The Use of Buffers in the Determination of Fluoride by an Ion-Selective Electrode at Low Concentrations and in the Presence of Aluminum

Abstract

The influence of the composition of buffer solutions on fluoride analyses by the fluoride ion selective electrode was studied. Residual fluoride content of reagents was observed to restrict the use of some buffers and reagents in low-level work. The optimum pH for low-level fluoride determinations was found to be around 5, which can be maintained by a sodium acetate-acetic acid buffer. Of the complexing agents studied, citrate was observed to be the most efficient masking agent for aluminum, but this ability depended strongly on ligand concentration. Citrate was also effective in masking iron (III) and magnesium ions. Tris (hydroxymethyi) aminomethane showed a similar ability to complex aluminum at a pH around 8. However, at this pH the hydroxyde ion interferes in fluoride analysis below 0.1 ppm [fbar].     

The successive determination of chloride, fluoride and sodium in single samples of orthophosphate minerals by means of ion-sensitive electrodes

A buffer system composed of perchloric acid, citric acid and triethanolamine has been used for the successive determination of chloride, fluoride and sodium in a single sample of an orthophosphate mineral. The conventional sodium-sensitive glass electrode compares favourably with the more expensive Orion sodium-sensitive electrode.     

Potentiometric determination of iron using a fluoride ion-selective electrode-the application of the Apple II-ISE intelligent ion analyzer

A new method for determining iron is based on both nonlinear regression calibration plots and parabolic interpolation using a fluoride ion-selective electrode (ISE) and the Apple II-ISE intelligent ion Analyzer developed by ourselves. The experimental conditions for determining iron are discussed. The appropriate acidity of the experimental solution is pH 3, controlled by total ionic strength adjustment buffer (TISAB) that is composed of glycine (aminoacetic acid), nitric acid and sodium nitrate. The suitable total concentration of fluoride is equal to the highest concentration of iron in the standard series. Because the mathematical model of the method coincides with the experimental data the Apple II-ISE intelligent ion Analyzer can perform data acquisition and data processing, and the performance of fluoride electrode is excellent, the new method for determination of iron is fast and accurate. This method has been used successfully in the determination of iron in mineral samples.     

离子选择性电极电位法测定钼矿石和钨矿石中氟

采用过氧化钠熔融钼矿石、钨矿石样品,乙二胺四乙酸钠和5-磺基水杨酸混合溶液浸取盐分,将样品溶液静置12h,吸取上层清液,以乙二胺四乙酸钠-硝酸钾组成的混合溶液作为总离子强度缓冲剂,控制溶液pH值为5.1,使用pF-1型氟离子选择电极,以饱和甘汞电极作参比电极测定溶液的平衡电位值。采用标准曲线法测定钼矿石和钨矿石中氟。钼矿石标准物质测定值的相对标准偏差(n=11)为3.36%,经4种国家一级钼矿石、钨矿石标准物质的分析验证,测定结果与标准值吻合。     

New suppressor technology improves trace level anion analysis with carbonate-hydrogencarbonate mobile phases

Sodium carbonate-hydrogencarbonate mobile phases are preferred over sodium hydroxide for anion analysis by suppressor-based ion chromatography (IC). Unlike hydroxide, carbonate-hydrogencarbonate has strong eluting power and its buffering capacity can be used as a selectivity tool for controlling separations. However, carbonate-hydrogencarbonate mobile phases fell out of favor for trace level analysis because the carbonic acid suppressor effluent has some background conductivity, which reduces sensitivity compared to sodium hydroxide. This paper describes a new suppressor technology that improved anion analysis with carbonate-hydrogencarbonate mobile phases. In addition to converting the carbonate-hydrogencarbonate buffer to carbonic acid like other traditional IC suppressors, the new DS-Plus suppressor also removed carbonic acid from the suppressor effluent. Anions are now detected in water background, just like when using sodium hydroxide as the mobile phase. The lower background conductivity improves sensitivity and reduces detection limits. The water-dip often seen with conventional suppressors is greatly reduced, improving fluoride quantification.     

An automatic potentiometric analyzer for atmospheric hydrogen fluoride determinations

An automatic potentiometric analyzer for the determination of atmospheric hydrogen fluoride is described. Hydrogen fluoride is collected from the air, which is pumped at 25 l min^-1, in a thin layer of sodium carbonate in a spiral absorber, and measured every hour by washing the absorber with a citrate buffer and measuring the fluoride with a fluoride-selective electrode. The analytically useful range is 0.1–15 μg HF m^-3.     

Enhancement of Demasking of Fluoride Ion From its Aluminum Complexes by Dilution in the Determination With a Fluoride Ion-Selective Electrode

Abstract

In the determination of fluoride ion with an ion-selective electrode the permissible concentration of aluminum increases markedly with decreasing the fluoride concentration in 0.5M citrate buffer solutions at pi I 6. As the accuracy is constant over a concentration range down to 10^?5 M F^? where a Nernstian relation holds fluoride determinations can be accomplished by the successive dilution method. The dilution steps are repeated until the last two results are in agreement, while the concentration of citrate is kept constant. As the ionic strength is kept constant with citrate, the addition of sodium chloride to the buffer is not necessary. Several samples, especially glasses, have been analyzed successfully.     

Determination of fluoride with thorium nitrate by catalytic titration

Amperometry, constant-current potentiometry and spectrophotometry were used to follow the course of catalytic titrations of fluoride and silicofluoride with thorium nitrate. The hydrogen peroxide-iodide system was used as the indicator reaction. Titrations were performed in 50% ethanolic acetate buffer, pH 3.6. Amounts of 3.70-6.85 mg of ammonium fluoride, 5.53-10.79 mg of potassium fluoride and 4.34-8.41 mg of sodium silicofluoride were determined with a maximum average deviation of 0.9%. The results obtained are in good agreement with those of comparable methods.     

Sodium glycylglycine as effective electrolyte run buffer for ascorbic and uric acid separation by CZE: a comparison with two other CE assays

A new CE method for ascorbic acid (AA) and uric acid (UA) detection in human plasma has been developed. Analytes were resolved in less than 4 min by employing sodium glycylglycine (Glygly) as electrolyte run buffer at pH 8.0. Using the diode array detector ability to measure multiple wavelengths simultaneously, detection was optimized by monitoring the run at 262 nm for AA and at 288 nm for UA. Electrophoretic parameters such as resolution, migration times, efficiency, and peak areas of this new method were compared to those obtained by the two CE assays described in literature, in which the analytes separation was achieved by using sodium borate (that allows faster migration times but poor resolution) or tricine (with the highest resolution but elevated migration times) as electrolyte run buffer. Sodium Glygly allows to obtain the same good resolution given by the tricine buffer but with the faster analysis times of the sodium borate run buffer. Ascorbate and urate levels were measured in 35 healthy volunteers by the three methods and the obtained data were compared by three different statistical tests (mountain plot, Passing-Bablok regression, and Bland-Altman test) in order to verify the accuracy of our proposed method.     

Voltammetric,potentiometric and amperometric studies with a rotated aluminum wire electrode : Amperometric titration of fluoride with aluminum

The rotated aluminum electrode is a suitable indicator electrode in the amperometric titration of fluoride, Fluoride in concentrations varying between 1.10^-4 and 2.10^-3M was titrated with a standard aluminum nitrate solution in aqueous buffer solutions (pH between 3.6 and 46) Equilibrium was established within 15 mim. The fluoride-aluminum ratio at the (true) end-point was found to increase from 2 2 in 10^-4M fluoride to 28 in. 2.10^-3M fluoride. The titration calculated from the stability constants of the various aluminum-fluoride complexes were found to be in excellent agreement with the experimental curves.From a practical point of view titration in an acetate buffer in 50% alcohol in the presence of 0 5 M potassium or sodium nitrate is recommended. The fluoride-aluminum ratio at the end-point was found to be 5 9 ± 0 1 and independent of the fluoride concentration.     

Influence of solution composition and iron powder characteristics on reduction of 2,4,6-trinitrophenol

Kinetics of the 2,4,6-trinitrophenol reaction with iron powder was investigated voltammetrically. The process was found to be mainly governed both by the iron powder characteristics and by the solution composition. Degradation kinetics was generally represented by a pseudo-first-order rate law. Consecutively, the 2,4,6-trinitrophenol reduction reaction rates for three fractions of iron powder as well as the effect of individual ions presented in the reaction system were evaluated. A correlation between the reaction rate and both the grain size of iron particles and the state of their surface was found. The effect of the reaction system composition was investigated for two types of buffered medium: Britton-Robinson buffer (boric acid, orthophosphoric acid, and glacial acetic acid) and acetate buffer solution (sodium acetate and acetic acid).     

Rapid EDTA determination of lead in binary alloys of lead and tin

Binary alloys of lead and tin were dissolved in nitric acid (1 + 1) containing 10% sodium fluoride. The tin(IV) was effectively masked by the fluoride. The lead was quickly and accurately titrated with EDTA in a hexamine-buffered solution, with Xylenol Orange as indicator.     

Direct determination of fluoride in aluminium reduction materials by using an ion-selective electrode

Macro amounts of fluoride in aluminium reduction materials are successfully determined with a fluoride electrode. Except for anhydrous aluminium fluoride, which requires fusion with sodium hydroxide, samples are dissolved in aqueous media. Cryolite and sodium fluorosilicatc are dissolved in boiling sodium hydroxide solution. Other materials containing fluoride, such as fluorspar and the reduction cell bath and pot-lining, require dissolution in a hydrochloric acid solution of aluminium chloride. Potential interference from large amounts of aluminium (and calcium, if present) is eliminated and pH control attained by using ammoniacal sulphosalicylate (and EDTA). The procedures are reasonably rapid. Relative errors of less than 2% and a relative standard deviation of 1% are achieved.     

Spectrophotometric study of the reaction of the uranyl ion with 4-(2-thiazolylazo) resorcinol

The uranyl ion forms only 1:1 chelates with 4-(2-thiazolylazo) resorcinol (TAR) in solution, UO(2)(TAR)H(+) being formed below pH 3 and UOS(TAR) above pH 3-5. The latter complex may also be precipitated at pH > 3. The quantitative formation of UO(2)(TAR) at pH 7.5-7.8 in solutions containing a small excess of reagent and some triethanolamine as buffer can be used for the sensitive spectrophotometric determination of uranium. Several interfering ions can be masked with a mixture of sodium fluoride, cyclohexanediaminetetraacetic acid and 5-sulphosalicylic acid. TAR is slightly less sensitive than 4-(2-pyridylazo)resorcinol as a reagent for uranium but is more selective.     

New insights into structural alteration of enamel apatite induced by citric acid and sodium fluoride solutions

Attenuated total reflectance infrared spectroscopy and complementary scanning electron microscopy were applied to analyze the surface structure of enamel apatite exposed to citric acid and to investigate the protective potential of fluorine-containing reagents against citric acid-induced erosion. Enamel and, for comparison, geological hydroxylapatite samples were treated with aqueous solutions of citric acid and sodium fluoride of different concentrations, ranging from 0.01 to 0.5 mol/L for citric acid solutions and from 0.5 to 2.0% for fluoride solutions. The two solutions were applied either simultaneously or consecutively. The citric acid-induced structural modification of apatite increases with the increase in the citric acid concentration and the number of treatments. The application of sodium fluoride alone does not suppress the atomic level changes in apatite exposed to acidic agents. The addition of sodium fluoride to citric acid solutions leads to formation of surface CaF2 and considerably reduces the changes in the apatite P-O-Ca framework. However, the CaF2 globules deposited on the enamel surface seem to be insufficient to prevent the alteration of the apatite structure upon further exposure to acidic agents. No evidence for fluorine-induced recovery of the apatite structure was found.     

Titrages “thermochimiques” par formation de fluorures complexes de fer,aluminium, antimoine,etain et plomb

A thermochemical study of the titration of aluminium, iron, copper, lead, tin and antimony salts with sodium fluoride is described. The destruction of fluoride cumplexes by boric acid has been studied. The measurement apparatus consists of two thermistors and a bridge. Clear breaks were obtained for iron, aluminium, copper and lead but no separation of iron and aluminium was possible. The action of boric acid also gave clear breaks in the curves.     

Influence of high‐conductivity buffer composition on field‐enhanced sample injection coupled to sweeping in CE

The aim of this work was to clarify the mechanism taking place in field‐enhanced sample injection coupled to sweeping and micellar EKC (FESI‐Sweep‐MEKC), with the utilization of two acidic high‐conductivity buffers (HCBs), phosphoric acid or sodium phosphate buffer, in view of maximizing sensitivity enhancements. Using cationic model compounds in acidic media, a chemometric approach and simulations with SIMUL5 were implemented. Experimental design first enabled to identify the significant factors and their potential interactions. Simulation demonstrates the formation of moving boundaries during sample injection, which originate at the initial sample/HCB and HCB/buffer discontinuities and gradually change the compositions of HCB and BGE. With sodium phosphate buffer, the HCB conductivity increased during the injection, leading to a more efficient preconcentration by staking (about 1.6 times) than with phosphoric acid alone, for which conductivity decreased during injection. For the same injection time at constant voltage, however, a lower amount of analytes was injected with sodium phosphate buffer than with phosphoric acid. Consequently sensitivity enhancements were lower for the whole FESI‐Sweep‐MEKC process. This is why, in order to maximize sensitivity enhancements, it is proposed to work with sodium phosphate buffer as HCB and to use constant current during sample injection.     

硅钙合金中钙、铝的联合测定

硅钙合金用硝酸、氢氟酸溶解后，加入高氯酸并加热至冒烟以驱除氟，然后定容。移取两份样品溶液，一份中加入三乙醇胺溶液掩蔽铁、铝等干扰离子，再加入氢氧化钾溶液，使pH=12，用EDTA容量法测定钙。另一份中加入铁标准溶液、混合显色液（Zn-EDTA与络天青S的混合溶液）及六次甲基四胺缓冲溶液，用光度法测定铝。方法简便，结果准确、可靠。     

沉淀分离EDTA返滴定法测定卡尔多炉渣中的铅量

采用沉淀分离-EDTA返滴定法建立了卡尔多炉渣中铅含量的测定方法,探讨了样品中共存元素干扰及操作细节等因素对分析结果的影响。实验表明,氟化氢铵用量0.10g、硫酸洗涤次数5～6次、陈化时间3h、氨水加入量5mL、乙酸乙酸钠缓冲溶液加入量30mL、微沸时间15～20min时,方法的加标回收率99.8%～100%,两个实际样品测定结果的相对标准偏差(RSD,n=8,分别为0.14%和0.15%。方法准确度高,精密度好。     

Fluorination of polyhydrofluoroethylenes. II. Formation of perfluoroalkyl carboxylic acids on the surface region of poly(vinylidene fluoride) film by oxyfluorination,fluorination, and hydrolysis

Oxyfluorination and postfluorination behaviors of poly(vinylidene fluoride) films, as well as hydrolysis of the films treated so far, have been studied by infrared (IR) spectrometry. By exposing the polymer film to a mixture of oxygen and fluorine at about 90°C acyl fluoride groups attendant on the scission of the polymer chains were formed. The oxyfluorinated molecules could be further perfluorinated with fluorine alone at about 90°C, leaving many of the acyl fluoride groups. When the properly oxyfluorinated and postfluorinated film was further treated with a hot 6M sodium hydroxide solution the opaque layer of perfluoroalkyl sodium carboxylate of high molecular weight was formed on the surface of the film, to about 3 μm in thickness, which behaved as a cation exchanger. This new type of cation exchanger of perfluoroalkyl carboxylic acid was significantly more acidic than the usual methacrylic acid exchanger. It was able to adsorb the sodium ions from a neutral sodium chloride solution up to about 70% of the exchange capacity and to keep the ions stable while washing them with water, though it could be regenerated to the hydrogen form with a dilute acetic acid solution. The nature of the new ion exchanger has been examined in some detail by IR spectrometry with Li⁺, Na⁺, and Cs⁺ ions.