Separation of common organic and inorganic anions in atmospheric aerosols using a piperazine buffer and capillary electrophoresis

The ability to monitor and quantify anionic components of aerosols is important for developing a better fundamental understanding of temporal and spatial variations in aerosol composition. Of the many methods that can be used to detect anions, capillary electrophoresis is among the most attractive ones because of its high separation efficiency, high resolving power for ionic compounds, and ability to be miniaturized for in-field monitoring. Here we present a method to baseline resolve common aerosol components nitrate, sulfate, chloride, and over two dozen organic acids in a single separation. A capillary electrophoresis separation utilizing a pH 5.78 piperazine buffer with 1,5-naphthalenedisulfonic acid as a probe for indirect UV absorbance detection was developed for this analysis. Previously, two different buffers were required to adequately separate all of these compounds. Electrophoretic mobilities, limits of detection, and migration time reproducibilities were measured for 38 organic and 8 inorganic anions. For solutions of low conductivity, detection limits for electrokinetic injections were found to be up to two orders of magnitude lower (0.2-0.4 microM) than those for pressure injection (1-45 microM). This separation was optimized and used for routine analysis of aqueous extracts of ambient atmospheric aerosols, but may be extended to other samples containing similar mixtures of anions.     

High-sensitivity microchip electrophoresis determination of inorganic anions and oxalate in atmospheric aerosols with adjustable selectivity and conductivity detection

A sensitive and selective separation of common anionic constituents of atmospheric aerosols, sulfate, nitrate, chloride, and oxalate, is presented using microchip electrophoresis. The optimized separation is achieved in under 1 min and at low background electrolyte ionic strength (2.9 mM) by combining a metal-binding electrolyte anion (17 mM picolinic acid), a sulfate-binding electrolyte cation (19 mM HEPBS), a zwitterionic surfactant with affinity towards weakly solvated anions (19 mM N-tetradecyl,N,N-dimethyl-3-ammonio-1-propansulfonate), and operation in counter-electroosmotic flow (EOF) mode. The separation is performed at pH 4.7, permitting pH manipulation of oxalate's mobility. The majority of low-concentration organic acids are not observed at these conditions, allowing for rapid subsequent injections without the presence of interfering peaks. Because the mobilities of sulfate, nitrate, and oxalate are independently controlled, other minor constituents of aerosols can be analyzed, including nitrite, fluoride, and formate if desired using similar separation conditions. Contact conductivity detection is utilized, and the limit of detection for oxalate (S/N = 3) is 180 nM without stacking. Sensitivity can be increased with field-amplified sample stacking by injecting from dilute electrolyte with a detection limit of 19 nM achieved. The high-sensitivity, counter-EOF operation, and short analysis time make this separation well-suited to continuous online monitoring of aerosol composition.     

微量金属元素的毛细管电泳分析方法及应用

综述了毛细管电泳分析微量金属元素的基本原理、分离模式(CZE、MKEC、非水电泳、芯片分离等)、检测方法(紫外、荧光、化学发光、安培、电导、质谱联用技术)等的进展和该技术在环境、生物医学领域的研究与应用。引用文献94篇。     

An electrostatic micro-collection interface for aerosol collection. Automated ion Chromatographic analysis of aerosols

A miniature aerosol collector based on electrostatic precipitation is described. The sampled aerosol is charged in the device by positive corona discharge and electrostatically collected. The device is operated as a collection interface for aerosol analysis, the collection surfaces can be washed in situ and the effluent subjected to Chromatographic analysis on-line, all in a fully automated manner. At a sampling rate of 0.5 1 min(-1), near unity collection efficiencies are obtained for aerosols of 1 microm and lower size, the size class of greatest environmental interest. Atmospheric aerosol constituents such as sulfate can be measured at the ng m(-3) level. The disadvantage of the present system is that some artifact nitrate is generated (due to NO(x) production in the corona) and reliable values of ambient nitrate aerosol cannot therefore be obtained.     

Performance evaluation of a capillary electrophoresis electrochemical chip integrated with gold nanoelectrode ensemble working and decoupler electrodes

This paper presents a capillary electrophoresis poly(methyl methacrylate) (PMMA) based microchip for electrochemical detection applications featuring embedded gold nanoelectrode ensemble (GNEE) working and decoupler electrodes. In fabricating the microchip, the GNEE films are pressed directly onto the metallic electrode structures using a hot embossing technique, and the microfluidic channels are then sealed using a low-temperature azeotropic solvent bonding method. The detection performance of the microchip is evaluated using dopamine and catechol analytes for illustration purposes. The experimental results show that the GNEE working electrode provides a significantly higher signal response than that obtained from a bulk gold electrode when applied to the detection of dopamine analyte. Compared to a conventional bulk palladium decoupler electrode, the GNEE decoupler electrode reduces both the amplitude of the charge current (3.5 nA vs. 18.7 nA) and the baseline drift at higher separation voltages. The measured baseline current drift for the microchip equipped the proposed GNEE decoupler electrode is around three times smaller than the microchip with the palladium decoupler electrode under the applied separation electric field from 40 V/cm to 240 V/cm. Finally, when detecting a mixture of 1mM dopamine and 1mM catechol, the calculated signal response of the microchip with a GNEE decoupler electrode is approximately five times higher than that obtained from a microchip with a bulk Pd decoupler electrode, resulting in the detection limit of 1 microM for the proposed GNEE-based microchip device. Overall, the results indicate that the proposed capillary electrophoresis-electrochemical detection (CE-ED) microchip with embedded GNEE working and decoupler electrodes provides an ideal solution for sample detection in lab-on-a-chip and micro total analysis applications.     

A highly efficient and versatile microchip capillary electrophoresis method for DNA separation using gold nanoparticle as a tag

A highly efficient and versatile method for DNA separation using Au nanoparticles (Au NPs) as a tag based on microchip capillary electrophoresis (MCE) was developed. The thiol-modified DNA-binding Au NPs were utilized as a tag. Target DNA was sandwiched between Au NPs and probe DNA labeled with horseradish peroxidase (HRP). In electrophoresis separation, the difference in electrophoretic mobility between free probe and probe-target complex was magnified by Au NPs, which enabled the resulting mixture to be separated with high efficiency by microchip capillary electrophoresis. Horseradish peroxidase was used as a catalytic label to achieve sensitive electrochemical DNA detection via fast catalytic reactions. With this protocol, 27-mer DNA fragments with different sequences were separated with high speed and high resolution. The proposed method was critical to achieve improved DNA separations in hybridization analyses.     

Ion Chromatographic Analysis of Sulfate and Nitrate in Ambient Aerosols

Abstract

Ion exchange has been known to provide excellent separation of ions since 1850, and ion exchange chromatography has been in use since 1940. However, ion exchange chromatography has not been widely used for the automated analysis of eluted ions because of the background produced by the electrolyte used for elution. H. Small, T. S. Stevens, and W. C. Bauman, (Anal. Chem., 47, 1801 (1975)) recently developed a technique whereby the background is reduced to a minimum with eluant suppression. Eluant suppression allows the use of ion exchange chromatography with conductimetric detection as a sensitive and selective means for the analysis of practically all ionic species. This communication describes the first successful application of ion chromatography (IC) to the analysis of total water soluble sulfate and nitrate in ambient aerosols. Analytical conditions and data on sensitivity, selectivity, accuracy and repeatability are described.

The application of this technique to the analysis of atniospheric anions and cations and their precursors is to be investigated in future studies.     

Capillary and microchip electrophoresis of basic drugs with contactless conductivity detection

The extension of contactless conductivity detection in electrophoresis to the determination of basic drugs is demonstrated using beta-adrenergic blocking agents (beta-blockers) and other physiologically active amines as examples. The high-voltage approach to conductivity detection was employed for conventional capillaries as well as microchip devices. Acidic buffers were used in all cases. A buffer consisting of 100 mM acetic acid and 1 mM histidine was deemed most optimal for the separation of six beta-blockers and best results for the analysis of the other amines were achieved with a 20 mM lactic acid buffer at low pH-value. The detection limits ranged from 0.06 to 5 microM. To demonstrate potential practical applications, a main component assay was conducted for three pharmaceutical formulations. On-chip, five pharmaceutical amines could be baseline-resolved in a 8 cm long microchannel in 90 s, albeit a reduced sensitivity and peak capacity compared to conventional capillary electrophoresis.     

Separation and quantitation of monovalent anionic and cationic species in mainstream cigarette smoke aerosols by high-performance ion chromatography

A simple method has been developed to separate and quantitate monovalent ionic species in mainstream cigarette smoke aerosols based on ion chromatography (IC) with conductivity detection. The method entails collecting the smoke aerosol particulate phase by electrostatic precipitation, dissolving the smoke condensate in methanol (MeOH), and separating the ionic species on either a cation- or anion-exchange column. The method has been applied to the analysis of smoke aerosols from two cigarettes, 1R4F Kentucky Reference cigarettes and a new cigarette that heats but does not burn tobacco. The predominant cations in smoke aerosols from 1R4F Kentucky Reference and the new cigarettes are sodium (Na+), ammonium (NH4+), and potassium (K+) ions; the predominant anions are acetate (AcO-) and formate (HCOO-). Trace amounts of chloride (Cl-), nitrite (NO2-), and nitrate (NO3-) ions are also present.     

Analysis of ions in polar ice core samples by use of large injection volumes in ion chromatography

In the present study a non-suppressed ion chromatography system with conductivity detection was tested in terms of sampling effects, the effects on the ion separation efficiency and analysis detection limits to find optimum conditions for the determination of chloride, nitrate, sulfate, sodium, ammonium, potassium, calcium and magnesium ions in polar ice core samples.     

Indirect laser-induced fluorescence detection for capillary electrophoresis using a frequency-doubled diode laser

A blue (452 nm) frequency-doubled diode laser with a quasi-cw optical output power of 10 microW is used for indirect laser-induced fluorescence detection in combination with the capillary electrophoretic separation of inorganic anions. As fluorescing probe ion the anion of 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) was selected having an absorption maximum of 454 nm in alkaline medium. Employing a capillary coated with linear acrylamide, baseline separation of eight inorganic anions was possible within 5 min. With a separation buffer containing 50 micromol.L(-1) HPTS and 10 mmol.L(-1) lysine the limits of detection for sulfate, nitrite, nitrate, azide, thiocyanate, and chlorate were between 0.9 and 4.7 micromol.L(-1). Separation of chloride and sulfate was achieved by adding 0.25 mmol.L(-1) calcium hydroxide to the separation buffer. Inorganic anions in several mineral and tap water samples have been determined with the technique developed and results are compared to data obtained by ion chromatography in combination with conductivity detection after conductivity suppression.     

Contactless conductivity detection for analytical techniques: Developments from 2016 to 2018

The publications concerning capacitively coupled contactless conductivity detection for the 2‐year period from mid‐2016 to mid‐2018 are covered in this update to the earlier reviews of the series. Relatively few reports on fundamental investigations or new designs have appeared in the literature in this time interval, but the development of new applications with the detection method has continued strongly. Most often, contactless conductivity measurements have been employed for the detection of inorganic or small organic ions in conventional capillary electrophoresis, less often in microchip electrophoresis. A number of other uses, such as detection in chromatography or the gauging of bubbles in streams have also been reported.     

毛细管电泳及芯片毛细管电泳的电容耦合非接触电导检测

综述了毛细管电泳(CE)及芯片毛细管电泳(MCE)的电容耦合非接触电导检测(Capacitively Coupled Contactless Conductivity detection,C4D)的研究状况;并分别对其装置、检测的影响因素及其应用进行了评述。引用文献81篇。     

Wall-jet conductivity detector for microchip capillary electrophoresis

A new end-column ‘hybrid’ contactless conductivity detector for microchip capillary electrophoresis (CE) was developed. It is based on a “hybrid” arrangement where the receiving electrode is insulated by a thin layer of insulator and placed in the bulk solution of the detection reservoir of the chip, whereas the emitting electrode is in contact with the solution eluted from the channel outlet in a wall-jet arrangement. The favorable features of the new detector including the high sensitivity and low noise, can be attributed to both the direct contact of the ‘emitting’ electrode with the analyte solution as well as to the insulation of the detection electrode from the high DC currents in the electrophoretic circuit. Such arrangement provides a 10-fold sensitivity enhancement compared to currently used on-column contactless conductivity CE microchip detector as well as low values of noise and easy operation. The new design of the wall-jet conductivity detector was tested for separation of explosive-related methylammonium, ammonium, and sodium cations. The new detector design reconsiders the wall-jet arrangement for microchip conductivity detection in scope of improved peak symmetry, simplified study of inter-electrode distance, isolation of the electrodes, position of the wall-jet electrode to the separation channel, baseline stability and low limits of detection.     

Determination of cationic neurotransmitters and metabolites in brain homogenates by microchip electrophoresis and carbon nanotube-modified amperometry

An electrophoretic method for simultaneous determination of catecholamines and their O-methoxylated metabolites on the microchip as well as in the capillary is presented. A complex separation system employing sodium dodecyl sulfate (SDS) micelles, dendrimers forming a second pseudostationary phase and borate complexation is needed for the satisfactory separation of the selected compounds on the short migration length. A carbon nanotube-modified working electrode has been applied for the sensitive amperometric detection with submicromolar detection limits. The applicability of this new method for the analytics of real samples is demonstrated by analysis of mouse brain homogenate on the microchip and human urine by capillary electrophoresis.     

芯片毛细管电泳及其在生命科学中的应用

芯片毛细管电泳 (Chip CE)技术在近几年已取得了很大的进展。本文着重介绍芯片毛细管区带电泳技术 ,对等电聚焦、等速电泳、自由溶液电泳及胶束电动色谱等其它芯片电泳模式也有所提及。讨论了芯片材料和制作技术、芯片的几何形状、样品的操作和衍生、检测及芯片毛细管电泳技术的应用 ,特别是在核酸和蛋白质的分离分析中的进展     

A thin cover glass chip for contactless conductivity detection in microchip capillary electrophoresis

A microfabricated thin glass chip for contactless conductivity detection in chip capillary electrophoresis is presented in this contribution. Injection and separation channels were photolithographed and chemically etched on the surface of substrate glass, which was bonded with a thin cover glass (100 μm) to construct a new microchip. The chip was placed over an independent contactless electrode plate. Owing to the thinness between channel and electrodes, comparatively low excitation voltage (20–110 V in V_p–p) and frequency (40–65 kHz) were suitable, and favorable signal could be obtained. This microchip capillary electrophoresis device was used in separation and detection of inorganic ions, amino acids and alkaloids in amoorcorn tree bark and golden thread in different buffer solutions. The detection limit of potassium ion was down to 10 μmol/L. The advantages of this microchip system exist in the relative independence between the microchip and the detection electrodes. It is convenient to the replacement of chip and other operations. Detection in different position of the channel would also be available.     

Capillary electrophoretic determination of inorganic ions in a prenatal vitamin formulation

Methods for the quantitative analysis of three cations (calcium, iron and zinc), and the qualitative analysis of several anionic species (chloride, sulfate, nitrate, citrate, fumerate, phosphate, carbonate and acetate) from a prenatal vitamin formulation by two different capillary ion electrophoresis methods are reported. The cation method was evaluated for detection and quantitation limits, precision, accuracy and linearity. For standard solutions, detection limits into the ng/ml range, and reproducibility that averaged less than 1% for migration time and 2% for area response were generated. Calibration plots exhibited linearity in excess of three orders of magnitude. In addition, excellent agreement between capillary ion electrophoresis and flame photometry quantitative results for the cation analyses were obtained.     

Determination of sulfur-containing inorganic anions by dual ion chromatography and capillary electrophoresis – application to the characterization of bacterial sulfur degradation

An analytical characterization of microbiological oxidation and reduction of sulfur anions has been performed with dual ion chromatography. The apparatus consisted of two chromatographic lines combined by a sample injection valve that allows the simultaneous introduction of a sample solution to both systems. With system 1 non-suppressed conductivity detection of sulfite and sulfate after separation in phthalate eluent was performed. For sulfide, thiosulfate and thiocyanate amperometric detection using a carbonate eluent was carried out on system 2. Parallel runs were possible for these species which could not be separated with one system. Optimizing separation and detection, limits of quantification of 0.02–0.3 mg/L could be obtained. The on-line coupling of a reaction vial to the injection valve was used to investigate the bacterial conversions, because the samples could be taken without contamination and air introduction. Thiosulfate was detected as a metabolite in both sulfur reduction and oxidation. Capillary electrophoresis with conductivity detection was applied as a complimentary technique for monitoring the bacterial sulfur oxidation. The results showed good correlation to the concentration values obtained by ion chromatography.     

Detection techniques in ion analysis: what are our choices?

Trends in detection techniques for ion analysis by ion-exchange chromatography and capillary zone electrophoresis are reviewed. Special attention is paid to conductivity, UV-Vis absorbance, amperometric and potentiometric detection, mass spectrometry (including inductively coupled plasma MS and atmospheric pressure ionization MS) and post-separation reaction detection. Applications reported within the last few years are summarized.