Linear relationship between potential and concentration in flow potentiometry

In potentiometric-flow systems, linear-potential responses for logarithmic concentrations can be attained for first-(or pseudo-first-) order reactions in which the monitored chemical species react with the analyte during a fixed time interval. To demonstrate this property, the determination of glycerol based on its oxidation by periodate and potentiometric monitoring of the remaining periodate was selected. Influence of reagent concentration and timing on the linearity of the analytical curve were investigated. A mathematical treatment was derived, and potentialities/limitations of the approach were outlined. The system was applied to analysis of soap and lixivia samples. The analytical curve within 200 and 2000 mg L-1 (r = 0.99975; n = 5) was described as E = 8.166 + 0.0478 (glycerol). The sample throughput was 100 h(-1), and a measurement repeatability within 0.5 mV was always observed. By applying a t-test, there was no statistical difference between the results obtained by the proposed procedure and by iodimetric titration at the 95% confidence level. (C) 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:41-45, 2000.

HMB-45 - A review

HMB-45, named for the immunogen used (human melanoma, black) is a monoclonal antibody developed 10 years ago by Gown and colleagues to a whole-cell extract of a human melanoma. Over the years, it has been demonstrated that HMB-45 is a highly sensitive and specific reagent for the identification of melanoma. More recently, it has been found that HMB-45 reacts with a protein designated gp100-cl, which is apparently related to the pmel 17 gene product. Because gp100-cl is a melanosomal matrix protein, HMB-45 is more correctly identified as an organelle-specific rather than tumor-specific reagent. HMB-45 immunoreactivity is seen in normal fetal and neonatal melanocytes but not in adult resting melanocytes. Reactive or proliferating melanocytes present in inflamed adult skin or in skin overlying certain dermal neoplasms, can also ''re-express'' the HMB-45-defined antigen. Whereas the vast majority of melanomas are HMB-45-positive, one important exception is desmoplastic malignant melanoma, which consistently demonstrates a much lower rate of expression of the HMB-45-defined antigen compared with other types of melanoma. In recent years there have been scattered reports of HMB-45 immunoreactivity in nonmelanomatous tumors, such as breast and other carcinomas, but virtually all these reports employed commercial ascites fluid preparations of HMB-45 antibody that were subsequently shown to be contaminated with nonspecific antibodies. Thus, for most practical purposes, a positive reaction with HMB-45 indicates active melanosome formation and, therefore, melanocytic differentiation. There is also a set of HMB-45-positive tumors that consistently manifest HMB-45 immunoreactivity but do not display obvious pigmentation: clear cell ''sugar'' tumor of the lung, angiomyolipoma, and lymphangiomyomatosis. Nonetheless, these lesions are all unified by recent ultrastructural studies that confirm the presence premelanosomes. Curiously, all three lesions also manifest evidence for simultaneous smooth-muscle differentiation. HMB-45 remains, therefore, a reliable marker of melanoma but may also provide insights into a rare group of tumors.

The azomethine-H modified colorimetric method of boron determination at fertilizers.

The present work studied the azomethine-H colorimetric method for boron determination to fertilizers analysis applications. The reagent azomethine-H needs lights conditions of reaction that, jointed to the big sensibility and specificity, diffused its use in boron's dosage in many materials. The most suitable experimental parameters were established for such colorimetry, and analysis conditions: standard curve between 0,200 e 2,25 mg. L(-1) boron, in maximum absorption at 415nm, I cm cell and reading between 30 and 90 minutes standing after the final homogenization of the boron's solution in analyse and with dye reactive (azomethine If 0,90 % m/v solution at buffer ammonium acetate 1,82 mol . L(-1) - potassium acetate 0,10 mol . L(-1) - acetic acid 1,67 mol . L(-1)-EDTA 2,7 . 10(-2) mol . L(-1)-NTA 2,1.10(-2) mol . L(-1) pH 5,5). Statistics analysis of the results didn't present big differences when the same results were got by the colorimetric method offered and by the potentiometric, from AOAG, whatever in manufactured fertilizers or in lab sintetized fertilizers.

Construction and performance of a drop cell for the nephelometric determination of sulfur dioxide

A nephelometric technique based on a liquid drop is described for the measurement of atmospheric sulfur dioxide. A 40-mul drop of barium chloride and hydrogen peroxide solution is suspended in a flowing-air sampling stream. The sulfur (IV) collected is oxidized to sulfur (VI) and finally precipitated as barium sulfate. Nephelometric detection of drop is achieved by an appropriate arrangement consisting of an optical fiber contacting the drop and a photodiode placed at 90degrees relative to the fiber. The design and characteristics of this drop-based gas sensor system are described. The analytical response, as photocurrent, is proportional to the product of the sampling period and the sulfur dioxide concentration. The detection limit is ca. 1.1 mg m(-3) for a 10-min sampling time. The present technique is fairly rapid and simple, uses a small amount of reagent and is set up with low-cost equipment, making this system economically viable. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Determination of low-aliphatic aldehydes indoors by micellar electrokinetic chromatography using sample dissolution manipulation for signal enhancement

This work describes a novel approach for the analysis of selected aldehydes (formaldehyde, acetaldehyde, propionaldehyde, and acrolein) and acetone in environmental samples using micellar electrokinetic chromatography (MEKC). The method is based on the reaction of carbonyl compounds with 3-methyl-2-benzothiazoline hydrazone (MBTH) that gives an azine intermediate with maximum absorbance at 216 nm. A systematic evaluation of sample dissolution medium was conducted as a means to enhancing sensitivity. In the best condition, samples were dissolved in 0.030 mol.L-1 tetraborate solution. This condition presented enhancement factors in the range of 35-54 for the aldehydes under investigation, computed as the improvement of the concentration limits of detection (LODs) with reference to the sample dissolved in pure water. The running buffer was 0.020 mol.L-1 tetraborate, pH 9.3, containing 0.050 mol-L-1 sodium dodecyly sulfate (SIDS). The overall methodology presented several advantages over established methods for aldehydes. Worthy mentioning that MBTH is available in high purity degree, dispensing laborious reagent purification procedures. A few method validation parameters were determined revealing good migration time repeatability (< 2.5% coefficient of variation, CV) and area repeatability (< 4% CV), excellent linearity (20-120 mug/L, r > 0.995) and adequate sensitivity for environmental applications. The LODs with respect to each single aldehyde were in the range of 0.54-4.0 mug.L-1 and 11 mug.L-1 for acetone. The methodology was applied to the determination of aldehydes indoors. Samples were collected in an impinger flask containing 0.05% MBTH solution, at a flow rate of 0.80 L.min(-1), during 2.5 h, at different times during the day. The most abundant carbonyls in the samples were acetone, followed by formaldehyde and acetaldehyde, with estimate peak concentrations of 452, 5.2 and 2.2 ppbv, respectively.

Red and blue emissions of europium doped gadolinium silicate from porous silica matrix and hydroxide carbonate with spherical shaped particles

In this work, Eu(III) and Eu(II) doped gadolinium silicates has been obtained as compact tubes starting from spherical gadolinium hydroxide carbonate using the pores of silica matrix as support and its surface as reagent. Eu(III) doped gadolinium silicate with hexagonal phase shows an interesting visible shifted charge transfer band when compared to disilicate with orthorhombic phase that was also obtained. Eu(II) gadolinium silicate has been prepared using CO atmosphere presenting an intense blue emission. The divalent europium system shows a potential application as an UV-blue converter. The samples were characterized by scanning electron microscopy (SEM), X-ray powder diffractometry (XRD) and photoluminescence spectroscopy. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Determination of oligoelements in parenteral formulations by planar chromatography and spectrophotometry

The authors have studied the chromatographic behavior of parenteral preparations for pediatric use containing inorganic cations. After separation and identification by thin-layer chromatography, Mn2+, Zn2+, and Cu2+ were analyzed by a method based on reaction with an appropriate reagent and extraction with an organic solvent which yielded elution and preconcentration, resulting in an appropriate solution for colorimetric quantitation. Cr3+ cation was determined by atomic absorption spectrophotometry after appropriate chromatographic separation, using microcrystalline cellulose (adsorbent) and an acetone:water:hydrochloric acid mixture (80:5:8) as the mobile phase.

Measurement of atmospheric formaldehyde using a drop collector and in-situ colorimetry

A sensitive and affordable approach is described for the in-situ measurement of ambient formaldehyde. Air is sampled around a 100 microliter aqueous drop containing 3-methyl-2-benzothiazoline hydrazone. After a desired period of sampling (typ. 5 min) and a waiting period of 10 min for the reaction to be completed, a second reagent (FeCl3) is added to the drop by means of a conjoined conduit. A blue product is formed and is read after an additional 10 min of reaction by a fiber-optic/light emitting diode based photodetector. A fresh drop is then formed and the process begins anew. As demonstrated here, the limit of detection is similar to 6.25 mu g m(-3) HCHO but can be significantly improved by using longer sampling times and a sampling rate higher than 100 mi min(-1) used in most of this work. This is the first example of a chromogenic drop sensor that utilizes sequential reagent addition.

Decomposição de argilas em forno de microondas e determinação simultânea dos seus constituintes principais por espectrometria de emissão óptica em plasma indutivamente acoplado

ANALYSIS OF CLAYS BY INDUCTIVELY COUPLED PLASMA OPTICAL EMISSION SPECTROMETRY AFTER CLOSED-VESSEL MICROWAVE-ASSISTED ACID DECOMPOSITION. In this work a closed-vessel microwave-assisted acid decomposition procedure for clays was developed. Aluminum, Ca, Fe, K, Mg, Na, Si, and Ti were determined in clay digestates by inductively coupled plasma optical emission spectrometry. The most critical parameter for total decomposition of clays was the composition of the reagent mixture. The applied power and the heating time exerted a less critical influence. Best decomposition conditions were attained using a reagent mixture containing 4 mL aqua regia plus 3 mL HF and the heating program was implemented in 12 min. The accuracy of the results was demonstrated using two standard reference materials and a paired t-test showed a good agreement between determined and certified values at a 95% confidence level.

Density and spatial distribution of Atta sexdens rubropilosa and Atta laevigata colonies (Hym., Formicidae) in Eucalyptus spp. forests

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A Semi-Continuous Analyzer for the Fluorimetric Determination of Atmospheric Formaldehyde

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Electrochemistry of organometallic compounds. Part II. Oxidations of alkyl and aryl derivatives of bis(salicylaldehyde)ethylenediimine cobalt(III) in dimethylformamide

The influence of the axial organic ligand R on the electrochemical oxidation of the compounds [RCoIII(salen)DMF)], where salen is bis(salicylaldehyde)ethylenediimine, and R CH3, C2H5, n-C3H7, n-C4H9, s-C4H9, i-C4H9, CH2Cl, CF3CH2, c-C6H11CH2, c-C6H11, C6H5, C6H5CH2, p-CH3C6H4CH2, and p-NO2C6H4CH2, was studied by means of cyclic voltametry in dimethylformamide (DMF), 0.2 M in tetraethylammonium perchlorate (TEAP), at 25 and -20°C, with a platinum disc working electrode. The above-mentioned compounds can be classified according to their electrochemical behavior. (a) The complexes with R CH3, C2H5, n-C3H7, n-C4H9, c-C6H11CH2, and C6H5 undergo a reversible one-electron oxidation in the 10-50 V s-1 potential scan range. At slower scan rates, the oxidized product decomposes chemically. At -20°C, this chemical step is slow, and a reversible one-electron electrochemical oxidation is observed. (b) The compounds with R CH2Cl, C6H5CH2, p-CH3C6H4CH2 and p-NO2C6H4CH2 undergo a quasi-reversible one-electron oxidation at room temperaure. At -20°C, the electrochemical process becomes more complex. A following chemical reactions is coupled to the quasi-reversible one-electron transfer. Two reduction peaks are observed. (c) The compounds with R i-C4H9, s-C4H9, and c-C6H11 undergo a reversible one-electron oxidation at -20°C. At room temperature, the irreversible chemical reaction following the electron transfer step is too fast to allow the isolation of the electrochemical step. (d) At -20°C, the derivatives with R C2H5, c-C6H11 CH2 and c-C6H11 are adsorbed at the electrode surface. Evidence indicates that the reagent in these reactions is the pentacoordinated species [RCoIII(salen)]. A linear free-energy relationship between E1/2 (for reversible processes) and the Taft polar parameters o* was obtained with a slope of ρ* = 0.25 ± 0.03. As expected, the benzyl derivatives which present mesomeric effects do not fit this polar correlation. The rated of the electrochemical oxidation is also affected by the nature of the ligand R. For the ligands which are strong electron-withdrawing groups and for the benzyl derivatives, the rate of the electrochemical oxidation of the metal ion decreases at room temperature. At lower temperatures, it is suggested that the oxidation to the CoIV-R species is followed by a chemical reaction in which this complex is partly transformed into a CoIII(R*) species, which is reduced at a much more cathodic potential than the Co(IV) species. © 1979.

Reação do tecido conjuntivo subcutâneo e de feridas incisas em contacto com gaze furacinada: estudo histológico

Strips of gauze and furacin gauze were implanted into the subcutaneous space and employed as dressing of dorsal incisions of albino rats. The animals were sacrificed after 24 hours, 2, 5, and 7 post-operative days. The pieces were processed for histological examination. It is possible to conclude that furacin gauze provokes more severe inflammatory reactions and does not favour connective neoformation and epithelization. Furacin gauze should be utilized only as a germicidal aim.

OBTENCAO DE MESALAZINA (5-ASA) POR CARBOXILACAO DE P-AMINOFENOL

The 5-aminosalicylic acid is usually prepared: 1. by the reduction of the azodye from diazotized aniline and salicylic acid and the posterior reduction of the formed compound; 2. for carboxylation with carbon dioxide under high pressure of p-aminophenol. Both do not present high yield, but the carboxylation process of p-aminophenol can easily be used and can reduce the obtainment process of 3 steps to only 2. Another advantage of this process is the fact that the product is produced without contaminants, because only one solid reagent (p-aminophenol) and the agent of carboxylation (CO2) is used.

Analytical chemistry in a liquid film/droplet

The measurement of nitrogen dioxide at the parts-perbillion level is described. The experimental arrangement consists of two optical fibers placed on opposite sides of and in contact with a liquid film (14-57 μL in volume) supported on a U-shaped wire guide and two tubular conduits (one of which constitutes the means for the delivery of the liquid), light from a green (555 nm) light-emitting diode enters the liquid film, composed of Griess-Saltzman reagent. The transmitted light is measured by a referenced photodetection arrangement. Sample gas flows past the droplet at a low flow rate (typically 0.10-0.25 L/min). The response is proportional to the sampling period and the analyte concentration. The limit of detection for this nonoptimized arrangement is estimated to be <10 ppb by volume for a 5 min sample. Some unusual characteristics are observed. The initial absorbance, when most of the analyte/reaction product is still near the surface, is higher than that when the content of the droplet is fully mixed. The signal depends on the sample flow rate in a nonmonotonic fashion, first increasing and then decreasing with increasing sampling rate; the specific chemistry involved in the collection and determination of NO2 may be responsible.