCs exhibited good linear relationships within the concentration range of 100-5000 μg L-1, with correlation coefficients (R2) above 0.99. The method detection limit (MDL = 3.3 Sy/m) was lower than 0.050 mg kg-1. At a spike concentration of 1 mg kg-1, the recovery rates of the 63 SVOCs were almost above 70% (n = 7). Compared with the rapid solvent extraction (ASE) method specified in US EPA 3545 standard, this method reduced the organic solvent usage by 14 times and significantly shortened the operation time. Furthermore, this method did not involve any transfer or concentration steps of the extractant during the experimental process, reducing the exposure time of toxic compounds and providing support for the principles of green analytical chemistry. Moreover, in the detection of most compounds in the same batch of contaminated soil, the extraction results obtained by QuEChERS were superior to those obtained by the ASE method, providing evidence for the practical application of this method. This method is rapid, simple, accurate, requires a small sample volume, and causes minimal environmental pollution. It provides a high-throughput detection method for the rapid screening of SVOCs in soil.

Quantitative Time-Resolved Visualization of Catalytic Degradation Reactions of Environmental Pollutants by Integrating Single-Drop Microextraction and Fluorescence Sensing

Current methods for evaluating catalytic degradation reactions of environmental pollutants primarily rely on chromatography that often suffers from intermittent analysis, a long turnaround period, and complex sample pretreatment. Herein, we propose a quantitative time-resolved visualization method to evaluate the progress of catalytic degradation reactions by integrating sample pretreatment [single-drop microextraction, (SDME)], fluorescence sensing, and a smartphone detection platform. The dechlorination reaction of chlorobenzene derivatives was first investigated to validate the feasibility of this approach, in which SDME plays a critical role in direct sample pretreatment, and inorganic CsPbBr₃ perovskite encapsulated in a metal-organic framework (MOF-5) was utilized as the fluorescent chromogenic agent (FLCA) in SDME to realize fast in situ colorimetric detection via the color switching from green (CsPbBr₃) to blue (chlorine lead bromide, inorganic CsPbCl₃ perovskite). The smartphone, which can calculate the B/G value of FLCA, serves as a data output window for quantitative time-resolved visualization. Further, a [Eu(PMA)]_n (PMA= pyromellitic acid) fluorescent probe was constructed to use as an FLCA for the in situ evaluation of cinnamaldehyde and p-nitrophenol catalytic reduction. This approach not only minimizes the utilization of organic solvents and achieves quantitively efficient time-resolved visualization but also provides a feasible method for in situ monitoring of the progress of catalytic degradation reactions.

An all-embracing analytical method comprising modified QuEChERS-dispersive micro-solid-phase extraction-dispersive liquid-liquid microextraction using FeGA MOF for the extraction and preconcentration of pesticides simultaneously from juice and flesh of watermelon

For the first time, a comprehensive analytical method based on a one-dimensional metal-organic framework comprising "quick, easy, cheap, effective, rugged, and safe-dispersive micro solid phase extraction-dispersive liquid-liquid microextraction" was introduced in this research. Moreover, the first-ever attempt was accomplished to apply the iron-gallic acid metal-organic framework in analytical method development. The goal of the research was to analyze the pesticide content of watermelon comprehensively in its flesh and juice. Based on this, comprehensive and reliable food safety monitoring can be done. Initially, pesticides of the watermelon flesh were extracted using an mL volume of acetonitrile by vortexing. At the same time, the pesticides of watermelon juice were extracted from the juice matrix onto the sorbent particles facilitated by vortexing. The obtained acetonitrile phase was also used to desorb the analytes from the sorbent surface by vortexing. As a result, the pesticide content of both juice and flesh was extracted into the acetonitrile. The pesticide-enriched acetonitrile was then used as the disperser solvent by being merged with µL level of 1,2-dibromoethane and injection into deionized water. A cloudy solution was created as the result. Centrifugation triggered extractant at the bottom of the conical glass test tube and an aliquot of it was injected into a gas chromatograph equipped with a flame ionization detector. High enrichment factors (210-400), appreciable extraction recoveries (42-80%), wide linear ranges (3.20-1000 µg kg^-1), relative standard deviations in the ranges of 3.6-4.4% for intra- (n = 6) and 4.4-5.3% for inter-day (n = 3) precisions, and low limits of detection (0.43-0.97 µg kg^-1), and quantification (1.42-3.20 µg kg^-1) were obtained by the application of the developed method.

Spatial Confinement of Single-Drop System to Enhance Aggregation-Induced Emission for Detection of MicroRNAs

Due to high incidence, poor prognosis, and easy transformation into pancreatic cancer (PC) with high mortality, early diagnosis and prevention of acute pancreatitis (AP) have become significant research focuses. In this work, we proposed a magnetic single-drop microextraction (SDME) system with spatial confinement to enhance the aggregation-induced emission (AIE) effect for simultaneous fluorescence detection of miRNA-155 (associated with AP) and miRNA-196a (associated with PC). The target miRNAs were selectively recognized by the hairpin probe and triggered the DNA amplification reaction; then, the DNA strands with two independent probes of G-quadruplex/TAIN and Cy5 were constructed on the surfaces of the magnetic beads. The SDME process, in which a drop containing the fluorescence probes was formed at the tip of the magnetic microextraction rod rapidly within 10 s, was performed by magnetic extraction. In this way, G-quadruplex/TAIN was enriched owing to the spatial confinement of the single-drop system, and the fluorescence signal given off (by G-quadruplex/TAIN) was highly enhanced (AIE effect). This was detected directly by fluorescence spectrophotometry. The approach achieved low limits of detection of 2.1 aM for miRNA-196a and 8.1 aM for miRNA-155 and wide linear ranges from 10 aM to 10 nM for miRNA-196a and from 25 aM to 10 nM for miRNA-155. This novel method was applied to the fluorescence detection of miRNAs in human serum samples. High relative recoveries from 95.6% to 104.8% were obtained.

Synergistic Combination of Facile Thiol-Maleimide Derivatization and Supramolecular Solvent-Based Microextraction for UHPLC-HRMS Analysis of Glutathione in Biofluids

Glutathione (GSH) is the most abundant non-protein thiol in biofluids, enabling diverse physiological functions. Among the proposed methods for GSH detection, ultra-high-performance liquid chromatography (UHPLC) coupled with high-resolution mass spectrometry (HRMS) has the advantages of high sensitivity and efficiency. In this study, a novel analytical method was developed for the determination of GSH using supramolecular solvent (SUPRAS)-based dispersive liquid–liquid microextraction (DLLME) and UHPLC–HRMS. N-Laurylmaleimide was dissolved in tetrahydrofuran, which served three functions: 1) precipitate the proteins present in the biofluid sample, 2) provide a reaction environment for derivatization, and 3) enable the use of SUPRAS as the dispersing agent. Critical parameters were optimized based on single factor testing and response surface methodology. The established method was validated in terms of linearity, accuracy, precision, and successful quantitative analysis of GSH in saliva, urine, and plasma samples. Experimental results showed that SUPRAS as an extraction solvent was particularly suitable for the extraction of GSH from complex matrices. The current study provides a useful tool for accurate measurements of GSH concentrations, which could potentially be used for clinical diagnostics.

Single-drop microextraction technique for the determination of antibiotics in environmental water

Growing concerns related to antibiotic residues in environmental water have encouraged the development of rapid, sensitive, and accurate analytical methods. Single-drop microextraction has been recognized as an efficient approach for the isolation and preconcentration of several analytes from a complex sample matrix. Thus, single-drop microextraction techniques are cost-effective and less harmful to the environment, subscribing to green analytical chemistry principles. Herein, an overview and the current advances in single-drop microextraction for the determination of antibiotics in environmental water are presented were included. In particular, two main approaches used to perform single-drop microextraction (direct immersion-single-drop microextraction and headspace-single-drop microextraction) are reviewed. Furthermore, the impressive analytical features and future perspectives of single-drop microextraction are discussed in this review. This article is protected by copyright. All rights reserved.

Recent applications of microextraction sample preparation techniques in biological samples analysis

Analysis of biological samples is affected by interfering substances with chemical properties similar to those of the target analytes, such as drugs. Biological samples such as whole blood, plasma, serum, urine and saliva must be properly processed for separation, purification, enrichment and chemical modification to meet the requirements of the analytical instruments. This causes the sample preparation stage to be of undeniable importance in the analysis of such samples through methods such as microextraction techniques. The scope of this review will cover a comprehensive summary of available literature data on microextraction techniques playing a key role for analytical purposes, methods of their implementation in common biological samples, and finally, the most recent examples of application of microextraction techniques in preconcentration of analytes from urine, blood and saliva samples. The objectives and merits of each microextration technique are carefully described in detail with respect to the nature of the biological samples. This review presents the most recent and innovative work published on microextraction application in common biological samples, mostly focused on original studies reported from 2017 to date. The main sections of this review comprise an introduction to the microextraction techniques supported by recent application studies involving quantitative and qualitative results and summaries of the most significant, recently published applications of microextracion methods in biological samples. This article considers recent applications of several microextraction techniques in the field of sample preparation for biological samples including urine, blood and saliva, with consideration for extraction techniques, sample preparation and instrumental detection systems.

Sample matrix influence on microdrop hold-up in single drop microextraction

Single drop microextraction has become a widespread liquid/liquid microextraction technique owing to its simplicity, high preconcentration factor and low consumption of organic solvents in the extraction due to direct introduction of the very low volume of extract into the analytical system. Crucial features ensuring excellent repeatability of single drop microextraction include: solvent volume, solvent type, sample agitation, salts addition, and pH. The influence of sample quality on the microdrop volume and agitation type was studied. Effect of the sample matrix, such as water, acid content samples (orange juice), sample containing alcohol (plum brandy) and protein content sample (milk), on the microdrop hold-up was also investigated. For water analysis, several organic solvents such as chloroform, dichloromethane, tetrachloromethane, tetrachloroethane and chlorobenzene were tested; last three mentioned were suitable for SDME experiments. For milk samples analysis, chlorobenzene microdrop was found to be optimal; advantage of salt addition has been reported. For orange samples, 1:10 dilution was suggested with stable microdrop volumes (toluene) of up to 6 µL for lower stirring rates (100 rpm and 250 rpm). For alcohol-content samples, the change of alcohol percentage of real-life samples had to be considered. A strong influence of the matrix quality on the microdrop stability has been proven.