Potentiometric titration of tellurium with a fluoride-selective electrode

Tellurium, as tellurite, can be determined with a fluoride-selective electrode by means of an indirect procedure based on precipitation of tellurite with excess of lanthanum(III), followed by back-titration with standard fluoride. The end-point is located by using the Gran method, and the titrations are suitable for tellurite concentrations above 1 mM.     

Amperometric titrations with the help of selenites

Summary A new procedure for rapid amperometric titration of cobalt based on precipitation of cobalt as the normal selenite is described. Potassium chloride (0.1 M) containing 0.01% gelatin as the maximum suppressor has been used as the supporting electrolyte. The use of 50% overall concentration of methanol was found essential for these titrations. The concentration of alcohol necessary for cobalt concentrations below 2 millimolars was 70%. The titrations have been performed at an applied potential of –1.5 volts vs. S.C.E. Effect of methanol on the equivalence point of the titration has also been studied. The procedure described gives accurate results, which agree well with the formula CoSeO₃ for the normal selenite of cobalt.     

Potentionetric Titrations Of Oxalate With A Fluoride-Selective Electrode

Abstract

Two methods for oxalate determination with a fluorideselective electrode are proposed. For oxalate amounts higher than 0.2 mmol, the joint precipitation of oxalate and standard fluoride with lanthanum(III) can be used. For smaller oxalate amounts, the precipitation of oxalate with excess of lanthanum(III) followed by back-titration with fluoride, is suitable. The end-points are located using the second derivative procedure and by means of the Gran method, respectively.     

Reaktion von Lanthanfluorid mit Halogenalkanen

Reactions of Lanthanum Fluoride with Halogenoalkanes Reactions are reported on lanthanum fluoride as a fluorinating reagent and as a catalyst for the fluorination and dismutation of halogenoalkanes. Carbon tetrachloride, monofluorotrichlormethane, and chloroform are partially fluorinated by lanthanum fluoride. In the presence of HF, lanthanum fluoride acts as catalyst the fluorine transfer to CCl₄, CHCl₃ and C₂F₃Cl₃. Monofluorotrichloromethane, difluorodichloromethane, and trifluorotrichloroethane dismutate on lanthanum fluoride. Results on the thermal decomposition of the above-mentioned fluorochloroalkanes are communicated.     

Application of potentiometric stripping analysis to compleximetric titrations

Samples that are 0.1–10 mM in lead(II) or 0.025–0.25 mM in bismuth(III) can be titrated with EDTA and the titrations monitored by means of computerized potentiometric stripping analysis. The coefficients of variation are 0.12–0.40%; systematic errors are estimated from computer-calculated titration curves using conditional constants obtained from the titration curves. The conditional stability constants for calcium(II), manganese(II) and lanthanum(II) in 0.5 M sodium chloride are determined from the exchange reaction with the lead—EDTA complex.     

Substoichiometric precipitation of fluoride with lanthanum

The substoichiometric precipitation of fluoride with lanthanum was studied by using¹⁸F and¹⁴⁰La tracers and it was found that fluoride could be precipitated substoichiometrically with lanthanum and the reaction ratio between fluoride and lanthanum was 3∶1. The pH range at which fluoride can be separated substoichiometrically with lanthanum is between 2 and 8. Barium and indium interfere in the precipitation of fluoride, sodium, copper and manganese, however, not. Fluorosilicate can also be precipitated substoichiometrically by using lanthanum as a precipitant and the reaction ratio between fluorosilicate and lanthanum was 1∶2. This separation was applied for the determination of oxygen in silicon crystals. The concentration of oxygen measured in some silicon crystals was between 5 and 27 ppm and in good agreement with those by non-destructive method and infrared spectrophotometry.     

An improved method for the spectrophotometric determination of fluoride by addition of sodium dodecyl sulphate to the fluoride/lanthanum (III)/Alizarin fluorine blue system

The conventional spectrophotometric method for the determination of fluoride, based on the fluoride/lanthanum(III)/alizarin fluorine blue ternary complex, is improved by addition of sodium dodecyl sulphate. In 15% (v/v) acetone medium, the absorbance of the binary reagent complex is decreased and the reaction time is only 3 min under sonication. Beer's Law is obeyed at 574 nm for fluoride concentrations in the ranges 0.075–0.30 and 0.20–1.2 mg 1^?1; the apparent molar absorptivities are (1.6 ± 0.1) × 10⁴ and (1.5 ± 0.1) × 10⁴ mol^?1 cm^?1 fluoride levels, respectively. This method is applied to the determination of fluoride in bottled mineral waters.     

Differential potentiometric titrations of binary mixtures of halides with two ion-selective indicator electrodes

Differential potentiometric titrations with two different ion-selective indicator electrodes are described. Ion-selective electrodes for Cl^-, Br^-, I^-, F^-, S^2-, as well as glass and silver billet electrodes were used. The method was tested in the determination of binary mixtures of halides (Cl^-, Br^-, I^-, and F^-) by titration with solutions of silver nitrate, alone and mixed with lanthanum or thorium nitrate as required. Various factors influencing the determination were investigated. Results of simultaneous determinations of mixtures were in good agreement with the results of separate determinations within certain concentration limits. The method was successfully applied to the determination of a four-component halide mixture. Titrations of mixtures of fluoride with thiocyanate or hexacyanoferrate(III), and some other possibilities, are also reported.     

Thin‐Layer Chemical Modulations by a Combined Selective Proton Pump and pH Probe for Direct Alkalinity Detection

We report a general concept based on a selective electrochemical ion pump used for creating concentration perturbations in thin layer samples (～40 μL). As a first example, hydrogen ions are released from a selective polymeric membrane (proton pump) and the resulting pH is assessed potentiometrically with a second membrane placed directly opposite. By applying a constant potential modulation for 30 s, an induced proton concentration of up to 350 mM may be realized. This concept may become an attractive tool for in situ titrations without the need for sampling, because the thin layer eventually re‐equilibrates with the contacting bulk sample. Acid–base titrations of NaOH and Na₂CO₃ are demonstrated. The determination of total alkalinity in a river water sample is carried out, giving levels (23.1 mM ) comparable to that obtained by standard methods (23.6 mM ). The concept may be easily extended to other ions (cations, anions, polyions) and may become attractive for environmental and clinical applications.     

Amperometric Titration of Small Amounts of Aluminum

Abstract

It is demonstrated that an amperometric titration of aluminum is possible using iron(III) as amperometric indicator and thorium as the titrant. The method is based on the fact that aluminum interferes in fluoride titrations. At a fixed fluoride concentration there is an inverse linear relationship between the amount of thorium used and the aluminum concentration.     

Synthesis of La-incorporated chitosan beads for fluoride removal from water

In this study, lanthanum incorporated chitosan beads (LCB) were synthesized using precipitation method and tested for fluoride removal from drinking water. The effect of various parameters like complexation and precipitation time, lanthanum loading and ammonia strength on fluoride removal have been studied. It is observed that the parameters for the synthesis of LCB have significant influence on development of LCB and in turn on fluoride removal capacity. The optimal condition for synthesis of LCB includes lanthanum loading: 10 wt%, complexation time: 60 min, precipitation time: 60 min, drying temperature: 75 °C for 72 h. The maximum fluoride adsorption capacity of LCB was found to be 4.7 mg/g and negligible release of lanthanum ion was observed. XRD analysis shows the presence of lanthanum hydroxide and amorphous nature of LCB. SEM of LCB shows the presence of oval lanthanum hydroxide particles spread over the chitosan matrix. Fluoride adsorption capacity has been calculated by applying Langmuir and Freundlich isotherms. The comparative study suggests that LCB shows four times greater fluoride adsorption capacity than the commercially used activated alumina.     

Contributions to the basic problems of complexometry--XXIII: determination of thorium, scandium and some lanthanides in the presence of each other

A new method is described for the determination of thorium, scandium, and the sum of light lanthanides, in the presence of each other. The method is based on the titration of thorium plus scandium with DCTA (1,2-diaminocyclohexanetetra-acetic acid) at pH 2.5-3.5, with Xylenol Orange as indicator. After addition of TTHA (triethylenetetraminehexa-acetic acid) the thorium-DCTA complex is converted into the thorium-TTHA complex according to the equation Th-DCTA + TTHA = TH-TTHA + DCTA. Simultaneously, free lanthanum, cerium, praseodymium and neodymium react with TTHA. The excess of TTHA and the liberated DCTA are then determined by titrations with zinc and with lanthanum solutions according to the equations DCTA + TTHA + 3Zn = Zn-DCTA + Zn(2)-TTHA and DCTA + TTHA + 2La = La-DCTA + La-TTHA. From the results, the amounts of thorium and scandium, and the sum of the lanthanide concentrations, can easily be calculated. Further possibilities, e.g., determination of heavier lanthanides, are briefly discussed.     

Titrations using an apparatus for recording the antilogarithm of pH or pM

A titration apparatus plotting either the concentration of sample ion or the concentration of titrant ion has been tested. An antilog apparatus, converting measured e.m.f. values into concentrations is connected to ordinary titration equipment. The instrument has been tested by means of acid—base titrations (titrations of mixtures of weak acids and of a weak and a strong acid), precipitation titrations (determination of the chloride concentration in tap-water, titration of mixtures of halides), titrations with ion-selective electrodes (determination of the fluoride content of toothpaste) and complexometric titrations (determination of copper with EDTA, using mercuric ion as indicator ion and amalgamated silver rod as indicator electrode, or using a copper-selective indicator electrode). The method considerably simplifies the evaluation of the results as compared to conventional potentiometric titrations.     

Synthesis of halide glasses by reactive processing of sol-gel materials

This paper aims to introduce fluoride materials, their conventional processing and how sol-gel processing can be used both to simplify processing and to improve properties. A multistep process incorporating sol-gel synthesis and reactive treatment is used to prepare a monolithic ZBLA fluoride glass. The first step is synthesis of a porous, monolithic, atomically homogeneous hydrous oxide gel containing zirconium, barium, lanthanum, aluminum and possibly sodium as components (ZBLA or ZBLAN). The second step is a relatively low-temperature reactive treatment of the gel with a fluorinating agent to achieve a porous fluoride glass. Subsequently, the gel is viscous sintered to a dense glass. The present status and future challenges in the preparation of optical-quality fluoride glasses via this method will be presented.     

Indirect determination of trace amounts of fluoride in natural waters by ion chromatography: a comparison of on-line post-column fluorimetry and ICP-MS detectors

An alternative method for the determination of trace levels of fluoride in drinking and sea-water samples is presented. It is based on the formation of the aluminium monofluoride complex in excess of Al3+ and separation of the two species formed (AlF2+ and Al3+) in a small (5 cm long, CG2) ion exchange guard column. The final determination is accomplished by both ICP-MS specific detection and post column derivatisation with fluorimetric detection. Fundamental studies on the formation kinetics of the complex, ion chromatographic separation and optimum aluminium concentration were carried out using spectrofluorimetric detection by post-column reaction of the species with 8-hydroxyquinoline-5-sulfonic acid in a micellar medium of cetyltrimethylammonium bromide. Fluorimetric detection showed good detection limits, but interferences from cations such as Mg2+ and Zn2+ required the use of the longer CS2 ion exchange column. Iron interfered in relatively large amounts but adding EDTA to the sample solution eliminated the interference. A similar separation methodology was applied using ICP-MS detection for the indirect determination of fluoride, by monitoring aluminium at mass 27. In this case, a detection limit of 0.1 ng ml-1 was obtained using 0.45 M HNO3 as eluent and no interference caused by high concentrations of iron was observed. The proposed method was applied to the determination of very low levels of fluoride in natural waters.     

Semi-automated fluorimetric determination of nanogram quantities of selenium in biological material

A semi-automated method, based on the solvent extraction and fluorescence of 4,5-benzopiazselenol, is described for the determination of selenium in biological material. Samples, in batches of up to 150, are digested in a mixture of nitric and perchloric acids in temperature-controlled aluminium blocks. Selenate formed in the perchloric acid is reduced to selenite with hydrochloric acid. Metal ion interferences, including hydroxide adsorption of selenite, are prevented by ethylenediaminetetraacetic acid. Sulphate above 50 mM precipitates the 2,3-diaminonaphthalene, so wool digests were diluted accordingly. The digests are analysed from their digestion tubes at the rate of 40 per hour by the semi-automated method. Results for blood and a variety of food samples compare favourably with those obtained by other methods including hydride/atomic absorption and instrumental neutron-activation analysis.     

The development of fluoride-sensitive membrane electrodes : Part I. Membranes containing thorium,lanthanum or calcium fluoride

Fluoride-sensitivc membrane electrodes of the Pungor type are described. In these electrodes, a fluoride precipitate is incorporated in a silicone rubber membrane; fluorides of thorium, lanthanum and other rare earths, and calcium have been examined. The method of preparing the precipitate is important; an excess of metal is vital for correct functioning of the final electrode. The most reliable results were obtained with calcium fluoride electrodes, though their sensitivity was less than that of the best lanthanum fluoride electrodes. With these electrodes, linear responses are obtained in the l0^-2–10^-4M fluoride range.     

Potentiometric behaviour of lanthanum polyalkoxylate complexes in PVC membrane electrodes: effect of plasticizers and applications

Tetraphenylborate salts of lanthanum complexes of nonylphenoxypolyethyleneoxyethanol (Antarox CO-880) and polypropylene glycol-425 (PPG-425) have been prepared and examined for their applicability as sensing species for lanthanum ions by incorporating them in a poly (vinyl chloride) membrane system in the presence of 2-nitrophenyl phenyl ether (NPPE), dioctylphenyl phosphonate or a mixture of both as plasticizers. Almost all of the systems studied showed an excellent response for lanthanum ions in pure solutions with a near Nernstian response of 18–20 mV per decade between 10^?5 and 10^?1 M lanthanum and a static response time of less than 1 min. Among the systems studied, lanthanum(Antarox CO-880)TPB/100% NPPE (TPB=tetraphenylborate) was the best in terms of tolerance to interfering ions. K⁺, Ba²⁺, Pb²⁺ and Al³⁺ were serious interferents, but most other interferents investigated were tolerable at [La³⁺] > 10^?4 M. Plasticizers were found to be decisive in determining the sensor selectivity towards the different metal ions. A lanthanum(Antarox CO-880)TPB/100% NPPE PVC membrane electrode was utilized for the potentiometric titration of fluoride, in sodium fluoride, against lanthanum nitrate solutions. It proved to be successful for fluoride concentrations of ? 10^?3 M.     

Contributions to the basic problems of complexometry-XXVIII New method for successive determination of calcium and magnesium

A new method for successive determination of calcium and magnesium is proposed. It is based on the indirect determination of calcium in borax media by back-titration of excess of EGTA with lead nitrate. Magnesium is then determined in ammonia buffer with DCTA. For both titrations Thymolphthalexone is used as indicator. The exceptional role of DCTA in direct titration of magnesium is established experimentally and explained.     

Determination of oxygen in gallium arsenide by3He activation analysis using substoichiometric precipitation

Distillation of fluoride as fluorosilicic acid and substoichiometric precipitation as lanthanum fluoride was studied for the determination of oxygen in gallium arsenide by³He activation analysis. Fluoride could be separated substoichiometrically with a good reproducibility by two distillations and successive precipitation with lanthanum. The oxygen concentration in gallium arsenide prepared by the horizontal Bridgman technique was 10 to 36 ppb and increased a little along the front, middle and tail portions in the crystal.