Sample Preconcentration Techniques Research Articles

Application of on-line sample preconcentration by large-volume dual preconcentration by isotachophoresis and stacking (LDIS) on straight-channel microchips.

In this study, large-volume dual preconcentration by isotachophoresis and stacking (LDIS) which is an on-line sample preconcentration technique coupling large-volume sample stacking with an electroosmotic flow pump (LVSEP) with transient isotachophoresis (tITP) was applied to microchip electrophoresis (MCE) for improving both detection sensitivities and peak shapes. To realize LDIS in MCE, we investigated experimental procedures for injecting a short plug of a leading electrolyte (LE) solution into a straight microchannel without any sophisticated injector apparatus. We found that a short LE plug could be injected into a sample-filled straight-channel only by making the liquid level of the LE solution in an outlet reservoir higher than that in an inlet one. By applying a reversed-polarity voltage to the microchip, anionic analytes injected throughout the microchannel were first enriched by LVSEP, followed by tITP. Through the second preconcentration effect by tITP in LDIS, sensitivity enhancement factor (SEF) and asymmetry factor for a standard dye were improved from 878 and 0.62 to 1330 and 1.14, respectively, relative to those in conventional LVSEP. It should be noted that more viscous running buffer containing sieving polymers could be employed to the LDIS analysis, which was effective for improving the SEF and the separation efficiencies, especially for bio-polymeric compounds. Finally, LDIS was applied to the oligosaccharide and protein analyses in MCE, resulting in the SEFs of 1410 and ca. 50 for maltotriose and bovine milk casein, respectively.

Innovative analysis of diazepam, zolpidem and their main metabolites in human urine by micelle-to-solvent stacking in capillary electrophoresis

Diazepam and zolpidem are the most widely used medications for managing insomnia. However, significant concerns regarding the potential risks of misuse and abuse problems arose in many literatures. While urine analysis is a valuable diagnostic tool, a challenge arises from the fact that some parent drugs may remain undetectable in urine. This necessitates concurrent monitoring of their metabolites. Here, we described an innovative on-line sample preconcentration technique known as micelle to solvent stacking (MSS) for the analysis of diazepam, zolpidem, and their main metabolites in urine. Several key parameters warrant further discussion to optimize the MSS model, enhancing its performance in terms of sensitivity and resolution. After optimizing the conditions, we conducted a validation test, achieving high correlation coefficients (greater than 0.9977) for intra-day and inter-day regression lines. Additionally, both the relative standard deviation (RSD) and relative error (RE) remained below 6.10% and 12.55%, respectively. The limits of detection (LODs, S/N = 3) for all five analytes ranged from 2.0 to 56 ng/mL. Compared to the conventional capillary zone electrophoresis method, this new approach exhibited remarkable sensitivity enhancements, ranging from 123 to 235-fold. Upon applying this method to actual urine samples from patients, we successfully detected nordiazepam, zolpidem, and its metabolites. This simple and sensitive approach has promising applications in supporting patient medication safety and bolstering forensic investigations.

On-line sample preconcentration by LVSEP-FASI with simple voltage control on Y-channel chips.

To eliminate complicated voltage controls for highly sensitive microchip electrophoresis (MCE) analyses on the basis of combining two online sample preconcentration techniques, large-volume sample stacking with an electroosmotic flow (EOF) pump (LVSEP) and field-amplified sample injection (FASI), cross-channel microchips and a multichannel high-voltage power supply were replaced to Y-channel chips and a conventional power supply designed for capillary electrophoresis, respectively. By simple switching of the electric circuit after the LVSEP-FASI sample enrichments, the focused analytes could be separated during anodic migration in a separation channel. In the LVSEP-FASI analysis of fluorescein using the Y-channel microchip, the maximum sensitivity enhancement factor (SEF) of 7400 was achieved, resulting in a 30-fold detectability increase compared to the conventional LVSEP. The developed method was applied to the oligosaccharide analysis in MCE. As a result, the SEF for maltotriose was improved from 450 to 2300 and the baseline separation of the oligosaccharides was achieved without any complicated voltage control in LVSEP-FASI on the Y-channel chips.

Recent advances in ultra‐trace determination of uranium in natural water using total reflection X‐ray fluorescence (TXRF) spectrometry

AbstractThis review article describes some of the recent advances in ultra‐trace determination of uranium in various natural water bodies such as drinking water, underground water, seawater, etc. using total reflection x‐ray florescence (TXRF) spectrometry. Uranium is one of the most hazardous element having chemical as well as radio‐toxicity. However, due to its low concentration in water samples, direct determination is seldom possible in samples with high salt content. Various sample preconcentration and selective extraction techniques for uranium such as solvent extraction, dispersive liquid–liquid micro extraction, solid phase extraction, and membrane based preconcentration methods are summarized in this article. TXRF is a very versatile micro‐analytical technique with detection limits in picogram range and having multielemental analysis capability. TXRF determination of uranium using U Lα as the analytical line has many analytical challenges and difficulties, mainly due to the severe interference with Rb and Br, both are commonly available in natural water samples. This article highlights some of these challenges, along with the advantages and disadvantages of the different sample preparation techniques used so far for uranium determination in natural water samples by TXRF.

Three-dimensional ready-to-pick reservoir-based preconcentrator with a pillar-structured channel for miRNA applications

A sample preconcentration technique that exceeds a microfluidic device’s limited processing volume (up to microliters) is critical for real sample pretreatment applications. Here, we have developed a 3D-printed preconcentrator with a pillar structure (3DP2) to enrich the biological samples up to hundreds of microliter scales (700 μL) within 20 min by utilizing ion concentration polarization (ICP). We designed three-dimensional ready-to-pick reservoirs serially connected with a pillar-structured channel to enable large-volume preconcentration by balancing the preconcentrating forces (depletion, electrophoretic, and electroosmotic force) generated by ICP. Using the I-t and I-V curves, we confirmed that ICP performance was enhanced due to a pillar structure’s suppression of the vortex. Finally, we preconcentrated bovine serum albumin (BSA) and micro ribonucleic acid-21 (miRNA-21) two-fold. Moreover, depending on their size and charge, these were concentrated at different locations and could be extracted easily using pipettes. We believe that this study provides a novel strategy for downstream applications.

Recent Applications of Dynamic On-Line Sample Preconcentration Techniques in Capillary Electrophoresis

This review highlights recent applications of on-line sample preconcentration techniques in capillary electrophoresis (CE) from 2019 to 2021. Various preconcentration techniques based on the analyte velocity change in two or three discontinuous solutions system including field-amplified sample stacking, transient isotachophoresis, pH-mediated stacking, sweeping, and their modified and combined techniques have been employed to enrich and separate biological, environmental, food samples, and so on, in CE. More than 60 published research articles collected from Scopus databases described the dynamic on-line sample preconcentration techniques. This review provides comprehensive tables listing the applications of the on-line sample preconcentration techniques.

Development and validation of a direct injection liquid chromatography-tandem mass spectrometry method for the analysis of illicit drugs and psychopharmaceuticals in wastewater

A direct injection liquid chromatography-tandem mass spectrometry method was successfully developed for the analysis of 19 illicit drugs and psychopharmaceuticals in raw and treated wastewater. The method includes the analysis of stimulants and opioids, and antidepressant, antipsychotic, antianxiety, appetite suppressant and hallucinogen drugs. The method limits of quantification range from 5 – 59 ng L−1 and 2 – 38 ng L−1 in raw and treated wastewater, respectively. Analysis of raw and treated wastewater samples collected daily for a week from a wastewater treatment plant operating with oxidation ditch technology showed that codeine and tramadol were the drugs with the highest median mass concentrations in raw wastewater (1800 and 1000 ng L−1, respectively). The presence of some of the drugs in treated wastewater samples implies incomplete removal of illicit drugs and psychopharmaceuticals during wastewater treatment. This method offers an alternative to existing methods for faster screening of wastewater samples without the need for sample pre-concentration techniques, such as solid-phase extraction, with limits of detection in the low nanogram per litre range.

Nanoextraction based on surface nanodroplets for chemical preconcentration and determination.

Liquid-liquid extraction based on surface nanodroplets, namely nanoextraction, can continuously extract and enrich target analytes from the flow of a sample solution. This sample preconcentration technique is easy to operate in a continuous flow system with a low consumption of organic solvent and a high enrichment factor. In this review, the evolution from single drop microextraction to advanced nanoextraction will be briefly introduced. Moreover, the formation principle and key features of surface nanodroplets will be summarized. Further, the major findings of nanoextraction combined with in-droplet chemistry toward sensitive and quantitative detection will be discussed. Finally, we will give our perspectives for the future trend of nanoextraction.

Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis.

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

CE-MS for Proteomics and Intact Protein Analysis.

This chapter aims to explore various parameters involved in achieving high-end capillary electrophoresis hyphenated to mass spectrometry (CE-MS) analysis of proteins, peptides, and their posttranslational modifications. The structure of the topics discussed in this book chapter is conveniently mapped on the scheme of the CE-MS system itself, starting from sample preconcentration and injection techniques and finishing with mass analyzer considerations. After going through the technical considerations, a variety of relevant applications for this analytical approach are presented, including posttranslational modifications analysis, clinical biomarker discovery, and its growing use in the biotechnological industry.

Online sample preconcentration techniques in nonaqueous capillary and microchip electrophoresis

One of the major drawbacks of electrophoresis in both capillary and microchip is the unsatisfactory sensitivity. Online sample preconcentration techniques can be regarded as the most common and powerful approaches commonly applied to enhance overall detection sensitivity. While the advances of various online preconcentration strategies in capillary and microchip employing aqueous background electrolytes are well-reviewed, there has been limited discussion of the feasible preconcentration techniques specifically developed for capillary and microchip using nonaqueous background electrolytes. This review provides the first consolidated overview of various online preconcentration techniques in nonaqueous capillary and microchip electrophoresis, covering the period of the last two decades. It covers developments in the field of sample stacking, isotachophoresis, and micellar-based stacking. Attention is also given to multi-stacking strategies that have been used for nonaqueous electrophoresis.

Recent Advances in Trace Bioanalysis by Capillary Electrophoresis.

Recently, single cell analysis is becoming more and more important to elucidate cellular heterogeneity. Except for nucleic acid that can be amplified by PCR, the required technical level for single cell analysis is extremely high and the appropriate design of sample preparation and a sensitive analytical system is necessary. Capillary/microchip electrophoresis (CE/MCE) can separate biomolecules in nL-scale solution with high resolution, and it is highly compatible with trace samples like a single cell. Coupled with highly sensitive detectors such as laser-induced fluorescence and nano-electrospray ionization-mass spectrometry, zmol level analytes can be detected. For further enhancing sensitivity, online sample preconcentration techniques can be employed. By integrating these high-sensitive techniques, single cell analysis of metabolites, proteins, and lipids have been achieved. This review paper highlights successful research on CE/MCE-based trace bioanalysis in recent 10 years. Firstly, an overview of basic knowledge on CE/MCE including sensitivity enhancement techniques is provided. Applications to trace bioanalysis are then introduced with discussion on current issues and future prospects.

Highly Sensitive and Robust Capillary Electrophoresis-Electrospray Ionization-Mass Spectrometry: Interfaces, Preconcentration Techniques and Applications

Abstract Capillary electrophoresis (CE) coupled with mass spectrometry (MS) through electrospray ionization (ESI) is a promising alternative technique to liquid chromatography-ESI-MS (LC-ESI-MS) due to its high separation efficiency and high detection sensitivity. A sensitive and robust interface is essential in CE-ESI-MS. Continued development of CE-ESI-MS interfaces in the last decade, including junction-at-the-tip interfaces and sheathless interfaces, has improved the sensitivity and robustness of CE-ESI-MS significantly. The limited loading capacity of CE, one of major reasons that limits the utility of CE as a routine separation method, has also been addressed effectively by the use of in-capillary sample preconcentration techniques, such as transient CITP/CZE and dynamic pH junction. CE-ESI-MS could yield higher sensitivity as compared with the conventional LC-ESI-MS, and, therefore, is capable of identifying more proteins and peptides when the sample amount is very limited, such as single cell analysis. To improve the protein sequence coverage, CE-ESI-MS can also be used as a complementary technique to LC-ESI-MS, or combined with reversed phase LC to form a two dimensional separation technique. CE-ESI-MS is also effective in quantifying targeted peptides/proteins in complex bio-matrix.

Rat cardiomyocyte H9c2(2-1)-based sulforhodamine B assay as a promising in vitro method to assess the biological component of effluent toxicity

The treatment of wastewaters is crucial to maintain the ecological status of receiving waters, and thereby guarantee the protection of aquatic life and human health. Wastewater quality evaluation is conventionally based on physicochemical parameters, but increasing attention has been paid to integrate physicochemical and biological data. Nevertheless, the regulatory use of fish in biological testing methods has been subject to various ethical and cost concerns, and in vitro cell-based assays have thus become an important topic of interest. Hence, the present study intends: (a) to evaluate the efficiency of two different sample pre-concentration techniques (lyophilisation and solid phase extraction) to assess the toxicity of municipal effluents on rat cardiomyoblast H9c2(2-1) cells, and (b) maximizing the use of the effluent sample collected, to estimate the environmental condition of the receiving environment. The gathered results demonstrate that the H9c2(2-1) sulforhodamine B-based assay is an appropriate in vitro method to assess biological effluent toxicity, and the best results were attained by lyophilising the sample as pre-treatment. Due to its response, the H9c2(2-1) cell line might be a possible alternative in vitro model for fish lethal testing to assess the toxicity of municipal effluents. The physicochemical status of the sample suggests a high potential for eutrophication, and iron exceeded the permissible level for wastewater discharge, possibly due to the addition of ferric chloride for wastewater treatment. In general, the levels of carbamazepine and sulfamethoxazole are higher than those reported for other countries, and both surpassed the aquatic protective values for long-term exposure.

Laser-Induced Graphene Electrochemical Immunosensors for Rapid and Label-Free Monitoring of Salmonella enterica in Chicken Broth.

Food-borne illnesses are a growing concern for the food industry and consumers, with millions of cases reported every year. Consequently, there is a critical need to develop rapid, sensitive, and inexpensive techniques for pathogen detection in order to mitigate this problem. However, current pathogen detection strategies mainly include time-consuming laboratory methods and highly trained personnel. Electrochemical in-field biosensors offer a rapid, low-cost alternative to laboratory techniques, but the electrodes used in these biosensors require expensive nanomaterials to increase their sensitivity, such as noble metals (e.g., platinum, gold) or carbon nanomaterials (e.g., carbon nanotubes, or graphene). Herein, we report the fabrication of a highly sensitive and label-free laser-induced graphene (LIG) electrode that is subsequently functionalized with antibodies to electrochemically quantify the food-borne pathogen Salmonella enterica serovar Typhimurium. The LIG electrodes were produced by laser induction on the polyimide film in ambient conditions and, hence, circumvent the need for high-temperature, vacuum environment, and metal seed catalysts commonly associated with graphene-based electrodes fabricated via chemical vapor deposition processes. After functionalization with Salmonella antibodies, the LIG biosensors were able to detect live Salmonella in chicken broth across a wide linear range (25 to 105 CFU mL-1) and with a low detection limit (13 ± 7 CFU mL-1; n = 3, mean ± standard deviation). These results were acquired with an average response time of 22 min without the need for sample preconcentration or redox labeling techniques. Moreover, these LIG immunosensors displayed high selectivity as demonstrated by nonsignificant response to other bacteria strains. These results demonstrate how LIG-based electrodes can be used for electrochemical immunosensing in general and, more specifically, could be used as a viable option for rapid and low-cost pathogen detection in food processing facilities before contaminated foods reach the consumer.

Hyphenation of capillary zone electrophoresis with mass spectrometry for proteomic analysis: Optimization and comparison of two coupling interfaces

Capillary electrophoresis tandem mass spectrometry (CE–MS/MS) is an interesting tool for proteomic analysis as the separation principle is orthogonal to liquid chromatography tandem mass spectrometry (LC–MS/MS). The combination of both techniques can bring complementary information to enlarge proteome coverage.In this study, sample preconcentration techniques were investigated in order to improve sample loading and therefore sensitivity. Dynamic pH junction (DPJ) was found to be the most interesting approach by using 200 mM ammonium acetate (NH4Ac) adjusted to pH 10.0 as sample matrix. The use of DPJ allowed the identification of more peptides and proteins compared to conventional injections. Moreover, the sheath liquid (SL) composition was optimized in order to enhance signal intensity.A nanoflow SL interface (EMASS-II) was compared to the traditional coaxial SL interface (Triple tube) in terms of number of identified and proteins as well as detection sensitivity (peak area and peak height). MS acquisition was performed using both data-dependent acquisition (DDA) and data-independent acquisition (DIA) modes. The results showed that the combined use of these two acquisition modes provided additional information in terms of identification. Moreover, the use of EMASS-II interface allowed the identification of approximately two times more peptides and proteins. Besides, there was an improvement in sensitivity using EMASS-II as peak height and peak area were improved by 4 and 6-fold, respectively, compared to the Triple tube. Altogether, by combining an efficient sample preconcentration method, a nanoflow CE–MS interface and a hybrid ion-mobility qTOF mass spectrometer, a satisfying sequence coverage was obtained by analyzing 1 µg of E. coli proteome digest.

Advances in the Analysis of Veterinary Drug Residues in Food Matrices by Capillary Electrophoresis Techniques.

In the last years, the European Commission has adopted restrictive directives on food quality and safety in order to protect animal and human health. Veterinary drugs represent an important risk and the need to have sensitive and fast analytical techniques to detect and quantify them has become mandatory. Over the years, the availability of different modes, interfaces, and formats has improved the versatility, sensitivity, and speed of capillary electrophoresis (CE) techniques. Thus, CE represents a powerful tool for the analysis of a large variety of food matrices and food-related molecules with important applications in food quality and safety. This review focuses the attention of CE applications over the last decade on the detection of different classes of drugs (used as additives in animal food or present as contaminants in food products) with a potential risk for animal and human health. In addition, considering that the different sample preparation procedures have strongly contributed to CE sensitivity and versatility, the most advanced sample pre-concentration techniques are discussed here.

Research and Application Progress of Paper-based Microfluidic Sample Preconcentration

Abstract Sample pretreatment is an important part in detection and analysis of samples, especially for those with low initial concentration. Preconcentration technology can improve the accuracy of analytical method and expand its application range. However, conventional sample preconcentration technology is often cumbersome, costly, time-consuming, and relies on expensive equipment. Paper-based microfluidic sample preconcentration technique has many advantages such as easy preparation, low cost and high efficiency, which can simplify operation and reduce detection cost. This paper focuses on the research and application progress of paper-based microfluidic sample preconcentration in recent years, including enrichment principle, selection of paper-based materials, design of device structure, and the application of this technology. Finally, the development trend of this technique was prospected.

Characterization of Selected Pharmaceutical Micropollutants in River Water Using In-Situ Suspended Aggregate Microextraction and Field Enhancement Sample Injection-Capillary Electrophoresis

A new sample preconcentration technique known as in-situ suspended aggregate microextraction (iSAME) was used for the extraction of acetaminophen, ibuprofen, indomethacine, ciprofloxacin and diclofenac in river waters. The iSAME has been optimized in terms of surfactants selection and concentration, sample volume and extraction time. A combined surfactant of hexadecyltrimethyl ammonium bromide (CTAB) with 5-sulfosalicylic acid dihydrate (SSA) was studied to attain better extraction recoveries for the targeted pharmaceuticals. The separation of analytes was performed using capillary electrophoresis (CE) with online preconcentration by field enhancement sample injection (FESI) mode. The linearity, detection limits and recoveries were recorded and the sensitivity increased with enhancement factor of 11-140 folds. The developed method was successfully applied for the detection of selected pharmaceuticals in river water samples.

Sample Preconcentration Protocols in Microfluidic Electrophoresis.

Electrophoretic on-line sample preconcentration techniques in microfluidic channels improve the sensitivity prior to the separation. Among various techniques, the most important field-amplified sample stacking and sweeping on cross-channel microchips are demonstrated. As a novel microfluidic preconcentration approach, a large-volume sample stacking with electroosmotic flow pump (LVSEP) on straight-channel chips is also presented, which can omit a complicated voltage program for sample injection processes. In this chapter, we describe how to prepare and how to run these on-line sample preconcentration methods in microchip electrophoresis.