Determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with sepiolite

Summary A method is described for the determination of tetramethrin (neo-pynamin) by differential pulse voltammetry with a carbon paste electrode modified with 10% (w/w) sepiolite. Preconcentration was carried out under open circuit conditions in 0.01 mol/l acetic acid/potassium acetate medium at pH 5.3 over 10 min, recording the voltammogram in 0.01 mol/l of KH₂PO₄/K₃PO₄ at pH 12. This led to the appearance of a peak at –1.32 V against SCE at 40 mVs^–1 and a pulse amplitude of 100 mV. Under these conditions determination limits of 45 ng ml^–1 were achieved. The method was applied to the determination of tetramethrin in soil and water samples.

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Bestimmung von Tetramethrin (Neo-Pynamin) durch Differential-Puls-Voltammetrie unter Verwendung einer mit Sepiolit modifizierten Kohlepaste-Elektrode

     

Determination of 2-amino-5-nitrothiazole by square-wave cathodic stripping voltammetry

An electrochemical method has been developed for the detection and determination of 2-amino-5-nitrothiazole (2,5-ANT) by adsorption square-wave voltammetric stripping. The best sensitivity/resolution ratio was obtained by adsorption at pH 8.0 using a phosphate buffer, an accumulation potential of –10 mV (vs. Ag/AgCl 3 mol/l) and an accumulation time of 15 s. Under these conditions, the proposed method provides a linear electrode response over the 2,5-ANT concentration range 5–300 ng ml^–1, and a detection and determination limit of 4 and 7.5 ng ml^–1, respectively. The method was applied to the determination of 2,5-ANT in bacon.     

Voltammetric determination of nitrobenzene with a chemically modified carbon paste electrode. Application to wines, beers and cider

Summary A method for the determination of nitrobenzene with a sepiolite modified carbon paste electrode is presented. Nitrobenzene is adsorbed on the electrode at open circuit (pH 3.5), and determined by differential pulse voltammetry and cyclic voltammetry at pH 5.5 in 0.5 mol/l KNO₃. The calibration is linear up to 0.4 g × ml^–1. The method was applied to the determination of nitrobenzene in wines, beers and cider. The error was ±2% and the standard deviation 5%.

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Voltammetrische Bestimmung von Nitrobenzol mit Hilfe einer chemisch modifizierten Kohlepaste-Elektrode. Anwendung auf Weine, Biere und Apfelwein

     

Determination of thiram in water and soils by cathodic stripping voltammetry based on adsorptive accumulation

Summary A very sensitive electrochemical stripping procedure for thiram is reported. Accumulation is achieved by adsorption of the compound on the hanging mercury drop electrode. Optimal experimental parameters include an accumulation potential of –0.2 V vs. Ag/AgCl, a 0.075 mol/l ammonia solution as supporting electrolyte and a differential pulse stripping mode. The detection limit is 0.3 ng ml^–1 after 120 s accumulation and 0.03 ng ml^–1 after 600 s accumulation. Results are reported for water and soil samples.

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Bestimmung von Thiram in Wasser und Böden mit Hilfe der Cathodic-Stripping Voltammetrie aufgrund adsorptiver Anreicherung

     

Fluorimetric determination of calcium by ion-pair extraction with cryptand 2.2.1 and eosin

A fluorimetric study on the extraction of calcium into 1,2-dichloroethane as an ion-pair, formed between the cryptand 2.2.1-calcium complex and the eosinate anion, is described. Optimum conditions for extraction are established and a new fluorimetric determination of ultratraces of calcium is proposed. A linear working range from 1.5 ng ml^–1 (detection limit) to 100 ng ml^–1 of calcium and a relative standard deviation of ± 2.9% at the 70 ng ml^–1 level are obtained. The equilibrium constants involved in the extraction process have been calculated and refined by the Letagrop-DISTR program. The proposed method has been tested for the direct determination of calcium in sugars.     

Simultaneous determination of cobalt and chromium by ion chromatography with chemiluminescence detection and its application to glass analysis

A method is described for the simultaneous determination of very low levels of Co and Cr by high performance ion chromatography coupled with a chemiluminescence detection system. 0.1M K₂SO₄ solutions, adjusted to pH 3.0, were used as eluent to separate Co(II) and Cr(III) between them and from interferents. The detection system was the chemiluminescence of luminol/ H₂O₂ in alkaline medium catalyzed by such transition metals. Using a matrix solution analogous to soda-lime silica glass (dissolved in acids) calibration graphs were linear up to 0.5 ng ml^–1 for cobalt and up to 250 ng ml^–1 for chromium. The corresponding calculated detection limits (3 s) in such matrix were 0.05 ng ml^–1 and 15 ng ml^–1 for Co and Cr, respectively. The relative standard deviations were 1.4% at 0.5 ng ml^–1 Co level and 2.8% at the 200 ng ml^–1 Cr level. No interferences were observed from the more common metals, particularly those present in glass samples. The ion chromatography/ chemiluminescent method proposed has been successfully applied to the analysis of Co and Cr in glasses.     

Simultaneous determination of halogenated benz(a)anthracenes in water by HPLC with fluorometric detection

Summary A HPLC method using a fluorescence detector is described for the determination of halogenated benz(a)anthracenes (BAX, x=Cl or Br) in water. It consists of the following three procedures; (1) liquid-liquid extraction of BAX with benzene, (2) elimination of interfering compounds from the extracts by one dimensional dual-band thin layer chromatography, and (3) quantitative determination of BAX by HPLC equipped with a fluorescence detector. The recoveries of BAX from water samples through the entire analytical procedure amounted to more than 72%. The calibration curves for BAX were linear, e.g., with a range from 1 to 20 ng ml^–1 for 7-chlorobenz(a)anthracene (BACl). The lower detection limit for BACl was 20 pg for an injection volume of 20 l. This method has been applied to BAX in river water spiked with benz(a)anthracene [B(a)A] at 10 ng ml^–1 after chlorination. B(a)A, BACl and BABr were found in the levels of 2.01, 0.16 and 0.13 or less ng ml^–1, respectively.     

Application of adsorptive stripping voltammetry to the determination of the psychoactive drug temazepam in urine

Summary The influence of various operational parameters on the stripping response for temazepam is discussed. Interfacial and redox behaviour was also studied. 205 Ų was the average surface area per adsorbed molecule.The determination of temazepam in urine can be performed by using adsorption as a preconcentration step previous to its measurement at the hanging mercury drop electrode by differential pulse voltammetry in 0.01 mol/l Britton-Robinson buffer at pH 3.0 with a –0.50 V accumulation potential. The detection limit was 17 ng temazepam per ml of urine (15 s accumulation time) and the relative standard deviation was lower than 6.0% for 500 ng ml^–1 samples (10 s). The effects of various urine components on the voltammetric response have also been studied.

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Anwendung der adsorptiven Stripping-Voltammetrie zur Bestimmung des Psychopharmakons Temazepam in Urin

     

Cobalt-Selective Electrode Based on Titanium Ditelluride Intercalated with Cobalt

A cobalt-selective solid-contact electrode was prepared on the basis of titanium ditelluride. The electrode exhibits the slope of the electrode function –(29 ± 1) mV/pC and provides the determination of 1 × 10^–5–1 × 10^–1 M cobalt(II) in the pH range 4.5–6.5. The electrode was used for the potentiometric indication of the titration end point in the determination of cobalt(II) in lanthanum–strontium cobaltite La_0.5Sr_0.5CoO₃. The intercalant concentration range providing optimal ion-selective properties was determined.     

Determination of palladium, platinum and gold by first derivative spectrophotometry

Summary The application of first-derivative spectrometry to the simultaneous determination of palladium(II), platinum(IV) and gold(III) is described. Light absorption of stable chlorocomplexes formed in 1 mol/l hydrochloric acid provides the basis of their determinations. A difference in the derivative amplitudes between two first-derivative zero crossing points of one metal A is read, corrected for the contribution of metal B and used for quantitation of metal C. Palladium (0.48–20 g ml^–1), platinum (0.16–24 g ml^–1) and gold (0.32–24 g ml^–1) have been determined with good precision and accuracy without any separations. Results are also presented for the simultaneous determination of the three precious metals in the presence of several major constituents.     

Differential pulse polarographic determinations of iodate, bromate and periodate

Summary The application of differential pulse polarography for quantitative trace determination of iodate, periodate and bromate has been investigated. Optimum conditions were found (pulse amplitude 100 mV, scan rate 2 mV s^–1, drop time 2 s). The detection limit for IO ₃ ^– , BrO ₃ ^– and IO ₄ ^– is ca. 2.4×10^–6M at pH 3 whereas at pH 9.3 the reduction of IO ₃ ^– and IO ₄ ^– gave concentration sensitive peak heights down to 9.9 ×10^–7M. A differential pulse polarographic method has been developed for the simultaneous determination of iodate-bromate or periodate-bromate.

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Bestimmung von Iodat, Bromat und Periodat durch Differential-Pulse-Polarographie

Zusammenfassung Optimale Bedingungen zur Bestimmung dieser Ionen im Spurenbereich wurden ausgearbeitet (Pulsamplitude 100 mV, Scangeschwindigkeit 2 mV s^–1, Tropfzeit 2 s). Die Nachweisgrenze für die drei Ionen liegt bei 2,4 · 10^–6 M für pH 3. Bei pH 9,3 ergaben sich für Iodat und Periodat konzentrationsabhängige Peakhöhen bis herab zu 9,9 · 10^–7 M. Da der Bromatpeak bei wesentlich negativerem Potential auftritt als der Iodat bzw. Periodatpeak konnten Iodat und Bromat bzw. Periodat und Bromat nebeneinander bestimmt werden.

     

Determination of medecamycin by adsorptive stripping voltammetry with an activated electrode

The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l^–1 NH₃-NH₄Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH₃-NH₄Cl buffer (pH 9.0) at a potential of –0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 g ml^–1 to 50.0 g ml^–1. The detection limit (three times the signal-to-noise) was 1.0 g ml^–1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 g ml^–1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

Cathodic stripping voltammetry of pipemidic acid and ofloxacin in pharmaceutical dosages and human urine

Sensitive cathodic stripping voltammetric methods have been developed for two quinolone antibacterial drugs, pipemidic acid (PIP) and ofloxacin (OFL) using hanging mercury drop electrode as working electrode vs. Ag/AgCl reference electrode. The methods were developed for the determination of drugs individually as well as simultaneously. 0.1 M and 0.01 M hydrochloric acid was used as medium for PIP and OFL, respectively, 0.1 M potassium chloride was used as base electrolyte. Reduction waves were observed for PIP within ?700 mV to ?800 mV and for OFL within ?1100 mV to ?1200 mV. Linear calibration ranges for PIP and OFL were observed within 10–100 μg ml^?1 with detection limits of 50 ng ml^?1 and 1 μg ml^?1, respectively. Relative standard deviations (RSD) for the analysis of 10 gµg ml^?1 of PIP and OFL (n = 6) were 0.5% and 1.4%, respectively. The presence of glucose, lactose, sorbitol, gum arabic, starch, magnesium stearate, methylparaben and propylparaben did not affect the determinations of both PIP and OFL. The methods were used for the analysis of pharmaceutical preparations and the results indicated relative deviation of 0.5–5.5% from labeled values with RSD within 0.49–2.5%. PIP and OFL could also be determined simultaneously, and were determined from spiked human urine.     

Determination of selenomethionine by high performance liquid chromatography-direct hydride generation-atomic absorption spectrometry

A simple, reliable, trace determination of selenomethionine (Semet) based on a direct hydride generation atomic absorption spectrometric method was developed using sodium tetrahydroborate (0.3% in 0.2% NaOH) and hydrochloric acid (3 M). The method excluded any chemical pretreatment prior to hydride generation (HG). The optimized HG system was successfully coupled with the HPLC system. The detection limit (3σ of blank; n=5), reproducibility (R.S.D. of three successive analyses/day, performed on three different days), and repeatability (R.S.D. of three successive analyses) of the method were 1.08 ng ml⁻¹, 9.8% for 9.04 ng ml⁻¹ and 2.1–9.5% for 30.0–1.27 ng ml⁻¹ Semet as Se (standards prepared in Milli-Q water). Calibration graph was linear up to 30 ng ml⁻¹. This HPLC-HG-AAS method is very promising and successfully determined Semet (spiked) in human urine.     

Simultaneous determination of chromium(VI) and chromium(III) by flame atomic absorption spectrometry with a chelating ion-exchange flow injection system

Summary Simultaneous Determination of Chromium(VI) and Chromium(III) by Flame Atomic Absorption Spectrometry with a Chelating Ion-Exchange Flow Injection System A simple method is described for the simultaneous determination of chromium(VI) and chromium(III) in a flow injection system comprising chelating ion-exchange and flame atomic absorption spectrometry. Sampling rates for 2001 and 1 ml sample volumes were 120 and 60 h^–1 (240 and 120 speciations per hour), respectively. Typical relative standard deviations were 0.52% for Cr(VI) (0.50g ml^–1 and 0.67% for Cr(III) (0.10,g ml^–1) and the corresponding limits of detection were 85 ng ml^–1, and 16 ng ml^–1, respectively.On leave from University of Belgrade.     

Speciation of silicon and phosphorous using liquid chromatography coupled with sector field high resolution ICP-MS

Sector-field high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) has been used, at R=3000, to resolve spectral interferences caused by N₂⁺ and CO⁺ on ²⁸Si⁺, and NOH⁺ and NO⁺ on ³¹P⁺, thereby facilitating the speciation of these elements. Polydimethylsiloxanes (PDMS), ranging from 162 g mol⁻¹ to 16 500 g mol⁻¹, and their silanol breakdown products, have been separated by size exclusion and reverse phase chromatography, respectively, and detected using HR-ICP-MS. Detection limits (as Si) of between 12–30 ng ml⁻¹ and 0.1–4 ng ml⁻¹ were obtained for the PDMS and silanol compounds, respectively. Quantitative and reproducible methods have been developed for the analysis of four common organophosphorous pesticides in blood plasma, and inorganic phosphates in food, with detection limits of between 0.9–2 ng ml⁻¹ and 1–39 ng ml^−1, respectively.     

Adsorptive stripping voltammetric determination of 1-(4′-bromophenyl)-3,3-dimethyltriazene

The optimum conditions were established for the determination of the genotoxic substance 1-(4-bromophenyl)-3,3-dimethyltriazene by differential-pulse voltammetry at a hanging mercury drop electrode in the concentration range 1 × 10^–4 to 1 × 10^–7 mol dm^–3. The sensitivity of the determination can be improved through adsorptive accumulation of the investigated substance on the surface of the hanging mercury drop electrode: differential pulse adsorptive stripping voltammetry can be used in the concentration range 1 × 10^–7 to 2 × 10^–10 mol dm^–3. The relative standard deviation (for ten determinations at 2 × 10^–10 mol dm^–3) was 7.5%.     

Determination of a new calcium antagonist in human plasma by liquid extraction enrichment and HPLC with UV detection

Summary An HPLC method has been developed for the determination of SL 85.1016, a new calcium antagonist arylbenzylamide methylthioether derivative. SL 85.1016 and the internal standard, SL 87.0210, are extracted from alkaline human plasma withn-hexane and back extracted into 0.05 M phosphate buffer (pH 2.5; 0.2 ml). Acetonitrile (50 l) is added to the final aqueous extract in order to prevent absorption of the compounds of interest onto the walls of the glass tube; this solution then is partially processed by HPLC on a C₁₈ column with UV detection (254 nm). The determination limit of the method is 2 ng.ml^–1 of SL 85.1016 in human plasma; the response to the drug is linear in the range 2–200 ng.mg^–1.     

Polarographic and voltammetric determination of trace amounts of 2-nitronaphthalene

The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2×10^–6–1×10^–4, 2×10^–7–1×10^–4, 1×10^–8–1×10^–4 and 2×10^–9–1×10^–8 M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid–liquid and solid-phase extraction with limits of determination of 3×10^–10 M (drinking water) and 3×10^–9 M (river water).