•Two strategies were applied to investigate the photochemical reaction mechanism in CE.•A rapid, simple and sensitive method for determination of seven essential amino acids was developed.•This method shows a great potential for the rapid and sensitive detection of low or non-UV absorbing compounds.Some low or non-UV absorbing compounds like amino acids might be accessible to direct UV detection by capillary electrophoresis (CE), due to the photochemical reaction in the detection window of the separation capillary under extremely strong alkaline conditions. However, with regards to the photochemical reaction procedure and the influencing factors in CE, no comprehensive studies have been done. Herein, two strategies were applied to investigate the photochemical reaction mechanism including the introduction of an additional UV lamp and the utilization of driving pressure. The former confirmed the occurrence of photolysis, while the latter solved the interference of electroosmotic flow (EOF). Furthermore, the online photochemical reaction and online preconcentration technique were combined to develop a rapid, simple and sensitive method for determination of seven essential amino acids (valine, leucine, phenylalanine, methionine, tryptophan, threonine and lysine). Eventually, the developed method was successfully applied to the analysis of real samples with good reproducibility and reliability. This novel and simple method, based on the photochemical reactions occurring in the detection window and coupling with online preconcentration techniques, shows a great potential for the rapid and sensitive detection of low or non-UV absorbing compounds.Two strategies were applied to investigate the photochemical reaction mechanism including the introduction of an additional UV lamp and the utilization of driving pressure.

•A new strategy to fabricate SWCNTs array-based electrochemical chiral sensor was presented.•Its practicability was validated by chirally recognizing 3,4-dihydroxyphenylalanine as a model molecule.•This method enriches the fabrication of SWCNTs array and the preparation of chiral interface at electrodes.How to align the single-walled carbon nanotubes (SWCNTs) onto the electrode vertically and to control their density and orientation are still a major challenge. Theoretically, properly selected chiral SWCNTs can discriminate enantiomers through their different dielectric response to the adsorption of chiral species, few reports can confirm this theoretic model. Herein, we presented a new strategy to fabricate SWCNTs array-based electrochemical chiral sensor. Carboxylated chiral SWCNTs were vertically attached to the oxidized glass carbon electrode with ethylenediamine as a linker by electrosynthesis. The electrode surface was characterized with atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The practicability of the sensor was validated by chirally recognizing 3,4-dihydroxyphenylalanine as a model molecule. We found that both the highly ordered standing of SWCNTs and the application of square wave voltammetry (SWV) amplified the intrinsic chirality of chiral SWCNTs.A new strategy to fabricate SWCNTs array-based electrochemical chiral sensor was presented.

A simple, cheap and practicable miniaturized electrochemical device based on a biconical microchannel was developed, for which only 1 μL sample solution was needed to implement a typical electrochemical experiment. The practicability of the designed device was validated by detecting uric acid as a model molecule in human serum.

A sensitive, rapid and simple CE-UV method with large-volume sample stacking (LVSS) and polarity switching has been developed and validated for the analysis of copper(I) and copper(II) simultaneously. Benefiting from the combination of the LVSS method, a limit of detection (LOD) of 30 nM was obtained which was much lower than those of the current detection methods. Several factors, such as the concentration and pH of the background solution, injection time and pressure, stacking voltage and inversion electric current, were systematically optimized. Under the optimum conditions, the detection limits of copper(I) and copper(II) were improved nearly 1000 times compared with the conventional methods by CE-UV, which made it possible to determine trace copper in cell specimens. Eventually, the proposed method was successfully applied to detect copper(I) and copper(II) in spiked cell samples with good recoveries.

We developed a simple, cheap and bidirectional ionic current rectification system based on the integration of a biconical micro-channel, working electrode and reference electrode. This system may have potential and realistic future value for studying two-way ionic transport in the cell membrane.

A rapid, sensitive and cost-effective CE-UV method has been developed for the simultaneous separation and sensitive determination of clenbuterol, salbutamol, ractopamine and fenoterol in pig blood and human urine samples. Field-enhanced sample injection (FESI) as an effective online concentration technique was applied to improve the detection sensitivity of β2-agonists. Several factors, such as the concentration and pH of the background solution, sample matrix, injection time and voltage, and the length of the water plug, were systematically optimized. Under the optimum conditions, the detection limits of the β2-agonists range from 2.7 to 7.2 nM, which were improved nearly 2000 times by CE-UV compared with conventional methods, except for fenoterol. Eventually, the proposed method was successfully applied to the analysis of spiked blood and urine samples with good recoveries, which provides a novel method to monitor the illegal use of β2-agonists in athletes and livestock.

We demonstrate, for the first time, an electrochemical sensor that provides antipodal signals upon application of square wave voltammetry (SWV), for enantioselective recognition of 3,4-dihydroxyphenylalanine based on chiral single-walled carbon nanotubes (SWCNTs) in the presence of sulphuric acid. Interestingly, the enantioselectivity was not observed using the common method of cyclic voltammetry (CV) but the SWV peak currents of enantiomers were found to be quite different and hence the enantiomers could be successfully recognized. Moreover, the antipodal signals provided by two SWV scan modes offer the possibility for results to be confirmed mutually, showing a great practical value and analytical application prospects.

•The trace copper in cell is determined by the proposed CE2–FESI method.•This method covers the simplicity of cell extraction and the power of CE–FESI.•The application of such a CE2–FESI method proved its promising value in cell analysis.A new separation system of capillary electrophoresis (CE1) for the highly sensitive determination of copper was established by using ethylenediaminetetraacetic acid (EDTA) as a complexing agent and employing cetyltrimethylammonium chloride (CTAC) as a capillary inner wall modifier. Benefitted from the combination of field-enhanced sample injection (FESI) method, a limit of detection (LOD) of 2.7 nM was obtained, which was much lower than that of the conventional methods. This made it possible to determine trace copper in HeLa cell only by a simple cell extraction (CE2) treatment. Two copper-extraction methods—acid-hydrolysis and freeze–thaw—were compared. Limited by the requirement of low ion strength in FESI, only the extract using freeze–thaw could be successfully applied in the determination. The effectiveness assessment of this CE2–FESI method was adopted by inductively coupled plasma-atomic emission spectrometry (ICP-AES) as a gold standard.The trace copper in cell is determined by using a simple cell extraction and capillary electrophoresis combined with field-enhanced sample injection (CE2–FESI).

A novel chiral electrochemical sensor based on multi-walled carbon nanotubes (MWCNTs)/ionic liquids (ILs) nanocomposite was developed and applied to the enantiomeric recognition of propranolol (PRO). Mechanisms for chiral sensing were discussed in terms of the formation of an efficient chiral nanospace originating from the weak interactions between quasi-chiral MWCNTs and versatile ILs. This work provided new evidence that the electro-oxidation of PRO should result from its hydroxyl group. Herein the ratio of oxidation peak currents, instead of the commonest shift of peak potential, was used to sense the enantiomeric fraction (EF) of (R)-PRO with a linear correlation coefficient of 0.9936. This simple and reliable sensor was successfully applied in an accurate determination of the enantiomeric purity of reagent, as well as the evaluation of waste water treatment efficiency.Highlights► A novel chiral electrochemical sensor for propranolol is developed. ► Chiral sensing results from an efficient chiral nanospace regarding quasi-chiral MWCNTs and versatile ILs. ► Its application to rapid detection of EF values matches the therapeutical and environmental needs.

Successful simultaneous enantioseparation and sensitive determination of three β-blockers (PIN, OX and PRO), have been achieved by capillary electrophoresis using an achiral ionic liquid, [GTMA]Cl, as a modifier to cooperate with dual CDs containing DM-β-CD and TM-β-CD. The influence of aIL was investigated in details, including various aILs, the concentration of aIL and molar ratio of aIL to CD. The ratio of DM-β-CD to TM-β-CD in dual CDs was also discussed. DM-β-CD and TM-β-CD favor the enantioseparations of PIN/OX and PRO, respectively. Meanwhile, the presence of [GTMA]Cl was found to play a key role in enantioseparations, and it widened the scope of application of DM-β-CD and TM-β-CD. Furthermore, FESI as an effective on-line sample enrichment technique was developed to improve the detection sensitivity. Under the optimum conditions, the detection limits of the three pairs of enantiomers range from 0.10 to 0.65 nM, which are much lower than those in the conventional methods. Eventually, the proposed method was successfully applied to the analysis of spiked urine sample with good recoveries.Highlights► The combination of aIL and dual CDs enhances the enantioseparation of β-blockers. ► We propose a hypothesis of enantioseparation mechanism using [GTMA]Cl and HDTM-β-CD. ► With FESI the LOD of the three pairs of enantiomers are greatly improved.

Gold nanoparticles (GNPs) embedded in a Bucky gel consisting of carbon nanotubes (CNTs) and ionic liquid (IL) show an excellent electrocatalytic activity to glucose oxidation owing to some synergistic effects among GNPs, CNTs and IL. Each component in such a composite has its specific function while there are complicate interactions among them. Based on this strategy, the use of composite as the modified coating allows the fabrication of a novel nonenzymatic glucose electrochemical sensor, which shows a substantial enhancement in detection sensitivity. This paper centers on the influence of several ILs with various anions and cations as well as alkyl branch lengths on the function of sensor. Based on our results, the performance of the sensor is strongly influenced by ILs. A few conclusions can be drawn. Firstly, an imidazolium cation facilitates both the stability of sensor and the efficiencies of GNPs and CNTs, while the alkyl branch lengths have few effects on the performance of sensor. Secondly, a hydrophilic anion is beneficial to the formation of environment where the direct oxidation of glucose takes place. Thirdly, other anions such as BF4− and PF6− do not matter for imidazolium-based IL. Fourthly, non-imidazolium-based IL militates against the dispersion of CNTs and GNPs in Bucky gel, reducing the detection sensitivity to glucose. Of the ILs studied, the best performance for glucose determination is obtained with an IL mainly benefitted by the combination of imidazole and sulfonate.

A reliable and highly sensitive electrochemical sensor was first developed for analysis of non-electroactive melamine (Mel) based on its conversion to an electroactive complex by coordination of copper salt to Mel. This provides a simple and easy approach to the detection of Mel in milk products.

In this paper, a novel nonenzymatic glucose voltammetric sensor based on a kind of nanocomposite of gold nanoparticles (GNPs) embedded in multi-walled carbon nanotubes (MWCNTs)/ionic liquid (IL) gel was reported. The surface morphology of this nanocomposite was characterized using X-ray photoelectron spectrometer (XPS), scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. It can be found that most of GNPs lie close to the ektexine of MWCNTs and the others have obviously inserted the inner of MWCNTs through the defects or ends of MWCNTs, due to the attraction between GNPs and MWCNTs as well as the repulsion between GNPs and IL. Voltammetry was used to evaluate the electrocatalytic activities of the nanocomposite biosensor toward nonenzymatic glucose oxidation in alkaline media. The GNPs embedded in MWCNTs/IL gel have strong and sensitive voltammetric responses to glucose, owing to a possible synergistic effect among GNPs, MWCNTs and IL. Under the optimal condition, the linear range for the detection of the glucose is 5.0–120 μM with the correlation coefficient of 0.998, based on the oxidation peak observed during cathodic direction of the potential sweep. The kinetics and mechanism of glucose electro-oxidation were intensively investigated in this system. This kind of nanocomposite biosensor is also highly resistant toward poisoning by chloride ions and capable of sensing glucose oxidation in the presence of 20 μM uric acid and 70 μM ascorbic acid. This work provides a simple and easy approach to the detection of glucose in body fluid with high sensitivity and excellent selectivity.

The chiral resolution of three beta-blockers including propranolol, pindolol and oxprenolol, was studied by affinity electrokinetic chromatography. The effect of various chiral selectors and some key parameters including buffer pH, buffer concentration, capillary temperature and applied voltage were carefully studied, respectively. At optimum condition, based on the signal-to-noise ratio of 3, the detection limits for the simple resolution and chiral resolution were found to be 1.0 × 10−5 and 4.0 × 10−5 M, respectively. In addition, the interactions of these beta-blockers with bovine serum albumin (BSA) were studied and the binding constant (Ka) between BSA and each of beta-blockers were calculated. Based on linear correlation coefficient, it can be concluded that the binding ratio of pindolol (oxprenolol) combining with BSA is 1:1, and that the binding number of propranolol interacting with BSA deviates one.

The electrochemistry of dopamine (DA) was studied by cyclic voltammetry at a glassy carbon electrode modified by a gel containing multi-walled carbon nanotubes (MWNTs) and room-temperature ionic liquid of 1-octyl-3-methylimidazolium hexafluorophosphate (OMIMPF6). The thickness of gel on the surface of the electrode has to be controlled carefully because the charging currents increase with the modified layer being thicker. The anodic peaks of DA, ascorbic acid (AA) and uric acid (UA) in their mixture can be well separated since the peak potential of AA is shifted to more negative values, while that of UA is shifted to more positive values due to the modified electrode. At pH 7.08 the three peaks are separated ca. 0.20 and 0.15 V, respectively; hence DA can be determined in the presence of UA and more than 100 times excess of AA. Under optimum conditions linear calibration graphs were obtained over the DA concentration range 1.0 × 10−6 to 1.0 × 10−4 M. The detection limit of the current technique was found to be 1.0 × 10−7 M based on the signal-to-noise ratio of 3. The modified electrode has been successfully applied for the assay of DA in human blood serum. This work provides a simple and easy approach to selectively detect dopamine in the presence of ascorbic acid and uric acid.

A reliable and highly sensitive electrochemical sensor was first developed for analysis of non-electroactive melamine (Mel) based on its conversion to an electroactive complex by coordination of copper salt to Mel. This provides a simple and easy approach to the detection of Mel in milk products.

We developed a simple, cheap and bidirectional ionic current rectification system based on the integration of a biconical micro-channel, working electrode and reference electrode. This system may have potential and realistic future value for studying two-way ionic transport in the cell membrane.