Mmol Dm Research Articles

Manganese phthalocyanine as a biomimetic electrocatalyst for phenols in the development of an amperometric sensor

The construction of an amperometric sensor for phenolic compounds using a carbon paste electrode modified with manganese phthalocyanine and histidine is reported. Under optimized conditions, at 0 mV vs Ag/AgCl in 0.1 mol dm-3 phosphate buffer solutions (pH 7.0) containing 250 µmol dm-3 H2O2, a linear response for catechol from 20 up to 130 µmol dm-3 was obtained with a sensitivity of 0.56 (± 0.02) µA dm3 µmol-1 cm-2. The detection limit was 1.1 µmol dm-3 and the response time was 2 s. The sensor presented stable response during 40 successive determinations. The repeatability, evaluated in terms of relative standard deviation, was 3.6% for n = 5 and [catechol] = 10 µmol dm-3. The sensor responses for other phenolic compounds were also investigated in details. Finally, the applicability of the sensor was tested in a pharmaceutical containing dopamine and the results compared favorably with those obtained with the official method.

Comparative Study on the Stability of Mn(III) Ion Prepared by Different Methods in H2SO4 and H3PO4 Media

The time‐periods required for the % of Mn(III) to disappear from the solution and the half‐life of Mn(III) was studied in 7 mol dm-3 H2SO4 and 7 mol dm-3 H3PO4 media at ambient conditions at three different Mn(III) concentrations viz. 4.98, 1.94 and 1.04 mmol dm-3 using spectrophotometric method. Half‐life periods in the presence of 7 mol dm-3 H2SO4 are more than those in presence of 7 mol dm-3 H3PO4. The time‐periods required for the 1% of Mn(III) to disappear that for H2SO4 medium from 1.94 mmol dm-3, Mn(III) solutions prepared from solid form is about 20 days, 10 days for electro‐generated Mn(III) and 6 days for chemical oxidation method.

Glucose biosensor based on polyaniline synthesized in ionic liquid

The use of good electro-active polyaniline at high pH for immobilizing glucose oxidase is reported. The response current increased with increasing potential from 0.35 to 0.70 V. The maximum response current occurred at about pH 7.0. The relationship between response current and the glucose concentration was linear from 0.005 to 10.0 mmol dm−3. The Michaelis–Menten constant Km', maximum response current imax and the apparent activation energy (Ea) were 31.59 mmol dm−3, 21.28 µA and 32.58 kJ mol−1, respectively. The response currents of the biosensor increased with increasing temperature. The biosensor was characterized by FTIR, UV-Vis spectra and AC impedance.

Water-solubilization of alkyloxo(methoxo)porphyrinatoantimony bromides

In order to develop water-soluble porphyrins, alkyloxo(methoxo)porphyrinatoantimony bromides (alkyl = hexyl (1a), decyl (1b), dodecyl (1c), tetradecyl (1d), octadecyl (1e)) were prepared. 1 had more than 1 mmol dm(-3) of solubility in water. From the dependence of the half-width of the bands in the absorption spectra and surface tension on the concentration of 1, it was estimated that 1b-d were present as aggregates in concentrations higher than 10 micromol dm(-3). From the NMR analysis in D(2)O, it was deduced that the alkyloxo ligands of 1 were arranged alternately in the aggregates. The diameter of the aggregates of 1 in water was determined to be around 100 nm by the dynamic light scattering method. Since the solubilities of di(methoxo)tetraphenylporphyrinatoantimony bromide and 5-(4'-decyloxyphenyl)-10,15,20-triphenylporphyrinato(dimethoxo)antimony(v) bromide were low, it was calculated that the long alkyl axial ligands were requisite for the high solubility in water.

Mapping the concentration changes during the dynamic processes of crevice corrosion by digital holographic reconstruction

The dynamic process of crevice corrosion during anodic dissolution of a crevice electrode in a 5.0 mmol dm-3 NaCl solution has been studied by digital holographic reconstruction. Digital holographic reconstruction has been proved to be an effective and in situ technique to detect the changes in the solution concentration because useful and direct information can be obtained from the three-dimensional images. It provides a valuable method for a better understanding of the mechanism of crevice corrosion by studying the dynamic processes of changes in the solution concentration at the interface of crevice corrosion.

Application of isotachophoretic and conductometric methods for neomycin trisulphate determination

AbstractDetermination of neomycin trisulphate (NMS) in a dosage form (Neox and Neosol) was carried out by capillary isotachophoresis (cITP) with conductometric detection. The following electrolytes: leading: 10 mmol dm−3 sodium acetate + 0.08 % hydroxyethylcelulose (HEC) and acetic acid to pH = 5.5, and terminating: 10 mmol dm−3 β-alanine were tested for isotachophoretic separation of NMS. The calibration curve was linear over the range of 10.00 mg dm−3 to 100.00 mg dm−3 with LOD = 5.69 mg dm−3 and LOQ = 18.96 mg dm−3. The results were compared to the conductometric determination of NMS with: ammonium molybdate (VI), silver nitrate (V) and Reinecke salt. Good accuracy was obtained from conductometric titration of NMS with Reinecke salt, the recoveries being as follows: 100 % (RSD = 1.99 %); 96.17 % (RSD = 2.10 %) and 95.22 % (RSD = 1.55 %) for NMS in pure form, Neosol and Neox, respectively.

Studies on interaction of molybdenum(VI) with modified lignocellulosics using a novel spectrophotometric method

A new adsorbent (PGPEP-COOH) bearing carboxylate functional group was prepared through graft co-polymerization of acrylic acid onto pulverized Phyllanthus emblica planks using ferrous sulphate/H 2 O 2 redox initiator system. The adsorbent obtained was tested for the uptake of molybdenum(VI) from aqueous solutions. The efficiency of the PGPEP-COOH to remove Mo VI ions at different time of contact, initial adsorbate concentration, adsorbent dose, pH, ionic strength and temperature was studied by batch experiments. The amount of molybdeitum(VI) in aqueous system was determined using a very simple and sensitive method of estimation using potassium hexacyanoferrate(II). Reddish brown solution of the molybdenum complex at pH 3.2 shows absorption maximum at 390 nm. To establish the most appropriate correlation for adsorption equilibrium, isotherm studies were performed using Langmuir, Freundlich and Redlich-Peterson models. The suitability of isotherm models was compared using linear least square fitting. Experimental kinetic data were described using a diffusion controlled first order reversible model and diffusion coefficient was evaluated at different temperatures. Applying Eyring equation thermodynamic parameters were calculated. PGPEP-COOH adsorbed 99.2% Mo VI from a solution of 10 μmol dm -3 concentration at 303 K. Desorption and regeneration studies of the adsorbent under different conditions were also studied.

Real time measurement of concentration ratio at an electrode/solution interface by calculating the inverse Laplace transform of SOWG spectroscopy

A novel technique for measuring the concentration rate of a redox compound at an electrode/solution interface was developed using slab optical waveguide (SOWG) spectroscopy. The electrolysis of 5 mmol dm −3 ferroin in 1 mol dm −3 potassium nitrate solution was carried out on an indium-tin oxide (ITO) electrode and plastic-formed carbon (PFC) electrode by cyclic voltammetry, using each spectroelectrochemical cell in SOWG spectroscopy. Their SOWG spectra were obtained every 0.05 mV during the potential sweep between +0.4 and +1.4 V for the ITO electrode and between +0.4 and +1.2 V for the PFC electrode. To obtain the concentration profiles near the electrode during the cyclic voltammetry of ferroin, the SOWG spectra were converted to concentration ratios at given locations, and these ratios were plotted against a penetration depth of evanescent wave. The theoretical derived concentration–distance profiles during CV were experimentally verified by the present technique.

Distribuição do amônio, nitrato, potássio e fósforo em colunas de latossolos fertirrigadas

Na fertirrigação, é conveniente aplicar os nutrientes de forma a conseguir sua localização na profundidade mais adequada para absorção por parte das culturas: em maior profundidadepara a cultura perene e, mais superficialmente, nas culturas de ciclo curto. Com os objetivos de estabelecer em que fração da lâmina de irrigação devem ser aplicada as doses de N (NH4+ e NO3-); K+ e H2PO4-, de investigar qual o melhor fracionamento de suas doses, de modo a localizá-los na profundidade adequada, e de determinar a distribuição na coluna de NH4+, NO3-, K+ e H2PO4- aplicados por fertirrigação, foi realizado um experimento em laboratório, utilizando colunas de percolação. Os tratamentos corresponderam a um fatorial 4 (1 + 7), sendo quatro Latossolos de Minas Gerais [dois Latossolos Vermelho-Amarelos distróficos (LVAd1 e LVAd2), um Latossolo Vermelho distroférrico (LVdf) e um Latossolo Vermelho distrófico (LVd)], uma testemunha (aplicação de água deionizada) e sete formas de aplicação de 1 mmol dm-3 de NH4+, 1 mmol dm-3 de NO3-, 2 mmol dm-3 de K+ e 0,667 mmol dm-3 de H2PO4-. A lâmina de água foi dividida em cinco frações iguais (F1 a F5) e a dose dos nutrientes aplicada integralmente (D), ou fracionada em duas (D1/2) ou em três vezes (D1/3). Assim, a aplicação dos nutrientes foi feita segundo o esquema: F2D, F3D, F4D, F2D1/2F3D1/2 , F3D1/2F4D 1/2, F2D1/2F4D1/2 ou F2D1/3F3D1/3 F4D1/3. Subamostras foram utilizadas na análise de NH4+; NO3-; K+ e H2PO4-, determinando-se a distribuição desses nutrientes na coluna de solo. A mobilidade apresentou a seguinte ordem nos solos LVAd1, LVAd2 e LVd: NO3- > NH4+ > K+ > H2PO4-. Já para o solo LVdf, a ordem foi NH4+ > NO3- > K+ > H2PO4-. A ordem de risco de contaminação de águas subterrâneas por NO3- foi a seguinte: LVAd1 > LVAd2 > LVdf > LVd. A quantidade de água acrescentada a cada coluna, inferior a meio volume de poros, não foi suficiente para deslocar o H2PO4- além do primeiro anel. Para os outros íons em estudo, a localização em maior profundidade, quando aplicados como pulso único, foi verificada com a maior concentração no pulso (D > D1/2 > D 1/3) e com a maior lâmina de água posterior à sua aplicação (F2D > F3D > F 4D e F2D1/2F3D1/2 > F3D1/2F4D1/2 ). Os resultados evidenciam que a mobilidade diferencial de N (NH4+ e NO3-) e K+ exigiria escolha cuidadosa das doses desses nutrientes na solução, a fim de evitar perdas de N (NH4+ e NO3-) por lixiviação, ou localização excessivamente superficial do K+. A baixa mobilidade do H2PO4- mostra que a fertirrigação não seria uma técnica apropriada para sua incorporação no perfil do solo, visando à fertilização das culturas.

Hybrid electrochemical biosensor for organophosphorus pesticides quantification

An electrochemical biosensor for organophosphorus (OP) pesticides trace level concentrations determination was developed and characterized. It integrates a hybrid biorecognition element consisting of immobilized Arthrobacter globiformis and free acetylcholinesterase (ACh) with a Clark type oxygen probe transducer. The bacteria convert the ACh-generated choline to betaine with oxygen consumption measured as a Clark probe current change. This change representing the sensor response correlates to the concentration of the OP pesticides inhibiting the Ach-catalyzed acetylcholine hydrolysis to choline. The conditions for maximal sensor response to choline were optimized according to the methodology of design of experiments. The analytical performances of the enzyme substrate determination in a wide concentration range (0.1–20 μmol dm −3 of acetylcholine) and different ACh activities were established. It was demonstrated that the biosensor ensures reproducible, accurate and reliable chlorophos quantification reaching a limit of detection (LOD) of 1 nmol dm −3 and a sensitivity of 0.0252 μA/p(mol dm −3) under optimal experimental conditions. The biosensor response time is 200 s and the storage stability is t L50 = 49 days for the bacterial membrane at ambient temperature. The device is reusable, the bacterial membrane being not affected by OP. The biosensor was applied to chlorophos determination in contaminated milk.

Interação da deficiência hídrica e da toxicidade do alumínio em guandu cultivado em hidroponia

O objetivo deste trabalho foi avaliar o efeito da interação da deficiência hídrica e da toxicidade do alumínio no crescimento inicial e teores de prolina livre em duas cultivares de guandu, IAPAR 43-Aratã e IAC Fava Larga, cultivadas em hidroponia. As plântulas foram submetidas aos estresses em solução nutritiva (pH 3,8), nos potenciais osmóticos de 0, -0,004, -0,006, -0,008 e -0,010 MPa, com 0, 0,25, 0,50, 0,75 e 1 mmol dm-3 de Al3+. O experimento foi conduzido em sala de crescimento, sob luminária com irradiância média de 190 mmol m-2 s-1 , fotoperíodo de 12 horas e temperatura de 25+1ºC. O delineamento experimental foi inteiramente casualizado, em arranjo fatorial 2x5x5 (duas cultivares de guandu, cinco potenciais osmóticos e cinco níveis de alumínio), com quatro repetições. Os dados foram submetidos às análises de regressão polinomial, agrupamento e componentes principais. A deficiência hídrica causa redução do crescimento da parte aérea do guandu, e a toxicidade do alumínio provoca diminuição do crescimento radicular. Houve aumento nos teores de prolina livre nas duas cultivares sob deficiência hídrica, e apenas na IAC Fava Larga sob toxicidade de alumínio. Na análise multivariada, foi observada alta correlação no crescimento e no acúmulo de prolina na cultivar IAC Fava Larga, o que evidencia provável tolerância aos estresses associados.

Precipitation of different calcite crystal morphologies in the presence of sodium stearate

The influence of sodium stearate (NaSt) on the precipitation of calcium carbonate during the semicontinuous process of slaked lime carbonation was studied in the systems in which process parameters, like concentration of total dissolved calcium, temperature, CO 2 flow rate and initial addition rate of slaked lime, were controlled. It was found that calcite was the only calcium carbonate polymorph that appeared under the investigated experimental conditions, while FT-IR spectroscopy and thermogravimetric analysis of samples confirmed the presence of stearate on the surface of precipitated calcium carbonate (PCC). Specific surface area of PCC increased with increasing stearate content: the highest value, s = 52.8 m 2 g −1 , was obtained at t = 20 °C , c tot = 17.0 mmol dm −3 and the stearate content of m NaSt / m CaO = 0.03 . It was also found that hydrophobic calcite crystals in the form of rhombohedral and scalenohedral morphology can be produced at m NaSt / m CaO > 0.01 . The exception is the case of nanosized PCC production, when much higher concentration of NaSt is needed, m NaSt / m CaO = 0.22 . Minimal amount of stearate necessary to build up the monolayer and corresponding cross sectional area of one stearate molecule were estimated for the obtained calcite morphologies.

Preparation of the electrochemically formed spinel-lithium manganese oxides

Electrochemically formed spinel-lithium manganese oxides were synthesized from manganese hydroxides prepared by a cathodic electrochemical precipitation from various concentrations of manganese nitrate solutions. Two types of manganese hydroxides were formed from diluted and concentrated Mn(NO 3) 2 aqueous solutions. Uniform and equi-sized disk shaped Mn(OH) 2 crystals of 0.2–5 μm in diameter were obtained on a Pt substrate after the electrochemical precipitation from lower concentration of ranging from 2 mmol dm −3 to 2 mol dm −3 Mn(NO 3) 2 aq., while the grass blade-like precipitate which is ascribed to manganese hydroxide with 20–80 μm long and 1–5 μm wide were formed from concentrated Mn(NO 3) 2 aq. Both manganese hydroxides gave the electrochemically formed spinel-LiMn 2O 4 onto a Pt sheet, which is ready for electrochemical measurement, after calcination of the Li incorporated precipitate at 750 °C without any additives. While the shape and size of the secondary particle frameworks (aggregates) of the electrochemically formed spinel-LiMn 2O 4 can be controlled by the electrolysis conditions, the nanostructured primary crystals of 200 nm in diameter were obtained in all cases except that the fiber-like nanostructured spinel-LiMn 2O 4 crystals with 200 nm in diameter were obtained from concentrated Mn(NO 3) 2 aq. Though these two types of electrochemically formed spinel-LiMn 2O 4 showed well-shaped CVs even in higher scan rates, it would be suitable for high power density battery applications. These behaviors are assumed to be ascribed to the crystal size and shape of the processed spinel-LiMn 2O 4.

Effect of Mn ion on the visible light induced water oxidation activity of photosynthetic organ grana from spinach

Abstract To develop the visible light induced hydrogen and oxygen production based on the water photolysis, 2,6-dichloroindophenol (DCIP) reduction based on the photoinduced water oxidation with oxygen evolved centre (OEC) of PSII in photosynthesis organ, grana from spinach was studied. It noted that manganese cluster consisted of four manganese ions in OEC, and the role and effect of manganese(II) and (III) ions on the DCIP reduction were investigated. By addition of manganese(III) acetate up to 80 μmol dm −3 , the concentration of the reduced DCIP with irradiation was increased compared with the system in the absence of manganese(III) acetate. The activity of DCIP reduction in the presence of 80 μmol dm −3 manganese(III) acetate was 4.7 times higher than that in the absence of manganese(III) acetate. In contrast, the concentration of the reduced DCIP with irradiation was increased by addition of manganese(II) acetate up to 40 μmol dm −3 compared with the system in the absence of manganese(II) acetate. These results show that the DCIP photoreduction with grana was promoted by addition of manganese(III) or (II) ion.

O.047 Investigation of the hydrodynamic properties of Polaris valve

Solutions of 236 mg dm−3 Acid Red 1 (AR1), an azo dye widely used in textile dying industries, at pH 3.0 have been comparatively treated by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at constant current density (j). Assays were performed with a stirred tank reactor equipped with a Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode for H2O2 generation from O2 reduction. The main oxidizing agents were hydroxyl radicals produced at the anode from water oxidation in all methods and in the bulk from Fenton's reaction between generated H2O2 and 0.5 mmol dm−3 Fe2+ in EF and PEF. For each anode, higher oxidation power was found in the sequence AO-H2O2 < EF < PEF. The oxidation ability of the BDD anode was always superior to that of Pt. Faster and similar decolorization efficiency was achieved in EF and PEF owing to the quicker destruction of aromatics with hydroxyl radicals produced in the bulk. The PEF process with BDD was the most potent method yielding almost total mineralization due to the additional rapid photolysis of recalcitrant intermediates like Fe(III)-carboxylate complexes under UVA irradiation. The increase in j always enhanced the decolorization and mineralization processes because of the greater production of hydroxyl radicals, but decreases the mineralization current efficiency. A total of 11 aromatic intermediates, 15 hydroxylated compounds, 13 desulfonated derivatives and 7 short-linear carboxylic acids were identified. NH4+, NO3− and SO42− ions were released during azo dye degradation. From the products detected, a comprehensive reaction sequence for AR1 mineralization is proposed. The relationship between decolorization, mineralization and products formed is finally discussed.

Photochemical and enzymatic methanol synthesis from HCO3− by dehydrogenases using water-soluble zinc porphyrin in aqueous media

We studied the photochemical and enzymatic synthesis of methanol from HCO3− using formate dehydrogenase (FDH) isolated from Candida boidinii, aldehyde dehydrogenase (AldDH) and alcohol dehydrogenase (ADH) isolated from yeast, and the photoreduction of methyl viologen (MV2+) by the visible-light sensitization using zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) in the presence of triethanolamine (TEOA). When a sample solution containing ZnTPPS, MV2+, FDH, AldDH, ADH, TEOA, and NaHCO3 in potassium phosphate buffer solution (pH 8) was irradiated, the amount of methanol produced increased with the irradiation time. After irradiation for 3h, 4.5μmoldm−3 of methanol was produced from 100μmoldm−3 NaHCO3. The conversion ratio of HCO3− to methanol was approximately 4.5%. This result indicates that a system for the photochemical synthesis of methanol from HCO3− can be developed by using three dehydrogenases (FDH, AldDH, and ADH) and for the photoreduction of MV2+ through the photosensitization of ZnTPPS in aqueous media.

Glucose isomerase production on a xylan-based medium by Bacillus thermoantarcticus

Abstract Effects of medium components on intracellular glucose isomerase (GI) production were investigated by Bacillus thermoantarcticus. The highest GI activity was obtained as 1630 U dm−3 in the medium containing (g dm−3): 10.6, birchwood-xylan; 5.6, yeast extract; 5.9 (NH4)2SO4 at T = 55 °C in 33 cm−3 shake-flasks. When birchwood-xylan was replaced with oat spelt- or beechwood-xylan, GI activity decreased to 1372 and 1308 U dm−3, respectively. Effects of pH at uncontrolled-pH (pHUC = 6.0) and controlled-pH (pHC = 6.0) operations, and oxygen transfer at the air inlet rate of 0.5 vvm and agitation rates of 300, 500 and 700 min−1, were investigated in 3.0 dm3 bioreactor system with 1.65 dm3 working volume in the designed medium. The highest GI activity was attained at 500 min−1, 0.5 vvm, pHUC = 6 as 1840 U dm−3 where cell concentration was 2.3 g dm−3. The use of agricultural waste xylan, as the carbon source resulted in concomitant production of xylanase and GI. The highest xylanase activity was attained as 9300 U dm−3 at 500 min−1 and 0.5 vvm. KLa varied between 0.008–0.033 s−1 whereas the highest oxygen uptake rate was 0.002 mmol dm−3 s−1. Initially biochemical reaction limitations were effective; thereafter, mass transfer resistances became more effective.

D-Fructose detection based on the direct heterogeneous electron transfer reaction of fructose dehydrogenase adsorbed onto multi-walled carbon nanotubes synthesized on platinum electrode

Multi-walled carbon nanotubes (MWCNTs) were synthesized on platinum plate electrodes by the chemical vapor deposition (CVD) method. From the results of X-ray photoelectron spectroscopy and voltammetric investigation, the iron nanoparticles used as a catalyst for the MWCNT synthesis were enclosed with MWCNTs. The MWCNTs synthesized on the Pt plate (MWCNTs/Pt) electrode were immediately immersed into solutions of d-fructose dehydrogenase (FDH) to immobilize the enzyme onto the MWCNTs/Pt electrode surfaces. After the FDH was immobilized onto the MWCNTs/Pt electrode, a well-defined catalytic oxidation current based on FDH was observed from ca. −0.15 V (versus Ag/AgCl/sat’d KCl), which was close to the redox potential of heme c as a prosthetic group of FDH. From an analysis of a plot of the catalytic current versus substrate, the calibration range for the fructose concentration was up to ca. 40 mmol dm −3, and the apparent Michaelis–Menten constant was evaluated to be 11 ± 1 mmol dm −3.

The role of air masses on iron concentrations in wet atmospheric deposition over the urbanized coastal zone of the Gulf of Gdańsk

Abstract This paper describes the role of air masses in transporting iron to the coastal zone of the Gulf of Gdansk. Fe(II) concentrations in rainfall were measured between 19th January and 30th November 2005 in Gdynia, during which time they varied from 0.74 μmol dm-3 to 97.45 μmol dm-3. The relationship between iron concentrations and precipitation amount, including during preceding rainless periods, was calculated. The effectiveness of washing iron out of the atmosphere is described by the exponential function of precipitation duration. Air masses arriving from west of the area transport terrigenous iron to the coastal zone of the Gulf of Gdańsk, while anthropogenic sources in Western Europe and Pomerania hardly affected the iron concentrations.

Application of Ti/RuO 2–Ta 2O 5 electrodes in the electrooxidation of ethanol and derivants: Reactivity versus electrocatalytic efficiency

The influence of the preparation method on the performance of RuO 2–Ta 2O 5 electrodes was evaluated toward the ethanol oxidation reaction (EOR). Freshly prepared RuO 2–Ta 2O 5 thin films containing between 30 and 80 at.% Ru were prepared by two different methods: the modified Pechini–Adams method (DPP) and standard thermal decomposition (STD). Electrochemical investigation of the electrode containing RuO 2–Ta 2O 5 thin films was conducted as a function of electrode composition in a 0.5-mol dm −3 H 2SO 4 solution, in the presence and absence of ethanol and its derivants (acetaldehyde and acetic acid). At a low ethanol concentration (5 mmol dm −3), ethanol oxidation leads to high yields of acetic acid and CO 2. On the other hand, an increase in ethanol concentration (15–1000 mmol dm −3) favors acetaldehyde formation, so acetic acid and CO 2 production is hindered, in this case. Electrodes prepared by DPP provide higher current efficiency than STD electrodes for all the investigated ethanol concentrations. This may be explained by the increase in electrode area obtained with the DPP preparation method compared with STD.