Milton Duffles Capelato

Biamperometric titration and flow injection determination of cyclamate in low-calorie products

Titration and flow injection (FI) methods with biamperometric detection at 0.7 V are proposed for determining cyclamate and are tested for various diet products. The titrant–reagent system was sodium nitrite in 1.0 mol l–1 phosphoric acid and there was no interference from glucose, fructose, sucrose, lactose, sorbitol, saccharin, benzoic acid, salicylic acid, fumaric acid, Sunset Yellow and Bordeaux-S. For the biamperometric titration method, the detection limit was 1.3 × 10–3 mol l–1 and the relative standard deviation (sr) was 1.0% for a solution containing 5.0 × 10–3 mol l–1 cyclamate (n= 9). The recovery of the sweetener from four low-calorie products ranged from 97.6 to 102.5% of the labelled amount. For the FI method there was a direct relation between cyclamate concentration and current decrease over 5.0 × 10–3 to 4.0 × 10–2 mol l–1 cyclamate with a detection limit of 2.5 × 10–3 mol l–1 and an sr of 1.7% for a solution containing 2.5 × 10–2 mol l–1 cyclamate (n= 10). Ninety results can be obtained per hour, and these, for various low-calorie products, are in good agreement with those obtained by a spectrophotometric FI method (r= 0.9993) and/or the labelled amount (r= 0.9937).

Flow Injection Potentiometric Determination of Coke Acidity and Acetic Acid Content in Vinegar Using an Antimony Electrode

Abstract A flow injection potentiometric procedure is proposed for the determination of acidity of several samples using an antimony/ antimony oxide electrode. The ΔE/pH curve in phosphate buffer solutions in the pH range from 1.58 to 12.00 showed a linear sub-Nernstian behavior with an operational slope S =-42.1mV/pHc and a conditional standard potential of 264.8mV. This flow potentiometric electrode responds linearly to low acidity variations of dilute acetic acid solutions from 3.16 to 100mM with a slope of 30.1mV/dec and analytical frequency of 23 results/h. Good reproducibility and an average standard deviation of ±0.5% was obtained. The application of this sensor for the determination of coke acidity and acetic acid in vinegar is reported.

Complexing power of alkanesulfonate ions: the lead-methanesulfonate system

The interaction between lead(II) and methanesulfonate ions was studied by conventional d.c. polarography at 2.0 M ionic strength and pH 4.0. Two stepwise lead complexes are formed in solution: [Pb(CH3SO3)]+, ß1 = 1.76 ± 0.03 M−1 and [Pb(CH3SO3)2], β2 = 0.25 ± 0.05 M−2 which are reversibly reduced at the DME. At high ligand concentrations, above 1.0 M, a third lead complex, [Pb(CH3SO3)3] 433= 0.30±0.07M −3, is formed.

Potencialidades do dióxido de chumbo eletrodepositado como sensor potenciométrico

This paper proposes an experiment to be performed in both instrumental analysis and experimental physical-chemistry curricular disciplines in order to open options to develop challenging basic research activities. Thus the experimental procedures and the results obtained in the preparation of electrodeposited lead dioxide onto graphite and its evaluation as potentiometric sensor for H3O+ and Pb2+ ions, are presented. The data obtained in acid-base titrations were compared with those of the traditional combination glass electrode at the same conditions. Although a linear sub-Nernstian response to free hydrogen ions was observed for the electrodeposited PbO2 electrode, a good agreement was obtained between them. Working as lead(II) sensing electrode, the PbO2 showed a linear sub-Nernstian behavior at total Pb2+ concentrations ranging from 3,5 x 10-4 to 3,0 x 10-2 mol/L in nitrate media. For the redox couple PbO2/Pb(II) the operational slope converges to the theoretical one, as the acidity of the working solution increases.

Synthesis of Dibenzocyclooctadienes by Anodic Oxidation

Abstract the use of electrochemical oxidation was applied to the synthesis of dibenzocyclooctadiene lactones related to steganacin skeleton. This reaction, performed with compounds 1 and 2, led to results comparable with the oxidation with RuTFA, TTFA and VOF3.

Dióxido de chumbo eletrodepositado sobre grafite como sensor potenciométrico à ions chumbo e sulfato

The development of a PbO2 electrodeposited in a graphite substrate electrode and evaluation of its potenciometric response as a sensor for Pb2+ and SO42- ions, at constant pH and ionic strength is described. The electrode was applicated in the potenciometric titration in precipitation reaction of Pb2+ with SO42- in hydro-ethanolic medium. The results showed that the PbO2 electrodeposited electrode is useful as a potenciometric sensor to the Pb(II) ions presenting a linear response range between 3,98x10-4 a 3,09x10-2 mol L-1 in nitrate medium, with a practical detection limit of (4,98 ± 0,11)x10-4 mol L-1. For sulphate ions the PbO2 electrode did not responded directly. These ions might be dosed indirectly by potentimetric titration with standard Pb(II) solution in acidic media, in 1:1 ethanol-water (v/v), with good definition of the equivalence volumes. The reprodutibilidade of the potenciais and of the equivalence volumes obtained in samples with concentration at milimolar level in sulphate, indicate the possibility of the use of this electrode in quantifying sulphate ions.

The Reduction of CS2N3 − Ion In Acidic Solution

Abstract The electrochemical behaviour of 1, 2, 3, 4-thiatriazol-5-thiolate CS2N3 − ion in acidic solutions has been investigated. A cathodic wave has been detected, (E1/2 =−1.05V versus S.C.E., M=1.0M (NaC104) and NaCS2N3 1.00 × 10−3M). The characteristics of this wave have been investigated by D.C., A.C. polarography and controlled potential electrolysis. A mechanism which involves the interaction of CS2N3 − with mercury and cyclic regeneration of mercury has been proposed. The reduction of CS2N3 − by amalgamated zinc has been also investigated and the results correlated with the pseudo-halide electrochemical reduction.

Desenvolvimento de experimento didático de eletrogravimetria de baixo custo utilizando princípios da Química Verde

In this paper, we describe the development of low-cost teaching experiments of electrogravimetry for undergraduate students using principles of green chemistry. Copper was electrochemically deposited on brass under an electrical current density of 50 mA cm−2 from acidic solutions containing nitrate anions. Color changes at the brass electrode and of the solution were observed, indicating that the reduction of copper ions had occurred. The deposition efficiency values were between 92.8% and 93.8%, and the electrochemical efficiency values were between 85.6% and 86.5%. There was no significant contribution from parallel reactions. These experimental conditions facilitated the didactic exploration of gravimetric and electrochemical concepts. Following the principles of green chemistry, the experiments produced no toxic substances, all the materials could be recycled, and the energy consumption was the lowest. For this reason, this experiment was considered to be very interesting for didactical purposes.

Utilização de um eletrodo de grafite recoberto com PbO2 incorporado em matriz de PVC como eletrodo indicador em titulações coulométricas

The use of an H3O+ sensitive electrode obtained by recovering a graphite rod with a polymeric membrane containing PbO2 attached in a PVC matrix, as a working electrode in coulometric acid-base titrations is described. The coulometric curves obtained with the proposed electrode were similar to those obtained with the glass electrode and the equivalence times agreeded within a 95% confidence level. The time response of the PbO2-PVC electrode was faster than that of the glass electrode with standard deviations (n=3) of ± 0,01 s. The PbO2-PVC electrode presented a slope of -57,6 mV/pH and linear response from pH 1 to 12 (r=0,9998). The proposed electrode is of easy construction, low cost and a life time of at least 7 months, equivalente to at least 1200 determinations.