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Analytical and Bioanalytical Chemistry (v.358, #6)
Modified solid electrodes for stripping voltammetric determination of tin by C. Faller; G. Henze; N. Stojko; S. Saraeva; K. Brainina (pp. 670-676).
The paper describes the determination of tin by ASV using modified thick film electrodes. Three different types of electrodes were developed: One modified with a mixture of Nafion and mercury(II)acetate, one modified with diethyldithiocarbamate (DDC) or pyrrolidinedithiocarbamate (PDC) and mercury(II)acetate, and one modified with calomel. The analyte was accumulated on the electrode surface after special electrochemical pretreatment of the modified electrode. After recording the voltammogram the electrodes were electrochemically regenerated. By virtue of their lifetime and their measurement reproducibility, we preferred the DDC and PDC modified electrodes. They can be used for months without changing their chemical characteristics. The linear range for tin determination with these electrodes is between 1 and 100 μg/L; the detection limit was calculated as 0.9 μg/L. The electrodes were applied to the direct determination of tin in different canned fruit juices without special sample pretreatment.
A flow system for calibration of dissolved oxygen sensors by P. Jeroschewski; D. zur Linden (pp. 677-682).
Well-defined oxygen standard solutions were obtained by the electrolysis of water in a coulometric oxygen generator. The generator was integrated into a flow system that includes the degassing of the carrier electrolyte, the generation of dissolved oxygen and the temperature control of the carrier electrolyte. The current efficiency of oxygen generation was found to be 100% by the Winkler titration method. Calibrations of a home made laboratory sensor and a WTW CellOx dissolved oxygen sensor have been made in a concentration range of 0.02 to 8 mg/L at temperatures from 5°C to 30°C. The calibration of the WTW sensor on water vapour saturated air was compared with the electrochemical calibration method. Both methods gave reliable results provided that the temperature equilibration between the sensor and the ambient air was successful.
Micro flow calorimeter for thermoelectrical detection of heat of reaction in small volumes by J. M. Köhler; M. Zieren (pp. 683-686).
A micro chip element with an integrated flow channel and thin film thermopiles was developed in order to realize a micro calorimeter for small volumes in a flow arrangement. The flow channel consists of two inlets, a mixing region, a measurement region, and one outlet. Thermopiles of BiSb/Sb thermocouples were used as thermal transducers because of their extraordinary high thermopower. A thin film heater of a NiCr alloy was integrated in order to yield the possibility of internal electrical calibration. In addition, this heater can be used for thermal modulation of the whole measurement system. The calorimeter was prepared using vacuum evaporation, PECVD and magnetron sputtering for thin film deposition and photolithography as well as chemical wet etching for microstructuring. The function of the device was tested to neutralize 400 nmole, 100 nmole and 10 nmole NaOH by H2SO4.
Development and laboratory investigation of a denuder sampling system for the determination of carbonyl compounds in stack gas by G. Kallinger; R. Niessner (pp. 687-693).
A method for sampling and detection of low volatile carbonyl concentrations (aldehydes and ketones) in stack gas is proposed. For this purpose, a novel fourfold glass annular-denuder, coated with acidified 2,4-dinitrophenylhydrazine (DNPH) has been developed for the sampling of carbonyl compounds under high temperature and high humidity emission conditions. After sampling, the hydrazones are eluted with acetonitrile and analyzed using RP-HPLC. They are detected by UV-absorbance, with maximum sensitivity obtained between 350 and 380 nm. The sampling efficiency has been investigated for different flow rates, temperatures and relative humidities. The influence of other trace gases (ozone, nitrogen dioxide) on the sampling system was investigated as well.
A new concept for the quasi non-destructive microsampling of historical glasses by G. Schulze; I. Horn; H. Bronk (pp. 694-698).
A mobile and easily practicable microsampling technique for historical glasses and its application is presented. About 100 μg of material is scraped off the object with a fine grinding file. The analysis of main, minor and trace elements in the digested sample is performed by IC, GFAAS and FIA with photometric detection. The procedure has been verified by measurements of standard glasses. Investigations of baroque ruby glasses showed the suitability of the microsampling technique for archaeometrical application.
Indirect determination of the sum of chelons in drinking- and ground-waters by anodic stripping voltammetry by Peter Schön; K.-H. Bauer; Volker Wiskamp (pp. 699-702).
The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions.
Sequential flow analysis coupled with ACSV for on-line monitoring of cobalt in the marine environment by Anne Daniel; Alex R. Baker; C. M. G. van den Berg (pp. 703-710).
The development of a compact instrument for on-line measurement of trace metals in seawater is described. The system is based on adsorptive cathodic stripping voltammetry (ACSV), and on the concept of sequential flow analysis, to perform on-line measurements with controlled perturbation of natural equilibria of the element. The design combines a low volume flow cell with a miniature solenoid pump and valves to achieve low power consumption. The flow segmentation is time-controlled and the detection step takes place in a well-defined part of the flow stream where reagent and sample occur mixed. The system was tested on the determination of cobalt in seawater but it is likely that the same technique can be used to determine other metals detectable by CSV. The determination range was 6–1050 pmol/L cobalt with a detection limit (3σ) of 6 pmol/L. The measurement rate was about 60 h–1. Comparative measurements were carried out using continuous flow analysis. The apparatus was used continuously on board a ship to determine the distribution pattern of cobalt in surface waters off the coast of California.
Determination of free and total copper and lead in wine by stripping potentiometry by Alison M. Green; Andrew C. Clark; G. R. Scollary (pp. 711-717).
Stripping potentiometry has been employed for the measurement of the labile and total copper concentrations in white wine. Conditions have been optimised for a supporting electrolyte consisting of 1.0 mol/L hydrochloric acid and 0.5 mol/L calcium chloride. Mercury(II) was found to be a more suitable oxidant than O2 and, for the determination of the labile concentrations, this required the use of medium exchange. With lead, O2 proved to be an efficient oxidant for the stripping step and this allowed the direct measurement in the wine without the need for medium exchange. It was observed that red wine rapidly binds added lead, demonstrating that wine has a high complexation capacity for lead. A similar complexation effect was also observed for white wine, but the degree of lead complexation was less than that for red wine. The impact of this lead complexation effect for the use of standard additions is discussed.
Strategy for copper speciation in white wine by differential pulse anodic stripping voltammetry, potentiometry with an ion-selective electrode and kinetic photometric determination by Claudia Wiese; G. Schwedt (pp. 718-722).
Differential pulse anodic stripping voltammetry (DPASV), potentiometry with a copper ion-selective electrode and a kinetic photometric method were used to determine copper species in white wines. The kinetic method is based on the catalytic effect of labile copper(II) species on the oxidation of 3-hydroxybenzaldehyde azine by potassium peroxidisulfate in an ammonical medium at room temperature. The total copper concentrations were determined by flame atomic absorption spectrometry. Free copper(II) ions, labile and tightly bound copper species could be quantified in 16 non pre-treated wine samples.
Determination of cadmium, lead and copper in wine by potentiometric stripping analysis by P. Ostapczuk; H. R. Eschnauer; G. R. Scollary (pp. 723-727).
A procedure for the determination of Cd, Pb and Cu in different wine samples after simple sample preparation on a mercury film electrode (MFE) by potentiometric stripping analysis (PSA) is presented. In 150 German wine samples collected in 1993/94 the following values were found: Cd mean: 0.63 ng/mL (range: 0.003– 0.98 ng/mL); Pb mean: 50 ng/mL (range: 4–254 ng/mL); Cu mean: 250 ng/mL (range: 50–394 ng/mL).
A constant current coulometer for the high precision analysis of uranium by G. Finoly; W. Leidert; W. Stüber; Y. Le Duigou; M. Bickel (pp. 728-735).
A constant current coulometry device was designed, built and evaluated. It is capable of controling the coulometric titration process and to deliver the necessary current and time supplies/measurements with extremely high accuracy. The device was applied to the coulometric titration of uranium. The chemical part of the system was adapted and improved and a reliable procedure was developed. The method is highly accurate, standard deviations lie around 0.06% relative. It is an absolute method and directly traceable to the SI units.
Cathodic stripping voltammetric determination of selenium(IV) at a thin-film mercury electrode in a thiocyanate-containing electrolyte by Britta Lange; F. Scholz (pp. 736-740).
The well-known method for the determination of selenium(IV), which is based on the cathodic stripping voltammetry of copper(I) selenide, has been adapted for application at the thin-film mercury electrode on glassy carbon (TFME). Insufficient reproducibility and sensitivity have been overcome by using a 0.1 mol/L HClO4 electrolyte solution containing 0.02 mol/L thiocyanate ions. Thiocyanate ions have been found to increase the peak height of the selenium response and shift it to more positive potentials. This behaviour is explained by an adsorption of SCN– at the interface glassy carbon/Cu2Se and its action as an electron transfer catalyst between glassy carbon and copper(I) selenide. A 3σ-detection limit of 75 ng/L Se(IV) has been achieved. The relative standard deviation is 5.2% at 5 μg/L selenium(IV). The influence of cadmium(II), arsenic(III), zinc(II), iron(III) and lead(II) ions on the selenium response has been studied. In case of lead ions, a new signal occurred at more negative potentials than the reduction of Cu2Se. This signal, which is probably due to the reduction of PbSe, can also be used for the determination of selenium(IV).
Speciation of arsenic(V) and arsenic(III) by cathodic stripping voltammetry in fresh water samples by G. Henze; Wolfram Wagner; Sylvia Sander (pp. 741-744).
A voltammetric stripping procedure is described for the determination of arsenic(V) in a mannitol-sulphuric acid medium. The arsenic is coprecipitated with copper and selenium and reduced to arsine at the hanging mercury drop electrode. Using an accumulation time of 240 s, the detection limit is 0.52 μg L–1, the determination limit is 0.9 μg L–1. The method has been applied to the determination of arsenic in water samples. By varying the composition of the supporting electrolyte it is possible to differentiate between arsenic(III) and arsenic(V). As both oxidation states have different toxicological characteristics, the ability to discriminate between both is an distinct advantage of the proposed method.
Determination of antibilharzial antimony compounds by direct current, differential pulse, square-wave and alternating current anodic stripping voltammetry by K. Brodersen; H. N. A. Hassan; M. E. M. Hassouna; I. H. I. Habib (pp. 745-748).
A simple, rapid and sensitive method has been developed for the determination of Sb(III) in five antimonial antibilharzial drugs using anodic stripping voltammetry. The method is based on the reduction of Sb(III) on the HMDE, followed by a selected mode of oxidative sweep, i.e. direct current, differential pulse, square-wave or first harmonic alternating current sweep, using 2 mol/L HCl as a supporting electrolyte. Voltammograms for various sample concentrations in the range 3–47 ppb Sb(III) were recorded and the respective calibration graphs constructed. To overcome the expected effect of adsorption of surface active organic compounds on the mercury drop, the standard addition technique of Sb2O3 solution was applied to calculate the recoveries of all the tested antimonials. The method gave reproducible results within 2% and the limit of detection for all measurement modes was 3 ppb. SW and AC modes seem to achieve lower detection limits than the other two modes. The four modes proved to be of equal accuracy and precision.
Determination of phenols in environmental samples by liquid chromatography – electrochemistry by N. Cardellicchio; S. Cavalli; V. Piangerelli; S. Giandomenico; P. Ragone (pp. 749-754).
A reverse-phase high-performance liquid chromatography procedure with gradient elution and electrochemical detection is described for the determination of phenolic compounds, including several priority pollutant chlorophenols, in sea-water and sediments. In addition, a method for concentrating phenols from sea-water was examined. A solid-phase extraction using a derivatized poly(styrene-divinylbenzene) copolymer is discussed. The recovery, repeatability and detection limits are shown. Electrochemical detection provided selectivity as well as sensitivity. Phenols at the ng/l level were detected. The method was applied to the analysis of the most important phenolic compounds in sea-water and marine sediments.
Voltammetric detection of avidin and biotin by biotin labeled with cysteine by K. Sugawara; Suwaru Hoshi; Kunihiko Akatsuka (pp. 755-759).
An avidin-biotin assay was developed from a voltammetric procedure using biotin labeled with cysteine. Mercury(II) as a marker was used to detect avidin and biotin, because the oxidation wave of mercury decreases when the cysteine part of labeled biotin(LB) complexes with mercury(II).The formation of the mercury(II)-cysteine complex is suppressed when the LB binds to the biotin site of avidin. Accordingly, the concentration of avidin can be estimated from the increasing mercury peak current. Detection of biotin is also carried out by a competitive reaction of biotin and the LB to the binding site on avidin, where the addition of biotin decreases the peak current of mercury. Limits of detection for avidin and biotin were in the 10–9 mol/L range. The length of the spacer between the cysteine and biotin was investigated. It was observed that the strength of binding increased with increasing length of spacer. Size considerations rules out steric influences, so it is suggested that the binding constant depends on hydrophobic interactions in the binding site.