Gongjun Yang

Fabrication of highly ordered microporous thin films by PS-b-PAA self-assembly and investigation of their tunable surface properties

A facile approach is presented to fabricate three-dimensional ordered microporous thin films by self-assemblyvia an amphiphilic block polymer, polystryene-b-polyacrylic acid (PS-b-PAA). The highly ordered microporous thin films were formed by casting a PS-b-PAA tetrahydrofuran (THF) solution onto a glass slide under high humidity conditions. The condensed water droplets act as sacrificial templates on the air–polymer solution interface based on thermocapillary convection. Some critical influencing factors, such as the concentration of the block polymer solution, the relative humidity of the atmosphere, the properties of the solvent, the spreading volume and the substrates, were investigated to control micropore size and tune film surface properties. The surface composition and wettability of the film were found to be dramatically changed in aqueous solution, and the contact angle of the film surface was interestingly reduced from nearly hydrophobic to super-hydrophilic, which was shown by optical contact angle measurements. The influence of porosity and the ionization degree of PAA on the above properties was investigated. Micropore diameters of the films determine the initial contact angle, while the PAA ionization degree determines the transformation time of the wettability behavior and the final contact angle. The microporous thin films, as potential functional materials, are expected to play an important role in future applications.

Poly(amidosulfonic acid) modified glassy carbon electrode for determination of isoniazid in pharmaceuticals.

Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 x 10(-8)- 1.0 x 10(-5) M, and a detection limit of 1.0 x 10(-8) M (S/N = 3) was obtained after 120 s at the accumulation potential of - 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results.

Open‐tubular capillary electrochromatography using a capillary coated with octadecylamine‐capped gold nanoparticles

Octadecylamine‐capped gold nanoparticles (ODA‐Au‐NPs) were prepared and characterized by using UV–Vis adsorption spectrum, transmission electron chromatography (TEM), SEM, and FT‐IR. A simple but robust hydrophobic coating was easily developed by flushing a capillary with a solution of ODA‐Au‐NPs, because the positive charges were carried by the nanoparticles which strongly adsorb to the negatively charged inner surface of a fused‐silica capillary via electrostatic and hydrophobic interactions. The chromatographic characteristics of the coated capillary was investigated by varying the experimental parameters such as buffer pH, buffer concentration, and percentage of organic modifier in the mobile phase. The results show that (i) resolution between thiourea and naphthalene is almost the same when comparing the electrochromatograms obtained using pH 7 buffer as mobile phase after and before the capillary column was operated using pH 11 and 3 mobile phase; (ii) no significant changes in retention time and deterioration in peak efficiency were found after 60 runs of test aromatic mixtures; and (iii) column efficiency up to 189 000 theoretical plates/meter for testosterone was obtained. All of the results indicated that the coating could act as a stable stationary phase for open tubular CEC as well as for bioanalysis.

Open-tubular gas chromatography using capillary coated with octadecylamine-capped gold nanoparticles.

The octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and directly used to coat the capillary wall. The hydrophobic coating acted as the stationary phase for open-tubular gas chromatography (OTGC). The ODA-Au-NPs can be adsorbed tightly onto the inner surface of fused silica capillary column via electrostatic interaction and enhanced interaction of van der Waals between gold nanoparticles and the capillary wall. Thus, the modification of the inner surface of capillary column by ODA-Au-NPs can be achieved simply by flushing the capillary with a solution of ODA-Au-NPs and the resulted ODA-Au-NPs coating is very stable. No perceptible degradation in the ODA-Au-NPs-based separation was observed after approximately 1900 sample runs. This type of columns also provided excellent chromatographic performances: high number of theoretical plates, outstanding run-to-run and column-to-column reproducibility, and high selectivity for a wide range of test mixtures. An efficiency of 2474 theoretical plates per meter for chlorobenzene was obtained on an ODA-Au-NPs-modified 1.6 m x 100 microm i.d. fused silica capillary column.

Voltammetric determination of terbinafine in biological fluid at glassy carbon electrode modified by cysteic acid/carbon nanotubes composite film.

The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.

One step fabrication of nanoelectrode ensembles formed via amphiphilic block copolymers self-assembly and selective voltammetric detection of uric acid in the presence of high ascorbic acid content.

A novel one-step approach to glassy carbon nanoelectrode ensembles (NEEs) with the pores of 20-120nm in radii has been developed using an amphiphilic block copolymer [polystyrene-block-poly (acrylic acid)] self-assembly. This procedure is simple and fast, and requires only conventional, inexpensive electrochemical instrumentation. Electrochemical methods were used to characterize the NEEs prepared using this new procedure. The NEEs drastically suppressed the response of ascorbic acid (AA) and resolved the overlapping voltammetric response of uric acid (UA) and AA into two well-defined peaks with a large anodic peak difference (DeltaE(pa)) of about 310mV. The peak current obtained from differential pulse voltammetry (DPV) was linearly dependent on the UA concentration in the range of 0.25-50microM at neutral pH (PBS, pH 6.86) with a correlation coefficient of 0.999, and the detection limit was 0.04microM (S/N=3). The NEEs has also been demonstrated to be applicable in the detection of UA in serum and urine samples with excellent sensitivity and selectivity. The NEEs will hopefully be of good application for further sensor development.

Determination of Theophylline in Drugs and Tea on Nanosized Cobalt Phthalocyanine Particles Modified Carbon Paste Electrode

Abstract Metallophthalocyanine (MPc) and its derivatives are well known as electrocatalysts to catalyze oxidation or reduction of some species, such as cysteine, nitric oxide. Their nanosized particles may display the potential optics, electronic, catalytic, and structural properties. In this paper, carbon paste electrodes (CPE) modified with nanosized cobalt phthalocyanine (Nano‐CoPc) particles (Nano‐CoPc‐CPE) are fabricated. The electrocatalytic oxidation of theophylline (THP) on the Nano‐CoPc‐CPE is investigated by means of differential pulse voltammetry. The Nano‐CoPc particles perform better electrocatalytic activity to THP, the response current enhanced about 3.4 times compared to bulk CoPc‐modified CPE (B‐CoPC‐CPE). On optimal conditions, there is a good linear relationship between anodic peak current and THP concentration in the range of 4.0 × 10−7–1.0 × 10−4 mol L−1 with the detection limit of 1.4 × 10−7 mol L−1 (S/N = 3). The current responses of successive 40 measurements at the identical surface and at the renewed ones of Nano‐CoPc‐CPE are examined with relative standard deviation of 2.1% and 3.5%, respectively. It indicates that the electrode shows a good stability and reproducibility. It can be used to determine THP in tea and drug without separation from the matrix. The possible electrocatalytic mechanism is investigated by means of electrochemical method and UV/VIS spectroscopy.

DIFFERENTIAL PULSE VOLTAMMETRY FOR DETERMINATION OF PARACETAMOL AT A PUMICE MIXED CARBON PASTE ELECTRODE

A method for determination of paracetamol is established by the differential pulse voltammetry (DPV) using a pumice mixed carbon paste electrode with the pumice weight percent of 6% (m/m) in 0.1 mol l−1 H2SO4. The anodic peak potential is ca. 0.640 V (vs. SCE). There is a good linear relationship between the peak current and paracetamol concentration in the range of 6.0 × 10−8 – 1.0 × 10−6 mol l−1, and 2.0 × 10−6 – 9.8 × 10−5 mol l−1 with the detection limit of 2.0 × 10−8 mol l−1. Compared with the carbon paste electrode, the detection limit of this method decreases two orders of magnitude. This method is rapid, simple, accurate and highly sensitive. Satisfactory results for determination of paracetamol in pharmaceutical preparations and urine are obtained.

Electrochemical Detection Coupled with High-Performance Liquid Chromatography in Pharmaceutical and Biomedical Analysis: A Mini Review

Recent advances in electrochemical detection techniques coupled with high-performance liquid chromatography (HPLC-ECD) in pharmaceutical and biomedical analysis are reviewed. ECD classification and modes including common amperometric, coulometric, conductimetric, and potentiometric detector, are outlined and the some typical examples of determinations in pharmaceutical and biomedical analysis are described. The electrochemical detection system can offer superior merits over other detectors commonly used with HPLC. These techniques have great potential owing to their prominent characteristics in high-throughput screening procedures of drugs in various matrices. Fundamental 67 references from last 5 years related with a field are cited in this review.

Monolithic silica xerogel capillary column for separations in capillary LC and pressurized CEC

Monolithic capillary columns were prepared by the reaction of a mixture of potassium silicate solution and formamide. The surface of the monolith was coated with a thin film formed by a sol–gel method to increase the surface area of the monolith and simultaneously covered with C8 as stationary phase for reversed‐phase separation. The morphology of the monolithic column was investigated by SEM. Monolithic columns prepared in this manner showed high permeability and can be operated in capillary LC (CLC) mode at a pressure of 20 psi. PAHs were used to evaluate the separation performance of the stationary phase using CLC and pressurized CEC (pCEC). Efficiencies of 20 000 and 28 000 plates per meter for naphthalene were obtained in CLC and pCEC modes, respectively. Improvement in column efficiency and reduction in analysis time over CLC and improvement in operation facility and separation selectivity over CLC were found using pCEC mode.