Conductimetric,Potentiometric and Visual Titrimetric Methods for Analysis of Nadolol

Abstract

Nadolol, a beta-blocking agent, has been assayed in pure form and in pharmaceutical formulation by acidimetric titrations using visual, potentiometric and conductimetric methods for detecting the end point in aqueous as well as in non-aqueous media. The method of assay involves the determination of the amount of nadolol in a given weight of sample. Six samples were run for each method and the percentages of recovery of nadolol from its tablets were calculated. For aqueous titrations, the average percentages of recovery for the visual, potentiometric and conductimetric methods are 100.6 ± 1.0, 99.3 ± 1.9 and 100.1 ± 2.0 respectively. For the non-aqueous titrations, the average percentages of recovery are 98.6 ± 0.8, 99.5 ± 0.5 and 98.4 ± 1.3 for the visual, potentiometric and conductimetric methods respectively.     

THE THERMODYNAMIC PARAMETERS OF FORMATION OF LANTHANIDE SQUARATE COMPLEXES

Abstract

The thermodynamic parameters of complexation of the lanthanide ions by squarate anions have been measured by potentiometric and calorimetric titrations. The design and operation of the calorimeter is described as it has some unique features. The complexes are weaker than analogous complexes with other hydroxy-keto ligands due to a more endothermic enthalpy of complexation.     

A Simple Sensor for Potentiometric Titrations

Abstract

A sensor for potentiometric titrations was prepared by coating a spectroscopic graphite rod with a solution of poly(vinyl chloride) and dioctylphthalate in tetrahydrofuran. The reference was a Ag/AgCl single-junction electrode. The sensor was used in the following potentiometric titrations:

1. precipitation titrations 2. acid-base titrations, 3. compleximetric titrations, and 4. redox titrations.

A survey of its use in such titrations is presented.

Preparation of the coated-graphite sensor is simple and rapid. Moreover, it is quite inexpensive. A limitation is its applicability in aqueous media only, because organic solvents will dissolve the membrane.     

Potentiometric Determination of Acids and Bases using Silicone Rubber Based Graphite Electrode

Abstract

A silicone rubber based graphite electrode has been used as an indicator electrode for potentiometric acid-base titrations. The electrode potential changes an average of 30 mV per pH-unit. If the electrodes are pretreated with a solution of an oxidant before use, the pH-sensitivity is increased. The electrode can be used in both aqueous and non-aqueous solutions. A measuring cell, composed of a silicone rubber based graphite electrode of small surface area and a chloride-selective reference electrode, can be used for acid-base titrations in the micro range.     

The Use of μ-Oxo-ditrifluoroacetato-diphenyl-diiodine in Potentiometric Titrations

Abstract

The use of μ-oxo-ditrifluoroacetato-diphenyl-diiodine (μ-ODDD) in potentiometric titrations has been studied. This reagent is more powerful oxidizing agent and more stable than bis(trifluoroacetoxy) iodobenzene (BTIB). The general analytical conditions for using this oxidant and the procedures for potentiometric determinations of sulfite, thiosulphate, nitrite, selenocyanate, thiocyanate and iron(II)ions as well as hydrogen peroxide and hydrazine sulphate are described.

A simultaneous determination of hydrazine sulphate and nitrite ions and also of selôenocyanate and thiocyanate ions has been carried out.     

Analytical Evaluation of the Silver Sulfide Membrane Electrode

Abstract

A membrane electrode selective for sulfide and silver ion has been described. No interferences were found for sulfide ion measurements, and only mercuric ion had a measurable interference with silver ion. Other characteristics of this electrode which are evaluated include speed of response and temperature coefficients. The use of the silver sulfide membrane electrode as an end-point detector in potentiometric titrations under oxidizing conditions is illustrated.     

18-Crown-6-potassium Ferricyanide Complex as a Potentiometric Titrant

Abstract

An oxidimetric titrant, 18-Crown-6-potassium ferricyanide complex, has been prepared in acetonitrile. This reagent is proposed for redox titrations in aqueous - acetonitrile media of some reductant compounds. The general analytical conditions for using this complex and the procedures for potentiometric determinations of oxalate, arsenic (III), thiocyanate, nitrite, sulfite, thiosulphate and iodide ions, as well as hydrazine sulphate and hydrogen peroxide are presented.     

Comparison of a single-use pH test strip and a glass electrode for potentiometric titration

The potentiometric titration of a carbonate mixture or an acetate solution is a common experiment in analytical laboratories. Typically, a glass electrode combined with a calomel or Ag/AgCl reference electrode is used to locate the equivalence points in neutralization titrations. The dissociation constants of weak acids and bases can be calculated from the pH at the half-neutralization point. Recently, a new commercial product for measuring pH has been developed. This novel acid–base detection strip is a single-use sensor that requires neither storage in a preservation liquid nor calibration prior to use. This study examined its suitability for the continuous monitoring of pH changes in potentiometric titrations of carbonate mixtures, acetate solutions, or ammonia solutions. There were no significant differences in the concentrations of solutions tested using a glass electrode and a pH test strip. The pK_a, pK_b, and pH values determined using the two systems differed by less than 5%. The results confirmed that the pH strips are suitable for continuously monitoring pH changes during neutralization titrations. However, the strips can only be used once.     

A complex between ammonia and chlorine studied at 20°K in a nitrogen matrix

UV and IR spectra of ammonia and chlorine codeposited in a nitrogen matrix at 20°K have been recorded. An intense absorption band round 2500 Å has been observed. An IR-active chlorine stretch frequency of about 460 cm^?1 and small shifts on the ammonia absorptions were determined. The results are discussed in terms of a charge transfer complex between ammonia and chlorine. From the complex shifts for ammonia and ammonia-d₃ an opening up of the HNH bond angle on complexing by about 3.6° has been calculated.     

Differential Titration Based on Transient ISE Response

Abstract

A new way of evaluating potentiometric titrations based on the transient response of some ISE's is described. The method is illustrated using the titra 2+ tion of sulphate with a Ba solution using a Na-ISE in weakly mineralized waters.     

Potentiometric Determination of Nitrilotriacetate in Water and Sewage

Abstract

A potentiometric titration of nitrilotriacetate in wastewater and sewage samples and a procedure of sample treatment to eliminate the interferences are described. T1³⁺ and Cu²⁺ solutions were the titrants and the potentiometric titrations were monitored with a platinum redox electrode. T1³⁺ :2NTA complex formation was found. The lower detection limit was 0. 1 ppm of NTA. The relative standard deviation in sewage samples was 5% and the recovery varied from 90–110%.     

Simultaneous Determination of Selenocyanate and Thiocyanate Ions in the Presence of Cyanide by Oxidation with bis (Trifluoroacetoxy) iodobenzene

Abstract

An investigation of the use of potentiometric titrations of selenocyanate and thiocyanate aqueous solutions, in the presence of cyanide ions, with bis (trifluoroacetoxy) iodobenzene in acetonitrile and then the gravimetric determination of the products of the reactions, elemental selenium and sulphate ions, has been carried out.

Selenocyanates are first oxidized to selenium and then thiocyanates are oxidized to sulphate ions. Break point curves are identified. The rose-pink precipitate is filtered and the clear filtrate is warmed on a hot plate for evaporation of acetonitrile. A solution of barium chloride is added to the hot solution in order to precipitate the sulphate ions.     

The suitability of various calcium electrodes based on metal salts of di-(n-octylphenyl)phosphoric acid and some derivatives for the measurement of calcium in sea water

The calcium salts of di-(n-octylphenyl)-phosphoric acid, di-(p-n-octyl-o-nitrophenyl)-phosphoric acid and di-(p-n-octyl-o-bromophenyl)-phosphoric acid have been investigated as calcium sensors in membrane electrodes. The electrodes have been used for potentiometric titrations of calcium in sea water. The effect of varying the membrane solvent and the chelate metal has been studied.     

An Apparatus for Titrations in Liquid Ammonia

An apparatus for titrations in liquid ammonia is described. The titrations can be carried out in the absence of air, and the utility of the apparatus is demonstrated for a number of conductometric and potentiometric titrations.     

Determination of the protonation constant and partition coefficient of 4-methylpyridine in KNO3-toluene at 25°C

The protonation constant in 1.0 mol-dm^–3 KNO₃, and partition coefficient of 4-methylpyridine (B) between 1.0 mol-dm^–3 KNO₃, and toluene have been determined at 25°C by measuring the H₃O⁺ ion concentration with a glass electrode. The experimental work consisted of two sets of potentiometric titrations. In the first case, the titrations were carried out in an aqueous system of constant ionic strength and in the second, two-phase titrations using toluene as organic phase were performed. All the titrations were conducted automatically by the use of a computer controlled potentiometric system. The results were treated using graphical and numerical methods and the systematic erros were also considered. The formation constant of the protonated 4-methylpyridine was correlated with the composition of the aqueous phase by means of Bromley's theory.Recently deceased. This paper is dedicated to the memory of Dr. José Maria Castresana.     

Spectrophotometric and potentiometric study of the acid—base equilibria of indophenols in aqueous media

Six indophenols, with redox and acid—base indicator properties, have been examined by spectrophotometric and potentiometric methods. By analysing the absorption spectra obtained at different pH values, three independent values were obtained for their K_Ox dissociation constants, which are closely related to their properties as acid—base indicators. Three of the indophenols have also been examined by acid—base and redox potentiometric titrations. All K_Ox and E° values agree well with polarographic values. The use of these substances as visual acid—base and redox indicators is discussed.     

COMPLEXATION OF ALKALINE EARTH CATIONS BY NONCYCLIC POLYETHERS,CROWN ETHERS,AND CRYPTANDS IN ACETONE

Abstract

The complexation of akaline earth cations by non-cyclic polyethers, crown ethers and cryptands was studied in acetone by means of potentiometric and calorimetric titrations. The results show that the stabilities of the complexes decrease in the order: cryptands, crown ethers and noncyclic polyethers. Interactions between the different ligands and solvent molecules influence the stability of the complexes formed when compared with methanol as solvent.     

Preparation and Response Properties of Selective Bio-Electrodes Utilizing Polymer Membrane Electrode-Based Ammonia Gas Sensors

Abstract

A new type of potentiometric ammonia gas sensor is employed in the preparation of selective bio-electrodes for urea and glutamine. The bio-electrodes are constructed by immobilizing the enzyme urease and intact porcine kidney cells, respectively, at the surface of a disposable ammonium selective polymer membrane electrode-based ammonia gas sensor. The resulting electrodes have favorable response properties when compared to corresponding devices previously assembled with costly commercial gas sensors. Preliminary studies with the urea electrode demonstrate its usefulness for the rapid determination of urea in serum samples.     

Determination of total chlorine in waste oil

Summary A simple method has been developed to determine the concentration of organic chlorine in waste oil. The determination is based on the conversion of organic chlorine to inorganic chloride by reaction with sodium biphenyl followed by extraction with nitric acid and a mixture of nitric acid and water. The concentration of chloride is determined by direct potentiometry with an ion-selective electrode. The limit of determination amounts to 3·10^–5 mol·l^–1 chloride ions with a standard deviation of 3.5%. Different samples of waste oil have been analyzed and the results have been compared to those obtained by combustion in a H₂/O₂ flame followed by potentiometric titration with silver nitrate.     

Determination of Acid Dissociation Constants of Neamine by Potentiometric and Electrospray Mass Spectral Techniques

The acid dissociation constants of neamine have been measured using potentiometric titrations. The pK_a1, pK_a2, and pK_a3 values of neamine are 6.35 ± 0.2, 7.73 ± 0.15, and 8.62 ± 0.08, respectively. Neamine is readily characterized using positive-ion electrospray ionization–mass spectrometry (ESI–MS). Various protonated species and their solvated ions are mainly observed. Nevertheless, the abundances of the observed speciation over the pH range 5.0–9.8 do not reflect the variation in the bulk solution. Hence, reaction quotients determined from the ESI–MS investigations vary significantly from the pK_a's determined from potentiometric titrations, thereby illustrating that care must be taken in determining thermodynamic properties using the former technique.