Potentiometric determination of chloride and bromide in airborne dust

Summary A simple, rapid and reproducible potentiometric titration method for determination of both bromide and chloride in airborne dust is described. The use of a precise microburette and a differentiating recorder allows good resolution of the two species determined. The method can be easily applied for routine environmental control analysis.

---

Zusammenfassung Die Anwendung eines einfachen, schnellen und reproduzierbaren potentiometrischen Verfahrens zur Bestimmung von Bromiden und Chloriden in Stauben wurde beschrieben. Der Einsatz einer Motorkolbenbürette für die relativpotentiometrische Titration und die Verwendung eines Differentiators erlauben eine exakte Bestimmung des Titrationsendpunktes und ermöglichen so das gute Auflösungsvermögen des Verfahrens. Die Methode wurde routinemäßig in der Umweltanalytik eingesetzt.

---

---

On leave from Faculty of Chemistry, University of Sofia, Sofia, Bulgaria.     

Potentiometric titrations of organotin chlorides with tetraphenylarsonium chloride in acetonitrile media

Tetraphenylarsonium chloride was used for the potentiometric titration of R₄-_nSnCl_n compounds (R = Me, Et, Pr, Bu, Ph ; n = 2,3) in acetonitrile media. Evidence for penta-coordinated R₄-_nS_nCl_n+1- complexes was obtained. A stability scale as a function of R groups is given.     

Potentiometric method for determination of kinetic characteristics of radical reactions in aqueous media

Kinetic features of the reactions of K₄[Fe(CN)₆] with radicals initiated by water-soluble azo-initiator 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) at 37 °C were studied using the potentiometric method. Potassium ferrocyanide was shown to be a radical acceptor, whereas K₃[Fe(CN)₆] formed by the oxidation with the radicals in combination with K₄[Fe(CN)₆] is an electrochemical system, the study of which makes it possible to determine kinetic characteristics of radical reactions. The rate constants for the reactions of peroxide radicals RO₂ · with K₄[Fe(CN)₆] were calculated.     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Potentiometric determination of cephalothin

The composition of a pseudo-liquid potential-determining phase for the cephalothin-selective electrode has been determined and the following basic electrode parameters were examined: measurement range, slope, limit of detection, selectivity and lifetime. This paper discusses the effect of side-chain substituents on the electrode properties, the electrode having been used for cephalothin determination in the range 43-436.5 mg l-1 (standard deviation, 0.64-4.5 mg l-1).     

Reactions of (benzamidomethyl)triethylammonium chloride with some inorganic nucleophiles in aqueous media

A variety of benzamidomethyl derivatives were prepared in water under alkaline conditions (pH>9) via reaction of (benzamidomethyl)triethylammonium chloride (1) with different inorganic nucleophiles. Reaction of 1 with hydroxylamine did not give the expected mono(benzamidomethyl)-hydroxylamine (3) but rather gave N,N- di(benzamidomethyl)hydroxylamine (2). Reactions of 1 with sodium azide and potassium cyanide gave benzamidomethyl azide (4a) and benzamidomethyl cyanide (4b) respectively. Potassium thiocyanate and sodium iodide reacted with 1, and the anion- exchanged products (benzamidomethyl)triethylammonium isothiocyanate (5a) and (benzamidomethyl)triethylammonium iodide (5b) were thus obtained. Cyanamide and potassium cyanate reacted readily with 1 and both gave the same mixture of di(benzamidomethyl)amine (7) and tri(benzamidomethyl)amine (8). All the reactions occurred smoothly, under mild conditions, to give the products in moderate to high yields.     

Potentiometric determination of the dissociation constants of L-histidine, proline and tryptophane in various hydroorganic media

The dissociation constant values of L-histidine, proline and tryptophane were determined at 25 +/- 0.1 degrees C by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetone and dioxane. Initial estimates of the dissociation constant values of the different amino acids studied have been refined with ESAP2M computer program. It was observed that changing the medium permittivity as the solvent is enriched in methanol or ethanol has little influence on the pK*(a) values of the amino acids studied. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogeneity of the salvation shells around the solute.     

Potentiometric determination of 8-chlorotheophylline

Two methods are described for the potentiometric determination of 8-chlorotheophylline in aqueous solution. Both methods are based on the reaction of 8-chlorotheophylline with silver ions. In the first, the nitric acid produced in the reaction is titrated with sodium hydroxide. In the second, the 8-chlorotheophylline is titrated directly with silver nitrate in sodium carbonate medium. Both methods give reasonably accurate and reproducible results, and are suitable for the assay of 8-chlorotheophylline in pharmaceutical preparations.     

Potentiometric determination of potassium ferricyanide

A rapid and accurate electrometric method for the determination of potassium ferricyanide solutions has been investigated. It consists in titrating ferricyanide solutions potentiometrically against standard AgNO₃, using a silver indicator electrode in conjunction with a saturated calomel electrode connected by a KNO₃ bridge. Either of the reagents may be used as the titrant. A marked change in e.m.f is observed at thc end-point corresponding to the formation and precipitation of Ag³[Fe(CN)₆]. The curves have a regular form, a pronounced maximum in dE/dV occurs at the end-point and the results are very accurate and reproducible. The reaction, though simple, affords a quantitative method for the determination of ferricyanide or silver. The effect of neutral salts and ethanol on the accuracy of the end-point has been studied.     

Potentiometric determination of sulphur in secondary alumina

Summary A procedure for determination of sulphur in adsorbates based on combustion of samples in a high-frequency induction furnace, and subsequent registration by potentiometric titration in an alcoholic medium is described. Optimum conditions for the titration are discussed. A new type of indicator electrode with integrated impedance transformation electronics has been used. The technique was applied with good results to samples of secondary alumina (standard deviation 0.01%).

---

Potentiometrische Bestimmung von Schwefel in sekundärem Aluminiumoxid

Zusammenfassung Das beschriebene Verfahren zur Schwefelbestimmung in Adsorbaten beruht auf der Verbrennung der Probe in einem Hochfrequenz-Induktionsofen und nachfolgender potentiometrischen Titration in alkoholischem Medium. Die optimalen Titrationsbedingungen werden diskutiert. Es wurde eine neuartige Indicatorelektrode mit integrierter Impedanztransformation benutzt. Bei der Anwendung auf sekundäres Aluminiumoxid wurden gute Ergebnisse erzielt (Standardabweichung 0,01%).

     

Potentiometric and thermometric determination of mercaptopyrimidines

Summary Potentiometric and Thermometric Determination of Mercaptopyrimidines Potentiometric and thermometric methods for the determination of several 2- and 6-mercaptopyrimidines are described. Mercapto groups can be titrated as acids in water or in dimethylformamide media. The use of acetic acid as solvent allows titration of the basic pyrimidine nucleus. Thermometric titrimetry is also a valuable procedure for the titration of mercapto groups, either directly with sodium hydroxide or by back-titration with hydrochloric acid after addition of excess of alkali. About 10–25 mg of sample can be determined with an error better than 1%.     

Potentiometric determination of silver with dithiooxamide

Potentiometric titration with dithiooxamide solution can be used to determine silver in the 0.0100–50.0 p.p.m range with an average accuracy of ca. 0.5% and a relative standard deviation ranging from 1.26% to 0.03% The metals commonly associated with silver can be masked with fluoride and EDTA The advantages of the method over other potentiometric and common spectrophotometric methods are outlined.     

Potentiometric determination of dialysate urea nitrogen

An enzymatically modified ammonium ion-selective electrode has been applied for the determination of urea in spent dialysate. The biosensor has been used in a simple flow-injection analysis (FIA) system. The system enables one to perform over 25 dialysate urea nitrogen (DUN) determinations per hour. The interferences from other components of posthemodialysis fluid were eliminated by simultaneous measurements with non-modified enzymatically ion-selective electrode. It is possible to use both the sensors in a simplified differential potentiometric system. The results of DUN determination using the biosensor/FIA system and a conventional method of urea determination were comparable. The presented analytical system can potentially find wider biomedical application in the monitoring of hemodialysis progress.     

Potentiometric titration of heterocyclic nitrogen bases in non-aqueous media

Pyridine, quinoline, isoquinoline, acridine, alpha-picoline, beta-picoline, gamma-picoline and 2,6-lutidine have been titrated potentio-metrically (calomel and glass electrodes), with chlorosulphonic acid in methyl ethyl ketone-acetic acid (1:1) medium, with an error of less than 1%.     

Methods of the determination of inorganic arsenic species by stripping voltammetry in weakly alkaline media

Two methods are considered for the direct determination of trace amounts of As(III) and As(V) in solutions by stripping voltammetry (SVA) using an ensemble of gold microelectrodes (Au-MEA) previously developed by the authors of this paper. In both methods, analyzing a mixture of As(III) and As(V), analysts first record an SVA signal of As(III) in a supporting Na₂SO₃ electrolyte. To record an analytical SVA signal of As(V), in the first method one should use the reduction of As(V) to As(III) on the surface of an Au-MEA catalyzed by the system Mn(II)/Mn(0) and followed by the formation of As(0) and its anode dissolution. In the second method, the photoreduction of As(V) to As(III) in a Na₂SO₃ solution is conducted under UV irradiation followed by the reduction of As(III) to As(0) and its electrooxidation on Au-MEA. The two methods are compared taking into account their performance characteristics and interfering ions. To improve the reliability of the results of analysis at an insignificant increase in its cost, we propose the consecutive use of both methods. The procedures are simple and rapid, do not require the removal of dissolved oxygen or toxic reactants, and can be used for the analysis of aqueous solutions at the place of sampling. The results of analyses of real objects, snow, river water, and process solutions are presented.     

Potentiometric determination of aminal stability constants

Potentiometric titration was used to determine the logarithms of the stepwise equilibrium constants for the species formed between morpholine and formaldehyde in aqueous solution, ionic strength 0.5 and 2.5M (KCl) at 25 degrees C. The instrumental and computational techniques developed for metal-ligand stability constant determination were applied. Formaldehyde is equivalent to the metal-ion and is represented by M while neutral morpholine is equivalent to the ligand and is represented by L. The stability constants of the following equilibria were determined by non-linear regression (figures in parentheses are at ionic strength 2.5 M KCl): M + L left arrow over right arrow ML (hemi-aminal) logK(1) = 2.90 +/- 0.02 (2.980 +/- 0.004); ML + L left arrow over right arrow ML(2) (bis-aminal); log K(2) = 1.3 +/- 0.2 (1.41 +/- 0.07); MLH left arrow over right arrow ML + H(+) (protonated hemi-aminal) pK(a) = 5.87 +/- 0.01 (6.411 +/- 0.005); ML(2)H left arrow over right arrow ML(2) + H(+) (protonated bis-aminal) pK(a) = (7.6 +/- 0.2). the pK(a) of the protonated bis-aminal could only be determined at the higher ionic strength. The results are in good agreement with reported values determined using the classic formol titration. The automated titration system acquired the full time course of the pH change upon each titrant addition allowing a kinetic analysis to be performed as well as an equilibrium analysis. The forward and reverse rate constants for M + L left arrow over right arrow ML were 0.77M(-1) sec(-1) and 8.1 x 10(-4) sec(-1). respectively.     

Potentiometric determination of EDTA and NTA in detergents

A method is described for the potentiometric titration with iron(III) of EDTA and NTA in detergents, a platinum electrode being used as indicator. EDTA and NTA were extracted at pH 9 and 50–60 °C in the presence of magnesium(II). Interference from polyphosphates was minimized by hydrolysis to orthophosphate followed by remotion as magnesium ammonium phosphate. Complexometric titration was carried out at pH 4.7 in acetate medium, in the presence of ferroin. A preliminary cleaning of the platinum electrode with thiosemicarbazide in hydrochloric acid was found to improve significantly the potential measurements. A mean recovery of 93% for EDTA and 89% for NTA was observed.