Sensitive determination of chloroanilines in water samples by hollow fiber‐based liquid‐phase microextraction prior to capillary electrophoresis with amperometric detection

A hollow fiber‐based liquid‐phase microextraction method has been developed for enrichment of trace chloroanilines in water samples. Target analytes including aniline, three mono‐chlorinated aniline isomers (o‐chloroaniline, m‐chloroaniline, and p‐chloroaniline) and four mono‐chlorinated methylaniline isomers (2‐chloro‐4‐methylaniline, 3‐chloro‐4‐methylaniline, 4‐chloro‐2‐methylaniline, and 5‐chloro‐2‐methylaniline) were determined by CE with amperometric detection after microextraction. Several factors that affect separation, detection, and extraction efficiency were investigated. Under the optimum conditions, eight aniline compounds could be well separated from other components coexisting in water samples within 25 min, exhibiting a linear calibration over three orders of magnitude (r > 0.998); the obtained enrichment factors were between 51 and 239, and the LODs were in the range of 0.01–0.1 ng/mL. The proposed method has been applied for the analyses of real environmental water and sewage samples with relative recoveries in the range of 83–108%.     

Simultaneous determination of nitroaromatic compounds in water using capillary electrophoresis with amperometric detection on an electrode modified with a mesoporous nano‐structured carbon material

In this article, a carbon disk electrode modified with mesoporous carbon material (CMK‐3) was used in CE with amperometric detection system for the simultaneous determination of four types of important nitroaromatic compounds, including 2,4,6‐trinitrotoluene (TNT), 1,3,5‐trinitrobenzene (TNB), 2,4‐dinitrotoluene (DNT) and 1,3‐dinitrobenzene (DNB). Compared with the bare carbon electrode, the CMK‐3 modified electrode greatly improved the sensitivity at a relatively positive detection potential due to its excellent electrocatalytic activities, high conductivity and large effective surface area. The four analytes could be well separated and detected within 480 s. A good linear response was obtained for TNB, DNB, TNT and DNT from 8.4 to 5.0×10³ μg/L, with correlation coefficients higher than 0.9992. And the detection limits were established between 3.0 and 4.7 μg/L for the four investigated nitroaromatic compounds (S/N=3). The CMK‐3‐modified electrode was successfully employed to analyze coking wastewater, tap water and river samples with recoveries in the range of 94.8–109.0%, and RSDs less than 5.0%. The presented results demonstrated that the CMK‐3‐modified carbon electrode used in CE with amperometric detection was of convenient preparation, high sensitivity and good repeatability, which could be employed in the rapid determination of practical samples.     

Determination of levodopa methyl ester and its metabolites in rat serum by CZE with amperometric detection

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE–AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L^–1 phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L^–1) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4×10^–2 to 2.2 g mL^–1 for LDME, 2.9×10^–1 to 49.5 g mL^–1 for L-DOPA, and 1.4×10^–2 to 1.5 g mL^–1 for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL^–1, respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.     

Electrostacking online sample pre-concentration capillary electrophoresis with amperometric detection for beta2-agonists in human urine

A simple, rapid, sensitive and specific method using capillary electrophoresis (CE) coupled with electrostacking and amperometric detection (AD) has been developed for the simultaneous separation and determination of clenbuterol (CLB), terbutaline (TER), salbutamol (SAL) and formoterol (FMT). In this paper, the CE separation and AD conditions were investigated in detail. The optimum conditions were: pH 8.6 Na(2)B(4)O(7)-H(3)BO(3) buffer solution (20.0 mmol/L), 9 kV for the separation voltage, and 1000 mV (versus Ag/AgCl) for the detection potential. When the sample which was dissolved in 70% ACN-water mixture solution was injected 60 s by 15 kV electrokinetic injection, the best stacking effects was obtained. Under the optimum conditions, the enhancement factors of these beta(2)-agonists had been greatly improved more than 5500-fold compared with the conventional electrokinetic injection. And then an excellent linear response was obtained with LODs (S/N = 3) of 0.098, 0.024, 0.063 and 0.920 pmol/L for CLB, TER, SAL and FMT in urine, respectively. The precision was determined in both intra-day (n = 5) and inter-day (n = 15) assays, and the RSDs were not more than 2.1 and 3.4% for migration time and peak current, respectively. The proposed method has been applied to analyze human urine samples successfully.     

毛细管电泳-电化学检测法测定黄芪及其制剂中的活性成分

采用毛细管电泳-电化学检测法(CE-ED)对中药黄芪的主要活性成分芦丁、阿魏酸、香草酸、绿原酸、槲皮素和咖啡酸进行了分离和测定。分别考察了工作电极电位、运行缓冲液的pH值和浓度、分离电压和进样时间等实验参数对实验结果的影响。在优化的实验条件下,以直径300 μm的碳圆盘电极为工作电极,检测电位为+0.95 V(相对于饱和甘汞电极),在10 mmol/L硼酸盐(pH 8.2)的运行缓冲溶液中,上述6种活性成分能在17 min内实现很好的基线分离,被测物浓度与峰电流在3个数量级范围呈良好的线性关系,检出限(S/N=3)范围为78～110 μg/L。在不同的加标水平下,6种活性成分的平均回收率为96.0%～103.0%,相对标准偏差为1.9%～3.6%(n=3)。该方法样品处理简单,无需预富集,已应用于实际样品的分析,并获得了令人满意的结果。     

Microwave‐assisted extraction followed by CE for determination of catechin and epicatechin in green tea

In this work, for the first time, microwave‐assisted extraction (MAE) followed by CE was developed for the fast analysis of catechin and epicatechin in green tea. In the proposed method, catechin and epicatechin in green tea samples were rapidly extracted by MAE technique, and then analyzed by CE. The MAE conditions and the method's validation were studied. It is found that the extraction time of 1 min with 400 W microwave irradiation is enough to completely extract catechin and epicatechin in green tea sample, whereas the conventional ultrasonic extraction (USE) technique needs long extraction time of 60 min. The method validations were also studied in this work. The calibration curve shows good linearity in 0.01–3 mg/mL for catechin (R²=0.993), and 0.005–3 mg/mL for epicatechin (R²=0.996), respectively. The RSD values for catechin and epicatechin are 0.65 and 2.58%, respectively. This shows that the proposed method has good reproducibility. The proposed method has good recoveries, which are 118% for catechin and 120% for epicatechin. The proposed method was successfully applied to determination of the catechin and epicatechin in different green tea samples. The experiment results have demonstrated that the MAE following CE is a simple, fast and reliable method for the determination of catechin and epicatechin in green tea.     

Application of ionic liquid as additive in determination of three β‐agonists by capillary electrophoresis with amperometric detection

CE coupled with amperometric detection method was developed using ionic liquid 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMImBF₄) as additive for the simultaneous detection of clenbuterol (CLB), terbutaline (TER), and ractopamine (RAC) in feed. The effects of detection potential, concentration of EMImBF₄, pH, and concentration of the running buffer, separation voltage as well as injection time on the separation and detection of these three β‐agonists were investigated in detail. Under the optimum conditions: the detection potential at 1.05 V, 50 mmol/L Tris‐HAc at pH 8.0 with 0.6% (v/v) EMImBF₄, electrokinetic injection 6 s at 16 kV and separation voltage at 16 kV, a baseline separation for these three analytes could be achieved within 11 min. Introduction of EMImBF₄ into the running buffer resulted in significant improvement in separation selectivity and enhancement in peak currents for those β‐agonists, especially for TER and RAC, which could not be separated in the running buffer without additive. The method exhibited wide linear range with LOD (S/N = 3) of 2, 1, and 2 nmol/L for CLB, TER, and RAC, respectively. The precision was determined in both intraday (n = 5) and interday (n = 3) assays, and the RSDs for both migration time and peak current were less than 6%. The proposed method was also applied to analyze β‐agonists in feed sample.     

Continuous intact cell detection and viability determination by CE with dual‐wavelength detection

We introduce here a method for continuous intact cell detection and viability determination of individual trypan blue stained cells by CE with ultraviolet–visible dual‐wavelength detection. To avoid cell aggregation or damage during electrophoresis, cells after staining were fixed with 4% formaldehyde and were continuously introduced into the capillary by EOF. The absorbance of a cell at 590 nm was used to determine its viability. An absorbance of two milli‐absorbance unit at 590 nm was the clear cut‐off point for living and dead Hela cells in our experiments. Good viability correlation between the conventional trypan blue staining assay and our established CE method (correlation coefficient, R²=0.9623) was demonstrated by analysis of cell mixtures with varying proportions of living and dead cells. The CE method was also used to analyze the cytotoxicity of methylmercury, and the results were in good agreement with the trypan blue staining assay and 3‐(4,5‐dimethyl‐2‐thiazyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide methods. Compared with the 3‐(4,5‐dimethyl‐2‐thiazyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide method, our established CE method can be easily automated to report cell viability based on the state of individual cells. Tedious manual cell counting and human error due to investigator bias can be avoided by using this method.     

Fast determination of sugars in Coke and Diet Coke by miniaturized capillary electrophoresis with amperometric detection

The fast separation capability of a novel miniaturized capillary electrophoresis with amperometric detection (CE-AD) system was demonstrated by determining sugar contents in Coke and diet Coke with an estimated separation efficiency of 60,000 TP/m. Factors influencing the separation and detection processes were examined and optimized. The end-capillary 300 microm Cu wire amperometric detector offers favorable signal-to-noise characteristics at a relatively low potential (+0.50 V vs. Ag/AgCl) for detecting sugars. Three sugars (sucrose, glucose, and fructose) have been separated within 330 s in a 8.5 cm length capillary at a separation voltage of 1000 V using a 50 mM NaOH running buffer (pH 12.7). Highly linear response is obtained for the above compounds over the range of 5.0 to 2.0 x 10(2) microg/mL with low detection limit, down to 0.8 microg/mL for glucose (S/N = 3). The injection-to-injection repeatability for analytes in peak current (RSD < 3.6%) and for migration times (RSD < 1.4%) was excellent. The new miniaturized CE-AD system should find a wide range of analytical applications involving assays of carbohydrates as an alternative to conventional CE and micro-CE.     

Separation and determination of flavonoids in three traditional chinese medicines by capillary electrophoresis with amperometric detection

Flavonoids are important active ingredients in many traditional Chinese medicines. In this paper, capillary electrophoresis with amperometric detection was employed to separate and detect eight flavonoids, rutin, quercetrin, quercetin, kaempferol, kaempferide, catechin, apigenin, and luteolin, in a home‐made capillary electrophoresis device. Under the separation voltage of 2000 V, the eight flavonoids could be completely separated within 33 min in 18 mM borax running buffer at pH 10.2. Good linear relationships were obtained for all analytes and the detection limits for flavonoids ranged from 0.46 to 0.85 μM. Then, the method was applied to separate and determine the flavonoids in three traditional Chinese medicines, hippophae rhamnoides, hypericum perforatum, and cacumen platycladi. Finally, rutin, kaempferol, quercetin, and quercetrin were discovered in these medicines and the concentrations ranged from 0.28 to 9.94 mg/g. The recoveries of flavonoids ranged from 84.7 to 113%, which showed the high reliability of this method.     

Method for rapidly discovering active components in Yupingfeng granules by UPLC‐ESI‐Q‐TOF‐MS

Yupingfeng granules (YPFG) were isolated from a traditional Chinese medicine (TCM) formulation composed of three herbs (Astragali Radix, Atractylodis Macrocephalae Rhizoma, and Saposhnikoviae Radix). This formulation is used in TCM to tonify qi, and it can help strengthen exterior and reduce sweating. Nevertheless, the active components of YPFG remain unclear. In this study, the chemical constituents of YPFG were systematically characterized by ultra‐performance liquid chromatography coupled with electrospray ionization/ quadrupole time‐of‐flight mass spectrometry (UPLC‐ESI‐Q‐TOF‐MS). Fifty‐eight compounds, namely, 20 flavonoids, 19 saponins, nine organic acids, four volatile coumarins, three lactones, one alkaloid, and two other components, were identified. In addition, the constituents of YPFG with the potential for in vivo bioactivities following oral administration were investigated in Sprague–Dawley rats. Thirteen compounds, namely, 11 flavonoid‐related and 2 saponin‐related components, were detected in rat plasma. After enriching flavonoids and saponins in YPFG by extraction, the extracts and YPFG were administrated to immunosuppressed rats, respectively. Plasma samples were analyzed by UPLC‐ESI‐Q‐TOF‐MS, and principal component analysis (PCA) confirmed that the extracts had similar effects to YPFG. This method could discover active ingredients in YPFG quickly and provide a scientific basis for quality control and mechanism research.     

Rapid separation and highly sensitive detection methodology for sulfonamides in shrimp using a monolithic column coupled with BDD amperometric detection

In this report, we aimed to extend our previous efforts toward the evaluation of sulfonamides (SAs) with a boron-doped diamond (BDD) electrode. We improved this method by reducing the analysis time using a monolithic column coupled with amperometric detection to determine seven sulfonamides (sulfaguanidine, sulfadiazine, sulfamethazine, sulfamonomethoxine, sulfamethoxazole, sulfadimethoxine and sulfaquinoxaline). Because of its rapid separation, low back-pressure and high separation efficiency compared to a particle-packed column, a monolithic column (100 mm × 4.6 mm) was used for sulfonamide separation. Chromatographic separation was performed in less than 8 min. The analysis was carried out using phosphate buffer (0.1 M, pH 3): acetonitrile: methanol in a ratio of 80:15:5 (v/v/v) as the mobile phase with a flow rate of 1.5 mL min⁻¹. The optimal detection potential using hydrodynamic voltammetry was found to be 1.2 V versus Ag/AgCl. The method was applied to determine seven sulfonamides in shrimp after sample preparation by solid-phase extraction. The recoveries of the sulfonamides in spiked shrimp samples at 1.5, 5 and 10 μg g⁻¹ were in the range of 81.7 to 97.5% with a relative standard deviation (R.S.D.) between 1.0 and 4.6%. Our methodology produced results that were highly correlated with HPLC-MS data. Therefore, we propose a method that can be used for the rapid, selective and sensitive evaluation of sulfonamides in contaminated food.     

Solid‐phase microextraction based method for determination of essential oils components in herbal beverages

A method employing the direct immersion solid‐phase microextraction followed by GC‐MS analysis is presented for the determination of essential oils components in herbal tea infusions, i.e. their direct content in the liquid phase. The extraction performances were compared using five different microextraction fibres. Significant parameters affecting sorption process such as sample amount, sorption and desorption time and temperature, stirring speed, pH adjustment and effect of ionic strength were optimised and discussed. By optimising the key parameters, a detection limits (LOD = S/N × 3) for ten target marker compounds were obtained in the range from 5.3 to 48.2 ng/mL with recoveries ranged between 93.03 and 100.50%. Intra‐day and inter‐day repeatability at three concentration levels were found to be 1.1–15.3 and 7.2–15.5% RSD, respectively. Finally, the optimised procedure enabling a rapid and simple analysis of essential oils was applied for the direct determination of these compounds in ten herbal tea infusions.     

Simultaneous determination of electroactive and non-electroactive food preservatives by novel capillary electrophoresis with amperometric detection

A novel capillary electrophoresis and amperometric detection method was achieved by adding an electroactive additive (3,4-dihydroxybenzylamine, 3,4-DHBA) to the running buffer, so that both electroactive and non-electroactive food preservatives were simultaneously determined. Under the selected optimum conditions, four electroactive preservatives (methylparaben, ethylparaben, propylparaben and butylparaben) and two non-electroactive preservatives (potassium sorbate and sodium lactate) were well separated and sensitively detected with detection limits (S/N = 3) ranging from 1.06 × 10⁻⁸ to 2.73 × 10⁻⁶ g mL⁻¹. This method has been successfully employed for the determination of both electroactive and non-electroactive preservatives in several food commodities.     

Combined use of ionic liquid and sulfobutylether‐β‐cyclodextrin as electrolyte additives for separation and determination of camptothecin alkaloids by CZE

This work reported that ionic liquid (IL) ([Bmim] [PF₆]) and sulfobutylether‐β‐CD (SBE‐β‐CD) were used as electrolyte additives for the separation and determination of camptothecin (CPT) alkaloids by CZE. Separation parameters such as the buffer type, pH, and concentration of the running buffer, the concentration of SBE‐β‐CD and IL, temperature, and separation voltage were all investigated in order to achieve the maximum possible resolution. The four analytes were baseline separated within 10 min in capillary at the separation voltage of 15 kV with a running buffer consisting of 20 mM borate buffer, 20 mM IL, and 100 mM SBE‐β‐CD at pH 9.0. Under such conditions, good linearity about two orders of magnitudes of peak areas was achieved for the investigated CPT alkaloids with the correlation coefficients ranging from 0.9946 to 0.9985. For all analytes, detection limits (S/N = 3) and quantitation limits (S/N = 10) range from 0.05 to 0.92 μg/mL and 0.17 to 3.06 μg/mL, respectively. The proposed method has not only been successfully applied to the separation and determination of CPT alkaloids but also showed that IL seemed to be a promising additive in CZE separation.     

Use of capillary electrophoresis with chemiluminescence detection for sensitive determination of homocysteine

A sensitive capillary electrophoresis (CE) method with chemiluminescence (CL) detection was developed for the determination of homocysteine (HCys) in human plasma. In this work, N‐(4‐aminobutyl)‐N‐ethylisoluminol was used as tagging reagent to label the analyte for achieving high assay sensitivity. N‐(4‐Aminobutyl)‐N‐ethylisoluminol‐tagged HCys after CE separation reacted with hydrogen peroxide in the presence of horseradish peroxidase, producing CL emission. Experimental conditions for labeling analyte, CE separation, and CL detection were studied. The CL intensity was proportional to the concentration of HCys in the range of 2.5×10^?8 to 5.0×10^?6 M. Detection limit (S/N=3) was 7.6×10^?9 M. Human plasma samples from healthy donors were analyzed by the presented method. HCys levels were found to be in the range of 9.50–15.3 μM.     

Solid‐phase purification and extraction for the determination of trace neonicotinoid pesticides in tea infusion

An analytical protocol that includes solid‐phase purification and extraction is successfully developed for the determination of trace neonicotinoid pesticides in tea infusion. The method consists of a purification on amino‐functionalized mesoporous silica SBA‐15 followed by a solid‐phase extraction based on graphene oxide before ultra high performance liquid chromatography with tandem mass spectrometry analysis. Parameters that significantly affected the extraction of the neonicotinoids onto graphene oxide, such as the amount of adsorbent, extraction time, pH, elution solvent, etc. were optimized. The amino‐functionalized mesoporous silica SBA‐15 has been proved to be an efficient adsorbent for removal of polyphenols especially catechins from tea infusion. Graphene oxide exhibits a very rapid adsorption rate (within 10 min) and high adsorption capacities for neonicotinoids at low initial concentration (0.01–0.5 mg/L). The analysis method gave a good determination coefficient (r² > 0.99) for each pesticide and high recoveries in the range of 72.2–95.0%. Powder X‐ray diffraction, Raman spectroscopy, transmission electron microscopy, and UV‐vis spectroscopy were utilized to identify the structure and morphology of graphene oxide. The adsorption driving force of neonicotinoids on graphene oxide mainly depends on π–π electron donor–acceptor interaction and electrostatic interaction.     

CZE separation of amitrol and triazine herbicides in environmental water samples with acid-assisted on-column preconcentration

A simple analytical scheme for the detection and quantification of amitrol and triazine herbicides (atrazine, ametryn and atraton) and degradation product (2‐hydroxyatrazine) in environmental water samples by CZE is reported. On‐column preconcentration of analytes from untreated water samples (mineral, spring, tap and river water) is accomplished by introducing an acid plug (200 mM citrate of pH 2.0) after the sample and then proceeding with the CZE separation, using 100 mM formiate buffer of pH 3.5 as running buffer and 25.0 KV as separation voltage. UV detection at 200 nm provides LODs from 50 to 300 nM in untreated samples and they were lowered tenfold by sample preconcentration by evaporation. Calculated recoveries were typically higher than 90%. Minimal detectable concentration of the electroactive amitrol could be decreased about 20‐fold when electrochemical detection was employed by monitoring the amperometric signal at +800 mV using a carbon paste electrode (LOD of 9.6 nM, 0.81 μg/L, versus 170 nM, 14.3 μg/L, using amperometric and UV detection, respectively) in untreated water samples.     

Simultaneous determination of phenylenediamine isomers and dihydroxybenzene isomers in hair dyes by capillary zone electrophoresis coupled with amperometric detection

The simultaneous determination of three isomers of phenylenediamines (o, m, and p-phenylenediamine) and two isomers of dihydroxybenzenes (catechol and resorcinol) in hair dyes was performed by capillary zone electrophoresis coupled with amperometric detection (CZE–AD). The effects of working electrode potential, pH and concentration of running buffer, separation voltage, and injection time on CZE–AD were investigated. Under the optimum conditions the five analytes could be perfectly separated in 0.30 mol L⁻¹ borate–0.40 mol L⁻¹ phosphate buffer (pH 5.8) within 15 min. A 300 μm diameter platinum electrode had good responses at +0.85 V (versus SCE) for the five analytes. Their linear ranges were from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁷ mol L⁻¹ (S/N = 3). This working electrode was successfully used to analyze eight kinds of hair dye sample with recoveries in the range 91.0–108.0% and RSDs less than 5.0%. These results demonstrated that capillary zone electrophoresis coupled with electrochemical detection using a platinum working electrode as detector was convenient, highly sensitive, highly repeatable and could be used in the rapid determination of practical samples. Figure Electropherograms obtained from 10 mg mL⁻¹ hair dye sample solutions at a platinum working electrode under optimum CZE–AD conditions: (a) natural black (I), (b) golden: (1) p-phenylenediamine, (2) m-phenylenediamine, (3) o-phenylenediamine, (4) resorcinol, and (5) catechol     

The role of mobile-phase pH in the determination of catecholamine-related compounds by reversed-phase liquid chromatography with amperometric detection

Summary A study was conducted for the optimization of the reversed-phase high performance liquid chromatographic separation of different types (acidic, basic, amphoteric and neutral) of catechol-related compounds by varying the pH. For pH to be used as the optimizing parameter, its effects on retention, peak width and peak shape had to be investigated. Therefore, the pH dependence of the amperometric detector response, as measured by the oxidation peak height or peak area, was taken into account.