Recent developments in coupled SPE-CE

Improved Sensitivity to Determine Antibiotic Residues in Chicken Meat by In-Line Solid-Phase Extraction Coupled to Capillary Electrophoresis-Tandem Mass Spectrometry

Traditionally, capillary electrophoresis (CE) has been ruled out of many food safety applications, despite its inherent advantages, because its concentration sensitivity has been not high enough, mainly in relation to the monitoring of contaminants and residues, such as pesticides, veterinary medicines, environmental contaminants, toxins, etc. For this reason, researchers have proposed several strategies to overcome this limitation. So far, approaches based on chromatographic principles have been the most successful solutions. These approaches, known as in-line solid phase extraction, consist of the introduction of a small amount of stationary phase in the inlet section of the electrophoretic capillary (analyte concentrator, AC) to retain the analytes before separation takes place. In this chapter, this strategy is applied to CE coupled to tandem mass spectrometry (MS/MS) for the multiresidue detection of quinolone antibiotic residues in chicken meat. A previous sample treatment based on pressurized liquid extraction to obtain an optimum performance is also described.

Integration of three-phase microelectroextraction sample preparation into capillary electrophoresis

A major strength of capillary electrophoresis (CE) is its ability to inject small sample volumes. However, there is a great mismatch between injection volume (typically <100 nL) and sample volumes (typically 20-1500 µL). Electromigration-based sample preparation methods are based on similar principles as CE. The combination of these methods with capillary electrophoresis could tackle obstacles in the analysis of dilute samples. This study demonstrates coupling of three-phase microelectroextraction (3PEE) to CE for sample preparation and preconcentration of large volume samples while requiring minimal adaptation of CE equipment. In this set-up, electroextraction takes place from an aqueous phase, through an organic filter phase, into an aqueous droplet that is hanging at the capillary inlet. The first visual proof-of-concept for this set-up showed successful extraction using the cationic dye crystal violet (CV). The potential of 3PEE for bioanalysis was demonstrated by successful extraction of the biogenic amines serotonin (5-HT), tyrosine (Tyr) and tryptophan (Trp). Under optimized conditions limits of detection (LOD) were 15 nM and 33 nM for 5-HT and Tyr respectively (with Trp as an internal standard). These LODs are comparable to other similar preconcentration methods that have been reported in conjunction with CE. Good linearity (R² > 0.9967) was observed for both model analytes. RSDs for peak areas in technical replicates, interday and intraday variability were all satisfactory, i.e., below 14%. 5-HT, Tyr and Trp spiked to human urine were successfully extracted and separated. These results underline the great potential of 3PEE as an integrated enrichment technique from biological samples and subsequent sensitive metabolomics analysis.

A critical retrospective and prospective review of designs and materials in in-line solid-phase extraction capillary electrophoresis

Several strategies have been developed to decrease the concentration limits of detection (LODs) in capillary electrophoresis (CE). Nowadays, chromatographic-based preconcentration using a microcartridge integrated in the separation capillary for in-line solid-phase extraction capillary electrophoresis (SPE-CE) is one of the best alternatives for high throughput and reproducible sample clean-up and analyte preconcentration. This review covers different designs (geometrical configurations, with frits or fritless, capillary types, compatibility with commercial instrumentation, etc.) and materials (sorbents, supports, affinity ligands, etc.) applied for almost 30 years to prepare in-line SPE-CE microcartridges (i.e. analyte concentrators), with emphasis on the conventional unidirectional configuration in capillary format. Advantages, disadvantages and future perspectives are analyzed in detail to provide the reader a wide overview about the great potential of this technique to enhance sensitivity and address trace analysis.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2016-2018)

One of the most cited limitations of capillary and microchip electrophoresis is the poor sensitivity. This review continues to update this series of biannual reviews, first published in Electrophoresis in 2007, on developments in the field of online/in-line concentration methods in capillaries and microchips, covering the period July 2016-June 2018. It includes developments in the field of stacking, covering all methods from field-amplified sample stacking and large-volume sample stacking, through to isotachophoresis, dynamic pH junction, and sweeping. Attention is also given to online or in-line extraction methods that have been used for electrophoresis.

Nanomaterials for sample pretreatment prior to capillary electrophoretic analysis

Nanomaterials are, in analytical science, used for a broad range of purposes, covering the area of sample pretreatment as well as separation, detection and identification of target molecules.

CE-ESI-MS for bottom-up proteomics: Advances in separation, interfacing and applications

With the development of more sensitive hyphenation strategies for capillary electrophoresis-electrospray-mass spectrometry the technique has reemerged as technique with high separation power combined with high sensitivity in the analysis of peptides and protein digests. This review will discuss the newly developed hyphenation strategies for CE-ESI-MS and their application in bottom-up proteomics as well as the applications in the same time span, 2009 to present, using co-axial sheathliquid. Subsequently all separate aspects in the development of a CE-ESI-MS method for bottom-up proteomics shall be discussed, highlighting certain applications and discussing pros and cons of the various choices. The separation of peptides in a capillary electrophoresis system is discussed including the great potential for modeling of this migration of peptides due to the simple electrophoretic separation process. Furthermore, the technical aspects of method development are discussed, namely; background electrolyte choice, coating of the separation capillary and chosen loading method. Finally, conclusions and an outlook on future developments in the field of bottom-up proteomics by CE-ESI-MS will be provided.

Evaluation of fritless solid-phase extraction coupled on-line with capillary electrophoresis-mass spectrometry for the analysis of opioid peptides in cerebrospinal fluid

Fritless SPE on-line coupled to CE with UV and MS detection (SPE-CE-UV and SPE-CE-MS) was evaluated for the analysis of opioid peptides. A microcartridge of 150 μm id was packed with a C18 sorbent (particle size > 50 μm), which was retained between a short inlet capillary and a separation capillary (50 μm id). Several experimental parameters were optimized by SPE-CE-UV using solutions of dynorphin A (DynA), endomorphin 1 (End1), and methionine-enkephaline (Met). A microcartridge length of 4 mm was selected, sample was loaded for 10 min at 930 mbar and the retained peptides were eluted with 67 nL of an acidic hydro-organic solution. Using SPE-CE-MS, peak area and migration time repeatabilities for the three opioid peptides were 12-27% and 4-5%, respectively. SPE recovery was lower for the less hydrophobic DynA (22%) than for End1 (66%) and Met (78%) and linearity was satisfactory in all cases between 5 and 60 ng/mL. The LODs varied between 0.5 and 1.0 ng/mL which represent an enhancement of two orders of magnitude when compared with CE-MS. Cerebrospinal fluid (CSF) samples spiked with the opioid peptides were analyzed to demonstrate the applicability to biological samples. Peak area and migration time repeatabilities were similar to the standard solutions and the opioid peptides could be detected down to 1.0 ng/mL.

Molecular imprinting science and technology: a survey of the literature for the years 2004-2011

Herein, we present a survey of the literature covering the development of molecular imprinting science and technology over the years 2004-2011. In total, 3779 references to the original papers, reviews, edited volumes and monographs from this period are included, along with recently identified uncited materials from prior to 2004, which were omitted in the first instalment of this series covering the years 1930-2003. In the presentation of the assembled references, a section presenting reviews and monographs covering the area is followed by sections describing fundamental aspects of molecular imprinting including the development of novel polymer formats. Thereafter, literature describing efforts to apply these polymeric materials to a range of application areas is presented. Current trends and areas of rapid development are discussed.

Low-picomolar analysis of peptides by on-line coupling of fritless solid-phase extraction to sheathless capillary electrophoresis-mass spectrometry

A novel fritless solid-phase extraction (SPE) microcartridge was designed for combination with sheathless capillary electrophoresis-mass spectrometry (sheathless CE-MS) employing a prototype porous-tip capillary for nanoelectrospray ionization (nanoESI). The inlet of the separation capillary (30μm inner diameter (id), 150μm outer diameter (od)) was inserted in a 4mm long SPE microcartridge (150μm id, 365μm od) packed with a C18 sorbent of 55-105μm particle size. Performance of the SPE-CE-MS system was evaluated using diluted solutions of the three opioid peptides dynorphin A (1-7) (DynA), endomorphin 1 (End1) and met-enkephalin (Met). Sample volumes of 1.5μL were loaded on the SPE microcartridge and the retained peptides were eluted with 22nL of an acidic methanol/water (60:40, v/v) solution. Using a pressure of 50mbar during separation to speed up the analysis, good peptide resolution was obtained with acceptable plate numbers (between 53,000 and 92,000). Intraday relative standard deviations (% RSD) for peptide migration times and peak areas were below 4% and 9%, respectively. The SPE-CE-MS method showed good linearity in the 0.05-5ngmL(-1) range and limits of detection (LODs) were 10pgmL(-1). However, loading a larger volume of sample (8μL), LODs could be decreased down to 2pgmL(-1) (2.2-3.5pM). This represents an improvement of up to 5000-fold with respect to the LODs achieved by sheathless CE-MS without on-line preconcentration demonstrating the potential of on-line SPE for further enhancing sensitivity.

ASPECTS: an automation-assisted SPE method development system

Background: A typical conventional SPE method development (MD) process usually involves deciding the chemistry of the sorbent and eluent based on information about the analyte; experimentally preparing and trying out various combinations of adsorption chemistry and elution conditions; quantitatively evaluating the various conditions; and comparing quantitative results from all combination of conditions to select the best condition for method qualification. The second and fourth steps have mostly been performed manually until now. Results: We developed an automation-assisted system that expedites the conventional SPE MD process by automating 99% of the second step, and expedites the fourth step by automatically processing the results data and presenting it to the analyst in a user-friendly format. Conclusion: The automation-assisted SPE MD system greatly saves the manual labor in SPE MD work, prevents analyst errors from causing misinterpretation of quantitative results, and shortens data analysis and interpretation time.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010-2012)

CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.

Solid-phase extraction of nitrophenols in water by using a combination of carbon nanotubes with an ionic liquid coupled in-line to CE

This paper describes the combined use of carbon nanotubes and an ionic liquid directly coupled in-line to commercial CE equipment for sample treatment. The extraction unit operates as a spin column to preconcentrate the analytes. The extraction unit is inserted into the sample vial. The elution is performed in-line, placing the vial on the carrousel of the CE equipment. The joint use of carbon nanotubes and ionic liquids as sorbent is based on the high adsorption capacity of these materials, which makes them highly suitable for microextraction purposes. The LOQ of analytes were within the range of 0.65-0.83 μg/L with a RSD of less than 7%. The values of recovery range between 90 and 112%. The absolute recovery obtained from samples containing 1 μg/L of analytes was 38%.

CE-MS for metabolomics: developments and applications in the period 2010-2012

CE-MS has emerged as a powerful technique for the profiling of (highly) polar and charged metabolites in biological samples. This review provides an update of the most recent developments in CE-MS for metabolomics covering the scientific literature from July 2010 to June 2012. The present paper is an update of two previous review papers covering the years 2000-2010 (Electrophoresis 2009, 30, 276-291; Electrophoresis 2011, 32, 52-65). Emerging technological developments used in CE-MS for metabolomics are discussed, such as the use of novel interfacing techniques for coupling CE to MS. Representative examples illustrate the applicability of CE-MS in the fields of biomedical, clinical, microbial, plant, environmental and food metabolomics. Concerning targeted and non-targeted approaches, a comprehensive overview of recent CE-MS-based metabolomics studies is given in a table. Information on sample type and pretreatment, capillary coatings and MS detection mode is provided. Finally, general conclusions and perspectives are provided.

Recent advances in enrichment techniques for trace analysis in capillary electrophoresis

CE is gaining great popularity as a well-established separation technique for many fields such as pharmaceutical research, clinical application, environmental monitoring, and food analysis, owing to its high resolving power, rapidity, and small amount of samples and reagents required. However, the sensitivity in CE analysis is still considered as being inferior to that in HPLC analysis. Diverse enrichment methods and techniques have been increasingly developed for overcoming this issue. In this review, we summarize the recent advances in enrichment techniques containing off-line preconcentration (sample preparation) and on-line concentration (sample stacking) to enhancing sensitivity in CE for trace analysis over the last 5 years. Some relatively new cleanup and preconcentration methods involving the use of dispersive liquid-liquid microextraction, supercritical fluid extraction, matrix solid-phase dispersion, etc., and the continued use and improvement of conventional SPE, have been comprehensively reviewed and proved effective preconcentration alternatives for liquid, semisolid, and solid samples. As for CE on-line stacking, we give an overview of field amplication, sweeping, pH regulation, and transient isotachophoresis, and the coupling of multiple modes. Moreover, some limitations and comparisons related to such methods/techniques are also discussed. Finally, the combined use of various enrichment techniques and some significant attempts are proposed to further promote analytical merits in CE.

Microextraction techniques combined with capillary electrophoresis in bioanalysis

Over the past two decades, many environmentally sustainable sample-preparation techniques have been proposed, with the objective of reducing the use of toxic organic solvents or substituting these with environmentally friendly alternatives. Microextraction techniques (MEs), in which only a small amount of organic solvent is used, have several advantages, including reduced sample volume, analysis time, and operating costs. Thus, MEs are well adapted in bioanalysis, in which sample preparation is mandatory because of the complexity of a sample that is available in small quantities (mL or even μL only). Capillary electrophoresis (CE) is a powerful and efficient separation technique in which no organic solvents are required for analysis. Combination of CE with MEs is regarded as a very attractive environmentally sustainable analytical tool, and numerous applications have been reported over the last few decades for bioanalysis of low-molecular-weight compounds or for peptide analysis. In this paper we review the use of MEs combined with CE in bioanalysis. The review is divided into two sections: liquid and solid-based MEs. A brief practical and theoretical description of each ME is given, and the techniques are illustrated by relevant applications.

Investigation of in-line solid-phase extraction capillary electrophoresis for the analysis of drugs of abuse and their metabolites in water samples

In this study, in-line solid-phase extraction (SPE) was used as an enrichment technique in combination with CE for the preconcentration and separation of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), cocaine (COC), codeine (COD) and 6-acetylmorphine (6AM). The separation buffer (BGE) used was 80 mM disodium phosphate anhydrous and 6 mM of HCl (final BGE pH of 3). The SPE extractor consists of a small segment of capillary filled with Oasis HLB sorbent and inserted into the inlet section of the electrophoretic capillary. Different parameters affecting preconcentration were evaluated, such as sample pH, the volume of the elution plug and sample injection time. The detection limits (LODs) reached for standard samples by in-line SPE-CE-UV ranged between 50 and 200 ng/L, with sensitivity enhancement factors ranging from 2300 to 5300. Reproducibility values (expressed in terms of relative standard deviation) were below 7.6% for standard samples. This is a simple and an effective method for the determination of the studied drugs of abuse and their metabolites. The applicability of the developed method was demonstrated in tap and river water samples which were directly analyzed without any off-line pretreatment. Analytical parameters were evaluated and LODs were between 70 and 270 ng/L with relative recoveries between 85 and 97%.

In-line solid-phase extraction-capillary electrophoresis coupled with mass spectrometry for determination of drugs of abuse in human urine

In-line solid-phase extraction-capillary electrophoresis coupled with mass spectrometric detection (SPE-CE-MS) has been used for determination of 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), codeine (COD), hydrocodeine (HCOD), and 6-acetylmorphine (6AM) in urine. The preconcentration system consists of a small capillary filled with Oasis HLB sorbent and inserted into the inlet section of the electrophoresis capillary. The SPE-CE-MS experimental conditions were optimized as follows: the sample (adjusted to pH 6.0) was loaded at 930 mbar for 60 min, elution was performed with methanol at 50 mbar for 35 s, 60 mmol L(-1) ammonium acetate at pH 3.8 was used as running buffer, the separation voltage was 30 kV, and the sheath liquid at a flow rate of 5.0 μL min(-1) was isopropanol-water 50:50 (v/v) containing 0.5% acetic acid. Analysis of urine samples spiked with the four drugs and diluted 1:1 (v/v) was studied in the linear range 0.08-10 ng mL(-1). Detection limits (LODs) (S/N = 3) were between 0.013 and 0.210 ng mL(-1). Repeatability (expressed as relative standard deviation) was below 7.2%. The method developed enables simple and effective determination of these drugs of abuse in urine samples at the levels encountered in toxicology and doping.

Recent approaches in sensitive enantioseparations by CE

The latest strategies and instrumental improvements for enhancing the detection sensitivity in chiral analysis by CE are reviewed in this work. Following the previous reviews by García-Ruiz et al. (Electrophoresis 2006, 27, 195-212) and Sánchez-Hernández et al. (Electrophoresis 2008, 29, 237-251; Electrophoresis 2010, 31, 28-43), this review includes those papers that were published during the period from June 2009 to May 2011. These works describe the use of offline and online sample treatment techniques, online sample preconcentration techniques based on electrophoretic principles, and alternative detection systems to UV-Vis to increase the detection sensitivity. The application of the above-mentioned strategies, either alone or combined, to improve the sensitivity in the enantiomeric analysis of a broad range of samples, such as pharmaceutical, biological, food and environmental samples, enables to decrease the limits of detection up to 10⁻¹² M. The use of microchips to achieve sensitive chiral separations is also discussed.

Preparation and full characterization of a micro-immunoaffinity monolithic column and its in-line coupling with capillary zone electrophoresis with Ochratoxin A as model solute

A micro-immunoaffinity monolithic column (μIAC) was developed and in-line coupled with capillary zone electrophoresis in a fully automated way with Ochratoxin A as test solute. The in-line micro-immunoaffinity columns based on monolithic methacrylate polymers (EDMA-GMA) were prepared in situ at the inlet end of a PTFE coated fused silica capillary by UV initiated polymerization and subsequently grafted with antibodies. These μIACs were thoroughly characterized. The synthesis of the polymeric support was first demonstrated to be reproducible in terms of permeability, surface properties and efficiency. The antibodies immobilization was then studied by a new original hydrodynamic method (ADECA) allowing the in situ quantitative determination (at a miniaturized scale) of the total amount of immobilized antibodies. The combination of this measurement with the binding capacity of the μIAC allowed, for the first time, the in situ determination of immobilized antibody activity. A total of 260 ± 15 ng (1.6 ± 0.1 pmol) of IgG antibodies/cm in 75 μm i.d. monolithic column (i.e. 18 μgmg(-1)) was obtained with (anti-Ochratoxin A/Ochratoxin A) as antibody/antigen model. 40% of the immobilized antibodies remain active corresponding to a binding capacity of 1.2 ± 0.2 pmol antigen/cm (i.e. 600 pg/cm of our test solute OTA), a very high capacity when dealing with trace analysis and with regard to the detection limits (30 pg and 0.5 pg with UV and LIF detection, respectively). The recovery yields were quantitative with negligible non-specific adsorption and allow analysis of diluted samples (1 ngmL(-1)) for a percolated volume of 10 μL. It was also demonstrated that despite the progressive denaturation of antibodies consecutive to the elution step, the binding capacity of the μIAC remained high enough to implement at least 15 consecutive analyses with the same column and in a fully automated way.

Staggered multistep elution solid-phase extraction capillary electrophoresis/tandem mass spectrometry: a high-throughput approach in protein analysis

An approach based on staggered multistep elution solid-phase extraction (SPE) capillary electrophoresis/tandem mass spectrometry (CE/MS/MS) was developed in the analysis of digested protein mixtures. On-line coupling of SPE with CE/MS was achieved using a two-leveled two-cross polydimethylsiloxane (PDMS)-based interface. Multistep elution SPE was used prior to CE to provide an additional dimension of separation, thus extending the separation capacity for the peptide mixture analysis. By decreasing in the number of co-eluting peptides, problems stemming from ionization suppression and finite MS/MS duty cycle were reduced. As a result, sequence coverage increased significantly using multistep elution SPE-CE/MS/MS compared to one-step elution SPE-CE/MS/MS in the analysis of a single protein tryptic digest (49% vs. 18%) and a six protein tryptic digest (22-71% vs. 10-44%). A staggered CE method was incorporated to increase the throughput. The electropherograms of consecutive CE runs were partially overlapped by injecting the sample plug at a fixed time interval. With the use of a 5 min injection interval, slightly poor results were obtained in comparison with the sequential CE method while the total analysis time was reduced to 28%.