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Analytical and Bioanalytical Chemistry (v.371, #4)
No Title by T. Ehmann; L. Fabry; L. Kotz; S. Pahlke (pp. 407-412).
Several methods are presented for the routine ultra-trace analytical monitoring of inorganic and organic anions and cations on the surface and in the native oxide of silicon wafers – the wafer-surface water-extraction method, the vapor-phase-decomposition method, and the re-dissolving method. Electrokinetic injection, sample stacking, and electrolyte composition were, therefore, optimized and made robust. For electrokinetic injection with transient isotachophoretic preconcentration a linear range of 0.05 to 0.5 µmol L–1 was obtained; for sample stacking the linear range was 0.5 to 10 µmol L–1, even in the presence of up to 750 µmol L–1 hydrofluoric acid. Inorganic anions and monovalent carboxylic acids are predominately dissolved in the aqueous layer on the wafer surface whereas dicarboxylic acids are chemically bonded to the silanol groups and form esters.
Effect of additives on the flow-analysis determination of weak-acid-dissociable and total cyanide by H.-J. Heckemann; B. Stadler; D. Schulz (pp. 413-419).
The effect of reductants, complexants, and nitrite eliminators on the flow-analysis determination of weak-acid-dissociable and total cyanide has been studied for: 1.cyanide recovery from copper, nickel, and iron complexes; 2.cyanide generation from the reagents in the presence of common interferents; and 3.cyanide consumption by the reagents in the presence of those interferents. In the absence of additives the UV-assisted recovery of (total) cyanide from the iron complexes (using a succinate buffer) was insufficient. Arsenite and hypophosphite had no measurable effect on the recovery, ascorbic acid resulted in total recovery but under these conditions nitrite and sulfite seemed to destroy cyanide. Phenanthroline promoted the recovery of cyanide from iron complexes but led to formation of cyanide from thiocyanate. Citrate resulted in good recovery but in the presence of nitrite cyanide was formed; the recovery with EDTA was also good. It proved necessary to destroy nitrite by use of sulfamic acid. If a combination of EDTA, citrate, and sulfamic acid is used rather high concentrations of thiocyanate, nitrite, thiosulfate, and sulfite can be tolerated in the samples. It is strongly advisable to test modifications of the cyanide determination comprehensively, because some surprising results have been obtained.
No Title by Stephanie Ossadnik; Georg Schwedt (pp. 420-424).
Several methods for quantitative determination of peroxomonosulfate in detergents, in the presence of other oxidants, have been investigated. The photometric technique applied was based on the well-known starch–iodine reaction. The oxidizing agent was quantified by determining the amount of iodine produced. The influence of other oxidants present was examined. Ion analysis was performed by capillary zone electrophoresis (CZE) and ion chromatography (IC). Because peroxomonosulfate in detergents is always accompanied by sulfate, the main goal was to separate the sulfur species without causing the decomposition of the unstable peroxomonosulfate ion. The sulfur species could be separated within less than 4 min by CZE with a pyromellitic acid electrolyte at pH 3.5 to 5.0. Sulfate and peroxomonosulfate were separated by IC within 11 min by use of a phthalic acid mobile phase at pH 3.0. The peroxomonosulfate content was determined by calibration. The calibration plot was linear from 5 to 50 µg mL–1 SO5 2– for IC and from 7.3 to 182.3 µg mL–1 SO5 2– (corresponding to 20 to 500 µg mL–1 triple salt) for CZE.
No Title by Sara Fäldt; Bo Karlberg; Wolfgang Frenzel (pp. 425-430).
The hyphenation of gas-diffusion separation and ion chromatography (IC) is described as a convenient, reliable, robust, and economic method for in-line sample pre-treatment. The high selectivity associated with this method permits direct analysis of samples containing microparticulates, colloidal matter, and/or high molecular weight compounds. The determination of sulfite serves as a first example of its application. The method is based on the diffusional separation of SO2 following in-line oxidation with hydrogen peroxide to sulfate and final determination of the sulfate formed using IC. The influence of operational parameters has been thoroughly investigated and gas-diffusion cells of different geometries compared with respect to the gas-transfer rates obtained. Application to the analysis of wines demonstrates the utility of the method.
No Title by H. Below; H. Kahlert (pp. 431-436).
A variety of parameters affecting the determination of iodide in biological materials by ion-pair chromatography and electrochemical detection were examined in detail. It became apparent that the pH value, the ion-pair concentration, the proportion of organic solvent and of organic bases as a component of the buffer solution, as well as the salt concentration in the eluent system could effectively influence the retention characteristics of iodide in the chromatographic system, resulting in the separation of potential interfering substances. The presence of other anions in the sample matrix has to be taken into consideration, particularly thiocyanate because of its long retention time. Investigations of the electrochemical detection mechanism revealed that the reaction hitherto assumed to be responsible for detector signal generation (formation of AgI) is incorrect. In addition, a much more sensitive detection of iodide than that cited in the literature to date is possible if the detector potential is optimally selected and any anticipated interfering substances are removed by chromatography. Use of a gold electrode rather than a silver electrode also considerably enhances the reliability of the procedure.
No Title by Maria J. Alda; Damià Barceló (pp. 437-447).
Steroid sex hormones and related synthetic compounds, e.g. those used in contraceptive pills, have been shown to be present in the aquatic environment, mainly as a result of inefficient removal in waste-water-treatment plants (WWTP). The concentrations of the compounds, although very low (low ng L–1), are sufficient to induce estrogenic responses and alter the normal reproduction and development of wildlife organisms. The compounds have been determined, by a variety of analytical procedures, in the influents and effluents of WWTP, within research programs conducted in different countries to evaluate the efficiency of the waste-water-treatment processes currently in use. Determination of natural and synthetic estrogens and progestogens in waste water is, however, a difficult analytical task, because the very low detection limits required and the complexity of the waste-water matrix necessitate the execution of a considerable number of steps. Thus, in general, complicated, time-consuming extraction and purification processes, usually based on the application of solid–liquid extraction, are performed before final determination by immunoassay, high-performance liquid chromatography, or, most often, gas chromatography coupled with mass spectrometry. This paper reviews the analytical methods so far described for the analysis of these important environmental pollutants in waste water and discusses the key procedural steps, from sampling to analysis, and the techniques most commonly used in the determination.
No Title by J. Riu; E. Martínez; D. Barceló; A. Ginebreda; LL. Tirapu (pp. 448-455).
Linear alkylbenzene sulfonates (LAS) have been determined in samples of the influent and the effluent, and in the sludge, from sewage-treatment plants (STP). LAS and sulfophenyl carboxylate compounds (SPC) were isolated by solid-phase extraction (SPE) with the polymeric phase Isolute ENV, then determined by liquid chromatography–electrospray mass spectrometry (LC–ESI–MS). The method enabled unequivocal identification of C10–C13 LAS by monitoring the ion at m/z 183 and the base peak corresponding to the [M–H]– ion. Average recoveries varied from 77–93% and the linear range of the method varied from 0.2 to 10 µg L–1, with a limit of detection ranging from 10 ng L–1 to 1.5 µg L–1 when 200 mL waste water were preconcentrated. For sewage sludge, recoveries varied from 58 to 90% and the linear range was between 0.2 and 100 µg L–1, with a detection limit ranging from 0.4 to 120 µg kg–1 when 2.5 g sewage sludge was extracted. Unequivocal identification and determination of some metabolites of the LAS, the sulfophenyl carboxylate compounds (SPC), was achieved by monitoring [M–H]– ions.
No Title by M. Fránek; J. Zeravík; S. Eremin; J. Yakovleva; M. Badea; A. Danet; C. Nistor; N. Ocio; J. Emnéus (pp. 456-466).
This brief overview summarises the immunoassay-based results obtained in the course of two years of the European INCO-Copernicus project BIOTOOLS. The project is aimed at simplifying the procedures for detection of surface active compounds (SAC) using, among others, antibody-based methods, i.e., microtiter plate-based enzyme-linked immunosorbent assays (ELISA), polarisation fluoro immunoassays (PFIA), and enzyme flow injection immunoassays (FIIA). Thirty-three rabbits were immunised with five different sulphophenyl moieties and three p-hydroxyphenyl moieties conjugated to protein immunogens to produce analytical antibodies against linear alkylbenzene sulphonates (LAS) and nonylphenol (NP). Although most of the antibodies exhibited binding reaction in indirect ELISA, only a few showed the required assay sensitivity. The best antibodies for LAS exhibited a 50% binding inhibition at IC50 19.8 µg L–1 in indirect ELISA. Similar inhibition was observed for direct ELISA using peroxidase tracers. Antibodies against NP allowed the establishment of an indirect assay operating in the mg L- -1 range. A rapid and simple protocol for the screening of NP and LAS using homogeneous PFIA is described. The assay time for 10 samples was 7 minutes, thus allowing fast detection of the selected SAC at the mg L–1 level. A generic competitive FIIA system, using a protein G column for separation of free and antibody-bound β-galactosidase (β-Gal) tracer, was developed for the screening of LAS, NP, and nonylphenol decaethoxylate (NPEO10). The FIIA had a sample throughput (STP) of 5–10 samples per hour, with limits of detection (LOD) for LAS, NP, and NPEO10 of 19.5, 52, and 2.4 µg L–1, respectively. The developed FIIAs were applied to spiked rain and surface water.
No Title by Marinella Farré; Damià Barceló (pp. 467-473).
A new amperometric biosensor based on inhibition of Pseudomonas putida has been developed to assess the acute toxicity of wastewater. This system uses the biological component immobilized on disposable screen-printed electrodes. The responses for a selected group of polar organic standard substances were studied using Pseudomonas putida as biological component. The results have been compared with responses obtained using the same system and Escherichia coli as biological component and with the bioluminescence inhibition of Vibrio fisheri using ToxAlert 100. Different properties, e.g. the standard deviation (SD) of the data, the goodness of fit (R2) and the standard deviation (Syx) of the vertical distances of the points from the inhibition curve, the 50% effective concentration (EC50) and the toxicity units (TII50) of the standard substance, were calculated and compared. This biosensor was used to assess the acute toxicity of real wastewater samples collected at different wastewater treatment plants (WWTP).Finally, a sequential solid-phase extraction (SSPE) procedure followed by liquid chromatography–mass spectrometry (LC–MS) was used to determine the polar organic toxic substances present in the wastewater samples.
No Title by I. Moreno-Garrido; M. Hampel; L. Lubián; J. Blasco (pp. 474-478).
Different microalgal species have been used in growth-inhibition tests to determine the toxic concentrations of anionic and non-ionic surfactants to phytoplankton. The species used were selected from different taxonomic groups, all of considerable ecological relevance to marine environments. The toxicity of the C13 LAS homologue to the microalgal species selected was usually one order of magnitude greater than that of the C11 homologue. The toxicity of a commercial LAS mixture to different microalgal species was also checked. For this material and C. gracilis, cellular counting by means of a Neubauer chamber and by use of a flow cytometer were compared; differences between the two methods were insignificant. The toxicity of decaethoxylated nonylphenol non-ionic surfactant to C. gracilis was also checked; the EC50 value for this compound was 1.0 mg L–1.
No Title by V. León; A. Gómez-Parra; E. González-Mazo (pp. 479-485).
An analytical method is presented for the determination of sulfophenylcarboxylic acids (SPC) produced by the biodegradation of linear alkylbenzene sulfonates (LAS) in marine samples. Isolation and concentration of the compounds was by solid-phase extraction. The different factors affecting extraction efficiency – packing composition, pH, clean-up, ionic strength, and elution solvents – were studied and optimized. With the proposed method C4–C13SPC and C10–C13 LAS recoveries varied between 65% and 105%, with standard deviations between 0.1 and 5, respectively, for 100-mL samples and 100 µg L–1 concentrations of each homolog. Detection limits within the range 0.5 g L–1 (for C4SPC) to 1.0 g L–1 (for C12SPC) were obtained by liquid chromatography with fluorescence detection. This method is the first to be proposed that enables the simultaneous determination of monocarboxylic SPC (C>3) and LAS homologs in marine samples by a simple, sensitive, and specific method giving high recoveries and reproducibility. SPC with from three to twelve carbon atoms in the carboxyl chain have been found in marine water samples.
No Title by M. Sáez; A. Gómez-Parra; E. González-Mazo (pp. 486-490).
Sorption experiments using different homologues of linear alkylbenzene sulfonate (LAS) and sulfophenylcarboxylic acid (SPC) on several marine microalgae have been carried out. The steady state seems to be reached in the first 4 hours. Longer exposure times lead to biodegradation of the compound and, therefore, to an overestimation of the bioconcentration factor. Sorption coefficients are higher for Nannochloropsis gaditana, for example, 1,293 Lkg–1 for C11-LAS and 525 Lkg–1 for C11-SPC versus 727 Lkg–1 for C11-LAS and 28 Lkg–1 for C11-SPC for Dunaliella salina. For both algae an increase in the sorption coefficient is observed when the polarity of the compound decreases (C5-SPC11-SPC11-LAS≈C12-LAS). The sorption of C11-LAS on D. salina is fitted to a linear Freundlich isotherm (K=176±0.02, n=0.964±0.02)
No Title by E. Papadopoulou-Mourkidou; J. Patsias; E. Papadakis; A. Koukourikou (pp. 491-496).
Caffeine and selected aniline and phenol compounds have been monitored in the river, lake, and ground water of Northern Greece (Macedonia–Thrace) from September 1999 to December 2000 by means of a fully automated on-line SPE–HPLC method. Among the target aniline and phenol compounds the most abundant was 2,6-di-tert-butyl-4-methylphenol, which was found to be present in both surface and ground water samples. Caffeine was also very frequently present in river and ground water, although its presence in lake water was rare. Caffeine and 2,6-di-tert-butyl-4-methylphenol were also monitored by off-line SPE of water samples and GC–ion-trap MS analysis of extracts.
No Title by Xiashi Zhu; Bin Hu; Lei Wang; Shengqing Li; Zucheng Jiang (pp. 497-501).
A novel method has been developed for the direct determination of traces of chromium, cobalt, and nickel in TiO2 powder; it entails slurry sampling and electrothermal atomic-absorption spectrometry (ETAAS) with a polytetrafluoroethylene (PTFE) slurry (6% m/v) as fluorinating reagent. The factors which could affect the vaporization of the matrix and analytes were studied in detail; the fluorinating vaporization behavior of the analyte both in the slurry and in solution were also investigated. Owing to the in-situ separation of the matrix, the matrix influences were reduced significantly. The proposed method has been applied to the direct determination of traces of chromium, cobalt, and nickel in high-purity TiO2 powder without chemical pretreatment. Under the optimum experimental conditions the detection limits of the analytes (Cr, Co, and Ni) were 1.9 ng g–1, 2.4 ng g–1 and 5.4 ng g–1, respectively, the relative standard deviations (RSD) were 3.4% (n=6, c=7.0 ng mL–1), 2.9% (n=6, c=0.70 ng mL–1), and 7.6% (n=6, c=4.0 ng mL–1), again respectively, and the characteristic masses for Cr, Co, and Ni were 8.4 pg/0.0044A, 9.3 pg/0.0044A, and 40.0 pg/0.0044A, respectively.
Modification of the electroosmotic flow and separation selectivity of anions in electrochromatography with pseudo-stationary phases of C14-alkyldimethylammoniopropane sulfonate zwitterionic surfactants by addition of salts to the background electrolyte by Takashi Yokoyama; Miroslav Macka; Paul R. Haddad (pp. 502-506).
The effects of salts (NaCl, NaClO4, MgCl2, CeCl3) added to background electrolyte (BGE) solutions (10 mmol L–1 sodium phosphate, pH 7.2) on electroosmotic flow (EOF) and the separation selectivity of anions (chloride, bromide, iodide, nitrite, nitrate, chlorate, thiocyanate, iodate, chromate, and molybdate ion) by capillary electrochromatography using the zwitterionic surfactant 3–(N,N–dimethylmyristylammonio)propane sulfonate (C14N3S) as a pseudo-stationary phase were investigated. There are two mechanisms affecting the separations: 1.the cations and anions of the added salts interact with the zwitterionic surfactant to varying degrees, thus changing the overall retention of the analytes; and 2.they change the EOF and the resulting apparent mobilities. It was shown that a BGE containing perchlorate and a low concentration of zwitterionic surfactant (2 mmol L–1) gave a stable and reproducible EOF and the concentration of perchlorate could be used to manipulate the separation selectivity for polarizable anions, such as iodide and thiocyanate. These effects are discussed in terms of measured association constants describing the interaction of anions and cations with the zwitterion.
No Title by María Pedrero; Pilar Salas; Rocío Gálvez; Javier F. Villena; José M. Pingarrón (pp. 507-513).
The flow injection amperometric performance of solid composite graphite electrodes with ethylene/propylene/diene (EPD) or Teflon as binding agents, and with Ru or RuO2 particles as electrocatalytic modifiers has been compared. Both, Ru and RuO2 modified electrodes exhibited electrocatalytic properties on the methionine oxidation process in alkaline media. The electrodes composition and the hydrodynamic and chemical variables were optimized. Graphite–EPD (GEPD) electrodes showed a better analytical performance than graphite–Teflon (GPTFE) electrodes. Furthermore, a better sensitivity, repeatability and reproducibility was observed for RuO2–GEPD electrodes when compared with Ru–GEPD electrodes. At an applied potential of +0.50 V, a detection limit for methionine of 4.8×10–5 mol L–1, similar to those reported in the literature for other RuO2-modified electrodes, was obtained. The analytical applicability of RuO2–GEPD electrodes was demonstrated by determining methionine in a complex pharmaceutical formulation.
No Title by Ramón Batlle; Anders Colmsjö; Ulrika Nilsson (pp. 514-518).
The design and evaluation of a portable diffusive sampler for isocyanates is described. The sampler employs dibutylamine (DBA) loaded onto 60-µm polydimethylsiloxane–divinylbenzene (PDMS–DVB) solid-phase microextraction (SPME) fibers. The DBA-isocyanate derivative is then desorbed by sonication and analyzed by LC–MS using atmospheric pressure chemical ionization (APCI).The samplers are calibrated (i.e. the uptake rate is calculated) by exposing them to a known concentration of hexamethylene diisocyanate (HDI) in a standard gas-generation chamber. The uptake rate for the proposed method, at room temperature (25 °C), is 1.13 pg (min ppbv)–1 and the method detection limit is 3.2 µg m–3, equivalent to less than 10% of the airborne time-weighted average (TWA) exposure limits recommended by both the National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH). Practical points that should be considered when using the SPME device as a diffusive sampler are discussed.
No Title by Christine Achten; Axel Kolb; Wilhelm Püttmann (pp. 519-525).
A simple and rapid method for the determination of methyl tert-butyl ether (MTBE) in water by headspace-solid-phase microextraction (headspace-SPME) at sub-µg/L concentrations is described. On using a cooled SPME fiber coated with a 75-µm layer of poly(dimethylsiloxane)/carboxene and heating the sample to 35 °C, about 4 times more MTBE is extracted compared to SPME extraction with the fiber placed in the water sample. Stable analytical conditions with a detection limit of 10 ng/L are achieved. By use of a sample volume of 4 mL in a 10 mL vial, a sodium chloride content of 10% (w/w), and an extraction time of 30 min, the total time of an analytical cycle was optimized to 39 min. Precise linearity of R 2>0.9991 and R 2>0.9916 in the calibration range of 20–5000 ng/L and 20–100 ng/L, both in addition to blanks, respectively, and relative standard deviations of 10% (100 ng/L, long-term) and 11% (20 ng/L, short-term) are presented. The recovery is well within the accepted limits of 83–118% at a concentration of 100 ng/L and even close thereto at trace levels of 20 ng/L (96–125%). The data presented for a concentration of 100 ng/L are examined by statistical methods and show results for the T test at the 95% confidence level. Due to the large concentration range covered, the method is well suited for the monitoring of MTBE in the aquatic environment.
No Title by V. Pino; J. Ayala; A. Afonso; V. González (pp. 526-531).
Cloud-point methodology has been used to develop a new procedure for preconcentration of polycyclic aromatic hydrocarbons previously extracted from marine sediment with a micellar polyoxyethylene-10-lauryl ether medium by microwave- or ultrasound-assisted extraction. The optimum conditions for preconcentration and determination of PAH by HPLC with UV detection were established. The optimized procedure was applied to determination of these analytes in fortified marine sediment. The mean recoveries obtained after extraction and preconcentration by use of microwave- or ultrasound-assisted extraction were 105.8 and 99.5%, respectively. Precision, however, is considerably higher when extraction is performed ultrasonically.
No Title by J. Sastre Toraño; S. Hattum (pp. 532-535).
A new method is presented for the quantitative analysis of compounds in pharmaceutical preparations – Fourier transform (FT) mid-infrared (MIR) spectroscopy with an attenuated total reflection (ATR) module. Reduction of the quantity of overlapping absorption bands, by interaction of the compound of interest with an appropriate solvent, and the employment of an internal standard (IS), makes MIR suitable for quantitative analysis.Vigabatrin, as active compound in vigabatrin 100-mg capsules, was used as a model compound for the development of the method. Vigabatrin was extracted from the capsule content with water after addition of a sodium thiosulfate IS solution. The extract was concentrated by volume reduction and applied to the FTMIR–ATR module. Concentrations of unknown samples were calculated from the ratio of the vigabatrin band area (1321–1610 cm–1) and the IS band area (883–1215 cm–1) using a calibration standard. The ratio of the area of the vigabatrin peak to that of the IS was linear with the concentration in the range of interest (90–110 mg, in twofold; n=2). The accuracy of the method in this range was 99.7–100.5% (n=5) with a variability of 0.4–1.3% (n=5).The comparison of the presented method with an HPLC assay showed similar results; the analysis of five vigabatrin 100-mg capsules resulted in a mean concentration of 102 mg with a variation of 2% with both methods.
No Title by Elma V. Carrilho; Ana A. Nogueira; Joaquim A. Nóbrega; Gilberto B. Souza; Geraldo M. Cruz (pp. 536-540).
The residual carbon content of a variety of bovine-derived samples and forage was determined by inductively coupled plasma optical emission spectrometry with radial view configuration (ICP–OES) after microwave-assisted digestion under high pressure in a closed vessel. The original carbon concentration in the samples was determined by elemental analysis. The highest amount of original carbon content (64%) was found in viscera. After digestion, up to 75% of it was destroyed. Viscera presented the highest ether extract and blood exhibited a high crude protein content of up to 99%. The efficiency in destroying the organic matter in biological materials seemed to be related to their fat content and showed no significant difficulty for protein-rich samples. The correlation coefficient between the fat content of the samples and the residual carbon after acid decomposition was 0.9173 indicating a fair fit. However, no correlation was observed between % RC and the protein content.
No Title by Mikko Ahro; Mari Hakala; Jyrki Kauppinen; Heikki Kallio (pp. 541-549).
Four apple wine fermentation processes have been observed by means of direct-inlet gas-phase FTIR spectroscopy. The apple juice concentrates were each fermented by two species of Saccharomyces cerevisiae starters, and the experiment was repeated. The development of the concentrations of 1-propanol, 4-methylpyridine, acetaldehyde, acetic acid, and ethyl acetate was monitored. Two different sampling methods were used – static headspace and direct injection of the must. The performance of the FTIR method is limited by the high ethanol concentration. It can be mathematically proven that the amount of sample can be selected so that any distortion due to ethanol is minimized. Headspace GC–MS was used for preliminary compound identification.
No Title by K. Bester; G. Bordin; A. Rodriguez; H. Schimmel; J. Pauwels; G. VanVyncht (pp. 550-555).
A high-performance liquid chromatographic method, with electrospray ionisation tandem mass spectrometry (HPLC–ESI–MS–MS) for detection, has been developed for the determination of thiabendazole, carbendazime, and phenylurea pesticides in fruit matrices. During the validation process the method was tested for matrix effects, blanks, and the stability of the system. Considerable unspecific matrix effects in the ESI (+) process were detected by comparing standard calibration, and matrix calibration, although blank values were very low and the specific calibration functions showed only small standard deviations. This effect was overcome by using a more complex clean-up, i.e. an additional size-exclusion step.
No Title by N. Ershova; V. Ivanov (pp. 556-558).
Chromaton-N-super and Silasorb C18 (SMT C18) were compared as solid supports for the direct determination of the immobilized beryllium complexes with eriochrome cyanine R by diffuse reflection spectroscopy. The advantage of Silasorb C18 was shown. A detection limit of 0.0002 µg mL–1 could be reached in a 100-mL sample. The method was used for the analysis of real water samples.
No Title by J. Lichtig; R. Andrade (pp. 559-561).
A differential pulse polarographic method has been developed for the quantitative determination of niobium in pyrochlore ore. One-step polarographic curves were obtained in 0.01 mol L–1 EDTA as supporting electrolyte. Analytical curves indicated that response was linearly dependent on Nb(V) concentration between 1.6 and 8.6 mg L–1 in the pH range 2–5. The system is quasi-reversible and controlled by diffusion in 0.01 mol L–1 EDTA as supporting electrolyte; the electrode process involves one-electron reduction of Nb(V) to Nb(IV). The results obtained so far for niobium in pyrochlore ore were comparable with those obtained by X-ray fluorescence determination. Ions such as Fe(III), Cr(III), As(III), Cu(II), Ni(II), Co(II), Mn(II), Sn(IV), Zn(II), V(V), Ta(V), W(VI), Ce(IV), and Ti(IV) did not interfere. Possible interference from Pb(II) can be avoided by complexation with the supporting electrolyte in the pH range 3.5 to 4.6; Mo(VI) ions can be tolerated when their concentration is one-tenth that of Nb(V).
No Title by Peter Tomčík; Dušan Bustin (pp. 562-564).
An interdigitated microelectrode array (IDA) sensor has been applied to the determination of iodide in mineral water. It is based on reversible charge transfer in the redox system I2/2I– at a platinum microelectrode. The analytical signal from the IDA system was obtained by use of a bipotentiostat in dual mode. One segment of the IDA (generator) was polarized to the limiting current for oxidation of iodide to iodine in 0.1 mol L–1 HClO4. The second segment (collector) was fixed at a potential value corresponding to the limiting current of iodine reduction. The geometrical arrangement of the IDA enables this transfer with high efficiency. Because the diffusion layer of both segments overlaps the iodide produced on the collector, the iodide diffuses back to the generator where it is reoxidized. Therefore, redox cycling will enhance the voltammetric signal of the IDA. The signal obtained with a vertically separated IDA was 20 times higher than that in the single mode. Because multiplication of the signal reduces the detection and determination limits, direct voltammetric determination of iodide in mineral water is possible.
No Title by B. Gawlik; T. Linsinger; G. Kramer; A. Lamberty; H. Schimmel (pp. 565-569).
The lack of suitable certified reference materials for the determination of organic pollutants in water has become a major problem within the framework of the new European water policy. This paper highlights approaches towards the production of certified reference materials and their drawbacks.On the basis of experience gained from proficiency-testing schemes, analytical practice, and reference material production a new concept for the production of liquid reference materials to be used in support of European legislation is presented and discussed briefly. The concept is based on a standard-addition approach and the simulation of effects interfering with the analytical process by use of individual matrix constituents or matrix-mimicking substances in combination with water-miscible solvents. The concept enables quantification of dissolved organic compounds in unknown water samples and evaluation of the analytical process with the help of a reconstituted sample. Open questions for further research are also outlined.
No Title by Han Gu; Hui-Min Ma; Shu-Chuan Liang (pp. 570-573).
A novel water-soluble fluorescent probe, monosodium 7-(4,6-dichloro-1,3,5-triazinylamino)-1,3-naphthalenedisulfonic acid (DTND), was synthesized by reacting cyanuric chloride with 7-amino-1,3-naphthalenedisulfonic acid monopotassium salt at 0–5 °C. This new reagent was used for the determination of methylamine. The linear range is 3×10–6–2×10–4 mol L–1 with a detection limit (S/N=3) of 7.2×10–8 mol L–1, and the relative S.D. is 1.3% for ten replicate determinations of 1×10–5 mol L–1 CH3NH2. Common species in the aqueous environment have no or only slight influence on the determination. The method can be used to determine methylamine in real water samples.