Determination of fluoride in fertilizers by means of the ion-selective electrode

Summary A method is described for the determination of acid and water soluble fluoride in some commercial fertilizers. The ground samples are stirred with water or with hydrochloric acid of different concentrations, filtered, citrate added as complexing agent, and then measured with an ion-selective electrode. With most of the investigated samples it was seen that the more concentrated the acid (up to 1.00 M HCl) the more fluoride was found in the solution, and this was supposed to be the same as the total amount.The relative standard deviation was usually between 0.5 and 1.5%. The recovery of added fluoride to some samples was between 97 and 100%. The results from this method were compared with the results from a reference method, and there was good correlation between them.

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Bestimmung von Fluorid in Düngemitteln mit Hilfe der ionen-selektiven Elektrode

Zusammenfassung Ein Verfahren wird beschrieben zur Bestimmung des säure- und wasserlöslichen Fluorids in einigen handelsüblichen Düngemitteln. Die gemahlenen Proben werden mit Wasser oder Salzsäure verschiedener Konzentration gerührt, filtriert, mit Citrat als Komplexbildner versetzt und dann mit Hilfe einer ionen-selektiven Elektrode gemessen. Bei den meisten Proben ergab sich, daß bei höherer Säurekonzentration (bis 1,0 M HCl) mehr Fluorid gefunden wurde, was dann dem Gesamtfluorid entsprach.Die relative Standardabweichung lag im allgemeinen zwischen 0,5 und 1,5%. Die Wiederfindung an zugesetztem Fluorid lag zwischen 97 und 100%. Die Ergebnisse wurden mit den nach einer Referenzmethode erhaltenen verglichen, und es ergab sich eine gute Übereinstimmung.

     

Studies on determination of fluoride in zinc and lead concentrates by using a fluoride ion-selective electrode

A modification of the potentiometric determination of fluoride has been developed, which allows use of aqueous fluoride standards in analysis of lead or zinc concentrates, instead of the need to use matrix-matching or standard additions.     

Rapid method for the determination of trace fluoride and activation of ion-selective electrode.

A method for activating ISE is proposed that can allow determination of the fluoride concentration at ng mL(-1) level with good precision and accuracy. Fluoride ISE is activated in 0.5 mol L(-1) HClO4 medium and then fluoride is determined in the same medium. The linear range for the determination of fluoride is between 1.00 x 10(-2)-1.00 x 10(-7) mol L(-1), and the detection limit of the method is 1.0 ng mL(-1). The advantage of this method is that it is free from the use of TISAB solution while being, time-saving and labor-saving. A mechanism study of the activation of FISE in HClO4 medium is explained. The method has been used for the determination of trace fluoride in milk and flour with satisfactory results.     

Effect of pH on the response of a cyanide ion-selective electrode

The influence of pH on the cyanide response of a silver iodide membrane electrode has been found to depend on the buffer system employed. A theoretical explanation of the results is attempted by assuming a pH-gradient in the vicinity of the electrode surface.     

Trifluoroacetate ion-selective electrode

The trifluoroacetate ion-selective electrode was prepared by using the organic solvent solution of trifluoroacetate salt of crystal violet or tris(bathophenanthroline) iron(II) chelate.The response is linear over the activity range 10^?1 to 3 × 10^?5M, with a Nernstian slope 60 mV/activity decade at 29 °C. The interferences of divalent ions, chloride, fluoride and acetate ions are extremely low. Iodide interferes greatly.     

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.     

An initial-rate potentiometric method for the determination of uric acid using a fluoride ion-selective electrode

The principle of a general potentiometric method based on Emerson-Trinder reaction for the assay of various hydrogen peroxide generating systems is reported. Emerson-Trinder reaction, habitually employed as a spectrophotometric indicator reaction, is exploited in this method as a potentiometric indicator reaction. This method is based on the detection of F⁻ ions, liberated from the oxidation of a fluorophenol compound used as hydrogen-donor in Emerson-Trinder reaction, by a fluoride ion-selective electrode. The ability and usefulness of this method are illustrated by an initial-rate potentiometric determination of uric acid in aqueous and human serum samples, for which, initial-rate reaction progress curves, linear calibration curve, within-day precisions, upper and lower detection limits, and also its analytical recovery were reported.     

The fluoride ion-selective electrode in flow injection analysis : Part 3. Applications

Flow-injection potentiometry with a combination fluoride-selective electrode is used to determine fluoride in tap water, beverages and urine. Excellent sensitivity (down to 1 μg l^?1) and long-term stability are obtained, with a sample throughput of 30–40 h^?1, based on triplicate injections at 120 h^?1. The commonly used buffer TISAB-III is unsuitable for the analysis of undiluted tea and urine samples. The application of a modified citrate-containing TISAB overcomes interferences caused by high natural ionic strength and avoids complexation of fluoride. Recoveries after spiking tap water, tea and urine with fluoride concentration ranging from 0.01 to 1 mg l^?1 are in the range 91–106%. The equipment used provides a flexible system allowing fast changes between different buffers and carrier streams depending on the samples presented.     

A new TISAB with Aluminon for fluoride determination in water with ion-selective electrode

The application of a new TISAB solution with Aluminon as a complexing agent for the determination of fluoride with a fluoride ion-selective electrode in various water samples has been studied. The proposed TISAB has been compared to some of the well-known TISABs in the literature, since it concerns the linear response and equilibrium time of the electrode, as well as the effectiveness on complexation of Al³⁺, Fe³⁺, Mg²⁺, and Ca²⁺. The experimental results showed that the use of TISAB-Aluminon results in high sensitivity of the electrode in low fluoride concentrations, short equilibrium time, and equal or better ability to eliminate the interferences of the cations mentioned.     

A battery-powered,computerized instrument for the field-based determination of fluoride by the ion-selective electrode technique

Battery-powered complementary metal-oxide semiconductor (CMOS) electronic devices are used to develop computerized instrumentation based on an ion-selective electrode for environmental monitoring in the field. The development of CMOS-based instrumentation for the determination of fluoride in drinking water, river water, lake water and sea water is described. The instrument is portable and completely field-programmable. Under software control, the equilibrium potential and fluoride concentration, based on a double standard-addition method, are calculated. The associated temperature, date and time form part of the data-logging record. Data obtained in the field are shown to compare satisfactorily with those obtained on samples which were stored and returned to the laboratory for examination by conventional mains-powered instrumentation. Accuracy is good and precision is only slightly poorer than that of mains-powered laboratory instrumentation.     

Stopped-flow kinetic determination of aluminum in Chinese tea leaves by fluoride ion-selective electrode potentiometry

A stopped-flow kinetic potentiometric method for the determination of aluminum is described, based on monitoring the reaction between aluminum and fluoride at pH 3.0 using fluoride ion-selective electrode. The initial rate of the reaction is proportional to the concentration of aluminum present in the solution. The method is simple and rapid and has been applied to the determination of aluminum in Chinese tea leaves after microwave digestion.     

The fluoride ion-selective electrode in flow injection analysis: Part 1. General Methodology

A simple flow-injection system for determination of traces of fluoride by means of the fluoride-selective electrode is presented. A comparison of several flow-cell arrangements confirmed the advantages of a well-jet design. Systematic investigations of the parameters affecting response times (i.e., polishing procedure, flow rate, carrier composition) established the optimal experimental conditions for measurements down to 1 μg l^?1 fluoride. Calibration plots in the lower μg l^?1 range were neither Nernstein nor linear, but good precision (0.5–5%) was obtained even when the potential differences for concentration steps of one decade were as small as 3 mV.     

Phosphate rock treatment with citric acid for the rapid potentiometric determination of fluoride with ion-selective electrode

A fast method for sample treatment of phosphate rock has been developed for the purpose of quantitative leaching (98-100%) of fluoride but less of the interfering cations such as iron and aluminum. Citric acid (0.5 M) was used to extract fluoride in 15-45 min. Leaching of iron and aluminum is minimal, and these ions are complexed with citric acid. The leaching method was optimized with respect to sample size, citric acid concentration, leaching time and temperature. The analysis was completed by the rapid determination of fluoride with ion-selective electrode. The proposed treatment method was applied to phosphate rock samples from Jordan and Morocco and yielded accurate results as compared to the standard steam distillation from strong acid solution followed by thorium nitrate titration.     

Determination of fluoride in natural waters by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate

The most effective conditions for masking aluminium in the determination of mug/1. levels of fluoride in water by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate have been re-examined. The effectiveness of citrate for masking aluminium increases with pH, and up to 1.5 x 10(-2)M aluminium can be masked quantitatively at pH 8.5. Fluoride (5-100 mug in 500 ml of sample solution) is quantitatively co-precipitated at pH 4.7 with approximately 90 mg of aluminium phosphate. After dissolution of the precipitate and adjustment of the solution to pH 8.5 with TISAB, the fluoride content can be measured with a fluoride ISE. The method is simple and rapid, and is suitable for the determination of trace amounts of fluoride in various water samples.