Determination of Ophthalmic Drug Proparacaine Using Multi-walled Carbon Nanotube Paste Electrode by Square Wave Stripping Voltammetry.

Proparacaine, one of the most common local anesthetics to facilitate diagnosis and treatment of eye diseases, was assayed by square wave voltammetry using a paste electrode prepared with carbon nanotubes. In cyclic voltammetric studies, proparacaine has exhibited a single irreversible anodic peak at around + 900 mV vs. Ag/AgCl in pH 6.0 Britton-Robinson buffer solution. It was suggested that the peak had appeared due to the oxidation of the NH2 group on the proparacaine molecule. Prior to the determination of the proparacaine by square wave stripping voltammetry (SWSV) on the fabricated multi-walled carbon nanotube paste electrode (MWCNTPE), the accumulation potential (Eacc), accumulation time (tacc), pulse amplitude (ΔE), step potential (ΔEs) and frequency (f ) parameters were optimized. The peak currents plotted in the range of 0.5 - 12.5 mg/L proparacaine exhibited two linear sections with a detection limit of 0.11 mg/L. The results for the determination of proparacaine on a pharmaceutical local anesthetic (Alcaine®) showed that relative standard deviation (RSD) and relative error (RE) were 4.1 and -2.0%, respectively. Selectivity has also been investigated and results showed recoveries of 5.0 mg/L proparacaine in the presence of 5.0 mg/L dopamine, ascorbic acid and uric acid as 106.9 ± 0.8, 99.9 ± 1.2 and 94.1 ± 0.7, respectively.

Apical extrusion of sodium hypochlorite activated with two laser systems and ultrasonics: a spectrophotometric analysis.

BACKGROUND: The aim of the present study was to compare the effect of ultrasonically or laser (Nd:YAG or diode) activated irrigation on the irrigating solution extrusion compared to non-activated syringe irrigation. METHODS: Extracted mandibular premolar teeth (n = 48) with single canals were instrumented. The teeth were secured through the lid of an Eppendorf tube filled with 1.0 mL distilled water to collect the apically extruded irrigating solution. The teeth were randomly divided into four groups: non-activated syringe irrigation, diode laser, Nd:YAG laser and passive ultrasonic irrigation (PUI) using 2% NaOCl. The irrigating solution extruded through the apical foramen was collected in the Eppendorf tube and evaluated by a chemical reaction with using a spectrophotometer. The data was analyzed using one-way ANOVA and Tukey's post hoc test (α = 0.05). RESULTS: All the groups showed apically extruded irrigating solution. There were significant differences among the groups (p < 0.05). Nd:YAG laser activated irrigation showed greater extrusion (p < 0.05), while the non-activated syringe irrigation showed less extrusion (p < 0.05). Only the difference between diode laser and PUI was not statistically significant (p > 0.05). CONCLUSION: Within the limitations of this in vitro study, the researchers concluded that non-activated syringe irrigation caused less apically extruded irrigating solution than PUI and LAI using Nd:YAG or diode lasers.

Electro-oxidation and determination of benomyl by square-wave adsorptive stripping voltammetry.

The electro-oxidation of the benomyl fungicide was studied by square-wave adsorptive stripping voltammetry. The voltammetric current at a glassy carbon electrode was acquired within the pH range 1.0-10.0. The quantitation was performed using the peak generated at +1144 mV by scanning the potential from +0.00 to +1600 mV (versus an Ag/AgCI reference electrode, 3 M NaCl). Accumulation potential = 0.0 mV, accumulation time=45 s, frequency=75 Hz, pulse amplitude=-60 mV, and staircase step potential = 7 mV were used as square-wave parameters. The peak current versus concentrations plot were rectilinear over the range from 0.081 to 1.496 microg/mL with an LOD of 0.024 microg/mL. Mean recovery was 99.0% (0.198 +/- 0.011 microg/mL), which was very close to the benomyl content spiked into river water (0.20 microg/mL). The method was efficiently applied for benomyl determination in the pesticide formulation Minelate 50WG, and the average determined content of 49.8 +/- 0.16 (n = 5) was consistent with the 50% benomyl (w/w) quoted by the manufacturer. The benomyl voltammograms recorded between days exhibited a negligible degradation into carbendazim metabolite, and therefore all results were given as the total benomyl concentration. The high recoveries and low RSD gave evidence of good accuracy and precision.

Electro-oxidation of herbicide halosulfuron methyl on glassy carbon electrode and applications.

Halosulfuron methyl, a fast-acting herbicide and is absorbed into leaf tissue within 1-2 days and translocated through the vascular system, interrupting amino acid production within the plant, can be detected using glassy carbon electrode the technique of adsorptive stripping voltammetry. The adsorptive stripping voltammetric behavior of halosulfuron methyl was investigated in pH range 1.0-10.0. Halosulfuron methyl was irreversibly oxidized at a glassy carbon electrode. Electrochemical techniques including adsorptive stripping voltammetry and cyclic voltammetry were employed to study the oxidation mechanism. The experimental parameters such as the accumulation potential, accumulation time and frequency were optimized. The linear range, detection limit and quantification for halosulfuron methyl were evaluated by adsorptive stripping voltammetry. Under the optimized conditions, the peak current is linear to halosulfuron methyl concentration in the range 4.1-50.0 µg mL(-1). Limit of detection and limit of quantification were 1.23 and 4.10 µg mL(-1), respectively. The interference of inorganic species and other some pesticides on the voltammetric response have been studied. The applicability to spiked soil and natural water was described and the recoveries for the standards added are 103.8% and 108.2%, respectively. The method is successfully applied for the determination of halosulfuron methyl in commercial formulation.

A direct method for the polarographic determination of herbicide triasulfuron and application to natural samples and agrochemical formulation.

Polarographic behavior of triasulfuron herbicide in a Britton-Robinson (B-R) buffer was investigated by differential pulse polarography (DPP) and cyclic voltammetry (CV). Optimum conditions for the analytical determination were found to be pH 3.0 at a reduction potential of -1031 mV. Experimental results indicate an excellent linear correlation between the peak current and the concentration in the range of 0.19-11.6 microg mL(-1) (0.47-28.9 microM) with a correlation coefficient of 0.993. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.06 and 0.19 microg mL(-1) (0.15 and 0.47 microM), respectively. The precision of the method is satisfactory at a very low level, and the relative standard deviation (RSD) is 2.37% (n=5). Satisfactory recoveries achieved with spiked soil and dam water samples were between 98.4-103.0% and 100.0-104.0% at concentration ranges of.5.0-25.0 microg g(-1) and 0.40-2.0 microg mL(-1) (12.4-62.2 and 1.0-5.0 microM), respectively, inferring that the established method can be applied to real sample analysis. The method was extended to the direct determination of triasulfuron in agrochemical herbicide formulation Lintur 70 WG and average content of 4.37+/-0.16 (n=5) % was in close agreement with the 4.10% quoted by the manufacturer. The influences of some other commonly used pesticides and inorganic salts on the determination of triasulfuron were also examined.

Determination of insecticide pymetrozine by differential pulse polarography/application to lake water and orange juice.

A simple, fast and sensitive differential pulse polarographic method (DPP) for the determination of pymetrozine insecticide in pure form, agrochemical formulation, natural water and orange juice samples is proposed. The polarographic behavior of pymetrozine exhibited a double well-defined polarographic peaks at -580 and 950mV (versus SCE), respectively. The peak potentials were strongly pH-dependent in that they shifted to more negative values with increasing pH. The polarographic reduction corresponding to the first peak at pH 2.0 (B-R buffer solution) showed quantitative increments with the additions of standard pymetrozine solution under the optimal conditions and the corresponding peak current was linearly proportional to pymetrozine concentration in the range of 4.97x10(-7) to 7.35x10(-5)molL(-1). The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 1.48x10(-7) and 4.93x10(-7)molL(-1), respectively. The mean recoveries of the 5.0x10(-6)molL(-1) pymetrozine spiked to lake water and orange juice were (4.89+/-0.23)x10(-6) and (4.97+/-0.19)x10(-6)molL(-1) at 95% confidence level, respectively. The method was extended to the determination of pymetrozine in agrochemical insecticide formulation Plenum and accuracy was in agreement with that obtained by HPLC comparison method. Influences of some interfering ions and some other pesticides were also investigated. The mechanistic study was not pursued.

Determination of triflumizole by differential pulse polarography in formulation, soil and natural water samples.

A novel electroanalytical procedure is proposed for the determination of the triflumizole in formulation, soil and natural water samples using differential pulse polarography (DPP). Triflumizole exhibited a single well-defined cathodic peak over the pH range of 1.0-9.0 in Britton-Robinson (B-R) buffers. The peak potentials were shifted to more negative values upon increasing the pH and a plot of reduction potentials (E(p)) versus pH exhibited two linear segments with a break at pH 4.0 which corresponded to the pK(a)+/-1 value of triflumizole. The peak appeared as a maximum at pH 2.0 (-810 mV versus saturated calomel electrode (SCE)) was well resolved and suitable to be investigated for analytical use. The current-concentration plot obtained using this peak was rectilinear over the range from 2.0 to 91.0 micromol L(-1) with a correlation coefficient of 0.993. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.72 and 2.39 micromol L(-1), respectively. The proposed method was successfully applied to the determination of triflumizole in spiked soil and lake water. The mean recoveries of the pesticide were 102.1 and 103.6% with a relative standard deviation of 1.01 and 2.68% in soil and lake water, respectively. The method was extended to the determination of triflumizole in agrochemical fungicide formulation Trifmine and results were in agreement with that obtained by high-performance liquid chromatographic analysis (HPLC). The influence of some diverse ions and some other pesticides was also investigated.