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.     

Deuteron activation analysis of carbon in gallium arsenide using substoichiometric precipitation

Ultra trace carbon in gallium arsenide has been determined by deuteron activation analysis. It consists of steam distillation of nitrogen as ammonia and successive substoichiometric precipitation as ammonium tetraphenylborate. It is confirmed that nitrogen is precipitated substoichiometrically as ammonium tetraphenylborate in spite of the various chemical species of¹³N. The procedure developed was applied to the deuteron activation analysis of carbon in carbon-doped and undoped gallium arsenides. It took 30 minutes from the end of irradiation to the start of the radioactivity measurement. The detection limit of carbon in gallium arsenide was as low as 1 ppb.     

A critical study on the determination of selenium in gallium arsenide by polarographic techniques

A simple voltammetric method is described for the determination of traces of selenium in gallium arsenide. Differential-pulse cathodic stripping voltammetry permits a direct determination of selenium without preliminary enrichment or separation processes. Selenium can be determined down to levels of 1–2 μg g^?1, with relative standard deviations of about 10%, in ? 100-mg samples of gallium arsenide. Results for gallium arsenide doped with 7–75 μg g^?1 selenium agree in most cases with those obtained by spectrophotometry based on 4-chloro-o-phenylenediamine.     

Determination of trace elements in gallium arsenide by graphite-furnace atomic absorption spectrometry after pretreatment in gas streams

Atomic absorption spectrometry (AAS) with a resistively-heated graphite furnace is used for the determination of chromium (0.3–1 atom/10⁶ atom) in chromium-doped gallium arsenide after pretreatment in a separate furnace in a stream of argon to remove arsenic, and of manganese and silver (0.03 and 0.04 atom/10⁶ atoms, respectively) by a similar procedure after pretreatment with argon and chlorine, the latter to remove both gallium and arsenic as volatile chlorides. Results for chromium were in agreement with those obtained by furnace AAS after dissolution and by spark-source mass spectrometry (SSMS) but AAS after dissolution is more precise. Results for manganese and silver obtained by both gas pretreatments were in good agreement, but were higher than those obtained for presparked material by SSMS, indicating that surface contamination of gallium arsenide was not completely removed by the etching methods used. The procedures established that the concentrations of bismuth, indium and lead in the gallium arsenide sample were below the limits of detection of 3 × 10^?3, 10 × 10^?3 and 1 × 10^?3 atom/10⁶ atoms, respectively. In all cases, calibration graphs were constructed from data obtained with aqueous solutions of appropriate salts.     

The determination of oxygen in copper by α-particle activation analysis

The determination of oxygen in copper by activation analysis with 45-MeV α-particles is described. The chemical separation of ¹⁸F produced from oxygen consists of steam distillation as fluosilicic acid, followed by precipitation of the interfering gallium activities as the hydroxide and of the fluoride as lead chlorofluoride or of cation exchange followed by lead chlorofluoride precipitation. This allows a total decontamination from matrix radiation in excess of 10⁶. As standard, mica foils are used, while, for the purp?ose of flux monitoring, the activity induced in a thin copper or mica foil, placed before the sample is counted. Alternatively, the intensity of the particle beam is measured. The method, which allows determination of oxygen at the 1 μg g^-1 level with a precision of about 10%, is applied to the determination of a concentration of 1.2 μg g^-1. Analysis of a reference material containing 70 μg O g^-1 proves the accuracy of the standardization methods applied.     

New Electrodes with Membranes Based on Semiconductor Compounds of the AIIIBV Type

The characteristics of new electrodes with semiconducting membranes based on gallium arsenide and gallium antimonide were studied in solutions of metal salts, halides, and complexing agents. The proposed electrodes can be used as indicator electrodes in acid–base, precipitation, and complexometric potentiometric titration.     

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.     

Determination of nickel,gold and silver in gallium arsenide by radioactivation analysis based on the quantitative isotope dilution principle

A method of radioactivation analysis has been developed for the determination of Ni, Au and Ag impurities in gallium arsenide. The separation and substoichiometric extraction of these elements were studied and analytical procedures are suggested for their determination. All components are separated by suitable procedures and determined by substoichiometric methods. Ni is extracted as diethyldithiocarbamate into toluene, Au as a complex of rhodamine-B in chloroform, and Ag as dithizonate in carbon tetrachloride. The contents of Ni, Au and Ag in a gallium arsenide crystal with a carrier concentration of 1.8·10¹⁶/cm³ were 0.05–0.08, 0.006–0.008 and 0.002–0.005 ppm, respectively.     

Control of the composition of lanthanum gallium silicate by laser ablation inductively coupled plasma mass spectrometry

The possibilities of determining the impurities and basic components of lanthanum gallium silicate using laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) were shown. A procedure for the determination of 54 impurity elements with the limits of determination from n × 10^?5 wt % for Mg, Ti, V, Cr, Mn, Ni, Cu, and Zn to 2 × 10^?7 wt % for U and also a procedure for the determination of a ratio between basic components were developed. It was found that the concentration ratios between gallium and lanthanum and silicon and lanthanum in the crystals of lanthanum gallium silicate remained constant upon consecutive melting operations with the addition of a charge mixture to the crucible.     

Solubilization of arsenic from gallium arsenide using aqueous suspensions of organic halides

The solubilization of arsenic in solid gallium arsenide by aqueous solutions/suspensions of organic halides is described. Although arsenic is removed from gallium arsenide surfaces, excess quantities of gallium are not found in the solution. The abilities of the organic halide to solubilize arsenic decreases as follows: C₂H₅Br> CH₃I> 2-C₃H₇I> 1-C₃H₇I> 2-C₄H₉Br> CH₂?CHCH₂I> 2-C₃H₇Br? 1-C₄H₉Br. The results correlate with a combination of organic halide solubility, bond enthalpy and carbonium ion stability factors. Other parameters investigated using gallium arsenide and iodomethane include concentration, physical state of the arsenide, pH, role of oxygen and role of light.     

Molekülabsorptionsspektrometrie mit elektrothermischer verdampfung in einer graphitrohrküvette: 12. Tei. bestimmung von cl-species in selen und AIIIBV-halbleitermaterialien

(Molecular absorption spectrometry with electrothermal vaporization in a graphite cuvette. Part 12. Determination of chloride species in selenium and A^IIIB^V-semiconductor materials after separation of the traces by adsorptive precipitation and distillation.) The determination of traces of chloride in chloride-dosed selenium and in gallium arsenide by molecular absorption spectrometry of AlCl is described. The traces of chloride are separated by adsorption precipitation (AgCl/Al₂O₃). The AgCl is dissolved in ammonia. After addition of Al³⁺ and Ba(OH)₂ the molecular absorption of AlCl is measured at 261.4 nm. It is possible to determine 0.2 μg g^?1 Cl in 500 mg of Se or GaAs.     

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.     

Fluoride removal using lanthanum incorporated chitosan beads

Highly selective material based on naturally occurring biomaterial namely chitosan has been designed for the defluoridation of water. Lanthanum incorporated chitosan beads (LCB) were prepared using precipitation method. The synthesis was optimized by varying different synthesis parameters namely lanthanum loading, complexation and precipitation time, strength of ammonia solution used for precipitation, drying time, etc. Lanthanum incorporated chitosan beads were characterized using SEM, FTIR, XRD and EDX. Surface area of LCB was observed to be 2.76 m² g⁻¹. The equilibrium adsorption data fitted well to Langmuir adsorption isotherm and showing maximum fluoride adsorption capacity of 4.7 mg g⁻¹ with negligible lanthanum release. Kinetic study reveals that adsorption of fluoride is fast and follows pseudo-first-order kinetics. The effect of pH was also studied and the best efficiency was observed at pH 5. Presence of sulphate, nitrate and chloride marginally affected the removal efficiency, however drastic reduction in fluoride uptake was observed in the presence of carbonate and bicarbonate. Negative value of change in free energy (ΔG°) and positive value of change in entropy (ΔS°) suggest the adsorption of fluoride by LCB is feasible and spontaneous process. Positive value of change in enthalpy (ΔH°) suggests the process of fluoride adsorption is endothermic in nature. Regeneration study reveals that 1 M ammonium chloride solution appears to be the promising regeneration media showing 81.22% regeneration. The adsorption capacity of LCB was similar in fluoride-contaminated ground water collected from Dhar district of Madhya Pradesh, India, as compared to simulated water.     

Potentiometric titrations of selenium with a fluoride-selective electrode

Selenite can be determined with a fluoride-selective electrode by two methods: a direct procedure based on the joint titration of selenite and standard fluoride with lanthanum and an indirect method based on precipitation of selenite with excess of lanthanum followed by back-titration with fluoride. In the first case the end-point is located by the second derivative method, and in the second case by means of a Gran plot. Direct titrations are suitable for selenite concentrations above 5 mM; indirect titrations are useful for concentrations as low as 0.5 mM.     

Substoichiometric precipitation of silicon as barium fluorosilicate

Distillation and substoichimetric precipitation for silicon have been developed for the determination of trace amounts of silicon. It is based on substoichiometric precipitation as barium fluorosilicate and the distillation of silicon tetrafluoride. The separation has been applied for the determination of silicon in gallium arsenide and NBS steel as standard reference material.     

The differential pulse polarographic determination of chromium in gallium arsenide

The method described for the determination of chromium in gallium arsenide is based on the catalytic current produced by nitrate in the electrolytic reduction of the chromium(VI)-diethylenetriaminepentaacetate complex. Matrix effects, primarily caused by gallium, are discussed in detail. The method is suitable for determinations of chromium at levels as low as about 1 μg g^?1 with about 50 mg of sample; the r.s.d. is better than 10%.     

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.     

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.     

Atomabsorptionsspektralphotometrische bestimmung von zink in galliumarsenid und galliumaluminiumarsenid

The determination by atomic-absorption spectroscopy of zinc in gallium arsenide and gallium aluminium arsenide is described. In 5–20 mg of sample, 0·1–3 μg of zinc can be determined. The coefficient of variation is 4·5%. The influence of the matrix is described and discussed.     

Determination of fluoride by use of a fluoride-selective cell

A concentration cell with a lanthanum fluoride membrane as the junction (fluoride-selective cell) was applied to the determination of fluoride in the concentration range 0.2–100 mg 1^?1. Fluoride was determined by direct potentiometry and/or by standard additions. Background fluoride levels in TISAB solutions were determined by means of standard additions. It is shown that the fluoride-selective cell makes possible the elimination of interferences in fluoride determination. Equations are give for the e.m.f. of the fluoride-selective cell and for standard additions. The advantages of the fluoride-selective cell over the conventional fluoride-selective electrode are summarized.