Synthesis and spectrophotometric studies of water-soluble amino[bis(ethanesulfonate)] azobenzene pH indicators

Three azobenzene pH indicators with amino[bis(ethanesulfonate)] substituents were synthesized and studied by UV–visible absorption spectroscopy in aqueous solution. The indicators exhibit brilliant and distinct colour changes with transitions between pH 1 and 4. Significant changes were observed in the UV–visible spectra on titration with acid with pK_a values ranging from 2.2 to 2.8. The indicators demonstrate individual changes in colour as a function of pH. These novel pH indicators complement the existing library of azobenzene indicator dyes and may be useful for environmental situations with high proton concentrations.     

Evaluation of colour changes of indicators: the supercolor program

SUPERCOLOR is a microcomputer program for the computation of chromaticity parameters from spectrophotometric data. The program is written in BASIC for the HP-200 computer series and it allows the characterization of indicator colour transitions in the standard CIE chromaticity systems. The numerical results for up to 12 indicators can be compared in the same plot for each chromatic system, so that colour changes are easily compared. The pK_a values, pH transition ranges, pH of maximum colour change, SCD values and optimum indicator concentration for visual titrations can be calculated, as well as the colour coordinates.SUPERCOLOR also provides subroutines for computation of screened indicators and simulation of the colour changes of these indicators or other indicator/inert dyes mixtures. The results for some common indicators are presented.     

Studies in the tetraarylborates: Part II. The preparation and reagent properties of sodium tetrakis(p-fluorophenyl)borate,a selective reagent for cesium

Sodium tetrakis(p-fluorophenyl)borate has been synthesized and found to be a very selective gravimetric reagent for the determination of cesium. It formed precipitates with cesium, silver, thallium(I) and rubidium but not with potassium and ammonium ions. The cesium tetrakis(p-fluorophenyl)borate separated as a white crystalline compound, which was easily filterable. It achieved constant weight rapidly at 110° and showed no signs of decomposition after 18 h of drying.     

The determination of cystine with p-aminodimethylaniline

The considerable background colour in previous methods for the absorptiometric determination of cystine by means of p-aminodimethylaniline has been almost eliminated by solvent extraction of the required coloured compound. Alkali treatment of the extract intensifies the colour. The improved test is two and a half times more sensitive than previous tests based on the same reaction and the colour produced has a more sharply defined absorption peak. Cystine (plus cysteine) in protein hydrolysates may be determined with an error of less than 1%.     

Acid—base equilibria in the mixed solvent 80% dimethyl sulfoxide—20% water : Part I. definition of ph scale and determination of pk values of aliphatic monocarboxylic acids

The acid—base equilibria in the mixed solvent, 80% dimethyl sulfoxide—water, have been investigated by potentiometric measurements with a glass—silver—silver chloride electrode couple. The response of the glass electrode is quick and reproducible over the whole pH scale. The autoprotolysis constant (itK_SH) of the mixed solvent has been determined; the value obtained, pK_SH = 18.40, agrees well with reported data. The pK_a values of the following aliphatic monocarboxylic acids are reported: formic, acetic, propionic, n-butyric, iso-butyric, n-valeric, iso-valeric, capric, pentadecanoic, stearic, monochloroacetic. The mixed solvent offers better titration conditions than water for the determination of these acids.     

Studies on adsorption indicators : Titration of iodide in presence of chloride. mechanism of the colour changes during argentometric titrations with congo red as adsorption indicator

Congo red is a suitable indicator for the titration of iodide in presence of chloride with silver solution at pH 5–5.5. The behaviour of congo red as an adsorption indicator is described in detail. The silver compound of congo red has been isolated and its properties investigated.     

N,N-bis-(2-benzimidazolylmethyl)L-methionine: An efficient Ag(I) extractant

A new ligand N,N-bis-(2-benzimidazolylmethyl)L-methionine has been synthesized and well characterized by different analytical techniques. The ligand has a very strong affinity for silver(I) and is used for the selective extraction of silver ions from aqueous solution into 1-butanol. The effect of concentration of Ag(I), pH, diverse ions, and temperature on the extraction is reported. The developed method has success-fully been applied to the determination of silver in different samples. Radiotracer technique, using ^110mAg(I) as a tracer, has been used for monitoring the concentration of silver ion.     

Effect of solvent on chain propagation and termination reaction rates in radical polymerization

The radical polymerizations of acrylamide and methacrylamide and of acrylic, methacrylic and fluoroacrylic acids have been studied in various solvents. The nature of the solvent affects the overall rate due to changes in k_p and E_p. It has been shown that the effect of solvent also depends on the nature of the monomer. A possible explanation of the observed behaviour is discussed.     

DFT study on hydrogen-bonding adsorption mechanism of rutin onto macroporous adsorption resins functionalized with amino, hydroxyl, and carboxyl groups

The adsorption mechanism of a series of macroporous adsorption resins (p-(CH₃NH)PhL (L = NH₂, OH, COOH)) with rutin have been investigated using density functional theory calculations at B3LYP/6-31G(d,p) level of theory. Solvent effects on these species were explored using calculations that included a polarizable continuum model for the aqueous solvent. In this article, the geometry structure, interaction energies and the infrared spectra for the stable reactants and the adsorption complexes were obtained and analyzed. The results show that the hydrogen-bonding have been formed in the adsorption complexes. The higher interaction energy is calculated for the carboxyl group, while the resin with amino group has the highest adsorption capacity for rutin. The adsorption complexes become more and more stable as increasing the number of adsorbents. Our theoretical study is in good explanation for the experimental results.     

Redox behavior of juglone in buffered aq.: Ethanol media

The present work reports the redox mechanism of 5-hydroxynaphthalene-1,4-dione (HND), commonly known as juglone, in buffered aqueous media having 50% of ethanol. HND followed different mechanistic routes depending upon the pH of the media and more than one pK_a were evaluated from the changes in the slope of the E_p vs. pH plot. The change of pH from acidic to neutral conditions was found to switch the mechanism from CEC to EE mechanism. Pulse techniques were utilized to determine the number of electrons involved in the oxidation and/or the reduction step and to ensure the nature of the redox process. Based upon the obtained results, an electrode reaction mechanism was proposed. Computational studies of HND supported the experimental results. UV-Visible spectroscopy was also employed for the detailed characterization of the compound in a wide range of pH and for the determination of its pK_a.     

Congo red as adsorption indicator

1. A new adsorption indicator 'Congo red' has been described for argentometric titraitions. 2. The new indicator differs from all those described earlier in having both acidic as well as basic character, on account of which it is adsorbed with different colours, by both the positively and negatively charged halide bodies. 3. The adsorbability of the indicator by both the positively as well as the negatively charged halide bodies, endows it with a sharp colour change at the end point, a ready reversibility and a large range of applicability in the argentometric titrations. 4. The great usefulness of the indicator lies in its being applicable both in the titrations of halide ions by silver ions and also in the reverse estimations of silver ions by halide solutions. 5. The end point is particularly sharp as the colour change occurs from one end of the spectrum to the other: blue to red and vice versa. 6. The effect of the addition of a protective colloid 'dextrin' has been found to make the end points even sharper.     

Experimental evaluation of adsorption and electrode field effect on the constants of weak acid dissociation near the mercury electrode surface

Two methods are described for the experimental evaluation of the weak acid dissociation constants in the near electrode surface. One of them, based on the dependence of differential capacity of pH of the solution at constant potentials, gives the pK_A^s values for adsorbed acids; the second one uses the ψ₁-value dependence on pH in the presence of the cationic acids (as pyridinium ions) and comparison of the pH of the buffer solution of the weak acid under investigation with pK_A^s of the cationic acid and gives the pK_A values in the volume just near the electrode.     

Determination of eight metals in the international biological standard by flameless atomic-absorption spectrometry

The reaction of p-cresol with acidified cobaltinitrite has been qualitatively and quantitatively studied. On an analytical scale, the reaction predominantly leads to 2-nitro-p-cresol. The dimer of this compound has also been identified as a minor product. Two methods have been devised for quantitative analysis. These procedures represent rapid, accurate and precise techniques for analyzing p-cresol and may be applicable to other p-substituted phenols.     

Potentiometric determination of tetraphenylborate with silver nitrate

A simple potentiometric method for determining the tctraphenylborate ion (C₆H₅)₄B- contents of organic amine tetraphcnylborate salts has been developed. The compounds arc dissolved in 1 : 1 aqueous acetone; and the solution is buffered at a pH of 5 with 3M acetic acid and 3M sodium acetate. The resulting solution is then titrated with 0.06N aqueous silver nitrate, using a silver indicating electrode, a glass reference electrode and a Beckman pH meter to indicate EMF changes. Platinum electrodes in conjunction with the Malmstadt automatic titrator can also be used. Good end-points were obtained for all structure types except the primary aromatic amine borates. Values for (C₆H₅)₄B- found were within 2% of theory for 22 compounds so analyzed.     

Palladium metal electrode and its analytical application to precipitation and acid–base analysis in aqueous and non-aqueous media

Electrochemical characterization of palladium electrode has been reported. The investigated electrode showed a linear dynamic response for p-toluensulfonic acid and iodide ions in the concentrations range between 5?×?10^?1 and 1?×?10^?5 mol L^?1 with a Nernstian slope of 55 mV for p-toluensulfonic acid and 63 mV per decade for iodide ions in water, as well as 53 mV for p-toluensulfonic acid and 51 mV per decade for iodide ions in dioxane. The response time of the electrodes was less than 10 s in the used solvents. Some potential analytical applications of the sensors have been pointed. Palladium electrode for the potentiometric titrations of acids (citric, barbituric, and p-toluensulfonic acid), bases (N,N’-diphenylguanidine, tributylamine, and 2,2'–bipyridine), halides, and some real samples in aqueous and non-aqueous solutions were studied. Тetrabutylammonium hydroxide, perchloric acid, and silver nitrate proved to be very suitable titrating agents for these titrations. The standard deviation of the determination of the investigated compounds was less than 0.9 % from those obtained with a glass electrode, i.e., silver electrode.     

Differential pulse polarographic behaviors of p-nitrosodimethylaniline: Application for microdetermination of NADH

The differential pulse polarographic behavior of p-nitrosodimethylaniline has been investigated in Britton-Robinson buffer and phosphate buffer. The peak obtained at pH 8.0 is recommended for the trace determination of this compound, with an experimental detection limit of 18 ppb (1.2 × 10^?7M) in simple aqueous solution. The method is also applied for the indirect microdetermination of NADH. The experimental detection limit of NADH is shown to be 1.05 × 10^?6M.     

The sensitized photodehydrochlorination of poly(vinyl chloride)—II. Model compound studies

p-Cresol, a model compound for an additive shown previously to be a potent photosensitizer of dehydrochlorination in poly(vinyl chloride) PVC, has been shown to sensitize dehydrochlorination in t-butyl chloride, a model for PVC. A quantitative study of the effect of chlorinated alkanes upon the fluorescence of p-cresol in solution reveals that quenching is due to charge transfer interactions, the halogenated compound acting as electron acceptor. Since the mono-halo compound t-butyl chloride does not quench p-cresol fluorescence, it was concluded that the photosensitization occurs via the triplet state of the p-cresol, and this view was confirmed by addition of triplet quenchers. A mechanism for the reaction is proposed, initial exciplex formation being followed by electron transfer.     

Hazards associated with the use of electrochemically prepared substrates in the qualitative analysis of aqueous solutions by surface-enhanced Raman spectroscopy

The different spectral behaviour of silver surface-enhanced Raman spectroscopy (SERS) substrates roughened electrochemically in and without the presence of an analyte has been shown clearly. These differences are associated with anomalous local pH conditions within the cavities in surfaces of high microporosity in the in-situ roughened silver substrates. In-situ roughened silver electrodes appeared to have a much higher porosity compared with ex-situ roughened surfaces.     

Fast high-throughput method for the determination of acidity constants by capillary electrophoresis: I. Monoprotic weak acids and bases

A new and fast method to determine acidity constants of monoprotic weak acids and bases by capillary zone electrophoresis based on the use of an internal standard (compound of similar nature and acidity constant as the analyte) has been developed. This method requires only two electrophoretic runs for the determination of an acidity constant: a first one at a pH where both analyte and internal standard are totally ionized, and a second one at another pH where both are partially ionized. Furthermore, the method is not pH dependent, so an accurate measure of the pH of the buffer solutions is not needed. The acidity constants of several phenols and amines have been measured using internal standards of known pK_a, obtaining a mean deviation of 0.05 pH units compared to the literature values.     

Investigation of the silver iodide—p-ethoxychrysoidine adsorbate by infrared spectroscopy

Infrared measurements for p-ethoxychrysoidine and the silver iodide—p-ethoxychrysoidine adsorbate indicate that the dye is bound to silver iodide through amino groups. The interaction is discussed on the basis of surface imperfections of silver iodide and the polar nature of p-ethoxychrysoidine. Of the two possible crystal structures of silver iodide, only the γ-modification is present in the adsorbate.