Check out our New Publishers' Select for Free Articles

Analytical and Bioanalytical Chemistry (v.374, #6)

Mercury as a global pollutant by Milena Horvat (pp. 981-982).

Mercury methylation in macrophytes, periphyton, and water – comparative studies with stable and radio-mercury additions by J. Mauro; J. Guimarães; H. Hintelmann; C. Watras; E. Haack; S. Coelho-Souza (pp. 983-989).

Comparative tests of net mercury methylation potentials, with cultivated and macrophyte-associated periphyton and using stable (²⁰⁰HgCl₂ and CH₃ ¹⁹⁹HgCl) and labeled (²⁰³HgCl₂) mercury, have been conducted in the Everglades nutrient removal area (Florida, USA) and in a tropical coastal Brazilian lake (RJ, Brazil). More methylmercury was formed by macrophyte-associated (up to 17% of added ²⁰³Hg(II)) than cultivated (up to 1.6%) periphyton and methylmercury formation was lower in periphyton exposed to light (0.2%). High methylation was also observed for samples incubated with stable mercury isotopes (1.5–7.7% of added ²⁰⁰Hg(II)), confirming the results obtained with labeled mercury. Simultaneous addition of ²⁰⁰HgCl₂ and CH₃ ¹⁹⁹HgCl indicated that CH₃ ¹⁹⁹HgCl had no inhibitory effect on Hg methylation. The elevated methylation potentials observed in macrophytes, because of their root-associated periphyton, might contribute significantly to the high levels of methylmercury observed in Everglades biota. Comparative mercury methylation tests were also conducted in the water of a stratified temperate lake (Wisconsin, USA). Similar trends were observed for both stable and radioisotopes, with increasing mercury methylation along the depth profile. The highest levels (0.9% ²⁰³Hg(II) and 0.8% ²⁰⁰Hg(II)) were obtained below the oxic/anoxic boundary, where sulfide starts to increase, probably as a result of the intense activity of sulfate-reducing bacteria in the anoxic layer.

Keywords: Everglades Hg-203 Stable isotopes Macrophyte Periphyton Sulfate-reducing bacteria Tropical lake Temperate lake

Total uncertainty budget calculation for the determination of mercury in incineration ash (BCR 176R) by atomic fluorescence spectrometry by Kristof Tirez; Filip Beutels; Wilfried Brusten; Bart Noten; Nicole De Brucker (pp. 990-997).

The mercury mass fraction has been determined by atomic fluorescence spectrometry (AFS) in the framework of the project "Certification of a reference material (trace elements in fly ash) in replacement of BCR CRM 176". Calculation of the uncertainty budget, as described in this manuscript, emphasizes a practical and realistic approach to estimation of uncertainty components on the basis of statistical assumptions. GUM Workbench software was used, and resulted in a mercury mass fraction of 1.58±0.11 mg kg^–1 (with coverage factor k=2.2, 95% probability) related to dry mass, submitted in the certification exercise. The calculated total uncertainty budget applies to analogous samples analyzed by this procedure.

Keywords: Uncertainty budget Mercury AFS BCR CRM 176 R

Anodic stripping voltammetric determination of mercury by use of a sodium montmorillonite-modified carbon-paste electrode by Wensheng Huang; Chunhai Yang; Shenghui Zhang (pp. 998-1001).

A sodium montmorillonite (SWy-2)-modified carbon-paste electrode has been examined for determination of trace levels of mercury. Because of its strong cation-exchange and adsorptive characteristics, SWy-2 greatly improves the sensitivity of determination of Hg²⁺. Hg²⁺ is preconcentrated and reduced on the modified electrode surface at –0.40 V and then stripped from the electrode surface during the positive potential sweep. The conditions used for determination, e.g. supporting electrolyte, pH, amount of SWy-2, accumulation potential, and accumulation time, were optimized. The peak current was linearly dependent on the concentration of mercury from 1×10^–9 to 5×10^–7 mol L^–1. The detection limit (signal-to-noise ratio=3) was 1×10^–10 mol L^–1 after accumulation for 6 min. When the SWy-2-modified carbon-paste electrode was used to detect mercury in water samples the average recovery was 101.11%.

Keywords: Mercury Determination Sodium montmorillonite (SWy-2) Carbon-paste electrode Anodic stripping voltammetry

Comparison of procedures for measurements of dissolved gaseous mercury in seawater performed on a Mediterranean cruise by Katarina Gårdfeldt; Milena Horvat; Jonas Sommar; Joze Kotnik; Vesna Fajon; Ingvar Wängberg; Oliver Lindqvist (pp. 1002-1008).

A comparison of manual procedures for measurements of dissolved gaseous mercury (DGM) in seawater was accomplished. The experiments were performed on board the Italian research vessel Urania during July 2000 as a subtask in the CNR "Med-Oceanor Project 2000". Water samples for DGM were collected by Go-Flo bottles and subsequently analysed for DGM on board the ship. Determinations of DGM were made in parallel by two groups using different analytical routines. The two sets of data obtained compare favourably. Based on the fieldwork and an additional laboratory study, analytical procedures are discussed and an optimised method to determine DGM is presented. In addition, a method for automated in situ measurements of DGM positioned in the water body was tested. This method has the potential to simplify studies of DGM dynamics, that is variation in concentration as a function of water temperature and solar radiation etc.

Keywords: In situ Evasion Phase equilibria Med-Oceanor

Comparison of methods for particulate phase mercury analysis: sampling and analysis by Mary M. Lynam; Gerald J. Keeler (pp. 1009-1014).

Accurate and reliable sampling and analysis of mercury forms is an overriding aim of any atmospheric monitoring effort which seeks to understand the fate and transport of the metal in the environment. Although a fraction of the total mercury forms found in the atmosphere, particulate phase mercury, Hg_p, is believed to play a prominent role in both wet and dry deposition to the terrestrial and aquatic environments. Currently, microwave acid extraction and thermoreductive methodologies for analysis of Hg_p samples are widely used. We report on the potential for the use of a thermoreductive method for Hg_p analysis to evaluate and optimize it for use in routine monitoring networks. Pre-baked quartz filters can be placed in particulate samplers with well-characterized size cuts, such as dichotomous samplers and microoriface impactors. The thermoreductive methodology facilitates rapid analysis after sample collection. It requires no chemical extraction thereby eliminating the potential for contamination and generation of hazardous waste. Our results indicate that, on average, the thermoreductive method yields 30% lower values for fine fraction Hg_p when compared with microwave acid digestion. This may be due to matrix interferents that reduce the collection efficiency of mercury onto gold preconcentration traps. Results for total particulate mercury samples indicate that on average the thermoreductive method yields 56% lower values for the coarse fraction when compared with microwave acid digestion.Experiments were also conducted in Detroit, MI, USA to investigate whether elevated reactive gaseous mercury (Hg²⁺ _g) in an urban environment can lead to an artifact during the collection of filters for Hg_p analysis. Our results indicate a significantly higher amount of Hg_p collected onto a filter using the conventional methodology as compared to a filter collected downstream of KCl-coated annular denuders in the absence of Hg²⁺ _g. These results point to the presence of Hg²⁺ _g as an artifact during Hg_p measurement. These results indicate that a denuder must be utilized upstream of a filter for Hg_p collection to prevent significant Hg²⁺ _g artifact formation.

Keywords: Particulate mercury Acid digestion Thermoreduction Denuder Sampling artifact

Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters by Martina Logar; Milena Horvat; Hirokatsu Akagi; Boris Pihlar (pp. 1015-1021).

The purpose of the present work was to develop a simple, rapid, sensitive and accurate method for the simultaneous determination of inorganic mercury (Hg²⁺) and monomethylmercury compounds (MeHg) in natural water samples at the pg L^–1 level. The method is based on the simultaneous extraction of MeHg and Hg²⁺dithizonates into an organic solvent (toluene) after acidification of about 300 mL of a water sample, followed by back extraction into an aqueous solution of Na₂S, removal of H₂S by purging with N₂, subsequent ethylation with sodium tetraethylborate, room temperature precollection on Tenax, isothermal gas chromatographic separation (GC), pyrolysis and cold vapour atomic fluorescence spectrometric detection (CV AFS) of mercury. The limit of detection calculated on the basis of three times the standard deviation of the blank was about 0.006 ng L^–1 for MeHg and 0.06 ng L^–1 for Hg²⁺when 300 mL of water was analysed. The repeatability of the results was about 5% for MeHg and 10% for Hg²⁺. Recoveries were 90–110% for both species.

Keywords: Mercury Methylmercury Speciation Water

Correction techniques for iodine and bromine interferences in continuous flow aqueous mercury analysis by Diana Babi; Frank H. Schaedlich; Dan R. Schneeberger (pp. 1022-1027).

An investigation of iodine and bromine interference on mercury measurements was carried out in aqueous samples by using continuous flow techniques. The role of acidity in the extent of the interference was also studied. A variety of methods for interference correction were tested, mostly aimed at changing the chemistry of the method to eliminate the offending complexes. The tests evaluated various methods of pH adjustment of the sample matrix prior to reduction with tin(II) chloride and the use of KBH₄ for reduction. On-line alkaline pH adjustment prior to tin(II) chloride reduction was found to be the most effective method for interference correction. Physical changes to the apparatus to extend the reaction time between the sample and SnCl₂ were also explored.

Keywords: Mercury Iodine Bromine interference Correction Continuous flow system

Extractability of HgS (cinnabar and metacinnabar) by hydrochloric acid by Nevenka Mikac; Delphine Foucher; Sylvie Niessen; Jean-Claude Fischer (pp. 1028-1033).

In this work we investigated the behaviour of pure HgS during extraction with dilute HCl to establish its extractability in 1 and 6 M HCl at the concentration level close to those occurring in natural sediments and soils. We found that neither cinnabar nor metacinnabar were soluble in 1 M HCl, whereas both were partially extracted by 6 M HCl. Metacinnabar precipitated in the laboratory was most prone to dissolution in 6 M HCl (up to 90%), followed by crystalline (commercial) metacinnabar (up to 70%) and cinnabar (up to 15%). Solubility of HgS in 6 M HCl was found to be dependant on its concentration, and an exponential relationship between quantity of HgS added to 20 mL of 6 M HCl (the range of 0.1–10 mg was used) and the solubility in 6 M HCl was established. For higher concentrations of HgS (10 mg in 20 mL of acid), a similarly low solubility of cinnabar was obtained as found in the literature. A study of dissolution kinetics of HgS in 6 M HCl indicated that it was a fairly slow process. Unexpected oxidation of HgS in water or 1 M HCl was found for extractions performed in Teflon vials previously used for the digestion of residual undissolved HgS by aqua regia. We presumed that the Teflon material could preserve some oxidising gasses (presumably Cl₂) developed during digestion with aqua regia which can then oxidise HgS during extraction with water or 1 M HCl. Regarding the extraction of Hg from natural sediments, we concluded that 6 M HCl could not be used to extract reactive Hg and predict bioavailability of mercury in sediments containing HgS and that experiments with model compounds should not be done at a concentration level several orders of magnitude higher than in natural samples.

Keywords: Extraction Cinnabar Hydrochloric acid Mercury Sediment

Determination of the different states of mercury in seawater near the Vlora and Durres Bays by Pranvera Lazo; Alqi Cullaj (pp. 1034-1038).

Because of the toxicity and mobility of organic mercury, there is a need for determination of organic and inorganic mercury at very low concentrations in the environment, especially in seawater. A procedure for extraction and determination of low concentrations of the different states of mercury – total, inorganic, and organic – in seawater, by cold vapour atomic absorption spectroscopy (CVAAS) is described.Inorganic mercury only was directly reduced to the Hg⁰ state by tin(II) chloride under strongly acid conditions (H₂SO₄) and mercury metal (Hg⁰) was determined by cold vapour atomic absorption spectroscopy. Organic and inorganic mercury were extracted, with toluene, as the bromide derivatives and re-extracted, together, into ammonium chloride solution. Organic mercury was converted into inorganic mercury by thermal digestion at 80–90 °C in the presence of strong oxidants. These two states of mercury were determined together as total mercury. Inorganic mercury was measured directly after pre-concentration of the sample by toluene extraction. Toluene dissolved in aqueous phase after re-extraction of the sample was removed by heating for 30 min at 80–90 °C. Organic mercury was calculated as the difference between total and inorganic mercury.The sensitivity of the method is 0.0001 ng mL^–1 Hg, depending on sample volume.

Keywords: Mercury Inorganic and organic mercury Extraction method Seawater Strong oxidants CVAAS

Direct measurement of the mercury content of exhaled air: a new approach for determination of the mercury dose received by S. Pogarev; V. Ryzhov; N. Mashyanov; S. Sholupov; V. Zharskaya (pp. 1039-1044).

A new rapid technique is presented for determination of the dose of mercury inhaled; it is based on direct measurement of the concentration of mercury in exhaled air by use of a Zeeman mercury spectrometer RA-915+. It has been demonstrated experimentally that the dose received during short-term exposure to mercury vapor is determined more reliably by this method rather than by conventional techniques based on measurement of the mercury content in blood or urine.

Keywords: Mercury vapor Dose Exhaled air

On the analysis of mercuric nitrate in flue gas by GC–MS by Edwin S. Olson; Ramesh K. Sharma; John H. Pavlish (pp. 1045-1049).

Recent research has demonstrated that in a simulated flue gas stream containing NO₂ and SO₂ elemental mercury is initially captured on a carbon or manganese oxide sorbent. After approximately an hour, however, mercury breaks through relatively rapidly, and the volatile form of mercury emitted is an oxidized species. The volatile mercury species emitted from a granular MnO₂ sorbent was trapped in an impinger containing cold acetonitrile. Subsequent evaporation of 95% of the acetonitrile in a Kuderna–Danish apparatus and gas chromatography (GC) of the concentrate resulted in a single mercury-containing GC peak at 5.5 min; the retention time and mass spectrum of this compound matched exactly those of a standard mercury(II) nitrate hydrate, Hg(NO₃)₂.H₂O dissolved in acetonitrile. The volatile mercury component analyzed from injection of this standard solution was shown to be a form of methylmercury that is produced in the GC column by reaction of the highly reactive mercury nitrate with the methylsiloxane GC phase. Because the on-column derivatization reaction seems to be unique to mercury nitrate, the GC–MS (gas chromatography–mass spectroscopic) analysis provides strong evidence for identification of the trapped oxidized mercury species as mercury nitrate although, because the nitrate becomes detached from the mercury atom in the on-column reaction, the identity is not proven.

Keywords: Mercury Mercuric nitrate Flue gas Sorbent

Simple enzyme-amplified amperometric detection of a 38-base oligonucleotide at 20 pmol L^–1 concentration in a 30-µL droplet by Yongchao Zhang; Hyug-Han Kim; Nicolas Mano; Murielle Dequaire; Adam Heller (pp. 1050-1055).

A 38-base DNA sequence has been detected at 20 pmol L^–1 concentration in 15–35-µL droplets by means of an electrochemical enzyme-amplified sandwich-type assay on a mass-manufacturable screen-printed carbon electrode. Formation of the sandwich brought the horseradish peroxidase-label of the detection sequence into electrical contact with a pre-electrodeposited redox polymer, making the sandwich an electrocatalyst for the reduction of hydrogen peroxide to water at +0.2 V (Ag/AgCl).Sensitivity twenty times better than that of a related system resulted from: 1. fivefold reduction of the noise by substituting the formerly used poly(N-vinyl imidazole)-co-acrylamide comprising redox co-polymer with poly(4-vinyl pyridine)-co-acrylamide comprising redox polymer, enabling use of the electrodes at a more oxidizing potential at which noise (the rate of non-enzyme catalyzed electroreduction currents of dissolved oxygen and hydrogen peroxide) was lower; 2. doubling of the catalytic electroreduction current upon electrodeposition of a second layer of the redox polymer on the capture sequence-containing film; and 3. doubling of the current by increasing the coverage by the capture sequence.

Keywords: DNA sandwich assay Enzyme-amplified amperometry Electrochemical microcell Screen-printed electrodes

An innovative strategy for immobilization of receptor proteins on to an optical fiber by use of poly(pyrrole–biotin) by Robert S. Marks; Andres Novoa; David Thomassey; Serge Cosnier (pp. 1056-1063).

We report an innovative and useful procedure for immobilization of antibodies on to a fiber-optic silica surface. The procedure consists in the chemical oxidation of pyrrole–biotin monomers that are readily deposited as a thin film of poly(pyrrole–biotin) polymer on to the end-face of the fiber. The film was shown to be sufficiently translucent to enable photon coupling within the fiber transducer and its presence was demonstrated by means of fluorescent micrographs of bound rhodamine-labeled avidin. Fiber-optics modified with cholera toxin B subunit molecules were tested for sensitivity, non-specificity, and overall practicality. It was shown that the fiber-optic immuno-assay for the detection of anti-cholera toxin antibody was up to three orders of magnitude more sensitive than the classical enzyme-linked immunosorbent assay (ELISA).

Keywords: Protein immobilization Fiber optic immunosensors Biotinylated polypyrrole Anti-cholera toxin antibody Chemiluminescence Diagnostics.

Controlled kinetics of non-enzymatic chemiluminescence reactions for simple imaging of DNA and protein by Choiwan Lau; Jianzhong Lu; Takashi Yamaguchi; Masaaki Kai (pp. 1064-1068).

A robust and sensitive non-enzymatic chemiluminescence (CL) imaging method is presented. In the method a fast-emitting CL reaction is tuned to furnish a slower-emitting reaction suitable for simple CL imaging. Typically, non-enzymatic CL reactions between luminol or fluorescein and oxygen species generated by KCN as catalyst, were rather fast and unsuitable for CL imaging; the speed of the reactions could, however, be reduced substantially by changing KCN for CH₃CN or benzonitrile. Light emission from the tuned CL reaction was intense and long-lived, and even with a simple arrangement high sensitivity could be achieved. The maximum CL peak was reached after approximately 1.5 min in the presence of 25% acetonitrile, and as little as 16 fmol commercial isoluminol-labeled streptavidin was detected and visualized on either microplate or membrane. The approach was further illustrated by imaging of DNA on a membrane and of antibody on a microplate by use of biotin–streptavidin chemistry. Overall, this simple, economical, and sensitive CL imaging system is expected to be very useful in biochemical analysis, and greatly complements currently used enzyme-based CL imaging methods, especially in routine applications.

Keywords: Chemiluminescence Kinetics Catalyst Imaging DNA Protein

High-throughput assay of (R)-phenylacetylcarbinol synthesized by pyruvate decarboxylase by Michael Breuer; Martina Pohl; Bernhard Hauer; Bettina Lingen (pp. 1069-1073).

A novel assay has been developed for the detection of (R)-phenylacetylcarbinol, (R)-PAC, a chiral intermediate in the industrial synthesis of ephedrine. It is the product of a biotransformation of benzaldehyde catalysed by the enzyme pyruvate decarboxylase. The assay, using 2,3,5-triphenyltetrazolium chloride, enables high-throughput photometric analysis of the activity of the enzyme thus avoiding time-consuming chromatographic procedures.

Keywords: High-throughput assay (R)-Phenylacetylcarbinol Pyruvate decarboxylase Tetrazolium red

Square-wave voltammetric techniques for determination of psychoactive 1,4-benzodiazepine drugs by Correia M. dos Santos; Vila Famila; Simões M. Gonçalves (pp. 1074-1081).

Direct square-wave voltammetry (SWV) and square-wave cathodic stripping voltammetry (SWCSV) at hanging mercury drop electrodes have been developed for determination of the psychoactive 1,4-benzodiazepine compounds clonazepam, bromazepam, midazolam, diazepam, medazepam, and flurazepam over a wide range of concentrations. Analysis was performed with better precision, lower detection limits, and much more rapidly than by previously reported voltammetric techniques.The applicability of both procedures is discussed. The methods were applied to the analysis of commercially available tablets with minimum sample manipulation. The accuracy of the results was accessed by comparison with those obtained by use of the methods described in official pharmacopoeias. A critical comparison with those procedures is also presented.

Keywords: 1,4-Benzodiazepines Bromazepam Clonazepam Diazepam Flurazepam Midazolam Medazepam Square-wave voltammetry

Separation and determination of vanadium in fertiliser by capillary electrophoresis with a light-emitting diode detector by Narumol Vachirapatama; Miroslav Macka; Paul R. Haddad (pp. 1082-1085).

A method has been developed for determination of vanadium, as an anionic ternary complex of vanadium(V) with 4-(2-pyridylazo) resorcinol (PAR) and hydrogen peroxide, after separation by capillary electrophoresis (CE). The optimum conditions for the formation of the ternary complex were acetate buffer (3 mmol L^–1) at pH 6 containing 0.15 mmol L^–1 PAR and 7.1 mmol L^–1 H₂O₂. The CE separation was conducted using 15 mmol L^–1 acetate buffer at pH 6 as the background electrolyte; the separation potential was –30 kV and the injection time100 s. The vanadium complex was detected photometrically at 568 nm, by use of a light-emitting diode (LED); the detection limit was 19 ppb. The method was applied to the analysis of vanadium in fertilisers. Clean-up of the digested fertiliser sample, with Sep-Pak C₁₈ coated with tetrabutylammonium hydroxide, before analysis was used to remove matrix ions which otherwise caused electrophoretic de-stacking. Vanadium levels found in the fertiliser samples by use of the CE method were found to be comparable with results obtained by HPLC and ICP–MS.

Keywords: Capillary electrophoresis Fertiliser Vanadium Ternary complexes

Determination of moniliformin in maize by ion chromatography by W. Kandler; M. Nadubinská; A. Parich; R. Krska (pp. 1086-1090).

An ion chromatographic method for the determination of the mycotoxin moniliformin in maize was developed. The method contains a fast and simple clean-up procedure, which allows high volume sample injection. No further pre-concentration step is required. The limit of quantification was estimated to be 0.12 mg/kg moniliformin in maize. In contrast to the two previously published ion chromatographic methods, the moniliformin peak is base line separated and occurs in a region of a smooth base line in the ion chromatogram. The newly developed method showed a recovery through the whole analytical procedure of 97±3.5 %, whereas most previously described analytical methods had recoveries in the 70% range.

Keywords: Determination Ion chromatography Maize Moniliformin Mycotoxin

Determination of ²³⁶U and transuranium elements in depleted uranium ammunition by α-spectrometry and ICP–MS by D. Desideri; M. Meli; C. Roselli; C. Testa; S. Boulyga; J. Becker (pp. 1091-1095).

It is well known that ammunition containing depleted uranium (DU) was used by NATO during the Balkan conflict. To evaluate the origin of DU (the enrichment of natural uranium or the reprocessing of spent nuclear fuel) it is necessary to directly detect the presence of activation products (²³⁶U, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Am, and ²³⁷Np) in the ammunition. In this work the analysis of actinides by α-spectrometry was compared with that by inductively coupled plasma mass spectrometry (ICP–MS) after selective separation of ultratraces of transuranium elements from the uranium matrix. ²⁴²Pu and ²⁴³Am were added to calculate the chemical yield. Plutonium was separated from uranium by extraction chromatography, using tri-n-octylamine (TNOA), with a decontamination factor higher than 10⁶; after elution plutonium was determined by ICP–MS (²³⁹Pu and ²⁴⁰Pu) and α-spectrometry (^239+240Pu) after electroplating. The concentration of Pu in two DU penetrator samples was 7×10^–12 g g^–1 and 2×10^–11 g g^–1. The ²⁴⁰Pu/²³⁹Pu isotope ratio in one penetrator sample (0.12±0.04) was significantly lower than the ²⁴⁰Pu/²³⁹Pu ratios found in two soil samples from Kosovo (0.35±0.10 and 0.27±0.07). ²⁴¹Am was separated by extraction chromatography, using di(2-ethylhexyl)phosphoric acid (HDEHP), with a decontamination factor as high as 10⁷. The concentration of ²⁴¹Am in the penetrator samples was 2.7×10^–14 g g^–1 and <9.4×10^–15 g g^–1. In addition ²³⁷Np was detected at ultratrace levels. In general, ICP–MS and α-spectrometry results were in good agreement.The presence of anthropogenic radionuclides (²³⁶U, ²³⁹Pu,²⁴⁰Pu, ²⁴¹Am, and ²³⁷Np) in the penetrators indicates that at least part of the uranium originated from the reprocessing of nuclear fuel. Because the concentrations of radionuclides are very low, their radiotoxicological effect is negligible.

Keywords: Alpha spectrometry Depleted uranium Inductively coupled plasma mass spectrometry Transuranium elements Uranium-236

Sequential separation of actinides by ion chromatography coupled with on-line scintillation detection by Scott H. Reboul; Emad H. Borai; Robert A. Fjeld (pp. 1096-1100).

The separation and measurement of actinides by ion chromatography (IC) coupled with on-line scintillation detection was investigated. Separation of ²³⁷Np, ²³⁹Pu, ²⁴¹Am, ²⁴⁴Cm, ²³⁰Th, and ²³³U was accomplished using a Dionex CG5 guard column, CS5 separation column, and an elution program utilizing oxalic, diglycolic, and nitric acid eluents. Np(V) was eluted as a weak anionic oxalate complex or as free NpO₂ ⁺ cation, Am(III) and Cm(III) as anionic oxalate complexes, Pu(IV) and Th(IV) as nonionic diglycolate complexes, and U(VI) as a free uranyl cation. Response of the flow-cell detector was linear over the full range of activities tested (4–1500 Bq). The minimum detectable activities for the investigated analytes ranged from 3.6 Bq for ²⁴⁴Cm to 5.4 Bq for ²³⁰Th and ²³⁹Pu. The corresponding minimum detectable concentrations based on a 1-L sample ranged from 3.6 to 5.4 KBq m^–3 (96 to 150 pCi L^–1).

Keywords: Actinide separation Ion chromatography Flow cell scintillation detector

Empirical method for prediction of the coordination environment of Eu(III) by time-resolved laser-induced fluorescence spectroscopy by T. Ozaki; M. Arisaka; T. Kimura; A. Francis; Z. Yoshida (pp. 1101-1104).

The number of water molecules in the inner-sphere (N_H2O) was determined for Eu(III) and the strength of ligand field (R_E/M) was evaluated for a variety of coordination environments from the luminescence lifetime and the relative intensity at 615 nm and at 592 nm, by time-resolved laser-induced fluorescence spectroscopy. When R_E/M and ΔN_H2O for Eu(III) with a known coordination environment were plotted clear regularity was apparent between the location of the R_E/M–ΔN_H2O plot and the coordination environment of Eu(III). Here, ΔN_H2O was calculated by use of the equation, ΔN_H2O=9–N_H2O. Unknown coordination environments of Eu(III) can, in turn, be characterized, including both the inner- and the outer-sphere, simply by plotting R_E/M and ΔN_H2O for Eu(III) on the diagram. This empirical method is effective for prediction of the coordination environment of hydrated and complexed Eu(III) in solutions and that of the adsorbed Eu(III) on ion-exchange resins and by microorganisms.

Keywords: Coordination environment Diagram Empirical prediction Europium(III) Luminescence TRLFS

Fluorescence spectrometry for quantitative characterization of cobalt(II) complexation by Leonardite humic acid by Fanny Monteil-Rivera; Jacques Dumonceau (pp. 1105-1112).

Quenching of the fluorescence of a Leonardite humic acid by Co(II) has been studied at different pH. The interaction was monitored by emission fluorescence and by synchronous fluorescence with two different offsets (Δλ=20 and 80 nm). It was found that synchronous fluorescence performed with the smaller offset resolves the individual components of the heterogeneous material better than emission or synchronous fluorescence performed with the larger offset. Enhancement of the signal induced by Cobalt(II) complexation resulted in more complex behavior for measurements performed by synchronous fluorescence with an offset of 20 nm, however. The quenching profiles obtained for pH 5.0, 6.0, and 7.0 ([KNO₃]=0.1 mol L^–1; [LHA]=3.3 mg_C L^–1; [Co(II)]=1.0×10^–6–1.6×10 ^–3 mol L^–1) by emission and synchronous (Δλ=80 nm) fluorescence were analyzed by two methods: 1. a non-linear least-squares procedure that leads to conditional constants; and 2. a pH-dependent discrete logK spectrum model that leads to stability constants. The first method resulted in poor fitting and unreasonable values for maximum capacities. The second procedure resulted in smooth fitting that accounted well for the pH changes when results for pH 6.0 and 5.0 were predicted by use of the four values of logK_Co(i) (4.31, 3.76, 7.32, and 7.67 corresponding to the four sites (i) of the respective pKa(i) values 4, 6, 8, and 10) calculated at pH 7.0 for the equilibrium $$ left( { m i} ight){ m :L}_{ m i}^{ m - } { m + Co}^{{ m 2 + }} mathbin{lower.3exhbox{$uildrel extstyle ightarrowover {smash{leftarrow}vphantom{_{vbox to.5ex{vss}}}}$}} { m CoL}_{ m i}^{ m + } { m .} $$

Keywords: Fluorescence quenching Co(II) Humic acid Complexation Stability constants

Analytical potential of the reaction between p-phenylenediamines and peroxodisulfate for kinetic spectrophotometric determination of traces of ascorbic acid by Alexandra Rustoiu-Csavdari; Ulrich Nickel (pp. 1113-1120).

The analytical potential of the redox reactions between N,N-dimethyl- or N,N,N′,N′-tetramethyl-p-phenylenediamine (DMPPD or TMPPD, respectively) and peroxodisulfate in acidic media for kinetic spectrophotometric determination of trace amounts of ascorbic acid (AA) has been investigated. The goal was to explore reaction conditions ensuring an excess or a deficit of S₂O₈ ^2–, and to identify some kinetic features of the global process for the purpose of calibration. Because the induction period of the overall reaction increases significantly in the presence of micromolar amounts of AA, the most suitable calibration graphs are generated by plots of induction period against the analyte concentration. The best sensitivity was achieved for oxidation of DMPPD with a deficit of S₂O₈ ^2–. The calibration line obtained has an RSD of 2.6% for 4×10^–6 mol L^–1 AA (n=3) and the detection limit is 4×10^–8 mol L^–1 (7 µg L^–1), a value comparable with the best mentioned by the literature. No systematic study of interferents was performed. Instead, the effect of buffer reagents (phosphate, phthalate, citrate) and dissolved oxygen on the results is discussed. Experiments were performed under closely controlled conditions. This is the first report of ascorbic acid analysis in which "contamination" by environmental oxygen was prevented by rinsing all vessels and saturating all solutions with argon, an approach which enables determination of the actual ascorbic acid content. Because of the effort involved, however, the method might not be suitable for routine analysis. Analysis of a commercially available vitamin C pellet gave good results when a "special" calibration graph, obtained in the presence of all other constituents of the sample except AA, was employed. The AA was "removed" from the pellet by oxidation with environmental air. Although it seems rather elaborate, this procedure did not require prior preparation of the sample nor extraction and/or concentration of ascorbic acid from it.

Keywords: Spectrophotometry Kinetic methods Fixed-concentration technique Ascorbic acid p-Phenylenediamine Peroxodisulfate

Spectrophotometric determination of selenium by use of thionin by H. Revanasiddappa; T. Kiran Kumar (pp. 1121-1124).

A simple, rapid, and sensitive spectrophotometric method has been developed for the determination of selenium in real samples of water, soil, plant materials, human hair, and synthetic cosmetic and in pharmaceutical preparations. The method is based on the reaction of selenium with potassium iodide in an acidic medium to liberate iodine. The liberated iodine bleaches the violet color of thionin, and which is measured at 600 nm. This decrease in absorbance is directly proportional to selenium concentration and obeys Beer's law in the range 1–5 µg selenium in a final volume of 10 mL (0.1–0.5 µg mL^–1). The molar absorptivity and Sandell's sensitivity of the method were found to be 7.33×10⁴ L mol^–1 cm^–1 and 0.0011 µg cm^–2, respectively. The optimum reaction conditions and other analytical conditions were evaluated. The effect of interfering ions on the determination is described.

Keywords: Thionin Selenium determination Spectrophotometry

Determination of trace molybdenum in vegetable and food samples by spectrophotometry with p-carboxyphenylfluorone by Li Zaijun; Pan Jiaomai; Tang Jian (pp. 1125-1131).

A new highly sensitive and selective chromogenic reagent, p-carboxyphenylfluorone (p-CPF), was studied for spectrophotometric determination of trace molybdenum. In 0.36 mol L^–1phosphoric acid medium, p-CPF reacts with molybdenum(VI) to form a 1:3 red complex, which has a sensitive absorption peak at 531 nm. Under optimal conditions, the reaction of molybdenum(VI) with p-CPF completed rapidly and absorbance remains almost constant for at least 24 h. Molybdenum(VI) obeyed Beer's law in the range 0–2.0 µg mL^–1; the apparent molar absorption coefficient, Sandell's sensitivity and the limit of detection were found to be 1.03×10⁵ L mol^–1 cm^–1, 1.028 ng cm^–2and 0.73 ng mL^–1 respectively; the effect of various foreign ions were examined in detail. It was found that most coexisting ions can be tolerated in considerable amounts, especially 800 mg of Mn(II), 200 mg of Mg(II), Fe(II), Co(III), Ni(II) and Cd(II), 50 mg of Ca(II) and Al(III), 25 mg of Cu(II) and Fe(III), 10 mg of Hg (II), La(III), Bi(III), Pb(II) and Zn(II) don't interfere with the determination of molybdenum(VI). The proposed method is very simple, sensitive and selective, it has been applied to determine molybdenum in vegetable and food samples with a very high precision and accuracy. Moreover, the synthesis of the reagent and the conditions of the colour reaction were also studied in detail.

Keywords: Spectrophotometry Molybdenum Vegetable and food p-Carboxyphenylfluorone

Ultrasound-assisted method for determination of chemical oxygen demand by Antonio Canals; M. del Remedio Hernández (pp. 1132-1140).

A method for determination chemical oxygen demand (COD) assisted by use of ultrasound has been successfully evaluated for the first time. The method uses instrumentation simpler and cheaper and, in some instances, safer than that used by previous methods for the same purpose. The new device used for sonication is an all-glass cylindrical sonotrode that can be introduced directly into the reaction mixture. Use of this device enables more efficient interaction between sample and ultrasonic energy. The optimized experimental conditions are high ultrasonic power (55% amplitude, 0.9-second pulses each second), high sulfuric acid concentration (>60%), and a sonication time of 2 min. Under these conditions the method has limitations similar to those of the official COD method with regard to the type of organic compound. It works adequately with easily oxidized organic matter (potassium hydrogen phthalate and dextrose) and other organic compounds difficult to oxidize by conventional methods (e.g. phenol and acetic acid) but the COD values obtained with volatile compounds and difficult organic matter are poor. Chloride is tolerated up to a concentration of 7000 mg L^–1 without any masking agent. Gasification of the sample is recommended to improve results; use of air and argon resulted in no significant differences – bubbling with air during sonication resulted in COD values for certified materials and real wastewater samples statistically identical with the certified COD values and those obtained by the classic (open reflux) method. The use of ultrasound energy for COD determination thus seems to be an interesting and promising alternative to conventional oxidation methods used for the same purpose.

Keywords: Chemical oxygen demand Ultrasound energy

Flow injection determination of gaseous sulfur dioxide with gas permeation denuder-based online sampling and preconcentration by Zhong-Xian Guo; Yuan-Zong Li; Xin-Xiang Zhang; Wen-Bao Chang; Yun-Xiang Ci (pp. 1141-1146).

A simple and novel flow injection method for the determination of gaseous SO₂ is described based on gas permeation denuder (GPD) online sampling and preconcentration. The GPD is easily prepared with poly(vinylidene) difluoride microporous membrane as gas permeable material and two Perspex blocks with smooth and flat interface and rectangular engraved channels of mirror image. The sample gas is on one side of the membrane and phosphate buffer of pH 7.0 as the absorbing solution is on the other side. Gaseous SO₂ permeates partially through the gas permeable membrane and dissolves in the absorbing solution. After preconcentration for 5.0 or 8.0 min, the solution is injected into the flow of 5.0×10^–4 mol L^–1 5,5'-dithiobis(2,2'-dinitrobenzoic acid) (DTNB) in 0.025 mol L^–1 phosphate buffer. The resulting product formed between DTNB and absorbed SO₂ is spectrophotometrically monitored at 410 nm with a charge coupled device (CCD) fiber optic spectrometer. The calibration graphs for preconcentration of 5.0 and 8.0 min are linear up to 4.0 and 3.2 mg m^–3 with detection limits of 50 and 35 µg m^–3, respectively. The corresponding analysis speeds are 8.5 and 6 samples h^–1. The method is selective and just suffer from interference of hydrogen sulfide at higher than 1% of SO₂ level (in m/V) with an error >+10%. The assay just uses cheap and common membrane and reagents and shows potential application in the monitoring of atmospheric SO₂.

Keywords: Sulfur dioxide Flow injection analysis Gas permeation denuder Fiber optic spectrometer Ellman reagent

The International Measurement Evaluation Programme, IMEP-8: carbon and oxygen isotope ratios in CO₂ by J. Nørgaard; S. Valkiers; L. Van Nevel; E. Vendelbo; I. Papadakis; O. Bréas; P. Taylor (pp. 1147-1154).

In IMEP-8, two samples of high purity CO₂(g), with different carbon and oxygen isotope ratios were distributed to 27 participants, originating from 14 countries and from various isotopic measurement domains (geochemistry, atmospheric and food chemistry), but particularly set up for food laboratories. In total 19 laboratories reported results. The outcome of this comparison exercise shows that the laboratories reported carbon and oxygen isotope results in good agreement with the reference values across the domains. The reported results for δ ¹³C_VPDB (carbon) for both materials are within 1‰. However, for the reported results of δ ¹⁸O_VPDB (oxygen) for both materials the overall spread of the reported results is about 11 ‰. Within this spread two distinct groups of participants can be identified, where the results within each group vary about 2‰. The latter seems to be caused by calculation errors by participants of the reporting δ ¹⁸O_VPDB values. As requested, participants also reported the isotope amount ratio for carbon and oxygen in the CO₂ samples. For carbon, all reported results for both materials agree with the isotope ratio value, which can be traced back to the value reported by Craig. For oxygen, all results are in good agreement and deviate by a maximum of 0.5% from the reference values measured at IRMM. Work carried out indicates the carbon isotope ratio, for both samples IMEP-8A and IMEP-8B, differ from those reported by Craig by as much as 1.2%. In the case of oxygen, this deviation is far smaller. Both data sets, i.e. the one realised by Craig and the one realised at IRMM, demonstrate traceability to SI. It is clear that both values significantly disagree.

Keywords: Carbon and oxygen isotope ratios Intercomparison CO2 Traceability

Carbon paste electrodes modified with Bi₂O₃ as sensors for the determination of Cd and Pb by Rasa Pauliukaite; Radovan Metelka; Ivan Švancara; Agnieszka Królicka; Andrzej Bobrowski; Karel Vytřas; Eugenijus Norkus; Kurt Kalcher (pp. 1155-1158).

Carbon paste electrodes bulk-modified with Bi₂O₃were used for the determination of Cd(II) and Pb(II). The best composition was 1% (wt%) Bi₂O₃ in the paste. The measurements were made by differential pulse voltammetry in the potential range from –1.2 V to –0.3 V. The peak potential of the reoxidation of Cd is –0.85 V, and of Pb –0.60 V vs. SCE. The lowest concentration that could be determined was 5 µg L^–1 of both metals (preconcentration time 240 s), the relative standard deviation was 3.5%–5.0% (four determinations). The correlation coefficient (r ²) of the calibration curves was 0.9966 (for Cd) and 0.9971 (for Pb). The Bi₂O₃-modified electrode could be used for the analysis of drinking water, mineral water and urine.

Keywords: Modified carbon paste electrode Bi2O3 Stripping voltammetry Cadmium Lead

Chemiluminescent investigation of tris(2,2'-bipyridyl)ruthenium(II) immobilized on a cationic ion-exchange resin and its application to analysis by Jin-Ming Lin; Feng Qu; Masaaki Yamada (pp. 1159-1164).

Tris-(2, 2'-bipyridyl)ruthenium(II) complex, Ru(bpy)₃ ²⁺, was immobilized on the Dowex-50 W cationic ion-exchange resin. The chemiluminescent characteristics of Ru(bpy)₃ ²⁺ in solution and in resin form were compared by using batch and flow injection methods. A strong chemiluminescence was observed during the reaction of Ru(bpy)₃ ²⁺ both in solution and in resin with KMnO₄ or Ce(SO₄)₂ under acidic or basic conditions. The Ru(bpy)₃ ²⁺ immobilized resin is stable, which can be used at least for 6 months when it reacts with the dilute KMnO₄ solution. Based on this property, Ru(bpy)₃ ²⁺ immobilized in the resin phase was developed as a flow-through chemiluminescent sensor that could be used to determine oxalate, sulfite and ethanol chemically or electronically with Ru(bpy)₃ ³⁺ generation on the surface of resin. The limits of detection were 1×10^–6 M for oxalate, 0.5% (v/v) for ethanol and 1×10^–7 M for sulfite. The method has been successfully applied to determine sulfite in sugar.

Keywords: Chemiluminescence Tris(2, 2'-bipyridyl)ruthenium(II) Cationic ion-exchange resin

Optimum conditions for effective use of the terminating ion in transient isotachophoresis for capillary zone electrophoretic determination of nitrite and nitrate in seawater, with artificial seawater as background electrolyte by Nobuhiro Ishio; Keiichi Fukushi; Kanako Michiba; Sahori Takeda; Shin-ichi Wakida (pp. 1165-1169).

We have examined transient isotachophoresis (ITP) conditions, e.g. the nature of the terminating ion, its concentration, and the injection procedure, to improve the limit of detection (LOD) for determination of nitrite and nitrate in seawater by capillary zone electrophoresis (CZE). Artificial seawater containing 3.0 mmol L^–1 cetyltrimethylammonium chloride (CTAC) was used as background electrolyte (BGE). After sample injection 600 mmol L^–1 acetate was separately injected into the capillary as the terminating ion for transient ITP. The LOD for nitrite and nitrate, obtained at a signal-to-noise ratio (S/N) of 3, were 15 and 7.0 µg L^–1 (as nitrogen), respectively. Relative standard deviations (RSD) of peak area for nitrite and nitrate were 7.3 and 0.8%, respectively, and the RSD of peak height were 5.7 and 1.2%, respectively, when the concentrations of nitrite and nitrate were 0.05 and 0.25 mg L^–1. The RSD of migration time for these ions was 0.2%. The proposed method was applied to the determination of nitrite and nitrate in seawater samples. The results for nitrite were nearly in agreement with those obtained by naphthylethylenediamine spectrophotometric analysis (SPA; correlation coefficient 0.9041).

Keywords: Seawater analysis Nitrate Nitrite Transient isotachophoresis Terminating ion Capillary zone electrophoresis

Sections

Personal tools

Analytical and Bioanalytical Chemistry (v.374, #6)

Sections

Personal tools

Local resources

Analytical and Bioanalytical Chemistry (v.374, #6)