Poly(methylene blue)-modified electrode for indirect electrochemical sensing of OH radicals and radical scavengers

ABSTRACT A new modified electrode for indirect sensing of OH· and radical scavengers was described. The electrochemical polymerization of methylene blue in aqueous solutions and the properties of the resulting films on a glassy carbon electrode were carried out using cyclic voltammetry. A surface coverage of 1.11 × 109mol cm2 was obtained, revealing a complete surface coverage of the polymeric film on the electrode surface. OH· was able to destroy the poly(methylene blue) film by exposure to a Fenton solution. The loss of the electrochemical signal of the residual polymeric film attached to the electrode surface was related to the extent of its dissolution. The applicability of the sensor was demonstrated by evaluating the OH radical scavenging effect on different concentrations of ascorbic acid. The obtained radical scavenging capacity were 31.4%, 55.7%, 98.9% and 65.7% for the ascorbic acid concentrations of 5, 10, 30 and 50 mM, respectively.

The effect of endodontic materials on the optical density of dyes used in marginal leakage studies

The aim of this study was to determine the effect of the exposure of different endodontic materials to different dye solutions by evaluating the optical density of the dye solutions. Seventy-five plastic tubes were filled with one of the following materials: AH Plus, Sealapex, Portland cement, MTA (Angelus and Pro Root) and fifteen control plastic tubes were not. Each specimen of material and control was immersed in a container with 1 ml of each dye solution. A 0.1 ml-dye solution aliquote was removed before immersion and after 12, 24, 48 and 72 hours of each specimen immersion to record its optical density (OD) in a spectrophotometer. Statistical analysis was performed with ANOVA and Tukey tests (5 percent). No significant difference was found among any of the solution OD values for AH Plus cement. Portland cement promoted different OD values after 12 hours of immersion. MTA-Angelus cement presented different OD values only for 2 percent rhodamine B and the MTA-Pro Root cement presented different OD values in all 2 percent rhodamine B samples. Sealapex cement promoted a reduction in the India Ink OD values. Dye evaluation through OD seems to be an interesting method to select the best dye solution to use in a given marginal leakage study.

Evaluation of adsorption potential of adsorbents: a case of uptake of cationic dyes.

Adsorption potential of a commercial activated carbon (FS300) has been evaluated for the uptake of cationic dyes namely methylene blue (MB) and rhodamine B (RB). Though, there are numerous studies in literature which report the sorption of MB (more than 40 studies) and RB (more than 10), however none of these use a common parameter to report the capacity of the sorbent. A protocol, based on the equilibrium dye concentration has been proposed to measure the sorption potential of a sorbent. The Langmuir model can very well describe the experimental equilibrium data for both dyes (coefficient of correlation > 0.999). MB (Qm = 312.5 mg g(-1)) is more adsorbable than the RB (Qm = 144.9 mg g(-1)). Molecular weight and chemical structure of dye molecules seem to affect the dye uptake. The effect of pH on dye uptake has also been evaluated by varyingpH from 3 to 11. Uptake of MB increases with pH, wherein RB removal decreases with pH. Dyes could not be desorbed either by distilled water (0.06 and 0.11% for MB and RB respectively), or by 0.1 NHCl (0.136 and 3.0% for MB and RB respectively) indicating, chemical adsorption type of adsorbent-adsorbate interactions.

Adsorptive removal of basic dyes from aqueous phase onto activated carbon of used tea leaves: a kinetic and thermodynamic study.

Activated carbon has been prepared from used tea leaves impregnated with H3PO4 (50%, w/v) and carbonized at 300 degrees C. Its adsorption capacity has been tested for the decolourisation of wastewater containing malachite green and methylene blue. The effect of system variables such as concentration, temperature, pH, contact time, adsorbent dosage and particle size was studied. The optimum pH range is 8-10 and dosage required is 1.2 g/L for 100% removal of both malachite green and methylene blue (100 mg/L). Break-through and exchaustive capacities for malachite green and methylene blue are 300.0 and 314.7 mg/g; 275.0 and 290.4 mg/g, respectively. The adsorption data follow Langmuir model as well as Freundlich model.

Análise "in vitro" da infiltraçäo marginal apical do corante azul-de-metileno, quando da obturaçäo do canal radicular diante da variaçäo dos métodos de secagem / Anals \"in vitro\" of the dental leakage with methylene blue colors, in root canal obturation in dry methods variation

A secagem do canal radicular, imediatamente antes da inserçäo dos materiais obturadores, pode ser obtida pelo emprego da aspiraçäo do conteúdo líquido do canal radicular ou pelo uso de cones de papel absorvente, ou ainda, pela associaçäo de ambos recursos. Remover líquidos da luz do canal radicular e, da própria intimidade do tecido dentinário, propicia melhor aderência entre os materiais obturadores e as paredes dentinárias. Empregando-se dentes humanos extraídos, avaliou-se, com o auxílio do corante azul-de-metileno e leituras lineares efetivas em um projetor de perfil, os níveis de infiltraçäo marginal apical que decorrem, diante da adoçäo de diferentes formas de secagem do canal radicular. O tratamento estatítistico dos resultados apurados tornou evidente que, quanto maior for o índice de remoçäo da umidade do interior do canal e da própria intimidade do tecido dentinário, de qualidade mais significativa, será a impermeabilizaçäo marginal apical da obturaçäo endodôntica. Assim, foi possível demonstrar que, associando-se à aspiraçäo do canal radicular, o emprego de cânulas caracterizadas por calibres decrescentes e aplicadas nos níveis cervical, médio e apical e complementando-se a secagem do canal radicular com cones de papel absorvente, é possível obter-se melhor coaptaçäo do material obturador às paredes dentinárias do que, em condiçöes outras, nas quais, recursos de menor efetividade de secagem do canal forem adotados