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Conventional molecularly imprinted polymers (MIP)-based electrochemical sensors are generally susceptible to the changes of personal operation, electrode surface, and solution conditions. Herein, a ratiometric strategy was employed through introducing Cu

A space-confined synthesis method is employed for the preparation of a single-layer MoS2–boron doped ordered mesoporous carbon nanocomposite. A phenol-formaldehyde resin is used as carbon source to create a confined space for the formation of single-layer MoS2. The addition of pluronic F127, as a soft template, suppresses the stacking of MoS2 layers and makes the composite porous. The nanocomposite is characterized by scanning electron and transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The single-layer MoS2 sheets have a lateral size of about 5 nm and are uniformly embedded in the composite. They possess numerous active edge sites and display a strong synergistic effect with other components. The composite is modified on a glassy carbon electrode, followed by the electrochemical imprinting of theophylline, and the resulting electrode exhibits good electrochemical response to theophylline. The linear response range is 0.01–250 μM by differential pulse voltammetry, and the lower detection limit is 5 nM. It has been successfully applied to the determination of theophylline in spiked tea drink samples.

A novel method, based on the coupling of ionic liquid-based headspace single-drop microextraction (SDME) with gas chromatography (GC), is developed for the determination of chlorobenzene derivatives. For the SDME of five chlorobenzene derivatives, a 1.0 μL 1-octyl-3-methylimidazolium hexafluorophosphate microdrop is exposed for 20 min to the headspace of a 15 ml aqueous sample containing 20% (w/v) NaCl placed in 25 ml vial at 40 °C. Then, the extractant is directly injected into the injector block of the GC instrument. To avoid ionic liquid leaking into the chromatographic column, a small glass tube is placed in the injection block. Under optimized operation conditions, linear relation between peak areas and analyte concentrations up to 1.5 mg L−1 has been obtained The detection limits range from 0.1 to 0.5 μg L−1 for the various analytes. The relative standard deviations at 1.0 μg L−1 range from 7.7 to 12.4%, and the enrichment factors from 41 to 127. The method is simple and sensitive, and does not suffer from the influence of a solvent peak. Its applicability is demonstrated by the determination of chlorobenzenes in wastewater samples.

The voltammetric behavior of tannic acid (TA) on a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode has been investigated by cyclic voltammetry. TA can generate a well-defined anodic peak on the modified electrode at around 0.42 V (vs. SCE) in 0.10 M phosphate buffer solutions (pH = 4.0). The electrochemical reaction involves 1e transfer, accompanied by one proton. The electrode process is controlled by adsorption. The parameters affecting the response of TA, such as solution pH, accumulation time and accumulation potential are optimized for the determination of TA. Under the optimum conditions, the peak current changes linearly with the TA concentration in the range of 5.0 × 10−8–1.0 × 10−6 M. The lowest detectable concentration of TA is 8.0 × 10−9 M after 180 s accumulation. This method has been successfully applied to the determination of TA in tea and beer samples. In addition, the influence of potential interferents is examined. In the presence of bovine serum albumin, the peak current of TA decreases linearly due to the formation of a super-molecular complex.

A graphite powder – ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) paste coated gold electrode (graphite – BMIMPF6/Au) is presented. The area and the thickness of the paste film are controlled through a sticking film with a hole. The electrode shows good stability and high electric conductivity, and K4Fe(CN)6 exhibits reversible voltammetric peaks at it. A voltammetric study of promethazine revealed that promethazine exhibits a sensitive anodic peak in pH 6.7 buffer solutions. Under the optimized conditions, the peak current is linearly related to the promethazine concentration in the range of 5.0 × 10−8–5.0 × 10−5 M. A 5 µM promethazine solution is measured successively for ten times with the same electrode, the relative standard deviation (RSD) of peak current is 1.7%. The promethazine content in a Chinese medicine (i.e. Complex Reserpine) is determined. The result is in accordance with the declared value, and the recoveries are 96.1–104%.

The voltammetric behavior of folic acid (FA) at a multi-walled carbon nanotube (MWNT) modified gold electrode has been investigated by cyclic voltammetry, chronoamperometry and chronocoulome- try. The modified electrode exhibits a good promoting effect on the electrochemical reaction of FA. FA can generate a well-defined anodic peak at around 0.83 V (vs. SCE) in 0.1 M H3PO4-NaH2PO4 buffer solution of pH 2.5. The peak results from a 2-electron transfer of FA, and the standard potential of FA is estimated to be 0.79 V (vs. SCE). The parameters affecting the re- sponse of FA, such as solution pH, accumulation time, accumulation potential, and amount of MWNTs are optimized for the determination of FA. Under the opti- mum conditions, the peak current changes linearly with FA concentration in the range from 2.0� 10 � 8 Mt o 1.0� 10 � 6 M. This method has been applied to the determination of FA in drug tablets, and the recovery is 93.9-96.9%. In addition, the influence of some co- existent species is examined. When a Nafion layer is introduced on the gold electrode before deposition of MWNTs, the resulting composite electrode can give better response to FA. At the same time, the interference by some foreign species is suppressed to some extent.

The voltammetric behavior of uric acid was studied at a single-walled carbon nanotube (SWNT) modified gold electrode. Uric acid can effectively accumulate at this electrode and produce an anodic peak at about 0.45 V (vs. SCE) in pH 5.0 sodium acetate buffer solutions (HAc-NaAc). The experimental parameters, such as solution pH, accumulation time, and amount of SWNT, were optimized for determination. Under the optimum conditions, the anodic peak current is linear to the uric acid concentration over the range of 1.0×10−7 M to 2.5×10−5 M with a correlation coefficient of 0.998. The detection limit was 5.0×10−8 M for 60 s accumulation. The electrode could be easily regenerated and exhibited good stability. A 5.0×10−6 M uric acid solution was measured ten times using the same electrode, and the relative standard deviation of the peak current was 1.3%. This method was successfully applied to the determination of uric acid in human urine samples, and the recovery was 97–99%. The feasibility for simultaneous determination of xanthine, ascorbic acid and uric acid was discussed. These species did not interfere with each other in a certain concentration range. The influence of some surfactants on the anodic peak was also examined.

A multi-walled carbon nanotube and dode-canethiol (DDT) modified gold electrode (i.e. MWNTs/DDT/Au) was prepared and characterized. When the gold electrode was modified with a DDT self-assembled monolayer (SAM) followed by a MWNT film, the electrode area increased by a factor of about 4. At the same time, the blocking action of the DDT SAM with respect to electron transfer disappeared. The conductivity of MWNT wires imbedded in the DDT SAM was thought to account for that. The resultant electrode was more stable than MWNTs/Au and more sensitive than MWNTs/GC. At the MWNTs/DDT/Au, prochlorperazine exhibited two anodic peaks at about 0.69 V and 0.88 V in pH 5.8 phosphate buffer solution. The peak at about 0.69 V was suitable for prochlorperazine determination. After an accumulation time of 180 s in an open circuit, the peak current was linear to prochlorperazine concentration over the range of 5×10−7 M–1.5×10−5M with correlation coefficient of 0.995; the detection limit was 1×10−7 M. Compared to DDT/Au, this electrode regenerated easily by repetitive cycling in a blank solution.