Analyte focusing by micelle collapse for liquid extraction surface analysis coupled with capillary electrophoresis of neutral analytes on a solid surface

Liquid extraction surface analysis (LESA) has an advantage of directly sampling analytes on a surface, thus avoiding unnecessary dilution by homogenization of the bulk sample commonly practiced in solid sample analysis. By combining LESA with CE, the additional advantage of separating analytes before detection can be accomplished. For neutral molecules, MEKC needs to be used. Since the detection sensitivity of CE in general suffers from the small capillary dimension, analyte focusing by micelle collapse was employed for enhanced extraction in LESA and sample preconcentration for MEKC. In addition, using a commercial CE instrument, the LESA process was performed much faster and more reliably compared to our first demonstration of LESA‐CE using a homemade CE setup. Three neutral water‐insoluble pesticides sprayed on an apple skin were directly extracted, preconcentrated, and analyzed by the automated LESA‐analyte focusing by micelle collapse‐MEKC with high sensitivity in 10 min. The relative standard deviations of the migration times and peak heights were 0.8–2.1 and 1.2–3.0%, respectively when ametryn was used as an internal standard. The limits of detection obtained with UV absorbance at 200 nm were 1.8–6.4 ppb.     

In situ determination of nerve agents in various matrices by portable capillary electropherograph with contactless conductivity detection

Rapid, efficient and robust methods for sampling and extracting genuine nerve agents sarin, soman and VX were developed for analyzing these compounds on various solid matrices, such as concrete, tile, soil and vegetation. A portable capillary electrophoretic (CE) system with contactless conductometric detection was used for the in situ analysis of the extracted samples. A 7.5 mM MES/HIS-based separation electrolyte accomplished the analysis of target analytes in less than 5 min. The overall duration of the process including instrument start-up, sample extraction and analysis was less than 10 min, which is the fastest screening of nerve agents achieved with liquid phase separation methods to date. The procedure can easily be performed by a person in a protective suit and is therefore suitable for real-life applications. The CE results were validated by an independent GC-MS method and a satisfactory correlation was obtained. The use of a proper sampling strategy with two internal standards and "smart" data-processing software can overcome the low reproducibility of CE. This has a significant impact on the potential acceptance of portable CE instrumentation for the detection and analysis of genuine chemical warfare agents (CWA).     

On-line simultaneous and rapid separation of anions and cations from a single sample using dual-capillary sequential injection-capillary electrophoresis

A novel capillary electrophoresis (CE) approach has been developed for the simultaneous rapid separation and identification of common environmental inorganic anions and cations from a single sample injection. The method utilised a sequential injection-capillary electrophoresis instrument (SI-CE) with capacitively-coupled contactless conductivity detection (C⁴D) constructed in-house from commercial-off-the-shelf components. Oppositely charged analytes from a single sample plug were simultaneously injected electrokinetically onto two separate capillaries for independent separation and detection. Injection was automated and may occur from a syringe or be directly coupled to an external source in a continuous manner. Software control enabled high sample throughput (17 runs per hour for the target analyte set) and the inclusion of an isolation valve allowed the separation capillaries to be flushed, increasing throughput by removing slow migrating species as well as improving repeatability. Various environmental and industrial samples (subjected only to filtering) were analysed in the laboratory with a 3 min analysis time which allowed the separation of 23 inorganic and small organic anions and cations. Finally, the system was applied to an extended automated analysis of Hobart Southern Water tap water for a period of 48 h. The overall repeatability of the migration times of a 14 analyte standard sample was less than 0.74% under laboratory conditions. LODs ranged from 5 to 61 μg L⁻¹. The combination of automation, high confidence of peak identification, and low limits of detection make this a useful system for the simultaneous identification of a range of common inorganic anions and cations for discrete or continuous monitoring applications.     

爆炸残留物的毛细管电泳检测

1引言爆炸是恐怖袭击的常用手段。对痕量爆炸残留物进行高效检测,从而准确判断炸药的成分和种类,能够为侦破案件提供重要的线索和证据[1,2]。近年来,毛细管电泳技术初步显示了其在爆炸物检验方面的巨大潜力[3～6]。本实验基于毛细管电泳间接紫外吸收检测[7,8]和胶束电动色谱[9],建立了痕量爆炸残余物的系统分析检验方法,通过对爆炸瞬间产生的痕量     

Coupled reversed-phase and ion chromatographic system for the simultaneous identification of inorganic and organic explosives

There are many methods available to detect and positively identify either organic or inorganic explosives separately, however no one method has been developed which can detect both types of explosive species simultaneously from a single sample. In this work, a unique coupled-chromatographic system is reported for the simultaneous determination of both organic and inorganic explosive species and is used for pre-blast analysis/identification purposes. This novel approach is based on the combination of reversed-phase high performance liquid chromatography and ion chromatography which allows trace levels of organic and inorganic explosives to be determined simultaneously from a single sample. Using this procedure, a 20 min reversed-phase separation of organic explosives is coupled to a 16 min ion-exchange separation of anions present in inorganic explosives, providing a complete pre-blast analysis/identification system for the separation and detection of a complex mixture containing organic and/or inorganic explosive species. The total analysis time, including sufficient column re-equilibration between runs, was <25 min using the coupled system. By this method, the minimum resolution for the organic separation was 1.16 between nitroglycerin and tetryl and the detection limits ranged from 0.31 mg L(-1) for cyclotetramethylene tetranitramine (HMX) and 1.54 mg L(-1) for pentaerythrite tetranitrate (PETN), while the minimum resolution for the inorganic separation was 0.99 between azide and nitrate, and the detection limits ranged from 7.70 μg L(-1) for fluoride and 159.50 μg L(-1) for benzoate.     

A high performance system to study the influence of temperature in on-line solid-phase extraction capillary electrophoresis

A novel high performance system to control the temperature of the microcartridge in on-line solid phase extraction capillary electrophoresis (SPE–CE) is introduced. The mini-device consists in a thermostatic bath that fits inside of the cassette of any commercial CE instrument, while its temperature is controlled from an external circuit of liquid connecting three different water baths. The circuits are controlled from a switchboard connected to an array of electrovalves that allow to rapidly alternate the water circulation through the mini-thermostatic-bath between temperatures from 5 to 90 °C. The combination of the mini-device and the forced-air thermostatization system of the commercial CE instrument allows to optimize independently the temperature of the sample loading, the clean-up, the analyte elution and the electrophoretic separation steps.     

Developments in sample preparation and separation techniques for the determination of inorganic ions by ion chromatography and capillary electrophoresis.

A review is presented of sample preparation and separation techniques for the determination of inorganic ions by ion chromatography (IC) and capillary electrophoresis (CE). Emphasis has been placed on those sample treatment methods which are specific to inorganic analysis, and the developments in separation methods which are discussed are those which enhance the capabilities of IC and CE to handle complex sample matrices. Topics discussed include solid-phase extraction for sample clean-up and preconcentration, dialytic methods, combustion methods, matrix-elimination IC, electrostatic IC, electrically polarised ion-exchange resins, electromigration sample preparation in CE, chromatographic sample preparation for CE, use of high-ionic strength background electrolytes, buffering of background electrolytes in CE, use of capillary electrochromatography for inorganic determinations, and methods for the manipulation of separation selectivity in both IC and CE. Finally, some possible future trends are discussed.     

Capillary electrophoresis-based immunoassays: principles and quantitative applications

The use of CE as a tool to conduct immunoassays has been an area of increasing interest over the last decade. This approach combines the efficiency, small sample requirements, and relatively high speed of CE with the selectivity of antibodies as binding agents. This review examines the various assay formats and detection modes that have been reported for these assays, along with some representative applications. Most CE immunoassays in the past have employed homogeneous methods in which the sample and reagents are allowed to react in solution. These homogeneous methods have been conducted as both competitive binding immunoassays and as noncompetitive binding immunoassays. Fluorescent labels are most commonly used for detection in these assays, but enzyme labels have also been utilized for such work. Some additional work has been performed in CE immunoassays with heterogeneous methods in which either antibodies or an analog of the analyte is immobilized to a solid support. These heterogeneous methods can be used for the selective isolation of analytes prior to their separation by CE or to remove a given species from a sample/reagent mixture prior to analysis by CE. These CE immunoassays can be used with a variety of detection modes, such as fluorescence, UV/Vis absorbance, chemiluminescence, electrochemical measurements, MS, and surface plasmon resonance.     

Quantitative analysis of microcystin variants by capillary electrophoresis mass spectrometry with dynamic pH barrage junction focusing

Dynamic pH junction is an online focusing method in CE based on the electrophoretic mobility difference of analytes in the sample matrix and the background electrolyte. An advantage of this method over the conventional CE is that the sensitivity can be significantly improved. By injecting a long sample plug in the capillary and focusing the analytes at the pH boundary between the background electrolyte and sample matrix, the LOD can be improved by 10–100 folds. The dynamic pH junction method can be easily coupled with ESI‐MS. In this work, we used this method for the analysis of microcystins (MCs). The detection limits and dynamic ranges were studied. The separation was optimized by adjusting the injection time, and concentrations and pH values of the background electrolyte. The optimization of analyte focusing leads to enhanced detection response compared to conventional injections, achieving 200–400 fold higher averaged peak heights for four microcystin (MC) variants. More importantly, this method was successfully used for the quantitative analysis of microcystins (MCs) in crude algae samples from natural water bodies, making it promising for practical applications.     

Fast and simple sample introduction for capillary electrophoresis microsystems

A newly designed capillary electrophoresis (CE) microchip with a simple and efficient sample introduction interface is described. The sample introduction is carried out directly on the separation channel through a sharp inlet tip placed in the sample vial, without an injection cross, complex microchannel layouts or hardware modification. Alternate placement of the inlet tip in vials containing the sample and buffer solutions permits a volume defined electrokinetic sample introduction. Such fast and simple sample introduction leads to highly reproducible signals with no observable carry over between different analyte concentrations. The performance of the system was demonstrated in flow-injection and CE measurements of nitroaromatic explosives and for on-chip enzymatic assays of glucose in the presence of ascorbic acid. Employing an 8 cm long separation channel and a separation voltage of 4000 V it offers high-throughput flow-injection assays of 100 samples h(-1) with a relative standard deviation of 3.7% for TNT (n= 100). Factors influencing the analytical performance of the new microchip have been characterized and optimized. Such ability to continuously introduce discrete samples into micrometer channels indicates great promise for high-speed microchip analysis.     

Combining tissue extraction and off-line capillary electrophoresis matrix-assisted laser desorption/ionization Fourier transform mass spectrometry for neuropeptide analysis in individual neuronal organs using 2,5-dihydroxybenzoic acid as a multi-functional agent

In this study we report an improved protocol that combines simplified sample preparation and micro-scale separation for mass spectrometric analysis of neuropeptides from individual neuroendocrine organs of crab Cancer borealis. A simple, one-step extraction method with commonly used matrix-assisted laser desorption/ionization (MALDI) matrix, 2,5-dihydroxybenzoic acid (DHB), in saturated aqueous solution, is employed for improved extraction of neuropeptides. Furthermore, a novel use of DHB as background electrolyte for capillary electrophoresis (CE) separation in the off-line coupling of CE to MALDI-Fourier transform mass spectrometric (FT-MS) detection is also explored. The new CE electrolyte exhibits full compatibility with MALDI-MS analysis of neuropeptides in that both the peptide extraction process and MALDI detection utilize DHB. In addition, enhanced resolving power and improved sensitivity are also observed for CE-MALDI-MS of peptide mixture analysis. Collectively, the use of DHB has simplified the extraction and reduced the sample loss by elimination of homogenizing, drying, and desalting processes. In the mean time, the concurrent use of DHB as CE separation buffer and subsequent MALDI matrix offers improved spectral quality by eliminating the interferences from typical CE electrolyte in MALDI detection.     

Determination of Phenols,Inorganic Anions,and Carboxylic Acids in Kraft Black Liquors by Capillary Electrophoresis

Two methods are presented for the quantitative capillary electrophoretic (CE) determination of phenolic lignin degradation compounds as well as of inorganic anions and organic acids in Kraft black liquors. Important phenolic lignin degradation compounds can be rapidly separated by co-electroosmotic CE after acidification of the liquors and subsequent extraction of the compounds with chloroform. A capillary electrophoretic separation of phenolic compounds is performed by using a phosphate/borate electrolyte system and UV detection at 214 nm. In addition, a HPLC method using a gradient with water, methanol, and acetic acid is also developed. Inorganic ions which are of importance to the pulping process can be determined by simply diluting the black liquors after sampling and subsequent analysis with a chromate electrolyte system and indirect UV detection at 185 nm. In addition, the concentration of low molecular aliphatic carboxylic acids can be determined simultaneously within the same run. By method optimization it is possible to separate the anions within one minute and, at the same time, to increase the resolution of the solutes. The electrolyte systems for the CE separations were optimized by varying the pH value and by adding organic solvents. Short separation times are obtained by adding a polycationic EOF modifier (hexadimethrine bromide) to the electrolyte which reverses the electroosmotic flow. A migration of the anionic analytes in the same direction as the electroosmotic flow is thus established.     

Capillary electrophoresis with wavelength-resolved laser-induced fluorescence detection

Capillary electrophoresis (CE) enables rapid separations with high separation efficiency and compatibility with small sample volumes. Laser-induced fluorescence detection can result in extremely low limits of detection in CE. Single-channel fluorescence detection, however, furnishes little qualitative information about a species being detected, except for its CE migration time. Use of multidimensional information often enables unambiguous identification of analytes. Combination of CE with information-rich wavelength-resolved fluorescence detection is analogous with ultraviolet-visible diode-array detection and furnishes both qualitative and quantitative chemical information about target species. This review discusses recent advances in wavelength-resolved laser-induced fluorescence detection coupled with CE, with an emphasis on instrument design.     

Micellar electrokinetic chromatography of organic and peroxide-based explosives

CE methods have been developed for the analysis of organic and peroxide-based explosives. These methods have been developed for deployment on portable, in-field instrumentation for rapid screening. Both classes of compounds are neutral and were separated using micellar electrokinetic chromatography (MEKC). The effects of sample composition, separation temperature, and background electrolyte composition were investigated. The optimised separation conditions (25 mM sodium tetraborate, 75 mM sodium dodecyl sulfate at 25 °C, detection at 200 nm) were applied to the separation of 25 organic explosives in 17 min, with very high efficiency (typically greater than 300,000 plates m⁻¹) and high sensitivity (LOD typically less than 0.5 mg L⁻¹; around 1–1.5 μM). A MEKC method was also developed for peroxide-based explosives (10 mM sodium tetraborate, 100 mM sodium dodecyl sulfate at 25 °C, detection at 200 nm). UV detection provided LODs between 5.5 and 45.0 mg L⁻¹ (or 31.2–304 μM), which is comparable to results achieved using liquid chromatography. Importantly, no sample pre-treatment or post-column reaction was necessary and the peroxide-based explosives were not decomposed to hydrogen peroxide. Both MEKC methods have been applied to pre-blast analysis and for the detection of post-blast residues recovered from controlled, small scale detonations of organic and peroxide-based explosive devices.     

Development of a capillary electrophoresis-77 K luminescence detection system for online spectral identification

We have demonstrated that capillary electrophoresis (CE) can be easily interfaced with 77 K luminescence spectroscopy (LS) for separation and online spectral identification of structurally similar analytes. This novel CE-LS apparatus consists of a regular CE system, instrumentation for LS and a specially designed capillary Dewar. When the separating molecules traverse into the cryostat detection window, liquid nitrogen is added, freezing the separating analyte zones within the capillary. At low temperature, detection limits are improved via signal averaging and the inherent increase in quantum yield at 77 K. We present the first application of the CE-LS system to structural isomers (2,3- and 3,4-methylenedioxymethamphetamine) and stereoisomers (trans- and cis-resveratrol). With this approach, the CE-LS interfacing provides a sensitive, accurate, rapid, simple and economic methodology for analytical chemistry.     

Inorganic oxidizer detection from propellants,pyrotechnics, and homemade explosive powders using gradient elution moving boundary electrophoresis

Advancement in rapid targeted chemical analysis of homemade and improvised explosive devices is critical for the identification of explosives-based hazards and threats. Gradient elution moving boundary electrophoresis (GEMBE), a robust electrokinetic separation technique, was employed for the separation and detection of common inorganic oxidizers from frequently encountered fuel-oxidizer mixtures. The GEMBE system incorporated sample and run buffer reservoirs, a short capillary (5 cm), an applied electric field, and a pressure-driven counterflow. GEMBE provided a separation format that allowed for continuous injection of sample, selectivity of analytes, and no sample cleanup or filtration prior to analysis. Nitrate, chlorate, and perchlorate oxidizers were successfully detected from low explosive propellants (e.g., black powders and black powder substitutes), pyrotechnics (e.g., flash powder), and tertiary explosive mixtures (e.g., ammonium nitrate- and potassium chlorate-based fuel-oxidizer mixtures). Separation of these mixtures exhibited detection without interference from a plethora of additional organic and inorganic fuels, enabled single particle analysis, and demonstrated semiquantitative capabilities. The bulk counterflow successfully excluded difficult components from fouling the capillary, yielding estimated limits of detection down to approximately 10 μmol/L. Finally, nitrate was separated and detected from postblast debris collected and directly analyzed from two nitrate-based charges.     

Contributions of capillary electrophoresis to neuroscience

Capillary electrophoresis (CE) is a small-volume separation approach amenable to the analysis of complex samples for their small molecule, peptide and protein content. A number of the features of CE make it a method of choice for addressing questions related to neurochemistry. The figures of merit inherent to CE that make it well suited for studying cell-to-cell and intracellular signaling include small sample volumes, high separation efficiency, the ability for online analyte concentration, and compatibility with sensitive and high-information content detection methods. A variety of instrumental aspects are detailed, including detection methods and sampling techniques that are particularly useful for the analysis of signaling molecules. Studies that have used these techniques to increase our understanding of neurobiology are emphasized throughout. One notable application is single neuron chemical analysis, a research area that has been greatly advanced by CE.     

Advantages and limitations of coupling isotachophoresis and comprehensive isotachophoresis-capillary electrophoresis to time-of-flight mass spectrometry

Capillary isotachophoresis (ITP) and comprehensive isotachophoresis-capillary electrophoresis (ITP-CE) were successfully coupled to electrospray ionization (ESI) orthogonal acceleration time-of-flight mass spectrometry (TOF-MS) using angiotensin peptides as model analytes. The utility of ITP-TOF-MS and ITP-CE-TOF-MS for the analysis of samples containing analyte amounts sufficient to form flat-top ITP zones (30 microM) as well as for samples with trace analyte amounts (0.3 microM) was studied. Separations were performed in 150 microm internal diameter (I.D.) capillaries for the ITP experiments, and in 200 microm I.D. (ITP) and 50 microm I.D. (CE) capillaries for ITP-CE experiments. The fused-silica columns were coated with poly(vinyl alcohol) to suppress electroosmotic flow that can disrupt ITP zone profiles. The sample loading capacity in both ITP and comprehensive ITP-CE was greatly enhanced (up to 10 microl) compared with typical nanoliter-sized injection volumes in CE. It was concluded that ITP-TOF-MS alone was adequate for the separation and detection of high concentration samples. The outcome was different at lower analyte concentrations where mixed zones or very sharp peaks formed. With formation of mixed zones, ion suppression and discrimination could occur, complicating quantitative determination of the analytes. This problem was effectively overcome by inserting a CE capillary between the ITP and TOF-MS. In such an arrangement, samples were preconcentrated in the high load WTP capillary and then injected into a CE capillary where they were separated into non-overlapping peaks prior to their detection by TOF-MS. The advantage of this comprehensive arrangement, which we have described previously, is that there is no need to discard portions of the sample in order to avoid overloading of the CE capillary. The whole sample is analyzed by multiple injections from ITP to CE. Thus, this method can be used for the analysis of complex samples with wide ranges of component concentrations.     

Fingerprinting postblast explosive residues by portable capillary electrophoresis with contactless conductivity detection

A portable capillary electrophoretic system with contactless conductivity detection was used for fingerprint analysis of postblast explosive residues from commercial organic and improvised inorganic explosives on various surfaces (sand, concrete, metal witness plates). Simple extraction methods were developed for each of the surfaces for subsequent simultaneous capillary electrophoretic analysis of anions and cations. Dual‐opposite end injection principle was used for fast (<4 min) separation of 10 common anions and cations from postblast residues using an optimized separation electrolyte composed of 20 mM MES, 20 mM l ‐histidine, 30 μM CTAB and 2 mM 18‐crown‐6. The concentrations of all ions obtained from the electropherograms were subjected to principal component analysis to classify the tested explosives on all tested surfaces, resulting in distinct cluster formations that could be used to verify (each) type of the explosive.     

Analytical potential of mesofluidic lab-on-a-valve as a front end to column-separation systems

The lab-on-a-valve (LOV) integrated microdevice has recently attracted much attention as a functional mesofluidic platform for programmable, pressure-driven flow as compared to lab-on-a-chip counterparts. We review the current state of the art of LOV as a versatile front end to column-separation techniques, namely, liquid chromatography (LC), gas chromatography (GC) and capillary electrophoresis (CE) for automatic mesofluidic handling at the low-microliter level, in-line sample processing and introducing the appropriate form of the analyte into the instrument for separation or detection.The open architecture of the LOV monolith unit has been to date exploited to accommodate micro solid-phase extraction in a renewable fashion, the so-called bead-injection analysis, encompassing reversed-phase materials and molecularly imprinted polymers, and in-valve microscale affinity chromatography. A plethora of interfaces have been recently devised for reliable injection of minute, well-defined volumes of analyte-containing solutions into LC,GC or CEWe illustrate these applications with representative examples in environmental and bioanalytical arenas.