Non-aqueous Background Electrolyte Research Articles

Combining amperometry and mass spectrometry as a dual detection approach for capillary electrophoresis.

Dual detection concepts (DDCs) are becoming more and more popular in analytical chemistry. In this work, we describe a novel DDC for capillary electrophoresis (CE) consisting of an amperometric detector (AD) and a mass spectrometer (MS). This detector combination has a good complementarity as the AD exhibits high sensitivity, whereas the MS provides excellent selectivity. Both detectors are based on a destructive detection principle, making a serial detector arrangement impossible. Thus, for the realization of the DDC, the CE flow was divided into two parts with a flow splitter. The DDC was characterized in a proof-of-concept study with ferrocene derivates and a nonaqueous background electrolyte. We could show that splitting the CE flow was a suitable method for the instrumental realization of the DDC consisting of two destructive detectors. By lowering the height of the AD compared to the MS, it was possible to synchronize the detector responses. Additionally, for the chosen model system, we confirmed that the AD was much more reproducible and had lower limits of detection (LODs) than the MS. The LODs were identical for the DDC and the single-detection arrangements, indicating no sensitivity decrease due to the CE flow splitting. The DDC was successfully applied to determine the drug and doping agent trimetazidine.

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.

Development of a capillary electrophoresis\u2013mass spectrometry method for the analysis of metformin and its transformation product guanylurea in biota

A method with capillary electrophoresis coupled to mass spectrometry was optimized to determine the uptake of metformin and its metabolite guanylurea by zebrafish (Danio rerio) embryos and brown trout (Salmo trutta f. fario) exposed under laboratory conditions. Metformin was extracted from fish tissues by sonication in methanol, resulting in an absolute recovery of almost 90%. For the extraction of guanylurea from brown trout, solid-phase extraction was implemented with a recovery of 84%. The use of a mixture of methanol and glacial acetic acid as a non-aqueous background electrolyte was vital to achieve robust analysis using a bare fused-silica capillary with an applied voltage of +30 kV. Problems with adsorption associated with an aqueous background electrolyte were eliminated using a non-aqueous background electrolyte made of methanol/acetic acid (97:3) with 25 mM ammonium acetate (for zebrafish embryos) or 100 mM ammonium acetate (for brown trouts), depending on the sample complexity and matrix influences. High resolution and high separation selectivity from matrix components were achieved by optimization of the ammonium acetate concentration in the background electrolyte. An extensive evaluation of matrix effects was conducted with regard to the complex matrices present in the fish samples. They required adapting the background electrolyte to higher concentrations. Applying this method to extracts of zebrafish embryos and brown trout tissue samples, limits of detection for both metformin and guanylurea in zebrafish embryos (12.2 μg/l and 15 μg/l) and brown trout tissues (15 ng/g and 34 ng/g) were in the low μg/l or ng/g range. Finally, metformin and guanylurea could be both quantified for the first time in biota samples from exposure experiments.

Combination of capillary electrophoresis and molecular modeling to study the enantiomer affinity pattern between β-blockers and anionic cyclodextrin derivatives in a methanolic and water background electrolyte.

In order to have deep insights into the mechanisms of enantiomer affinity pattern in both aqueous and non-aqueous systems, an approach combining capillary electrophoresis and molecular modeling was undertaken. A chiral β-blocker; acebutolol, was enantioseparated in aqueous capillary electrophoresis and non-aqueous capillary electrophoresis using two anionic β-cyclodextrin derivatives. The enantiomer affinity pattern of acebutolol was found to be opposite when an aqueous background electrolyte was replaced with non-aqueous background electrolyte in the presence of heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin but remained the same in the presence of heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin. Molecular docking of acebutolol into two β-cyclodextrin derivatives indicated two distinct binding modes called 'up' and 'down' conformations. After structure optimization by molecular dynamics and energy minimization, both enantiomers of acebutolol were preferred to the 'up' conformation with heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin while 'down' conformation with heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin. The further calculation of the complex energy with solvent effect indicated that heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin had higher affinity to S-acebutolol than R-acebutolol in non-aqueous capillary electrophoresis while it showed better binding to R-acebutolol in aqueous capillary electrophoresis. However, the heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin bound better to R-acebutolol in both aqueous and non-aqueous capillary electrophoresis, implying that the binding mode played more important role in chiral separation of heptakis(2,3-di-O-methyl-6-sulfo)-β-cyclodextrin while the solvent effect had prevailing impact on heptakis(2,3-di-O-acetyl-6-sulfo)-β-cyclodextrin.

Nonaqueous capillary electrophoresis mass spectrometry method for determining highly hydrophobic peptides.

A nonaqueous capillary electrophoresis mass spectrometry (NACE-MS) method was developed to separate and determine highly hydrophobic temporin peptides. The nonaqueous background electrolyte solution was a mixture of 20% acetonitrile, 78% methanol and 2% formic acid, with 20 mM ammonium formate. The separation of six peptides was completed within 12 min. The CE system was connected to a triple quadrupole mass spectrometer operating in MRM mode using a chemical modifier solution of 2 mM ammonium formate in ethanol with the flow through microvial interface. The mass spectrometer offered a second dimension of separation for peptides having identical migration times but different structures. The new method represents the first system capable of reliably determining hydrophobic peptides without using reversed phase liquid chromatography mass spectrometry.

Aqueous and non-aqueous microchip electrophoresis with on-chip electrospray ionization mass spectrometry on replica-molded thiol-ene microfluidic devices

This work describes aqueous and non-aqueous capillary electrophoresis on thiol-ene-based microfluidic separation devices that feature fully integrated and sharp electrospray ionization (ESI) emitters. The chip fabrication is based on simple and low-cost replica-molding of thiol-ene polymers under standard laboratory conditions. The mechanical rigidity and the stability of the materials against organic solvents, acids and bases could be tuned by adjusting the respective stoichiometric ratio of the thiol and allyl (“ene”) monomers, which allowed us to carry out electrophoresis separation in both aqueous and non-aqueous (methanol- and ethanol-based) background electrolytes. The stability of the ESI signal was generally ≤10% RSD for all emitters. The respective migration time repeatabilities in aqueous and non-aqueous background electrolytes were below 3 and 14% RSD (n=4-6, with internal standard). The analytical performance of the developed thiol-ene microdevices was shown in mass spectrometry (MS) based analysis of peptides, proteins, and small molecules. The theoretical plate numbers were the highest (1.2–2.4×104m−1) in ethanol-based background electrolytes. The ionization efficiency also increased under non-aqueous conditions compared to aqueous background electrolytes. The results show that replica-molding of thiol-enes is a feasible approach for producing ESI microdevices that perform in a stable manner in both aqueous and non-aqueous electrophoresis.

Determination of Curcuminoids and Their Degradation Products in Turmeric (Curcuma longa) Rhizome Herbal Products by Non-aqueous Capillary Electrophoresis with Photodiode Array Detection

Non-aqueous capillary electrophoresis (NACE) method was optimised for simultaneous determination of major bioactive curcuminoids (CCD) viz., curcumin (CC), desmethoxycurcumin (DC) and bisdesmethoxycurcumin (BC), and some of the degradation products viz., vanillin (VN), vanillic acid (VA), ferulic acid (FA) and 4-hydroxybenzaldehyde (HB) in turmeric milk and herbal products. Separation was achieved using non-aqueous background electrolyte (NA-BGE), consisting of a mixture of sodium tetraborate, sodium hydroxide, methanol and 1-propanol in a single run by capillary electrophoresis (CE). In the present study, a novel ultrasonication-assisted phase separation method (US-PS) was used for extracting the analytes in turmeric milk and the extract was directly injected into the capillary without any pretreatment. High-performance thin layer chromatographic (HPTLC) method for the separation of the analytes was also evaluated on pre-coated silica gel plate. Two different high-performance liquid chromatographic (HPLC) conditions were reported in the literature for the separation of above-mentioned target compounds. The proposed method NACE is simple, fast, convenient and economical.

Nonaqueous Capillary Electrophoresis Mass Spectrometry.

The term nonaqueous capillary electrophoresis (NACE) commonly refers to capillary electrophoresis with purely nonaqueous background electrolytes (BGE). Main advantages of NACE are the possibility to analyze substances with very low solubility in aqueous media as well as separation selectivity that can be quite different in organic solvents (compared to water)-a property that can be employed for manipulation of separation selectivities. Mass spectrometry (MS) has become more and more popular as a detector in CE a fact that applies also for NACE. In the present chapter, the development of NACE-MS since 2004 is reviewed. Relevant parameters like composition of BGE and its influence on separation and detection in NACE as well as sheath liquid for NACE-MS are discussed. Finally, an overview of the papers published in the field of NACE-MS between 2004 and 2014 is given. Applications are grouped according to the field (analysis of natural products, biomedical analysis, food analysis, analysis of industrial products, and fundamental investigations).

Very fast capillary electrophoresis with electrochemical detection for high-throughput analysis using short, vertically aligned capillaries.

A method for conducting fast and efficient capillary electrophoresis (CE) based on short separation capillaries in vertical alignment was developed. The strategy enables for high-throughput analysis from small sample vials (low microliter to nanoliter range). The system consists of a lab-made miniaturized autosampling unit and an amperometric end-column detection (AD) cell. The device enables a throughput of up to 200 separations per hour. CE-AD separations of a dye model system in capillaries of only 4 to 7.5cm length with inner diameters (ID) of 10 or 15μm were carried out under conditions of very high electric field strengths (up to 3.0kV/cm) with high separation efficiency (half peak widths below 0.2s) in less than 3.5s migration time. A non-aqueous background electrolyte, consisting of 10mM ammonium acetate and 1M acetic acid in acetonitrile, was used. The practical suitability of the system was evaluated by applying it to the determination of dyes in overhead projector pens.

Comparative enantioseparation of talinolol in aqueous and non-aqueous capillary electrophoresis and study of related selector–selectand interactions by nuclear magnetic resonance spectroscopy

The enantiomers of the chiral β-blocker drug talinolol were separated with two single component sulfated β-cyclodextrin (CD) derivatives, namely heptakis (2,3-di-O-methyl-6-sulfo)-β-CD) (HDMS-β-CD) and heptakis (2,3-di-O-acetyl-6-sulfo)-β-CD) (HDAS-β-CD), in aqueous and non-aqueous capillary electrophoresis (CE). The enantiomer affinity pattern of talinolol toward these two CDs was opposite in both aqueous and non-aqueous CE. However, the enantiomer affinity pattern for a given CD derivative did not change when aqueous buffer was replaced with non-aqueous background electrolyte. The structures of the analyte–selector complexes in both, aqueous and non-aqueous electrolytes were studied using rotating frame nuclear Overhauser effect (ROESY) NMR spectroscopy. Inclusion complex formation between the enantiomers of talinolol and HDAS-β-CD was confirmed in aqueous buffer, while the complex between the enantiomers of talinolol and HDMS-β-CD was of the external type. The complex of the talinolol enantiomers with HDAS-β-CD in non-aqueous electrolyte was also of the external type. In spite of external complex formation excellent separation of the enantiomers was observed in non-aqueous CE.

Analyzing small samples with high efficiency: capillary batch injection–capillary electrophoresis–mass spectrometry

We present an experimental approach to conducting fast capillary electrophoresis-mass spectrometry (CE-MS) measurements of very small samples in the nanoliter range. This is achieved by injecting sample very efficiently into a CE-MS system. Injection efficiency represents the ratio of injected sample to the amount of sample needed for carrying out the injection process (v/v). In order to increase this injection efficiency from typical values of 10(-3) to 10(-7), the concept of capillary batch injection is used to build an automated, small-footprint injection device for CE-MS. This device is capable of running true multi-sample measurement series, using minimal sample volumes and delivering an injection efficiency of up to 100 %. It is compatible with both aqueous and non-aqueous background electrolytes. As an additional benefit, CE-MS separations of a catecholamine model system in capillaries of 15 cm length under conditions of high electric field strength could be accomplished in 20 s with high separation efficiency. This report details design and specifications of the injection device and shows optimal parameter choices for injections with both high injection efficiency and high separation efficiency. Furthermore, a procedure is presented to coat the tip of a fused silica capillary with a silicone elastomer which acts as a seal between two capillaries.

Study on the use of boromycin as a chiral selector in capillary electrophoresis

The first application of boromycin as a chiral selector in capillary electrophoresis is described. Given boromycin's insolubility in water, a non-aqueous background electrolyte based on methanol was used for enantiomeric discrimination of selected chiral primary amines (α-methylbenzylamine, R,S-tryptophanol, R,S-norepinephrine, R,S-octopamine, R,S-p-hydroxynorephedrine and R,S-2-amino-1-phenylethanol). A basic study of experimental conditions including the influence of boromycin concentration, the composition and concentration of background electrolyte and also the influence of different organic solvents was performed. The best separation condition was 75mM Tris/50mM boric acid in methanol, pHws 9.0, with a positive separation voltage. The enantiomeric separation of the primary amines was achieved within 14min with resolution values greater than 1.5 for the majority of the studied analytes.

Fast separations by capillary electrophoresis hyphenated to electrospray ionization time-of-flight mass spectrometry as a tool for arsenic speciation analysis

Fast capillary electrophoresis (CE) hyphenated to time-of-flight mass spectrometry (TOF-MS) of four organoarsenic species (glycerol oxoarsenosugar, sulfate oxoarsenosugar, arsenobetaine, arsenocholine) are presented using short length CE capillaries under high electric field strengths of up to 1.3 kV cm(-1) with small inner diameter (ID). The separation of arsenosugars by CE is demonstrated for the first time. An aqueous formic acid solution was employed as the background electrolyte (BGE) for the separation. Various acid concentrations were evaluated for their influence on migration times, separation efficiency as well as with regard to controlling the charge of the arsenic species. A 0.1 M formic acid/ammonium formate buffer (pH 2.8) proved to be suitable for the separation of the four species. A non-aqueous BGE was tested as an alternative buffer system for fast speciation analysis. Separation of arsenobetaine and arsenocholine could even be achieved within 10 s by pressure-assisted CE. Application of the optimized method for the analysis of extracts of a seagrass and a Wakame algae sample as well as the brown algae homogenate reference material IAEA-140/TM revealed a clear signal for the glycerol arsenosugar.

Di- n-amyl l-tartrate–boric acid complex chiral selector in situ synthesis and its application in chiral nonaqueous capillary electrophoresis

A chiral selector, di- n-amyl l-tartrate–boric acid complex, was in situ synthesized by the reaction of di- n-amyl l-tartrate with boric acid in a nonaqueous background electrolyte (BGE) using methanol as the medium. And a new method of chiral nonaqueous capillary electrophoresis (NACE) was developed with the complex as the chiral selector. It has been demonstrated that the chiral selector is suitable for the enantioseparation of some β-blockers and β-agonists in NACE. Some chiral analytes that could not be resolved in aqueous microemulsion electrokinetic chromatography (MEEKC) with the same chiral selector obtained baseline resolutions in the NACE system. The enantioseparation mechanism was considered to be ion-pair principle and the nonaqueous system was more favorable for the ion-pair formation which is quite useful for the chiral recognition. The addition of a proper concentration of triethylamine into the BGE to control the apparent pH (pH*) enhanced the enantiomeric discrimination. In order to achieve a good enantioseparation, the effects of di- n-amyl l-tartrate and boric acid concentration, triethylamine concentration, applied voltage, as well as capillary length were investigated. Under the optimum conditions, all of the tested chiral analytes including six β-blockers and five β-agonists were baseline resolved.

Separation of open-cage fullerenes using nonaqueous capillary electrophoresis

In this study, nonaqueous capillary electrophoresis (NACE) was used to separate three open-cage fullerenes. Trifluoroacetic acid (TFA) was used as the nonaqueous background electrolyte to change the analytes’ mobilities. The selectivity and separation efficiency were critically affected by the nature of the buffer system, the choice of organic solvent, and the concentrations of TFA and sodium acetate (NaOAc) in the background electrolyte. The optimized separation occurred using 200 mM TFA/20 mM NaOAc in MeOH/acetonitrile (10:90, v/v), providing highly efficient baseline separation of the open-cage fullerenes within 5 min. The migration time repeatability for the three analytes was less than 1% (relative standard deviation). Thus, NACE is a rapid, useful alternative to high-performance liquid chromatography for the separation of open-cage fullerenes.

Determination of flurbiprofen enantiomers in plasma using a single‐isomer amino cyclodextrin derivative in nonaqueous capillary electrophoresis

A nonaqueous capillary electrophoresis (NACE) assay was developed for the separation and determination of flurbiprofen enantiomers in plasma samples using 6-monodeoxy-6-mono(3-hydroxy)propylamino-beta-cyclodextrin as chiral selector. The nonaqueous background electrolyte was made up of 40 mM ammonium acetate in methanol (MeOH), and flufenamic acid was employed as internal standard. Solid-phase extraction was used for sample cleanup prior to the NACE separation. The NACE method reproducibility was optimized by evaluating different capillary washing sequences between runs. After having tested various conditions, trifluoroacetic acid (1 M) in MeOH was finally selected. Concerning the solid-phase extraction procedure, good and reproducible analyte recoveries were obtained using MeOH for protein denaturation and a polymeric phase combining hydrophobic interactions with anion exchange properties (Oasis) MAX) was selected as extraction sorbent. The method selectivity was not only demonstrated toward a blank plasma sample but also toward other non-steroidal anti-inflammatory drugs. The method was then successfully validated with respect to response function, trueness, precision, accuracy, linearity and limit of quantification.

Identification of Inorganic Improvised Explosive Devices by Analysis of Postblast Residues Using Portable Capillary Electrophoresis Instrumentation and Indirect Photometric Detection with a Light-Emitting Diode

A commercial portable capillary electrophoresis (CE) instrument has been used to separate inorganic anions and cations found in postblast residues from improvised explosive devices (IEDs) of the type used frequently in terrorism attacks. The purpose of this analysis was to identify the type of explosive used. The CE instrument was modified for use with an in-house miniaturized light-emitting diode (LED) detector to enable sensitive indirect photometric detection to be employed for the detection of 15 anions (acetate, benzoate, carbonate, chlorate, chloride, chlorite, cyanate, fluoride, nitrate, nitrite, perchlorate, phosphate, sulfate, thiocyanate, thiosulfate) and 12 cations (ammonium, monomethylammonium, ethylammonium, potassium, sodium, barium, strontium, magnesium, manganese, calcium, zinc, lead) as the target analytes. These ions are known to be present in postblast residues from inorganic IEDs constructed from ammonium nitrate/fuel oil mixtures, black powder, and chlorate/perchlorate/sugar mixtures. For the analysis of cations, a blue LED (470 nm) was used in conjunction with the highly absorbing cationic dye, chrysoidine (absorption maximum at 453 nm). A nonaqueous background electrolyte comprising 10 mM chrysoidine in methanol was found to give greatly improved baseline stability in comparison to aqueous electrolytes due to the increased solubility of chrysoidine and its decreased adsorption onto the capillary wall. Glacial acetic acid (0.7% v/v) was added to ensure chrysoidine was protonated and to enhance separation selectivity by means of complexation with transition metal ions. The 12 target cations were separated in less than 9.5 min with detection limits of 0.11-2.30 mg/L (calculated at a signal-to-noise ratio of 3). The anions separation system utilized a UV LED (370 nm) in conjunction with an aqueous chromate electrolyte (absorption maximum at 371 nm) consisting of 10 mM chromium(VI) oxide and 10 mM sodium chromate, buffered with 40 mM tris(hydroxymethyl)aminomethane at pH 8.05. All 15 target anions were baseline separated in less than 9 min with limits of detection ranging from 0.24 to 1.15 mg/L (calculated at a signal-to-noise ratio of 3). Use of the portable instrumentation in the field was demonstrated by analyzing postblast residues in a mobile laboratory immediately after detonation of the explosive devices. Profiling the ionic composition of the inorganic IEDs allowed identification of the chemicals used in their construction.

Nonaqueous capillary electrophoresis in coated capillaries: An interesting alternative for proteomic applications

This work brings together some contributions for the use of nonaqueous media for proteomic analysis, for both capillary electrophoresis (CE) separation and the preparation of tryptic digests. First, a ternary nonaqueous buffer consisting of 60/30/10 v/v methanol/acetonitrile/acetic acid with 12.5 mmol/L ammonium acetate was optimized for CE separation of the tryptic digest of lysozyme. Lysozyme was chosen as a model system for the protein digestion, which has also been prepared in an organic-rich medium with methanol/50 mmol/L NH(4)HCO(3), pH 8.0 (60/40 v/v). The separation results were compared to in silico (PeptideCutter program) digestion conditions, and high-efficiency peak separation (18 peaks) was obtained in 20 min with an electric field of 350 V/cm. In addition, we have evaluated the stability of a coated capillary with poly-N,N-dimethylacrylamide (60/30 cm total/effective length and 75 microm ID) for over 100 runs of tryptic digest with the nonaqueous background electrolyte solvent system. The migration times for ten selected peptide peaks presented 3-7% relative standard deviation.

Analysis of neutral nitromusks in incenses by capillary electrophoresis in organic solvents and gas chromatography‐mass spectrometry

Nitromusks used as fragrances in a variety of personal-care products, cleansers, and domestic deodorants, including incense sticks, are neutral nitro aromatic compounds; some of these have been reported as photosensitizers. In this work, their analysis was performed by capillary electrophoresis (CE) in a methanol-based background electrolyte (BGE). In particular, a 10 mM solution of citric acid in methanol was used; under these conditions the strong suppression of the electroosmotic flow favored the use of negatively charged surfactants as additives for the anodic migration of the studied analytes. To this end, sodium taurodeoxycholate (TDC) was supplemented at high concentration (190 mM) to the organic background electrolyte (BGE), showing strong indication of the ability to give micelle-like aggregates. Since nitromusks are characterized by the presence of a nitroaromatic ring with low charge density, their association with TDC aggregates can be ascribed to donor-acceptor interactions. Separation of musk xylene, musk ketone, and the banned musk moskene and musk ambrette was obtained under full nonaqueous BGE; the addition of relatively small water percentages (15% v/v) was found to be useful in improving the separation of pairs of adjacent peaks. Under optimized conditions (190 mM sodium TDC in methanol-water, 85-15 v/v containing citric acid 10 mM) the system was applied to the analysis of nitromusks in incense sticks extracted with methanol. The results were compared with those obtained by the analysis of the same samples using gas chromatography with mass detector. The expected different selectivity of separation obtained using the two techniques can be useful in the unambiguous determination of the analytes; furthermore, a substantial accord of the preliminary quantitative results achieved with the two methods was assumed as the confirmation of the potential reliability of CE performed with high percentage of organic solvent.

Chiral separation by capillary electrophoresis in nonaqueous medium.

In the last few years, nonaqueous background electrolyte (BGE) solutions have attracted increasing interest, not only in capillary zone electrophoresis (CZE) but also in other capillary electrophoretic techniques (CE) (). Nonaqueous capillary electrophoresis (NACE) exploits the vastly different physicochemical properties of organic solvents. With mere adjustment of BGE composition, parameters such as resolution, analysis time, and selectivity can be fine-tuned or even altered dramatically (, , , , , , , ). The solubility of the analytes and additives can be enhanced, and the possible adsorption of the analytes on the capillary wall can be reduced. Because solvation of the analytes differs considerably from that in aqueous solutions, a strong effect on the separation selectivity can be seen. In addition, low currents make the use of higher electric field strengths possible in separations. The interactions, which hardly take place in water, can be utilized in nonaqueous solvents permitting capillary electrophoretic separation of even uncharged compounds after the formation of complexes with ionic additives (,). Moreover, the solutes labile in aqueous solutions can be stable in nonaqueous media.