Determination of polyphosphate ions using a lead ion-selective electrode

Summary A lead ion-selective electrode responding to polyphosphate ions, such as pyro-, hexameta- and tripolyphosphate ions, has been developed and successfully used for the determination of these ions in the concentration range of 10^–6–10^–2 Min neutral solution. Almost identical potential-activity curves were obtained and the largest potential change was observed in the concentration range of 10^–6–10^–5 M (about -35 mV per decade of the concentration of each ion at pH 7.0). The response time was 1–3 min.

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Bestimmung von Polyphosphationen mit Hilfe einer Blei-ionenselektiven Elektrode

Zusammenfassung Eine auf Polyphosphationen (Pyro-, Hexameta-, Tripolyphosphat) ansprechende Blei-ionenselektive Elektrode wurde entwickelt und mit Erfolg zur Bestimmung der genannten Ionen im Konzentrationsbereich 10^–6–10^–2 M in neutraler Lösung eingesetzt. Es wurden fast identische Potential-Aktivitäts-Kurven erhalten. Die größte Potentialänderung ergab sich im Bereich von 10^–6–10^–5 M (etwa -35 mV je Zehnerpotenz der Konzentration bei pH 7.0). Die Ansprechzeit betrug 1–3 min.

     

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.     

The determination of substituted aromatic amines in water and sediment samples

Summary Certain substituted aromatic amines (anilines and benzidines) are known to possess high toxicological potential. They are classical environmental pollutants by virtue of their high degree of water solubility and the large amounts produced annually in the chemical industry for the synthesis of dyes, pesticides and pharmaceuticals.The present paper describes a method for the determination of at least thirty-one of these compounds at lower g/l or g/kg (ppb) ranges in water or sediment samples.Capillary column gas chromatography is employed with NFI- or MS-detection.Dedicated clean-up procedures are described for the substituted anilines and benzidines in aqueous and sedimentary matrices. In addition, quality assurance aspects of the individual single component identification by NFI- or MS-detection are discussed.

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Bestimmung substituierter, aromatischer Amine in Wasser- und Sedimentproben

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

Fast determination of lead in lake sediment samples using electrothermal atomic absorption spectrometry with slurry samples introduction

An analytical method for the determination of glutamic acid by the sequential perturbation caused by different amounts of glutamic acid on the oscillating chemical system involving the Cu(II)-catalyzed oscillating reaction between hydrogen peroxide and sodium thiocyanate in an alkaline medium is proposed. The method relies on the linear relationship between the changes in the oscillation amplitude of the chemical system and the concentration of glutamic acid. The reaction is implemented in a continuous-flow stirred-tank reactor, and changes in the oscillation amplitude on each perturbation are proportional to the glutamic acid concentration. The use of the analyte pulse perturbation (APP) technique permits sequential determinations on the same oscillating system owing to the expeditiousness with which the steady state is regained after each perturbation. The dynamic range lies between 2.5x10(-6) and 3.2x10(-4) M of glutamic acid, with the regression coefficient is 0.9987. The precision is excellent (less than 0.68% as relative standard deviation (R.S.D.)). Some aspects of the potential mechanism of action of glutamic acid on the oscillating system are discussed.     

Kinetic-potentiometric determination of copper in real samples with a new antimony(V) ion-selective electrode

Summary A sensitive and selective kinetic method for the determination of copper is proposed. It is based on the catalytic effect of copper on the reaction between hexachloroantimonate(V) and hydroxylamine at pH 4.4 (acetic-acetate buffer). The rate of the reaction is potentiometrically monitored with a new antimony(V) ion-selective electrode using 1,2,4,6-tetraphenyl-pyridinium hexachloroantimonate(V) as electroactive material in a poly-(vinyl chloride) membrane. The proposed method allows the determination of copper(II) concentrations in the 5–510 ng ml^–1 range, with a variation coefficient of 3.5%. The method has satisfactorily been applied to a variety of real samples.     

Flow injection determination of bromide ion in a developer using bromide ion-selective electrode detector

A potentiometric flow injection determination method for bromide ion in a developer was proposed, by utilizing a flow-through type bromide ion-selective electrode detector. The sensing membrane of the electrode was Ag(2)S-AgBr membrane. The response of the electrode detector as a peak-shape signal was obtained for injected bromide ion in a developer. A linear relationship was found to exist between peak height and the concentration of the bromide ion in a developer in a concentration range from 1.0x10(-3) to 1.0x10(-2) mol l(-1). The relative standard deviation for 10 injections of a 6x10(-3) mol l(-1) bromide ion in a developer was 1.3% and the sampling rate was ca 17-20 samples h(-1). The present method was free from the interference of an organic reducing reagent, an organic substance in a developer sample solution for the determination of bromide ion in a developer.     

Flow-injection determination of phosphate with a cadmium ion-selective electrode

A flow-injection method is described, in which phosphate standards are introduced into a reagent stream containing Cd(2+) ,resulting in the formation of Cd(3)(PO(4))(2). The associated reduction in free metal concentration is sensed by a cadmium-selective electrode. With the exception of major interference from iodide and moderate interference from bromide and thiocyanate, the system exhibits excellent response to phosphate and selectivity over several common anions in solutions buffered at pH 8.4. A maximum sampling rate of 160/hr is possible for phosphate standards in the concentration range 10(-1)-10(-1)M with a 10(-4)M Cd(2+) reagent stream at a total flow-rate (carrier and reagent stream combined) of 8.4 ml/min.     

Electrochemical determination of nitrite in water samples using a glassy carbon electrode modified with didodecyldimethylammonium bromide

Multiwalled carbon nanotubes were used as solid phase extraction (SPE) adsorbent for the determination of four chloroacetanilide herbicides (alachlor, acetochlor, metolachlor and butachlor) in water. The primary factors that influence the efficiency of the SPE performance, such as the amount of the adsorbent, the eluent solvent, the pH and the sample volume, were investigated and optimized. Under optimized conditions, the recoveries of the four herbicides at three spike levels were in the range 76.7–104.4%, and the RSDs ranged from 2.5–12.7%. Good linearity was obtained for the pesticides in the concentration range 0.0025–2.5 mg L^?1, and the detection limits were 0.01–0.03 μg L^?1 at signal-to-noise ratios of 3:1. The method was successfully applied to the determination of these analytes in tap water and river water.     

Direct potentiometric water hardness determination using ion-selective electrodes

Summary The use of ion-selective electrodes for direct potentiometric water hardness determinations is restricted to relatively soft waters if they are to be competitive with other techniques in terms of uncertainty on the water hardness scale. The selectivity factorK _MgCa ^Pot must be within 1.1% of unity if a hardness of 10 degrees on the German scale is to be measured to within 0.1 degrees in the composition rangec _Mg:c _Ca=0.25 to 25. The expressionK _MgNa ^Pot ·a _Na ² / (a _Mg+a _Ca) must be less than 0.001 if freedom from sodium interference is to be achieved. Under these conditions a 1% relative standard deviation can be obtained for an uncertainty of the EMF100V.

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Direkte potentiometrische Bestimmung der Wasserhärte mit ionen-selektiven Elektroden

Zusammenfassung Die direkte potentiometrische Bestimmung der Wasserhärte mit ionenselektiven Elektroden kann nur für relativ weiches Wasser verwendet werden, sofern sie mit anderen Methoden konkurrenzfähig sein soll. Der SelektivitätsfaktorK _MgCa ^Pot sollte nicht mehr als 1,1% von 1 abweichen, um eine Messung von 10 deutschen Härtegraden auf 0,1 Grad genau zu ermöglichen, wenn gleichzeitig das Mischungsverhältnisc _Mg:c _Ca im Bereich 0,25 bis 25 schwankt. Der AusdruckK _MgNa ^Pot ·a _Na ² /(a _Mg +a _Ca) sollte 0,001 nicht überschreiten, wenn eine Störung durch Natrium vermieden werden soll. Unter den obigen Bedingungen läßt sich eine Wasserhärte auf 1% genau bestimmen, wenn die Unsicherheit der gemessenen EMK100V.

     

Stripping voltammetric determination of lead using a glassy-carbon electrode system

The effect of the electrochemical pretreatment of the surface of a glassy-carbon indicator electrode on the electrode response and the repeatability of measurements in the stripping voltammetric determination of lead was studied. It was shown that the analytical signal depends on the nature of an electrolyte used for the pretreatment. The electrolytes that gave the most satisfactory results in the pretreatment were proposed     

The determination of chlorinated long-chain paraffins in water,sediment and biological samples

Methods are described for the routine determination of traces of industrial chloro-n-paraffins having 13–30 carbon atoms and chlorine contents of 42–45% (frw/w), in environmental samples of water, sediments and biota. The procedures are based on thin-layer chromatography detection and measurement. All samples are cleaned up by liquid—solid adsorption chromatography and thin-layer chromatography but those rich in lipids require preliminary solvent extraction. The methods distinguish between chloro-n-paraffins based on long carbon chains (C₂₀–C₃₀) and those based on shorter chains (C₁₃–C₁₇). The methods cover the ranges 500 ng l^?1 to 8 μg l^?1 for water (i.e. from about the solubility limit upwards) and 50 μg kg^?1 to 16 mg kg^?1 for sediments and biota. The precision of the methods ranges from ± 50% relative at the lowest concentrations to ± 12% relative at the highest. Recoveries are about 90% for water, 80% for sediments and between 80 and 90% for biota according to sample type.     

Continuous flow hydride generation laser induced fluorescence spectrometry for trace determination of lead in water and sediment samples

Continuous flow hydride generation coupled with laser induced fluorescence spectrometry (HG-LIF) has been used for the determination of Pb in aqueous samples. Lead hydride is generated in K₃Fe(CN)₆-HCl medium using NaBH₄ as the reducing agent. Parameters such as acidity and the concentrations of oxidising and reducing agents have been studied in order to obtain the highest sensitivity. Laser excitation of Pb has been performed at 283.306 nm and fluorescence has been detected at 365 nm and 405.8 nm. The limit of detection calculated for the optimised conditions (1% K₃Fe(CN)₆ in 0.3% Oxalic Acid, 0.055 mol L^?1 HCl, 1% NaBH₄ in 0.1% NaOH) is 0.3 ng mL^?1. However, a significant Pb background was observed for blank measurements, which degraded the limit of detection. The limit of detection that is estimated for a Pb free blank was determined by detuning the laser to a wavelength of 282.806 nm and was found to be 0.45 pg mL^?1. Method repeatability is 3.5% RSD at the 10 ng mL^?1 level. The accuracy of this method has been evaluated by analysis of a water reference material. The results obtained for a multielement standard determined using the HG-LIF approach have been found to be in agreement with those obtained by using a comparison ICP-AES approach. The HG-LIF approach has been applied to the measurement of Pb in a contaminated sediment sample material. The results of this study demonstrate that a small tunable laser system combined with hydride generation sample introduction can be used to measure Pb with high sensitivity, precision and selectivity in different sample matrices.     

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.     

Pendimethalin determination in natural water, baby food and river sediment samples using electroanalytical methods

This work describes the electroanalytical determination of pendimethalin herbicide levels in natural waters, river sediment and baby food samples, based on the electro-reduction of herbicide on the hanging mercury drop electrode using square wave voltammetry (SWV). A number of experimental and voltammetric conditions were evaluated and the best responses were achieved in Britton-Robinson buffer solutions at pH 8.0, using a frequency of 500 s^− 1, a scan increment of 10 mV and a square wave amplitude of 50 mV. Under these conditions, the pendimethalin is reduced in an irreversible process, with two reduction peaks at − 0.60 V and − 0.71 V, using a Ag/AgCl reference system. Analytical curves were constructed and the detection limit values were calculated to be 7.79 μg L^− 1 and 4.88 μg L^− 1, for peak 1 and peak 2, respectively. The precision and accuracy were determinate as a function of experimental repeatability and reproducibility, which showed standard relative deviation values that were lower than 2% for both voltammetric peaks. The applicability of the proposed methodology was evaluated in natural water, river sediments and baby food samples. The calculated recovery efficiencies demonstrate that the proposed methodology is suitable for determining any contamination by pendimethalin in these samples. Additionally, adsorption isotherms were used to evaluate information about the behavior of pendimethalin in river sediment samples.     

A new ion-selective electrode for nitrate determination

Summary A new ion-selective electrode which can be used for the nitrate determination in a concentration range of 10^–1 to 10^–4 mol/l is described. The polymer ion-exchanger membrane is formed by an epoxy resin, after Nitron nitrate having been introduced serving as an anchor group. The selectivity constants k _t-i have been determined for Cl^–, ClO ₄ ^– , HCO ₃ ^– , SO ₄ ^2– , HPO ₄ ^2– , MoO ₄ ^2– and WO ₄ ^2– .

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Neue ionenselektive Elektrode für die Nitratbestimmung

Zusammenfassung Es wird eine neue ionenselektive Elektrode beschrieben, die für Nitratbestimmungen im Konzentrationsbereich von 10^–1 bis 10^–4 mol/l verwendet werden kann. Die Ionenaustauschermembran besteht aus Epoxidharz, in das Nitronnitrat als Ankergruppe eingeführt wurde. Die Selektivitätskonstanten K _T-I für Cl^–, ClO ₄ ^– , HCO ₃ ^– , SO ₄ ^2– , HPO ₄ ^2– , MoO ₄ ^2– und WO ₄ ^2– wurden bestimmt.

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Dedicated to Prof. Dr. H. Monien on the occasion of his 60th birthday     

Isolation of lead from water samples and determination of Pb

This paper describes the procedures of isolating lead and strontium from the larger volume of seawater and drinking water samples that enable the determination of ²¹⁰Pb on gamma spectrometer and ^89,90Sr on liquid scintillation counter. In one procedure, lead is directly isolated from water sample on the column filled with Sr resin by binding of lead on the Sr resin column from 0.2 M HCl in water sample, and successive elution with 0.2 and 8 M HCl. In others, lead and strontium are precipitated from sample with (NH₄)₂CO₃, followed by isolation on an anion exchange column. Lead, strontium and yttrium are bound onto anion exchange column (filled with Amberlite CG-400 in nitrate form) from alcoholic solutions of nitric acid. Lead, Sr and Y are separated from Mg, Ca, K, and other elements by elution with 0.25 M HNO₃ in the mixture of ethanol and methanol. After that, strontium and yttrium are separated from lead by elution with 0.25 M HNO₃ in the mixture of ethanol and water.

The procedure with the Sr resin (direct isolation) is simpler and faster in the phase of isolation on the column in comparison with the procedure with the anion exchanger. The procedure with the anion exchanger, however, makes possible the simultaneous isolation of lead, yttrium and strontium and rapid determination of ^89,90Sr. These procedures were tested by determination of ²¹⁰Pb and ^89,90Sr in real sample. Obtained results showed that Pb can be efficiently isolated (with high recovery) from sample and activity of 6 mBq l⁻¹ of ²¹⁰Pb and higher can be determined.