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The voltammetric behavior of uric acid (UA) has been studied at a multiwalled carbon nanotube-ionic liquid (i.e., 1-butyl-3-methylimidazolium hexafluorophosphate, BMIMPF6) paste coated glassy carbon electrode (MWNTs-BMIMPF6/GC). It is found that UA can effectively accumulate at this electrode and cause a sensitive anodic peak at about 0.49 V (vs. SCE) in pH 4.0 phosphate buffer solutions. Experimental parameters influencing the response of the electrode, such as solution pH and accumulation time, are optimized for uric acid determination. Under the optimum conditions, the anodic peak current is linear to UA concentration in the range of 1.0×10−8 M to 1.0×10−6 M and 2.0×10−6 M to 2.0×10−5 M. The detection limit is 5.0×10−9 M for 180 s accumulation on open circuit. The electrode can be regenerated by successively cycling in a blank solution for about 3 min and exhibits good reproducibility. A 1.0×10−6 M UA solution is measured for eight times using the same electrode regenerated after every determination, and the relative standard deviation (RSD) of the peak current is 3.2%. As for different electrodes fabricated by the same way the RSD (i.e., the electrode to electrode deviation) is 4.2%(n=9). This method has been applied to the determination of UA in human urine samples, and the recoveries are 99%–100.6%. In addition, comparison is made between MWNTs-BMIMPF6/GC and MWNTs/GC. Results show that the MWNTs-BMIMPF6/GC exhibits higher sensitivity, selectivity and ratio of peak current to background current.

The voltammetric behavior of rutin at a single-walled carbon nanotubes (SWNTs) modified gold electrode has been investigated. At the modified electrode rutin can generate a pair of peaks when the solution pH is smaller than 11. In a 0.1 M phosphate buffer solution (pH 5.0), the peak potentials are about 0.35 V, which changes with scan rate. The electrochemical reaction involves two electron transfer, accompanied by two protons. The electrochemical process is controlled by adsorption. The adsorption mode of rutin at the modified electrode basically belongs to Langmuir adsorption and the maximum adsorption amount is estimated to be about 1.4 × 10−9 mol cm−2. The diffusion coefficient of rutin in the solution is determined to be about 2.0 × 10−5 cm2 s−1. The experimental conditions such as solution pH, accumulation time and accumulation potential, are optimized. Under the selected conditions (i.e. solution pH 5.0 and accumulation time of 210 s under open circuit), the peak current is linear to the rutin concentration over the range of 2.0 × 10−8 M to 5.0 × 10−6 M, and the detection limit is estimated to be 1.0 × 10−8 M. The method has been applied to the determination of rutin in drug tablets and flos sophorae buds, and the recoveries are 98–105%. The electrode exhibits good stability and reproducibility. In addition, the influence of various foreign species has been studied. It is observed that in the presence of hemoglobin the peak current of rutin decreases linearly, which can be used for the indirect determination of hemoglobin.

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 adsorptive and stripping behavior of methylene blue (i.e. methylene blue chloride, MB) at a gold electrode has been studied with voltammetry, alternating current impedance spectra (ACIS) and quartz crystal microbalance (QCM). MB exhibits a pair of cyclic voltammetry peaks at about −0.3 V (versus SCE) in 0.05 M pH 6.9 phosphate buffer solutions. In the presence of cationic gemini surfactants such as C 16 H 33 N(CH 3 ) 2 –C 4 H 8 –N(CH 3 ) 2 C 16 H 33 Br 2 (C 16 –C 4 –C 16 ), C 16 H 33 N(CH 3 ) 2 –C 4 H 7 OH–N(CH 3 ) 2 C 16 H 33 Br 2 (C 16 –C 4 OH–C 16 ), C 16 H 33 N(CH 3 ) 2 –CH 2 –C 6 H 4 –CH 2 –N(CH 3 ) 2 C 16 H 33 Br 2 (C 16 –ph–C 16 ) and C 16 H 33 N(CH 3 ) 2 –C 12 H 24 –N(CH 3 ) 2 C 16 H 33 Br 2 (C 16 –C 12 –C 16 ), the anodic peak grows rapidly and moves in positive direction, but the cathodic peak gradually decreases, due to the association adsorption and electrostatic interaction of the geminis with MB and its reduced product (i.e. leuko methylene blue, LMB). With the aid of geminis the adsorption amount of MB increases under open-circuit, but the impedance of the mixed adsorption film to Fe(CN) 6 3−/4− almost keeps unchanged, compared with either bare gold electrodes or MB film, while the adsorption film of geminis exhibits greater impedance. This probably is due to the electron medium action of MB in the film. Gemini surfactants with same alkyl-chain (i.e. –(CH 2 ) 15 CH 3 ) but different molecular structure, exhibit different influence. The enhancing action of geminis studied follows such order as: C 16 –ph–C 16 > C 16 –C 4 –C 16 > C 16 –C 4 OH–C 16 > C 16 –C 12 –C 16 . The change of peak potential was ascribed to the interaction between MB and surfactants, as well as the blocking action of surfactant film. For comparison, the influence of dihexadecyldimethylammonium bromide (DCAB) and cetyltrimethylammonium bromide (CTAB) was studied, and the influence of other factors is discussed as well.

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.

The voltammetric behavior of methylene blue (MB, or MB+ in solution) at a silver electrode has been studied. MB+ can exhibit a cathodic peak at about −0.2 V (vs. SCE), while the electrogenerated LMB (leucomethylene blue) exhibits an anodic peak at almost the same potential in neutral phosphate buffer. In the presence of some surfactants such as cetyltrimethylammonium bromide (CTAB), cetylpyridinium bromide (CPB) and gemini surfactant butyl-α,ω-bis(dimethylcetylammonium bromide) (C16C4C16), the peaks, specially the anodic peak, become higher and shift to more positive potentials. This results from the associated adsorption or surface complexation of LMB/MB+ with adsorbed surfactants. Surfactants with same alkyl chain (i.e., (CH2)15CH3) but different molecular structure, show different influence due to their different adsorbability and hydrophobicity. C16C4C16, bearing two hydrophobic alkyl chains, makes the MB peaks occur at more positive potentials, while CPB makes the peaks grow more rapidly. Dihexadecyldimethylammonium bromide (DCAB), showing weaker adsorption under this condition, has little influence on the peak height of MB. The influence of other factors is discussed as well.

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.

The voltammetric behavior of 2-thiouracil at a silver electrode is described. 2-Thiouracil can deposit or chemisorb anodically at silver surface; when the potential is made more negative the deposited 2-thiouracil undergoes reductive desorption-process, yielding a cathodic peak at about −1.2 V (vs. SCE) in basic phosphate buffer solution (pH 10.3). In the presence of cationic gemini surfactant C4H8–1,4-(C16H33N+ (CH3)2Br−)2 (C16–C4–C16) the deposition of 2-thiouracil is greatly improved and the cathodic peak is enhanced. Meanwhile, the peak shifts to more negative potential. The role of C16–C4–C16 is thought to combine and coadsorb with 2-thiouracil at silver surface as well as reduce the electrostatic repulse in the deposited film, thus making it more easy to deposit and desorb at more negative potential. With C16–C4–C16 the lateral interaction of deposits reduces, the reductive desorption becomes faster and the cathodic peak becomes sharper. For geminis with different spacer groups and alkyl chains, their influence is mainly determined by their hydrophobicity and adsorbability. It was found that increasing length of alkyl chain was favorable for obtaining a high and sharp desorption peak, whose peak potential is more negative. For comparison, surfactants with single alkyl-chain and double alkyl-chain, such as cetyltrimethyl ammonium bromide and dicetyldimethyl ammonium bromide were studied. They made the desorption peak shift less due to their weaker combination with 2-thiouracil.

An electrochemical study of a deposition membrane of l -glutathione (GSH) and cetylpyridinium bromide (CPB) at polycrystalline Ag electrodes has been carried out. It is found that a deposition membrane containing GSH and CPB can form at the Ag electrode after deposition at 0.05 V (vs. SCE) from a solution containing both compounds, and this has been confirmed by cyclic voltammetry, IR and XPS spectroscopy. At pH 9.7, this deposition membrane gives a well-defined cathodic peak at about −1.1 V, accompanied by the appearance of multiple anodic peaks. Further investigation suggests that the cathodic peak should be attributed mainly to the reduction of CPB rather than the reductive desorption of GSH. The influence of deposition potential, deposition time, CPB concentration, pH and concentration of base solution and other surfactants on the transfer reaction of the deposition membrane were all investigated, and information on the formation of the deposition membrane was obtained. Many thio compounds and surfactants have been used for comparison. It was found that both the mercapto and carboxy groups play important roles in the formation of the mixed deposition membrane.

Surfactants are sometimes used to improve the accumulation of some electroactive organic compounds, but anionic surfactants have seldom been utilized for such a purpose yet. In this paper, the influence of the anionic surfactant sodium dodecylsulfate (SDS) on the accumulation of ethopropazine (EPZ) at a polycrystalline gold electrode has been studied. EPZ exhibits an anodic peak at about 0.67 V (vs. SCE) and a shoulder in pH 3.5 citric acid–biphthalate buffer solution. In the absence of SDS, the peak is small and ill defined, but it becomes high and well shaped when SDS is added. This results from the adsorption of EPZ in the SDS membrane, which forms spontaneously on the gold electrode surface. For both cases EPZ shows the same electrode reaction mechanism, which is similar to that of promethazine (PMZ). The influence of other factors, such as pH value, variety and concentration of buffers, other surfactants, accumulation potential and time etc has been discussed. It was found that only the anionic surfactants had an enhancement effect on the EPZ accumulation. Also, the solution should be acidic or neutral so as to maintain the interaction due to its electrostatic nature. The optimum SDS concentration for EPZ accumulation is about 0.1 mM regardless of whether or not an accumulation potential is adopted. When all the experiment conditions are optimized, the peak current of the anodic peak changes linearly with the concentration of EPZ over the range 0.4–4 μM, and is thus of analytical significance.

The interaction of DNA with several new synthesized gemini surfactants R-α,ω-(C16H33N+(CH3)2Br−)2 (R=C6H12, C12H24, CH2CHOHC2H4 and CH2C6H4CH2) and the construction of DNA–gemini films formed on gold electrode surface were investigated with electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. It was found that these surfactants could be bound to DNA, driven by the electrostatic and hydrophobic interaction between DNA and surfactants, and the driving force strength was related to the structure of the spacer group of gemini surfactants. Among these gemini surfactants, C6H12-1,12-(C16H33N+(CH3)2Br−)2 was bound to DNA, mainly driven by its hydrophobic interaction with DNA due to the strong hydrophobicity and flexibility of its spacer group, while others were bound to DNA, mainly driven by electrostatic interaction with DNA because of their relatively poor hydrophobicity and flexibility. Multi-layer films composed of DNA and R-α,ω-(C16H33N+(CH3)2Br−)2 were prepared at gold electrodes, based on their interaction, and the electrochemical property of the resulted modified electrodes was mainly determined by the out-layer. It was found that the first R-α,ω-(C16H33N+(CH3)2Br−)2 layer markedly neutralized the negative charges of DNA and the second R-α,ω-(C16H33N+(CH3)2Br−)2 layer made the film density increase. Keywords: Gemini surfactants, DNA, Cyclic voltammetry, Electrochemical impedance spectroscopy, Gold electrode

Epinephrine (EP) could exhibit an anodic peak at a bare gold electrode, but it was very insensitive. However, when the bare gold electrode was modified with 3-mercaptopropionic acid (3MPA) self-assembled monolayer (3MPA SAM), the peaks of EP became more reversible and sensitive due to the accumulation and mediate efficiency of 3MPA SAM. Conditions such as solution pH, concentration of supporting electrolyte and accumulation time were optimized. Under the selected conditions (i.e., 0.02 M pH 6.8 sodium phosphate buffer, accumulation time: 2 min under open- circuit.), the height of the anodic peak at about 0.18 V (vs. SCE) was linear to EP concentration in the range of 2×10−7 −1×10−6 M and 1×10−6−5×10−4 M with correlation coefficient of 0.995 and 0.999, respectively. When the 3MPA/Au was further modified with cysteamine, the interference of H2O2 and BrO3− was eliminated. But the resulting electrode still suffered from the interference of ascorbic acid. This method was used to determine the content of EP in adrenaline hydrochloride injections, and the recovery was in the range of 97.0% to 105.1%.

The voltammetric behavior of methylene blue (MB) at thiol self-assembled monolayers modified gold electrodes (SAMs/Au) has been investigated. MB exhibited a redox peak at about −0.35 V (vs.SCE) in alkaline solution at bare gold electrodes. When the gold electrodes were modified with thiol SAMs, the peak grew due to the accumulation of MB at SAMs. With the solution pH rising, more MB was accumulated, hence the peak height increased, which differed from that at bare gold electrodes. The electrode process at SAMs/Au featured the characteristics of adsorption and/or electrode reaction controlled. The enhancing action of glutathione monolayer (GSH SAM), 3-mercaptopropionic acid monolayer (3MPA SAM) and other thiol SAMs was compared. Among these, GSH SAM made the MB peak increase more. At GSH SAM/Au, the peak height varied linearly with MB concentration over the range of 2 μM to 400 μM. So this can be developed for the determination of MB and studies concerned. The accumulation behavior caused by GSH SAM and native fish sperm dsDNA was compared. The interaction between DNA and MB was also discussed under this condition.

Silver ions can be entrapped at the dl -dithiothreitol (HSCH 2 (CHOH) 2 CH 2 SH, DTT) self-assembled monolayer films modified gold electrodes. When the potential was made moving, an anodic peak was observed at about 0.23 V (vs. SCE). When the electrode Au/DTT was modified with dodecyl mercaptan further, more Ag (I) can be accumulated and the peak grows. Conditions, such as solution pH and supporting electrolyte, were optimized for Ag (I) determination. Under the selected conditions, i.e. 0.010 M pH 4.3 potassium hydrogen phthalate, preconcentration time of 5 min at open circuit, the anodic peak height is linear to the concentration of Ag (I) in the small range of 0.6–2.4 μM. The influence of some ions on the determination of Ag (I) was examined. The Br − ion makes the peak decrease and NCS − makes the peak increase. But the determination is not interfered by 1000-fold Pb 2+ , Cd 2+ , Hg 2+ , Fe 3+ , Ni 2+ , Co 2+ , Cu 2+ and Sn 2+ when EDTA was added into the solution. The mechanism involved was discussed.

In the presence of l-cysteine (l-cys), cetylpyridium chloride (CPC) exhibited a sensitive cathodic stripping peak at about −1.2 V (vs SCE). The square root of the peak height was linear with CPC concentration over the range of 2 µM to 50 µM, with a slope of 0.124 µA1/2/µM. This was developed for the determination of CPC concentration. The peak was thought to be generated by l-cys; CPC could catalyze/promote the electrochemical process and thus make the peak grow rapidly. However, other surfactants tested such as cetyltrimethyl ammonium bromide (CTAB) or sodium dodecyl sulfonate (SDS) did not behave so. Conditions such as solution pH, deposition potential and accumulation time were discussed. It was found that the cathodic stripping peak was well defined in 40 mM pH 10.9 sodium phosphate solutions; the optimum deposition potential was 0.5–0.1 V.

Gold electrode modified with N-acetyl-l-cysteine was studied by voltammetry and impedance spectroscopy. It was found that this modified electrode exhibited an excellent sensitivity and selectivity for Cu(II) determination. Conditions of determination were optimized, including parameters that govern the sensitivity and selectivity of this system. Under the optimum conditions, i.e., acetate buffer 0.01 M pH 4.0, modification time 5 h, preconcentration time 7 min, the N-acetyl-l-cysteine modified electrode showed two dynamic ranges of six orders of magnitude (from 10−10 to 10−7 M and from 10−7 to 10−4 M) and the detection limit as low as 1 × 10−10 M. The organic monolayer modified electrode was stable and simple to prepare. The method has been applied to the determination of Cu(II) in a reference material, East Lake water with 0.01 µM Cu(II).

A novel proton-type ionic liquid doped polyaniline (HIL-doped PANI) coating was presented, which was prepared on a stainless steel wire by electrodeposition in an aqueous solution containing aniline and 1-sulfobutyl-3-methylimidazolium hydrosulfate. The HIL-doped PANI coating showed granular nanostructure and had large specific surface. When it was applied to the headspace solid-phase microextraction of several amines (i.e., aniline, N -methylaniline, 3-methylaniline, 2-chloroaniline and 3-chloroaniline), it showed high extraction efficiency. The enrichment factors were 191.8–343.9 for different amines, much higher than those of common PANI and commercial polydimethylsiloxane/divinylbenzene coatings. Coupled with gas chromatographic analysis, the linear ranges were 0.097–100 μg/L with correlation coefficients above 0.9942, and the detection limits were 0.012–0.048 μg/L (S/N = 3) for different amines. The relative standard deviations (RSD) were smaller than 8.1% for five successive measurements with single fiber and the fiber-to-fiber RSDs were 8.6–13.8% ( n = 5) for these amines. The proposed method was successfully applied to the extraction and determination of amines in organic waste water samples, and the recoveries were 78.3–112.8% for different analytes.

Hollow AuPd (hAuPd) alloy nanoparticles (NPs) were prepared through simultaneous reduction of HAuCl4 and Na2PdCl4 using Co NPs as sacrificial template (i.e., reductant). Then, the hAuPd NPs were assembled on nitrogen-doped graphene (NG) to prepare an NG-hAuPd hybrid film. The obtained NG-hAuPd composite showed higher electrocatalytic activity toward the reduction of H2O2, compared with graphene-hAuPd hybrid, NG-solid AuPd hybrid, and hAuPd NPs. The enhanced performance was related to the hollow structure of hAuPd NPs and the synergistic effect between NG and hAuPd NPs. Under optimum conditions, the NG-hAuPd hybrid film showed a linear response to H2O2 in the range of 0.1-20 μM, with a sensitivity of 5095.5 μA mM(-1) cm(-2)and a comparable detection limit of 0.02 μM (S/N = 3). These results demonstrated that the NG-hAuPd composite was a promising electrocatalytic material for constructing sensors, etc.

A polycarbazole film was electrodeposited on a stainless-steel wire from a solution of N,N-dimethylformamide/propylene carbonate (1:9 v/v) containing 0.10 M carbazole and 0.10 M tetrabutylammonium perchlorate. The obtained polycarbazole fiber was immersed into an ionic liquid (1-hydroxyethyl-3-methyl imidazolium bis[(trifluoromethyl)sulfonyl]imide) solution (in dimethylsulfoxide) for 30 min, followed by drying under an infrared lamp. The resulting polycarbazole/ionic liquid fiber was applied to the headspace solid-phase microextraction and determination of aromatic esters by coupling with gas chromatography and flame ionization detection. Under the optimized conditions, the limits of detection were below 61 ng/L (S/N = 3) and the linear ranges were 0.061-500 μg/L with correlation coefficients above 0.9876. The relative standard deviations were below 4.8% (n = 5) for a single fiber, and below 9.9% for multi-fiber (n = 4). This fiber also exhibited good stability. It could be used for more than 160 times of headspace solid-phase microextraction and could withstand a high temperature up to 350°C.

In this work, a three-dimensional hybrid film with in- and out-of-plane pores was fabricated by using porous graphene as framework structure and porous PdCu alloy nanoparticles as building blocks. The porous PdCu alloy nanoparticles were prepared by chemical dealloying with acetic acid. The hierarchical pores had abundant active catalytic sites, and the material exhibited remarkable catalytic activity toward the oxidation of hydrazine. Based on this hybrid film, an electrochemical sensor of melamine was developed by further introducing melamine imprinted electro-polymer of para-aminobenzoic acid. Melamine was detected by differential pulse voltammetry using hydrazine as electrochemical probe. The detection signal was amplified due to the catalytic oxidation of hydrazine at this hybrid film. The linear determination range was 0.01-1 μM and the detection limit was 2 nM (S/N = 3). The sensor displayed high recognition capacity toward melamine and also showed good reproducibility and stability. It is promising in the determination of melamine in real samples.

A novel poly(3,4-ethylenedioxythiophene)-ionic liquid (i.e., 1-hydroxyethyl-3-methyl imidazolium-bis[(trifluoromethyl)sulfonyl]imide) composite film was electrodeposited on a Pt wire for headspace solid-phase microextraction. The film showed nodular structure and had large specific surface. In addition, it displayed high thermal stability (up to 300 °C) and durable property (could be used for more than 200 times). Coupled with gas chromatography-flame ionization detection, the resulting fiber was applied to the headspace solid-phase microextraction and determination of several alcohols (i.e., linalool, nonanol, terpineol, geraniol, decanol and dodecanol). It presented higher extraction capability in comparison with the poly(3,4-ethylenedioxythiophene) and commercial polydimethylsiloxane/divinylbenzene fiber. Under the optimized conditions, the linear ranges exceeded three magnitudes with correlation coefficients above 0.9952 and the low limits of detection were 34.2–81.3 ng L−1. For different alcohols the repeatabilities (defined as RSD) were

Herein, we present a novel electrochemical sensor for the determination of chloramphenicol (CAP), which is based on multiwalled carbon nanotubes@molecularly imprinted polymer (MWCNTs@MIP), mesoporous carbon (CKM-3) and three-dimensional porous graphene (P-r-GO). Firstly, 3-hexadecyl-1-vinylimidazolium chloride (C16VimCl) was synthetized by using 1-vinylimidazole and 1-chlorohexadecane as precursors. Then, C16VImCl was used to improve the dispersion of MWCNT and as monomer to prepare MIP on MWCNT surface to obtain MWCNTs@MIP. After that, the obtained MWCNTs@MIP was coated on the CKM-3 and P-r-GO modified glassy carbon electrode to construct an electrochemical sensor for the determination of CAP. The parameters concerning this assay strategy were carefully considered. Under the optimal conditions, the electrochemical sensor offered an excellent response for CAP. The linear response ranges were 5.0 × 10(-9)-5 × 10(-7)mol L(-1) and 5.0 × 10(-7)-4.0 × 10(-6), respectively, and the detection limit was 1.0 × 10(-10)mol L(-1). The electrochemical sensor was applied to determine CAP in real samples with satisfactory results.

The voltammetric behavior of L-cysteine at a silver electrode is described. L-Cysteine can be anodically accumulated at a silver electrode surface as a sparingly soluble silver salt; at more negative potentials, the insoluble compound is stripped cathodically yielding a small current peak at about -1.10 V (vs. SCE). In the presence of cetyl pyridine bromide (CPB), the stripping peak shifts slightly to a more negative potential, and the peak height increases significantly. Thus, the peak becomes more useful for the determination of L-cysteine. In contrast to other surfactants, CPB can improve the accumulation and stripping of L-cysteine obviously. The voltammetric behavior of cysteamine, 3-mercaptopropionic acid and homocysteine is discussed as well.

A novel electrochemical sensor is presented for the determination of cefotaxime (CEF), which is constructed by molecularly imprinted polymer (MIP), gold networks@IL (IL, 1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF 4 ]) (GNWs@IL), porous platinum nanoparticles (PPNPs) and carboxyl graphene (COOH-r-GO). The GNWs@IL is prepared by directly reducing HAuCl 4 with sodium citrate in [BMIM][BF 4 ] aqueous solution. The PPNPs are well embedded in GNWs@IL due to the adhesion of IL to form GNWs@IL-PPNPs suspension, which is coated on a COOH-r-GO modified glassy carbon electrode to construct a porous three-dimensional networks modified electrode. Then, MIP is prepared by cyclic voltammetry at the modified electrode, using CEF as template and o-phenylenediamine as monomer. The factors concerning this assay strategy are carefully investigated. Under the optimal conditions, the electrochemical sensor offers an excellent response for CEF, the linear response range is 3.9×10 −9 ~8.9×10 −6 mol L −1 and the detection limit is 1.0×10 −10 mol L −1 . The electrochemical sensor has been applied to the determination of CEF in real samples with satisfactory results.

A polyaniline–ionic liquid (i.e. 1-butyl-3-methylimidazolium tetrafluoroborate, [C 4 mim][BF 4 ]) composite film coated platinum wire (PANI–IL/Pt) was prepared by electrochemical method for the first time. Scanning electron microscopy image showed that the PANI–IL composite film was even and porous. When the PANI–IL/Pt was used as a fiber for the headspace solid-phase microextraction (HS-SPME) of some benzene derivatives (i.e. 1,3-dimethylbenzene, 1,2-dimethylbenzene, 1,4-dichlorobenzene, 1,2-dichlorobenzene, 1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene), followed by gas chromatographic analysis, it presented excellent performance, which was much better than that of PANI/Pt and commercial polydimethylsiloxane fiber. Hence the fiber was coupled with gas chromatography for the determination of these benzene derivatives. It was found that under the optimized conditions the linear ranges were 0.04–400 μg L −1 with correlation coefficients above 0.99, the detection limits were 9.3–48.1 ng L −1 (S/N = 3), the relative standard deviations (RSDs) were smaller than 5.1% for five successive measurements with single fiber, and the RSDs for fiber-to-fiber were 5.0–11.1% ( n = 3) for different benzene derivatives. The proposed method was successfully applied to the extraction and determination of benzene derivatives in waste water and tap water, and the recoveries were 87.1–108.1% for different analytes. Therefore, the PANI–IL/Pt is a promising SPME fiber.

A novel multiwalled carbon nanotubes–polyaniline composite (MWCNTs–PANI) film coated platinum wire was fabricated through electrochemical deposition. The coating was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry and thermogravimetry. It was found that the coating was porous and had large specific area and adsorption capacity; in the composite MWCNTs and polyaniline interacted with each other and the film kept stable up to 320 °C. The as-made fiber was used for the headspace solid-phase microextraction (HS-SPME) of some phenolic compounds (i.e. 2-chlorophenol, 2,4-dichlorophenol, 2-methylphenol, 3-methylphenol, 2,6-dimethylphenol, 2-nitrophenol), followed by gas chromatographic analysis. The MWCNTs–PANI coating showed better analytical performance than PANI. Under the optimized conditions, the detection limits were 1.89–65.9 ng L−1, the relative standard deviations (RSDs) were 2.7–6.5% for six successive measurements with single fiber, the RSDs for fiber-to-fiber were 5.2–12.4%, the linear ranges exceeded two magnitudes with correlation coefficient above 0.992. The fiber could be used for more than 250 times without decrease of efficiency. The proposed method was successfully applied to the extraction and determination of phenolic compounds in water sample, and the recoveries were 87.7–111.5% for different analytes. In addition, the fiber also presented advantages of easy preparation and low cost. Therefore, it is a promising SPME fiber.

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in polyvinyl alcohol (PVA)-room temperature ionic liquid (i.e., 1-octyl-3-methylimidazolium hexafluorophosphate [OMIM]PF(6)) composition has been investigated by using cyclic voltammetry and chronocoulometry. It is found that the composition can promote the direct electron transfer of Hb and the heterogeneous electron transfer rate constant (k(s)) of immobilized Hb is enhanced to 19.9 s(-1). The immobilized Hb also shows high electro-catalytic activity towards the redox of oxygen, hydrogen peroxide and nitrite. The Michaelis constants (K(m)) decrease to 1.2x10(-4) M (for hydrogen peroxide) and 9.4x10(-3) M (for nitrite). The surface concentration of electroactive Hb is estimated and it is ca. 1.4x10(-10) mol cm(-2), meaning that several layers of immobilized Hb take part in the electrochemical reaction. When gold nanoparticles (GNP) is introduced into the composition, the resulting PVA-GNP-[OMIM]PF(6) composition presents better performance. The electrochemical characteristic of immobilized Hb is improved further. Thus PVA-GNP-[OMIM]PF(6) composition is more suitable for the immobilization of Hb. Therefore, it is a good strategy to prepare novel composition for protein immobilization by using several materials with different function.

A novel carbon nanotubes modified electrode was fabricated, which was based on multi-walled carbon nanotubes (MWCNTs) dispersed in gold nanoparticles (AuNPs) colloid. It was observed that MWCNTs were dispersed in AuNPs colloid homogenously. Dihexadecyl hydrogen phosphate (DHP) was added into the suspension to prepare a more stable film modified electrode. The film showed net structure and had good electron-transfer function. On the composite film coated electrode, the electrochemical behavior of mefenamic acid was studied and an irreversible anodic peak was obtained, which was much larger than that on a bare glassy carbon electrode (GCE), due to the co-effect of MWCNTs and AuNPs on the electrochemical oxidation of mefenamic acid. Under the optimized conditions the anodic peak current was linear to the concentration of mefenamic acid in the range of 1.0 × 10-7 to 2.0 × 10-5 mol L-1. The detection limit was estimated to be 1.0 × 10-8 mol L-1 after 120 s preconcentration. The method was applied successfully to the determination of mefenamic acid in medicine sample. Um novo eletrodo modificado com nanotubos de carbono foi fabricado, com base em nanotubos de carbono multi-paredes (MWCNTs) dispersos em colóide de nanopartículas de ouro (AuNPs). Foi observado que MWCNTs foram dispersos no colóide AuNPs homogeneamente. Fosfato ácido de dihexadecil (DHP) foi adicionado à suspensão para preparar um filme mais estável. O filme mostrou estrutura em rede e teve boa função de transferência de elétron. O comportamento eletroquímico do ácido mefenâmico, no eletrodo coberto com filme composto, mostrou um pico anódico irreversível, o qual foi muito maior do que para o eletrodo de carbono vítreo (GCE), devido ao co-efeito de MWCNTs e AuNPs na oxidação eletroquímica do ácido mefenâmico. Sob ótimas condições, a corrente do pico anódico foi linear à concentração do ácido mefenâmico, no intervalo de 1,0 × 10-7 a 2,0 × 10-5 mol L-1. O limite de detecção foi estimado em 1,0 × 10-8 mol L-1 após 120 s de pré-concentração. O método foi aplicado com sucesso à determinação do ácido mefenâmico em amostra medicinal.

A novel composite film modified glassy carbon electrode has been fabricated and characterized by scanning electron microscope (SEM) and voltammetry. The composite film comprises of single-wall carbon nanotube (SWNT), gold nanoparticle (GNP) and ionic liquid (i.e. 1-octyl-3-methylimidazolium hexafluorophosphate), thus has the characteristics of them. The resulting electrode shows good stability, high accumulation efficiency and strong promotion to electron transfer. On it, chloramphenicol can produce a sensitive cathodic peak at −0.66 V (versus SCE) in pH 7.0 phosphate buffer solutions. Parameters influencing the voltammetric response of chloramphenicol are optimized, which include the composition of the film and the operation conditions. Under the optimized conditions, the peak current is linear to chloramphenicol concentration in the range of 1.0 × 10−8–6.0 × 10−6 M, and the detection limit is estimated to be 5.0 × 10−9 M after an accumulation for 150 s on open circuit. The electrode is applied to the determination of chloramphenicol in milk samples, and the recoveries for the standards added are 97.0% and 100.3%. In addition, the electrochemical reaction of chloramphenicol and the effect of single-wall carbon nanotube, gold nanoparticle and ionic liquid are discussed.

The voltammetric behavior of prochlorperazine and ethopropazine at a decanethiol (DEC) self-assembled monolayer (SAM) modified gold electrode (DEC/Au) has been studied. It was observed that prochlorperazine exhibited an anodic peak at about 0.60 V (vs SCE), while ethopropazine exhibited two anodic peaks at about 0.49 V and 0.58 V on DEC/Au in pH 10 sodium carbonate buffer. This was due to their different electrochemical oxidation mechanisms. In this case, the oxidation of prochlorperazine and ethopropazine included one 2e step and two 1e steps, respectively. In the presence of some reductants such as ascorbic acid, the oxidation products of them can catalyze the oxidation of the reductants and thus make the peaks grow. In addition, it was found that the SAM structure became not so compact when prochlorperazine and ethopropazine were present, resulting from their permeating in the SAM. Various conditions were optimized for their determination. Under the selected conditions (i.e. 0.080 M pH 10 sodium carbonate buffer, scan rate: 100 mV/s, accumulation potential: –0.4 V or 0 V, accumulation time: 60 s), the peak currents were linear to prochlorperazine concentration in the ranges of 0.1~2.0 μM and 5.0~50 μM, and linear with ethopropazine in the ranges of 10 nM~0.1 μM and 0.5~20 μM. The RSD was 4.28% for 8 successive measurements of 1.0 μM prochlorperazine. The influence of some coexistents was examined.

Nickel hexacyanoferrate (NiHCF) film was prepared and characterized on gold and thiol self-assembled monolayers (SAMs)-modified gold electrodes. It was found that the film exhibited some different electrochemical characteristics compared with that found on a carbon electrode. In the presence of K+, the film exhibited a redox peak at about 0.5 V. The peak potential shifted linearly with the K+ concentration over the range of about 0.1 mM - 0.1 M with slopes of 54 - 60 mV per log[K+]. However, in solutions containing Na+, Li+ or NH4+ ion the film did not generate well-defined peaks, or even a visible redox peak. Therefore, the film showed a selective potential response to K+. The voltammetric behavior of NiHCF film varied with thiols, the preparation procedure and the solution pH. Under certain conditions, the characteristics of the film could be improved to some extent.

AgPd nanoparticles were assembled on ionic liquid-functionalized graphene by electrostatic interaction to form a graphene–metal composite. The resulting hybrid nanomaterial was characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and ultraviolet-visible absorption spectrophotometry. The AgPd nanoparticles were confirmed to be alloy and they were well dispersed on the ionic liquid-functionalized graphene sheets. The hybrid nanomaterial showed striking electrocatalytic activity toward the reduction of trichloroacetic acid (TCA). At the hybrid nanomaterial modified glassy carbon electrode, TCA exhibited a cathodic peak at about −0.65 V (vs. SCE) in pH 7 phosphate buffer solution, which was further enhanced by cetyltrimethylammonium bromide. Under the optimal conditions, the determination of TCA was performed with a linear range of 0.5–50 μM and a detection limit of 0.2 μM (S/N = 3).

Glutathione (GSH) self-assembled monolayer (SAM) is prepared on a gold electrode. It has been found that the modified electrode exhibits selective response to cupric ions, and the Cu(II) wave appears at about 0.3 V (vs. SCE). Conditions of determination are optimized, including parameters that govern the sensitivity and selectivity of this system. When the gold electrode is modified with the mixture of GSH and 3-mercaptopropionic acid (3MPA), the resulting SAMs modified electrode shows better sensitivity and selectivity for Cu(II) compared with GSH SAM modified gold electrode. Under optimal conditions, the anodic wave height is linear to Cu(II) in the range of ca. 10 μM to 0.1 mM without preconcentration. The influence of various factors and related mechanism is discussed. The organic monolayer modified electrode is stable and simple to prepare.