Recent advances and trends in miniaturized sample preparation techniques

Advances in the area of sample preparation are significant and have been growing significantly in recent years. This initial step of the analysis is essential and must be carried out properly, consisting of a complicated procedure with multiple stages. Consequently, it corresponds to a potential source of errors and will determine, at the end of the process, either a satisfactory result or a fail. One of the advances in this field includes the miniaturization of extraction techniques based on the conventional sample preparation procedures such as liquid‐liquid extraction and solid‐phase extraction. These modern techniques have gained prominence in the face of traditional methods since they minimize the consumption of organic solvents and the sample volume. As another feature, it is possible to reuse the sorbents, and its coupling to chromatographic systems might be automated. The review will emphasize the main techniques based on liquid‐phase microextraction, as well as those based upon the use of sorbents. The first group includes currently popular techniques such as single drop microextraction, hollow fiber liquid‐phase microextraction, and dispersive liquid‐liquid microextraction. In the second group, solid‐phase microextraction techniques such as in‐tube solid‐phase microextraction, stir bar sorptive extraction, dispersive solid‐phase extraction, dispersive micro solid‐phase microextraction, and microextraction by packed sorbent are highlighted. These approaches, in common, aim the determination of analytes at low concentrations in complex matrices. This article describes some characteristics, recent advances, and trends on miniaturized sample preparation techniques, as well as their current applications in food, environmental, and bioanalysis fields.     

Solid‐phase microextraction for the human biomonitoring of environmental chemicals: Current applications and future perspectives

Sample preparation is one of the crucial steps in the analytical chemistry including human biomonitoring studies. Although there are several traditional approaches available, solid‐phase microextraction is emerged as one of the pioneering techniques due to its simplicity, rapidness, wide applicability, and miniaturization of traditional sample preparation (e.g., use of less or no organic solvents). There are few earlier review articles available on the advancements in solid‐phase microextraction and its use for the measurement of environmental chemicals in various types of environmental samples. However, a collective information on applicability and current usage of solid‐phase microextraction for the human biomonitoring of environmental chemicals are scarce, nonetheless, rising demands on innovative analytical approaches for human biomonitoring studies. Hence, in this review article, we covered the application of solid‐phase microextraction as extraction/purification methods for more than 15 classes of environmental chemicals to assess their respective exposure levels and associated health outcomes in various human population reported across the globe. Further, a detailed discussion on various types of matrix used, nature of coupled analytical instrumentations, and limitations and future perspectives of solid‐phase microextraction for human biomonitoring studies is presented in this review.     

Application of solid‐phase microextraction in current biomedical research

Extraction of endogenous compounds and drugs and their corresponding metabolites from complex matrices, such as biofluids and solid tissues, requires adequate analytical approach facilitating qualitative and quantitative analysis. To this end, solid‐phase microextraction has been introduced as modern technology that is capable of efficient and high‐throughput extraction of compounds due to its ability to amalgamate sampling, extraction, and pre‐concentration steps, while requiring minimal use of organic solvents. The ability of solid‐phase microextraction to enable analyses on small‐volume biological samples and growing availability of biocompatible solid‐phase microextraction coatings make it a highly useful technology for variety of applications. For example, solid‐phase microextraction is particularly useful for identifying biomarkers in metabolomics studies, and it can be successfully applied in pharmaceutical and toxicological studies requiring the fast and sensitive determination of drug levels, especially those that are present at low levels in biological matrices such as plasma, urine, saliva, and hair. Moreover, solid‐phase microextraction can be directly applied in in vivo studies because this extraction technique is non‐exhaustive and its biocompatible probes offer minimal invasiveness to the analyzed system. In this article, we review recent progress in well‐established solid‐phase microextraction technique for in vitro and in vivo analyses of various metabolites and drugs in clinical, pharmaceutical, and toxicological applications.     

The role of graphene‐based sorbents in modern sample preparation techniques

The application of graphene‐based sorbents in sample preparation techniques has increased significantly since 2011. These materials have good physicochemical properties to be used as sorbent and have shown excellent results in different sample preparation techniques. Graphene and its precursor graphene oxide have been considered to be good candidates to improve the extraction and concentration of different classes of target compounds (e.g., parabens, polycyclic aromatic hydrocarbon, pyrethroids, triazines, and so on) present in complex matrices. Its applications have been employed during the analysis of different matrices (e.g., environmental, biological and food). In this review, we highlight the most important characteristics of graphene‐based material, their properties, synthesis routes, and the most important applications in both off‐line and on‐line sample preparation techniques. The discussion of the off‐line approaches includes methods derived from conventional solid‐phase extraction focusing on the miniaturized magnetic and dispersive modes. The modes of microextraction techniques called stir bar sorptive extraction, solid phase microextraction, and microextraction by packed sorbent are discussed. The on‐line approaches focus on the use of graphene‐based material mainly in on‐line solid phase extraction, its variation called in‐tube solid‐phase microextraction, and on‐line microdialysis systems.     

Gas chromatographic detection of some nitro explosive compounds in soil samples after solid‐phase microextraction with carbon ceramic copper nanoparticle fibers

In this research, a new solid‐phase microextraction fiber based on carbon ceramic composites with copper nanoparticles followed by gas chromatography with flame ionization detection was applied for the extraction and determination of some nitro explosive compounds in soil samples. The proposed method provides an overview of trends related to synthesis of solid‐phase microextraction sorbents and their applications in preconcentration and determination of nitro explosives. The sorbents were prepared by mixing of copper nanoparticles with a ceramic composite produced by mixture of methyltrimethoxysilane, graphite, methanol, and hydrochloric acid. The prepared sorbents were coated on copper wires by dip‐coating method. The prepared nanocomposites were evaluated statistically and provided better limits of detection than the pure carbon ceramic. The limit of detection of the proposed method was 0.6 μg/g with a linear response over the concentration range of 2–160 μg/g and square of correlation coefficient >0.992. The new proposed fiber has been demonstrated to be a suitable, inexpensive, and sensitive candidate for extraction of nitro explosive compounds in contaminated soil samples. The constructed fiber can be used more than 100 times without the need for surface generation.     

The chromatographic assay of 4‐hydroxynonenal as a biomarker of diseases by means of MEPS and HPLC technique

The aim of this study was to develop and validate a new analytical method for the determination of 4‐hydroxy‐2‐nonenal (4‐HNE) in biological samples while applying microextraction by packed sorbent as a sample preparation method and HPLC with UV–vis detection. Various microextraction by packed sorbent (MEPS) sorbents like C₂, C₈, C₁₈, M1 (80% C₈ and 20% SCX) and silica were used to separate 4‐HNE from biological samples. The highest affinity of 4‐HNE was observed for sorbents like C₁₈. The extraction efficiency was in the range from 47.4 to 89.2% dependent on the concentration of 4‐HNE. Lower efficiency of 4‐HNE extraction was obtained with use of MEPS packings such as C₈ and M1. The extraction efficiency was in the range from 35.2 to 66.3% for packing C8 and from 34.2 to 64.3% for packing M1, respectively. The limit of detection and lower limit of quantitation for UV–vis detection were respectively 4.5 and 9.0 nmol/mL. The proposed method can be used for the evaluation of extraction efficiency of 4‐HNE in biological sample because the values of lower limit of quantitation are lower than the determined amounts of the analyte in samples. The method yields excellent performance of quantification and identification in analysis of inflammation biomarkers. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of graphene nanoplatelets silica composite,prepared by sol–gel technology,as a novel sorbent in two microextraction techniques

In this study, the application of a novel nanomaterial composite was investigated in two microextraction techniques of solid‐phase microextraction and a needle trap device in a variety of sampling conditions. The optimum sampling temperature and relative humidity were 10°C and 20%, respectively, for both techniques with two sorbents of graphene/silica composite and polydimethyl siloxane. The two microextraction techniques with the proposed sorbent showed recoveries of 95.2 and 94.6% after 7 days. For the needle trap device the optimums desorption time and temperature were 3 min at 290°C and for SPME these measures were 1 and 1.5 min at 240–250°C for the graphene/silica composite and polydimethyl siloxane, respectively. The relative standard division obtained in inter‐ and intra‐day comparative studies were 3.3–14.3 and 5.1–25.4, respectively. For four sample the limit of detection was 0.021–0.25 ng/mL, and the limit of quantitation was 0.08–0.75 ng/mL. The results show that the graphene/silica composite is an appropriate extraction media for both techniques. Combining an appropriate sorbent with microextraction techniques, and using these in conjunction with a sensitive analytical instrument can introduce a strong method for sampling and analysis of occupational and environmental pollutants in air.     

Conductive polymer-based microextraction methods: A review

Conductive polymers (CPs) are classified as materials which exhibit highly reversible redox behavior and the unusual combined properties of metal and plastics. CPs, due to their multifunctionality, ease of synthesis and their stability, have attracted more attentions in different fields of research, including sample preparation. CPs along with several commercial hydrophilic sorbents, are alternative to the commercially available hydrophobic sorbents which despite their high specific surface areas, have poor interactions and retentions in the extraction of polar compounds. This review covers a general overview regarding the recent progress and new applications of CPs toward their synthesis and use in novel extraction and microextraction techniques including solid phase microextraction (SPME), electrochemically controlled solid-phase microextraction (EC-SPME) and other relevant techniques. Furthermore the contribution of nano-structured CPs in these methodologies is also reviewed.     

Recent developments and applications of liquid phase microextraction in fruits and vegetables analysis

The sample preparation step has been identified as the bottleneck of analytical methodology in chemical analysis. Therefore, there is need for the development of cost‐effective, easy to operate, and environmentally friendly miniaturized sample preparation technique. The microextraction techniques combine extraction, isolation, concentration, and introduction of analytes into analytical instrument, to a single and uninterrupted step, and improve sample throughput. The use of liquid‐phase microextraction techniques for the analysis of pesticide residues in fruits and vegetables are discussed with the focus on the methodologies employed by different researchers and their analytical performances. Analytes are extracted using water‐immiscible solvents and are desorbed into gas chromatography, liquid chromatography, or capillary electrophoresis for identification and quantitation.     

Dispersive solid-phase extraction combined with dispersive liquid-liquid microextraction for the determination of polybrominated diphenyl ethers in plastic bottled beverage by GC-MS

A simple, inexpensive and reliable analytical method was developed for the determination of polybrominated diphenyl ethers (PBDEs) in polyethylene terephthalate (PET) bottled beverage using GC‐MS. The sample pretreatment using dispersive solid‐phase extraction (DSPE) for removing matrix and dispersive liquid–liquid microextraction (DLLME) for enriching analytes was performed. For the DSPE, different sorbents such as primary amine, secondary amine, C₁₈ and graphitized carbon black were tested for different sample matrices. By means of DSPE, 60–89% of the sample matrices could be removed. Acetonitrile solution obtained by DSPE cleanup was directly used as the dispersant for the subsequent DLLME, which made the combination of the DSPE with the DLLME much more straightforward. Under the optimal conditions, the enrichment factors (EFs) of PBDEs ranged from 199 to 292. Using matrix‐matched calibration, correlation coefficients above 0.994 were found and LODs ranged from 0.0023 to 0.15 μg/L. The recoveries were between 80 and 117% for beverages spiked at three different concentrations (1.0, 5.0 and 10 μg/L) with RSDs ranging from 3.7 to 14.7% (n=5). The results indicated that the combination of DSPE with DLLME was a powerful sample preparation tool for analysis of ultratrace analytes in complicated matrices.     

Rapid and accurate determination of trace volatile sulfur compounds in human halitosis by an adaptable active sampling system coupling with gas chromatography

Halitosis with the main components of trace volatile sulfur compounds widely affects the quality of life. In this study, an adaptable active sampling system with two sample‐collection modes of direct injection and solid‐phase microextraction was developed for the rapid and precise determination of trace volatile sulfur compounds in human halitosis coupled with gas chromatography–flame photometric detection. The active sampling system was well designed and produced for efficiently sampling and precisely determining trace volatile targets in halitosis under the optimized sampling and detection conditions. The analytical method established was successfully applied for the determination of trace targets in halitosis. The limits of detection of H₂S, CH₃SH, and CH₃SCH₃ by direct injection were 0.0140–23.0 μg/L with good recoveries ranging from 82.2 to 118% and satisfactory relative standard deviations of 0.4–9.5% (n = 3), respectively. The limit of detections of CH₃SH and CH₃SCH₃ by solid‐phase microextraction were 2.03 and 0.186 × 10^?3 μg/L with good recoveries ranging from 98.3 to 108% and relative standard deviations of 5.9–9.0% (n = 3). Trace volatile targets in positive real samples could be actually found and quantified by combination of direct injection and solid‐phase microextraction. This method was reliable and efficient for the determination of trace volatile sulfur compounds in halitosis.     

Recent development in liquid phase microextraction for determination of trace level concentration of metals—A review

As the drive towards green extraction methods has gained momentum in recent years, it has not always been possible to eliminate organic solvents completely. However, the volumes employed have been reduced remarkably, so that a single microdrop is sufficient in some cases. This effort has led to the development of various liquid phase microextractions namely single drop microextraction (SDME), hollow fiber liquid phase microextraction (HF-LPME), dispersive liquid-liquid microextraction (DLLME) and solidified floating organic drop microextraction (SFODME). In this review, the historical development and overview of these miniaturized liquid phase extraction methodologies have briefly been discussed and a comprehensive collection of application of the these methods in combination with different analytical techniques for preconcentration and determination of ultra trace amounts of metals and organometal ions in various matrices have been summarized.     

Three‐phase hollow‐fiber liquid‐phase microextraction based on deep eutectic solvent as acceptor phase for extraction and preconcentration of main active compounds in a traditional Chinese medicinal formula

A three‐phase hollow‐fiber liquid‐phase microextraction based on deep eutectic solvent as acceptor phase was developed and coupled with high‐performance capillary electrophoresis for the simultaneous extraction, enrichment, and determination of main active compounds (hesperidin, honokiol, shikonin, magnolol, emodin, and β,β′‐dimethylacrylshikonin) in a traditional Chinese medicinal formula. In this procedure, two hollow fibers, impregnated with n‐heptanol/n‐nonanol (7:3, v/v) mixture in wall pores as the extraction phase and a combination (9:1, v/v) of methyltrioctylammonium chloride/glycerol (1:3, n/n) and methanol in lumen as the acceptor phase, were immersed in the aqueous sample phase. The target analytes in the sample solution were first extracted through the organic phase, and further back‐extracted to the acceptor phase during the stirring process. Important extraction parameters such as types and composition of extraction solvent and deep eutectic solvent, sample phase pH, stirring rate, and extraction time were investigated and optimized. Under the optimal conditions, detection limits were 0.3–0.8 ng/mL with enrichment factors of 6–114 for the analytes and linearities of 0.001–13 μg/mL (r² ≥ 0.9901). The developed method was successfully applied to the simultaneous extraction and concentration of the main active compounds in a formula of Zi‐Cao‐Cheng‐Qi decoction with the major advantages of convenience, effectiveness, and environmentally friendliness.     

Solid‐phase microextraction based method for determination of essential oils components in herbal beverages

A method employing the direct immersion solid‐phase microextraction followed by GC‐MS analysis is presented for the determination of essential oils components in herbal tea infusions, i.e. their direct content in the liquid phase. The extraction performances were compared using five different microextraction fibres. Significant parameters affecting sorption process such as sample amount, sorption and desorption time and temperature, stirring speed, pH adjustment and effect of ionic strength were optimised and discussed. By optimising the key parameters, a detection limits (LOD = S/N × 3) for ten target marker compounds were obtained in the range from 5.3 to 48.2 ng/mL with recoveries ranged between 93.03 and 100.50%. Intra‐day and inter‐day repeatability at three concentration levels were found to be 1.1–15.3 and 7.2–15.5% RSD, respectively. Finally, the optimised procedure enabling a rapid and simple analysis of essential oils was applied for the direct determination of these compounds in ten herbal tea infusions.     

固相微萃取参数选择及其对有机锡分析的影响

固相微萃取是一种新型的、不断发展和完善的样品前处理方法，它与其它技术联用可对多种样品基体中挥发、半挥发性有机化合物进行测定。目前，该技术在毒性金属有机化合物中的应用很少。本文分析参数选择对固相微萃取的影响的同时，还对其在有机锡化合物分析中的应用作了综述。     

Use of volatile organic solvents in headspace liquid‐phase microextraction by direct cooling of the organic drop using a simple cooling capsule

A low‐cost and simple cooling‐assisted headspace liquid‐phase microextraction device for the extraction and determination of 2,6,6‐trimethyl‐1,3 cyclohexadiene‐1‐carboxaldehyde (safranal) in Saffron samples, using volatile organic solvents, was fabricated and evaluated. The main part of the cooling‐assisted headspace liquid‐phase microextraction system was a cooling capsule, with a Teflon microcup to hold the extracting organic solvent, which is able to directly cool down the extraction phase while the sample matrix is simultaneously heated. Different experimental factors such as type of organic extraction solvent, sample temperature, extraction solvent temperature, and extraction time were optimized. The optimal conditions were obtained as: extraction solvent, methanol (10 μL); extraction temperature, 60°C; extraction solvent temperature, 0°C; and extraction time, 20 min. Good linearity of the calibration curve (R² = 0.995) was obtained in the concentration range of 0.01–50.0 μg/mL. The limit of detection was 0.001 μg/mL. The relative standard deviation for 1.0 μg/mL of safranal was 10.7% (n = 6). The proposed cooling‐assisted headspace liquid‐phase microextraction device was coupled (off‐line) to high‐performance liquid chromatography and used for the determination of safranal in Saffron samples. Reasonable agreement was observed between the results of the cooling‐assisted headspace liquid‐phase microextraction high‐performance liquid chromatography method and those obtained by a validated ultrasound‐assisted solvent extraction procedure.     

Screening and quantification of anticancer compounds in traditional Chinese medicine by hollow fiber cell fishing and hollow fiber liquid/solid‐phase microextraction

Hollow fiber cell fishing, based on HepG‐2, SKOV‐3, and ACHN cancer cells, and hollow fiber liquid/solid microextraction with HPLC were developed and introduced for researching the anticancer activity of Rhizoma Curcumae Longae, Radix Curcumae, and Rhizoma Curcumae. The structures of curcumin, demethoxycurcumin, and bisdemethoxycurcumin screened were identified and their contents were determined. The compound target fishing factors and cell apoptosis rates under the effect of the three medicines were determined. The binding sites (cell membrane and cell organelle) and binding target (phospholipase C) on the cell were researched. Hollow fiber liquid/solid‐phase microextraction mechanism was analyzed and expounded. Before the application, cell seeding time, growth state and survival rate, compound nonspecific binding, positive and negative controls, repeatability in hollow fiber cell fishing with high‐performance liquid chromatography; extraction solvent, sample pH, salt concentration, agitation speed, extraction time, temperature and sample volume in hollow fiber liquid/solid‐phase microextraction with high‐performance liquid chromatography were investigated. The results demonstrated that the proposed strategy is a simple and quick method to identify bioactive compounds at the cellular level as well as determine their contents (particularly trace levels of the bioactive compounds), analyze multicompound and multitarget entirety effects, and elucidate the efficacious material base in traditional medicine.     

Membrane-based microextraction techniques in analytical chemistry: A review

The use of membrane-based sample preparation techniques in analytical chemistry has gained growing attention from the scientific community since the development of miniaturized sample preparation procedures in the 1990s. The use of membranes makes the microextraction procedures more stable, allowing the determination of analytes in complex and “dirty” samples. This review describes some characteristics of classical membrane-based microextraction techniques (membrane-protected solid-phase microextraction, hollow-fiber liquid-phase microextraction and hollow-fiber renewal liquid membrane) as well as some alternative configurations (thin film and electromembrane extraction) used successfully for the determination of different analytes in a large variety of matrices, some critical points regarding each technique are highlighted.     

Agarose‐ and alginate‐based biopolymers for sample preparation: Excellent green extraction tools for this century

Recently, there has been considerable interest in the use of miniaturized sample preparation techniques before the chromatographic monitoring of the analytes in unknown complex compositions. The use of biopolymer‐based sorbents in solid‐phase microextraction techniques has achieved a good reputation. A great variety of polysaccharides can be extracted from marine plants or microorganisms. Seaweeds are the major sources of polysaccharides such as alginate, agar, agarose, as well as carrageenans. Agarose and alginate (green biopolymers) have been manipulated for different microextraction approaches. The present review is focused on the classification of biopolymer and their applications in multidisciplinary research. Besides, efforts have been made to discuss the state‐of‐the‐art of the new microextraction techniques that utilize commercial biopolymer interfaces such as agarose in liquid‐phase microextraction and solid‐phase microextraction.     

Liquid‐phase microextraction combined with liquid chromatography‐mass spectrometry. Extraction from small volumes of biological samples

Liquid‐phase microextraction (LPME) is a sample preparation technique based on disposable polypropylene hollow fibres, which results in efficient sample clean‐up and high preconcentration. The present paper describes the combination of LPME with LC‐MS utilising electrospray ionisation for high sensitivity. Nine antidepressant drugs were extracted from 50 or 500 μL of plasma or whole blood samples, through a thin layer of dodecyl acetate immobilised in the pores of the hollow fibre, and into 15 μL of 200 mM formic acid as acceptor solution inside the hollow fibre. Analyte recoveries in the range 12–68% and 9–52% were obtained from 50 μL of plasma and whole blood respectively. The acceptor solution (15 μL) was diluted with 60 μL of 5 mM ammonium formate pH = 2.7 prior to injection into the LC‐MS system. The system was qualitatively investigated for matrix effects utilising a post‐column infusion system. Whole blood from 5 different persons was cleaned‐up by LPME and injected onto the analytical column while a solution of the 9 model compounds was continuously infused post‐column. No signs of ion suppression were seen for any of the model compounds. Limits of quantification (S/N = 10) were in the low ng/mL range for 6 of the 9 model compounds utilising a whole blood sample volume of only 50 μL. The repeatability of the extractions was investigated utilising paroxetine as internal standard. Acceptable RSDs (%) were obtained (< 20%) for 5 of the antidepressants. By increasing the sample volume from 50 to 500 μL of whole blood RSDs below 20% (3–16%) were observed for all 8 antidepressants.