Search

This study developed a sensitive method involving capillary electrophoresis (CE) coupled with ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugs at nanomolar concentration levels. The method consists of hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector and poly (diallyldimethylammonium chloride) (PDDAC)-based CE. Five pairs of d,l-phenothiazines were baseline separated using a background electrolyte containing 0.9% PDDAC, 5 mM Hp-γ-CD, and 100 mM tris(hydroxymethyl)aminomethane (Tris)-formate (pH 3.0). The five pairs were successfully stacked on the basis of the difference in viscosity between the PDDAC-containing background electrolyte and the sample solution, with almost no loss of resolution. The combination of a solid-phase extraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazine enantiomers. Under optimal conditions, calibration graphs displayed the linear range between 6 and 1500 nM, with relative standard deviation values lower than 3.5% (n = 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-fold enhancement was achieved. The practicality of using the proposed method to determine five pairs of d,l-phenothiazines in urine is also validated, in which recoveries between recoveries of all phenothiazines from urine ranged from 89% to 101%. [ABSTRACT FROM AUTHOR]

Transient isotachophoresis (tITP) with a system-induced terminator (SIT) was developed for capillary zone electrophoresis (CZE) determination of aniline (An + ) and pyridine (Py + ) in sewage samples. After sample injection, a water vial was set at the sample-inlet side. Then voltage was applied to generate a system-induced terminator (H + ). Experiments and simulations revealed a concentration effect by tITP with an SIT: background electrolyte (BGE) – 100 mM acetic acid (AcOH) and 50 mM NaOH (pH 4.6); detection wavelength – 200 nm for An + and 254 nm for Py + ; vacuum injection period – 15 s (190 nL); SIT generation – 10 kV applied for 80 s with the sample inlet side anode; separation voltage – 20 kV with the sample inlet side anode. The limits of detection (LODs, S/N = 3) of An + and Py + respectively reached 10 and 42 μg/L, with good repeatability (peak area RSDs ≤ 6.9%) and calibration graph linearity ( R 2 = 0.9997). The proposed method was applied for determination of An + and Py + in sewage samples. Recoveries of An + (0.50 mg/L) and Py + (2.0 mg/L) in spiked sewage samples were 94–104%. [ABSTRACT FROM AUTHOR]

This paper describes a simple, sensitive and environmentally benign method for the direct determination of aniline and its derivatives in environmental water samples by capillary zone electrophoresis (CZE) with field-enhanced sample injection. The parameters that influenced the enhancement and separation efficiencies were investigated. Surprisingly, under the optimized conditions, two linear ranges for the calibration plot, 1–50 ng/mL and 50–1000 ng/mL (R > 0.998), were obtained. The detection limit was in the range of 0.29–0.43 ng/mL. To eliminate the effect of the real sample matrix on the stacking efficiency, the standard addition method was applied to the analysis of water samples from local rivers.

A quantitative sample introduction method based upon inkjet injection was applied to capillary electrophoresis coupled with stacking and sweeping on-line concentration techniques. Methylxanthines were used as model compounds for the proof-of-concept of the method. The volume of injected sample could be easily manipulated by controlling the number of ejected droplets in the injection procedure. Under optimized conditions, a linear relationship between the ejected droplet number and peak area was obtained when the droplet number introduced into the capillary was less than 100. Under optimized quantitative on-line concentration conditions, the limits of detection for theobromine, caffeine, and theophylline were 1.0, 2.0, and 1.0 μM, respectively. The inkjet injection system was evaluated by comparing it with conventional injection methods. The electropherogram of the inkjet injection mode was the same as that for hydrodynamic injection mode, and no sample discrimination was observed compared with the electrokinetic injection mode. The established method was applied to the determination of methylxanthines in bottled green tea. The recoveries of theobromine, caffeine, and theophylline were 94.1, 110.6, and 86.8%, respectively. We conclude that proposed method can be used for quantitative concentration for capillary electrophoresis, thus resulting in an improved accuracy. [ABSTRACT FROM AUTHOR]

Glutamic acid (Glu) and aspartic acid (Asp), as two important neurotransmitters, have been the focus of increasingly intense research over the past several years. Glu and Asp are present in biological fluids such as serum at trace levels, but complex components in biological matrices make it difficult to determine them in biological samples. In this paper, a sensitive and simple method coupled with indirect UV detection, using benzoic acid (BA) as the UV-absorbing probe, was developed and validated for the quantitative determination of Glu and Asp in human serum and Compound Amino Acid Injection-18 AA. The method combines a dynamic pH junction with a sweeping technique using β-cyclodextrin (β-CD) as the complexing agent for sweeping. Employing this proposed method, low detection limits of 0.061 μg/mL for Glu and 0.032 μg/mL for Asp were obtained. The sensitivity was improved 30- and 55-fold for Glu and Asp compared to conventional CE method. Standard curves were linear ( r > 0.999) over the concentration range of 0.1–8.0 μg/mL. To further improve the resolution of Asp from interfering substances in human serum, 6% (v/v) methanol was added to the sample matrix, and resulted in the detection limits of 0.125 μg/mL for Glu and 0.057 μg/mL for Asp. With a simple precipitation of protein, the method has been successfully applied to the analysis of human serum, and the recoveries (82% for Glu and 87% for Asp) were achieved with relative standard deviations of 1.9% and 2.0%, respectively. [ABSTRACT FROM AUTHOR]

Unique properties of dendritic polymers make them promising candidates for application as additives in various analytical methods. From this point, we investigated the potential use of maltose-modified hyperbranched poly(ethylene imine) (PEI-Mal) as a dynamically or covalently bound coating and a pseudostationary phase in capillary electrophoresis. The EOF mobilities were measured at different pH values (2.2, 8.5, and 10.2) using PEI-Mal in the background electrolyte (BGE) and desirable repeatability of the EOF with % RSD ( n = 50) ≤3.3 was obtained. The influence of pH, polymer concentration, and density of maltose shell on the separation properties of a model mixture of four proteins (albumin, lysozyme, myoglobin, insulin) were investigated. Applying PEI-Mal as a dynamic coating, improved separation of the protein mixture with a high repeatability was achieved. Applying PEI-Mal as a covalent coating for concentrating proteins in the large volume sample stacking (LVSS) combined with the field-enhanced sample injection (FESI), up to 1320-fold enhancement of sensitivity was achieved. The detection limit of 100–500 ng/ml allowed successful analysis of albumin level both in blood and urine samples without additional preconcentration. [ABSTRACT FROM AUTHOR]

A novel, simple and sensitive method for the enantioseparation of terbutaline enantiomers was developed using capillary zone electrophoresis ( CZE) in combination with partial filling technique and field-amplified sample concentration. Under optimal conditions, the racemic terbutaline was resolved in less than 21 min by partially filling a fused-silica capillary with 15 mM β-cyclodextrin ( β-CD, 1.9 psi, 90 s) and carrying out an electrophoresis with 50 mM phosphate buffer (pH 1.8) at 15 kV separation voltage. The sensitivity was further improved by using field-amplified sample injection (0.2 psi, 2.5 s water plug). Compared with conventional CZE, the resolution and sensitivity of two enantiomers were much improved (the detection limit decreased by 18-25-fold). [ABSTRACT FROM AUTHOR]

This article highlights recent methodological developments in the on-line concentration and separation of amino acids and their enantiomers using capillary electrophoresis. Sections are dedicated to recent contributions to on-line concentration strategies such as field-amplified sample stacking, large-volume sample stacking, dynamic pH junction, transient isotachophoresis, sweeping, and the combination of two methods. The main applications, advantages, and limitations of these procedures in the biological, food, and pharmaceutical fields are addressed. Comprehensive tables listing on-line techniques for the concentration and separation of amino acids and their enantiomers, categorized by the stacking strategies used, background electrolytes, sample matrix, limit of detection, and enhancement factor, are provided. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel CE strategy combined chitosan trapping and CTAB assisted sample stacking. [•] Validation parameters of this method were investigated and satisfactory. [•] The method was used to detect organic acids in real Plateau alfalfa roots samples. [Copyright &y& Elsevier]

This paper describes a simple, sensitive and environmentally benign method for the direct determination of aniline and its derivatives in environmental water samples by capillary zone electrophoresis (CZE) with field-enhanced sample injection. The parameters that influenced the enhancement and separation efficiencies were investigated. Surprisingly, under the optimized conditions, two linear ranges for the calibration plot, 1-50 ng/mL and 50-1000 ng/mL (R > 0.998), were obtained. The detection limit was in the range of 0.29-0.43 ng/mL. To eliminate the effect of the real sample matrix on the stacking efficiency, the standard addition method was applied to the analysis of water samples from local rivers. [ABSTRACT FROM AUTHOR]

Abstract: This study describes for the first time, the ability of a normal stacking mode (NSM) on-line concentration step coupled with water-in-oil (W/O) microemulsion electrokinetic chromatography (MEEKC), using six common penicillin antibiotics (oxacillin, penicillin V, penicillin G, nafcillin, ampicillin, and amoxicillin) as test analytes. Optimization of penicillin separation in the conventional W/O MEEKC system demonstrated that change in the type and concentration of the oil phase (1-butanol) and column temperature had a pronounced effect on the separation. With the subsequent development of the NSM coupled with W/O MEEKC, improved separation and detection sensitivities were observed when an organic solvent plug (1-propanol; 1.04cm) was placed between the W/O microemulsion and the sample solutions. This could be attributed to the solution viscosity difference between the aqueous sample zone and the organic solvent plug causing the penicillin to be stacked in this 1-propanol plug. The optimal NSM W/O MEEKC provided about 12-fold increase in detection sensitivity compared with conventional sample injection (50mbar, 3s). Finally, this proposed method was successfully applied in the analyses of several food samples (porcine organs) spiked with penicillin. [Copyright &y& Elsevier]

Abstract: In this study, gold nanoparticles (Au NPs) were separated using the reversed electrode polarity stacking mode (REPSM) of a capillary electrophoresis (CE) system for on-line enhancement prior to performing surfactant-modified CE separation. Under optimized conditions [running electrolyte buffer, sodium dodecyl sulfate (70mM) and 3-cyclohexylamino-1-propanesulfonic acid (10mM) at pH 10.0; applied voltage, 20kV; operating temperature, 25°C; REPSM strategy for sample on-line concentration; REPSM applied prior to initializing separation], two parameters were varied to further enhance the concentration and separation of the Au NPs: (i) the rate of polarity switching (from −20 to +20kV) between the REPSM and surfactant-modified CE separation modes and (ii) the length of the capillary column. At a polarity switching rate of 1333kVmin−1 and a column length of ca. 83.5cm, the resolution of the separation of a mixture of 5.3- and 40.1-nm Au NPs was greater than 19; in addition, the numbers of theoretical plates for the 5.3- and 40.1-nm-diameter Au NPs were greater than 15,000 and up to 1.15×107, respectively—the latter being extremely high. Thus, this CE-based method for separating Au NPs provided high performance in terms of separation resolution and the number of theoretical plates, both of which were improved by greater than fivefold relative to those published previously. Notably, the sensitivity enhancement factors for the 5.3- and 40.1-nm-diameter Au NPs were improved (by ca. 20- and 500-fold, respectively) relative to those obtained using conventional surfactant-modified CE separation. [Copyright &y& Elsevier]

Abstract: This study describes the ability of on-line concentration capillary electrochromatography (CEC) coupled with UV or mass spectrometry (MS) for the determination of nine common non-steroidal anti-inflammatory drugs (NSAIDs) in water samples. A series of poly(stearyl methacrylate–divinylbenzene) (poly(SMA–DVB)) monolithic columns, which were prepared by single step in situ polymerization of divinylbenzene (DVB), stearyl methacrylate (SMA) and vinylbenzenesulfonic acid (VBSA, charged monomer), were developed as separation columns for the first time. The effects of polymerization condition of monolithic columns on analyte separations were examined, and the results indicated that separation performances were markedly improved in monolithic columns prepared with short reaction time (3h) and low SMA:DVB ratio (40/60 ratio of SMA:DVB). Subsequently, an on-line concentration step of step-gradient elution was combined to this CEC system, and by optimizing the difference in eluent strength between the sample matrix and mobile phase, all NSAIDs detection sensitivity were improved (limit of detection (LOD) was 3.4–10μg/L for UV, and 0.01–0.19μg/L for MS). When compared to the best CE and LC reports on NSAIDs analyses so far, this on-line concentration CEC method provided better detection ability within shorter separation time (12min) when either UV or MS detector was employed. This is the first report for on-line concentration CEC with MS detection applied in trace solute analyses of real samples. [Copyright &y& Elsevier]

Abstract: In this paper, a micellar electrokinetic chromatography (MEKC) method combined with cation-selective exhaustive injection (CSEI) and sweeping was developed to separate and concentrate four tobacco-specific N-nitrosamines (TSNAs) including N′-nitrosoanabasine (NAB), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and 4-(methylnitrosamino)-4-(3-pyridyl)-1-butanol (iso-NNAL). Experimental parameters affecting separation efficiency and enhancement factors were investigated in detail. Under the optimum MEKC condition, NAB, NNK, NNAL and iso-NNAL were baseline separated with high separation efficiencies and good peak shapes. Furthermore, with the preconcentration by CSEI–sweeping–MEKC, the sensitivity enhancement factors for NAB, NNK, NNAL and iso-NNAL in terms of peak areas ranged from 6.0×103 to 1.5×104, and the detection limits (LOD, S/N=3) of four TSNAs were in the range of 0.004–0.016μg/mL. In addition, this method had fairly good repeatability, and the RSDs of retention time and peak area were less than 1% and 5%, respectively. Finally, this method showed promising capabilities in the application of detecting and analyzing TSNAs in human urine samples. [ABSTRACT FROM AUTHOR]

A micellar electrokinetic chromatography method was developed for the simultaneous determination of three fat-soluble vitamins with UV detection. Several factors, such as the composition, concentration and pH of the background solution, different additives in the background solution, were optimized. Three on-line concentration methods, namely, sweeping, field-enhanced sample injection and pressure-assisted field-enhanced sample injection (PA-FESI), were utilized to improve the detection sensitivities of the analytes and compared. Of the three methods, PA-FESI can achieve the largest concentration efficiency for the fat-soluble vitamins. In the method, enhancement in the detection sensitivities of fat-soluble vitamins was in the range 42 to 103-fold, as compared to the usual injection method. The PA-FESI was used as an on-line concentration method for the determination of fat-soluble vitamins in multivitamin tablets and vitamin E soft capsules. [ABSTRACT FROM AUTHOR]

Abstract: In this study, an on-line concentration method which coupled cation-selective exhaustive injection (CSEI) sweeping technology with microemulsion electrokinetic chromatography (MEEKC) was used to detect and analyze several tobacco alkaloids (nornicotine, anabasine, anatabine, nicotine, myosmine and cotinine) that are commonly found in various tobacco products. First, the effects of microemulsion compositions (oil, cosurfactant and solution pH) were examined in order to optimize the alkaloid separations in conventional MEEKC. The pH value and the injection length of basic plug were found to be the predominant influences on the alkaloid stacking. This optimal CSEI sweeping MEEKC method provided approximately 180- to 540-fold increase in detection sensitivity in terms of peak height without any loss in separation efficiency when compared to normal MEEKC separation. Furthermore, this proposed CSEI sweeping MEEKC method was applied successfully for the detection of the minor alkaloids nornicotine, anabasine and anatabine in tobacco products. [Copyright &y& Elsevier]

Abstract: This paper proposed a method with capillary zone electrophoresis (CZE) for analysis of eight heterocyclic amines in a commercial meat matrix. The influence of composition, pH and concentration of buffer, and applied voltage were investigated. A 5mmol/L formic acid–ammonium formate solution at pH 2.20 was chosen as the running electrolyte. Also several solid-phase extraction actions were performed for the clean-up of the samples. With 3s hydrodynamic injection, detection limits ranging from 0.554 to 1.783μg/g was obtained. To improve sensitivity, field-amplified sample injection (FASI) was used with the conditions of 3s hydrodynamic injection of a water plug and 25s electrokinetic injection of the sample. And methanol–water (1:1 in volume) was applied as the sample solvent. Under above conditions, detection limits ranged from 1.329 to 19.39ng/g, which were at least 50 times lower than those with hydrodynamic injection. [Copyright &y& Elsevier]

Abstract: A pressurized capillary electrochromatography (pCEC) system was developed for the separation of water-soluble vitamins, in which UV absorbance was used as the detection method and a monolithic silica-ODS column as the separation column. The parameters (type and content of organic solvent in the mobile phase, type and concentration of electrolyte, pH of the electrolyte buffer, applied voltage and flow rate) affecting the separation resolution were evaluated. The combination of two on-line concentration techniques, namely, solvent gradient zone sharpening effect and field-enhanced sample stacking, was utilized to improve detection sensitivity, which proved to be beneficial to enhance the detection sensitivity by enabling the injection of large volumes of samples. Coupling electrokinetic injection with the on-line concentration techniques was much more beneficial for the concentration of positively charged vitamins. Comparing with the conventional injection mode, the enhancement in the detection sensitivities of water-soluble vitamins using the on-line concentration technique is in the range of 3 to 35-fold. The developed pCEC method was applied to evaluate water-soluble vitamins in corns. [Copyright &y& Elsevier]

Abstract: A method based on poly (methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-EGDMA) monolith microextraction (PMME) and field-enhanced sample injection (FESI) pre-concentration technique was proposed for sensitive capillary electrophoresis-ultraviolet (CE-UV) analysis of ephedrine (E) and pseudoephedrine (PE) in human plasma and urine. The PMME device consisted of a regular plastic syringe (1mL), a poly (MAA-EGDMA) monolithic capillary (2cm×530μm I.D.) and a plastic pinhead connecting the former two components seamlessly. The extraction was achieved by driving the sample solution through the monolithic capillary tube using a syringe pump, for the desorption step, an aliquot of organic solvent, which normally provided an excellent medium to ensure direct compatibility for FESI in CE, was injected via the monolithic capillary and collected into a vial for subsequent analysis by CZE. The best separation was achieved using a buffer composed of 0.1M phosphate electrolyte (pH 2.5) and 10% acetonitrile (v/v). The combination of both pre-concentration procedures allowed the detection limits of the analytes down to 5.3ng/mL and 8.0ng/mL in human plasma and urine, respectively. Excellent method of reproducibility was found over a linear range 50–5000ng/mL in plasma and urine sample. Plasma and urine samples from volunteers receiving pseudoephedrine have also been successfully analysed. [Copyright &y& Elsevier]

Abstract: In order to enhance the sensitivity of LC–MS, a novel on-line sample enrichment system was integrated by inserting a column-switching device containing a peak parking loop after conventional LC column and UV detector. The system consists of conventional LC, micro-LC, a parking loop, and a micro-precolumn, all connected through one eight-port switching valve. An analyte peak of interest detected on the conventional LC is stored in the parking loop with an appropriate amount of added water. The analyte is then directly transferred to the micro-precolumn to be concentrated, and then eluted from the precolumn with linear gradient and separated by the micro-LC column. The sensitivity of LC–MS can be increased by a factor of up to a 100. By combining the micro-LC column with ESI–TOF–MS, some structural information including accurate molecular weight were obtained from analyte samples in the pmol range. [Copyright &y& Elsevier]

Abstract: A simple, reproducible and sensitive micellar electrokinetic chromatography (MEKC) method was developed for the separation and determination of 10 saponins from Panax notoginseng. Field-enhanced sample injection with reverse migrating micelles (FESI–RMM) was used for on-line concentration of the saponins. The effects of concentrations of sodium dodecyl sulfate (SDS) and organic modifier, the sample matrix, the injection time of water plug, the injection voltage and injection time of sample on the separation and stacking efficiency were investigated. The optimum buffer contained 10mM H3PO4, 140mM SDS, 20% acetonitrile and 15% 2-propanol and the pH of buffer was 2.4. The sample solution was diluted with 15mM SDS and injected for 15s with −8kV after injection of 2s water plug. Under the optimum conditions, the analytes were well separated with very high plate number (8.0×105–1.2×106 N/m); the limits of detection of the analytes were 1.7–6.3μg/mL. The high sensitivity permitted the determination of two minor saponins Rh1 (1.01mg/g) and Rg2 (0.62mg/g) in P. notoginseng, which were not determined in the literature. [Copyright &y& Elsevier]

Abstract: Capillary electrophoresis (CE) is an effective tool to analyze carbohydrate mixture derived from glycoproteins with high resolution. However, CE has a disadvantage that a few nanoliters of a sample solution are injected to a narrow capillary. Therefore, we have to prepare a sample solution of high concentration for CE analysis. In the present study, we applied head column field-amplified sample stacking method to the analysis of N-linked oligosaccharides derived from glycoprotein separated by two-dimensional gel electrophoresis. Model studies demonstrated that we achieved 60–360 times concentration effect on the analysis of carbohydrate chains labeled with 3-aminobenzoic acid (3-AA). The method was applied to the analysis of N-linked oligosaccharides from glycoproteins separated and detected on PAGE gel. Heterogeneity of α1-acid glycoprotein (AGP), i.e. glycoforms, was examined by 2D-PAGE and N-linked oligosaccharides were released by in-gel digestion with PNGase F. The released oligosaccharides were derivatized with 3-AA and analyzed by CE. The results showed that glycoforms having lower pI values contained a larger amount of tetra- and tri-antennary oligosaccharides. In contrast, glycoforms having higher pI values contained bi-antennary oligosaccharides abundantly. The result clearly indicated that the spot of a glycoprotein glycoform detected by Coomassie brilliant blue staining on 2D-PAGE gel is sufficient for quantitative profiling of oligosaccharides. [Copyright &y& Elsevier]

A detailed study was carried out to investigate the origin of the peak‐splitting phenomena in on‐column concentration‐micellar electrokinetic capillary chromatography for aqueous sample solution. The system studied was a basic phosphate and borax mixed buffer with sodium dodecyl sulfate (SDS) as micellar phase. Phenol, benzyl alcohol, phenyl ethanol, salicylic acid, and p ‐hydroxy benzyl acid were selected as the analytes. Several factors that affect peak splitting were investigated. The injection time, SDS micellar concentration, hydrophobicity of the analytes, and analytes concentration were the most important factors. A hypothesis was proposed to explain the peak‐splitting phenomena. Several means to avoid peak‐splitting phenomena were proposed, such as controlling sample injection time and hydrophobicity of the analyte, decreasing SDS concentration and increasing sample concentration. However, the most practical method for avoiding peak splitting was to control the sample injection time. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the combined use of solid-phase extraction (SPE) and on-line preconcentration strategies as normal stacking mode (NSM) and stacking with matrix removal (SWMR) for the ultrasensitive and simultaneous capillary electrophoresis-ultraviolet analysis (CE-UV) of five triazolopyrimidine sulfonanilide pesticides (i.e., diclosulam, cloransulam-methyl, flumetsulam, metosulam and florasulam) in different types of water is investigated. An adequate separation electrolyte for the separation and stacking of these pesticides was obtained, considering also its compatibility with MS detection, which consisted of 24mM formic acid and 16mM ammonium carbonate at pH 6.4. It was observed that the use of this running buffer together with the SWMR preconcentration method provided the best results in terms of sensitivity (between 6.54 and 11.9μg/L) and peak efficiency (up to 550000 theoretical plates per meter, NTP/m). When this on-line preconcentration procedure was combined with an off-line sample preconcentration step as SPE using C18 cartridges, the selected herbicides could be detected in the ng/L range. The optimized SPE-SWMR-CE-UV method was applied to the determination of the selected group of pesticides in spiked and non-spiked mineral and stagnant waters. Recoveries ranged between 55 and 110% and limits of detection between 131 and 342ng/L. This work shows the great possibilities of the combined use of SPE-SWMR-CE-UV to overcome the sensitivity problems usually linked to CE analysis. [Copyright &y& Elsevier]

A specific and sensitive method for the determination for difluprednate (DFBA) and its metabolite (deacetylated DFBA, DFB) in aqueous humor was developed. DFBA and DFB were initially absorbed on a Pinkerton-type column, then analyzed by high-performance liquid chromatography using a semi-micro column after column switching. Under the optimized conditions, calibration curves for DFBA and DFB showed good linearity over the range of 1.0–50 and 0.5–50 ng/ml, respectively. We applied the method to the analysis of DFBA and DFB in rabbit aqueous humor, and found that DFBA in rabbit aqueous humor 1 h after instillation of 0.002% DFBA ophthalmic emulsion was not detected, but DFB was present at the concentration of 4.3±3.1 ng/ml. [Copyright &y& Elsevier]

This study developed a sensitive method involving capillary electrophoresis (CE) coupled with ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugs at nanomolar concentration levels. The method consists of hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector and poly (diallyldimethylammonium chloride) (PDDAC)-based CE. Five pairs of d,l-phenothiazines were baseline separated using a background electrolyte containing 0.9% PDDAC, 5 mM Hp-γ-CD, and 100 mM tris(hydroxymethyl)aminomethane (Tris)-formate (pH 3.0). The five pairs were successfully stacked on the basis of the difference in viscosity between the PDDAC-containing background electrolyte and the sample solution, with almost no loss of resolution. The combination of a solid-phase extraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazine enantiomers. Under optimal conditions, calibration graphs displayed the linear range between 6 and 1500 nM, with relative standard deviation values lower than 3.5% (n = 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-fold enhancement was achieved. The practicality of using the proposed method to determine five pairs of d,l-phenothiazines in urine is also validated, in which recoveries between recoveries of all phenothiazines from urine ranged from 89% to 101%., (Copyright © 2018. Published by Elsevier B.V.)

Using an improved dynamic pH junction as an on-line concentration procedure, we developed CZE for determining submicromolar phenol in seawater for chloride to phenol concentration ratios of 1 000 000. To enhance the effect of conventional dynamic pH junction, a saturated fatty acid solution was injected into the capillary after sample injection. We named the procedure an improved dynamic pH junction. The method requires no sample pretreatment. The following optimum conditions were established: BGE, 40 mM sodium tetraborate decahydrate adjusted to pH 9.8 containing 0.001% m/v hexadimethrine bromide; 190 nm detection wavelength; 18 s (370 nL) vacuum injection period of sample; a saturated fatty acid solution, 30 mM sodium n-hexanoate; 20 s (420 nL) vacuum injection period of the sodium n-hexanoate; and 15 kV applied voltage with the sample inlet side as the cathode. The LOD for phenol was 5.9 μg/L at S/N of 3. The respective values of the RSD (intraday) of the peak area, peak height, and migration time for phenol were 1.9, 2.9, and 0.46%. The recoveries of phenol (25-100 μg/L) spiked into the natural seawater sample obtained using the peak areas were 92-110%. The proposed method was applied to simple biodegradation experiments using natural seawater samples containing phenol., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A pressurized capillary electrochromatography (pCEC) method combined with an online concentration was developed for the separation and determination of five β 2 -blockers (terbutaline, salbutamol, formoterol, procaterol and salmeterol) in human urine. A stearyl methacrylate-based monolithic column was prepared as the separation column. The various separation parameters including acetontrile concentration, applied voltage, pH and concentration of the running buffer were investigated. On-line concentration methods in combination of the chromatographic zone-sharpening effect and field-enhanced sample-stacking effect were utilized to improve detection sensitivity. The on-line concentration parameters including injection voltage, injection time, as well as sample matrix were systematically studied. Compared with the conventional sample injection, the on-line concentration technique appeared to improve the corresponding sensitivities 20∽50-fold. Furthermore, good precision was obtained with relative standard deviations (RSDs) for retention times within 1.09% and for peak areas less than 3.55% (n = 5). The established method was successfully applied to the determination of above-mentioned β 2 -agonists in urine samples. The recoveries of spiked urine samples were between 85.0 and 113.3% with RSDs less than 5.39%., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This paper describes a simple, sensitive and environmentally benign method for the direct determination of aniline and its derivatives in environmental water samples by capillary zone electrophoresis (CZE) with field-enhanced sample injection. The parameters that influenced the enhancement and separation efficiencies were investigated. Surprisingly, under the optimized conditions, two linear ranges for the calibration plot, 1-50 ng/mL and 50-1000 ng/mL (R > 0.998), were obtained. The detection limit was in the range of 0.29-0.43 ng/mL. To eliminate the effect of the real sample matrix on the stacking efficiency, the standard addition method was applied to the analysis of water samples from local rivers.