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Analytical and Bioanalytical Chemistry (v.359, #7-8)
Basic equations and uncertainties in isotope-dilution mass spectrometry for traceability to SI of values obtained by this primary method by P. De Bièvre; H. S. Peiser (pp. 523-525).
A current interest in chemistry concerns traceability of analytical measurements to the International System of Units (SI) and the estimation of their uncertainties in accordance with principles of metrology, that is, measurement science. “Primary methods of measurement” achieve traceability to SI directly without intermediate reference standards or materials and without significant empirical correction factors. Isotope-dilution mass spectrometry should be regarded as such a method. It has the potential of smallest presently achievable uncertainties for analytical measurements directly or for the certification of reference materials including those with abnormal isotopic composition. A simple explanation of the method including its basic equations is given. Full uncertainty estimation is emphasized in terms of these equations. The wider use of concepts of metrology in chemistry is discussed.
Investigation of mercury-free potentiometric stripping analysis and the influence of mercury in the analysis of trace elements lead and zinc by J. E. T. Andersen; Laust Andersen (pp. 526-532).
The application of Potentiometric Stripping Analysis (PSA), without any mercury, to the determination of trace elements lead and zinc, results in linear responses between stripping-peak areas and concentrations within 0 to 2000 ng/g. The best response, as determined by the size of stripping areas, was obtained with an electrode prepared with mercury but without mercury ions in the electrolyte. Lead is analysed by a freshly polished glassy-carbon electrode in 0.09–0.1 mol/L HCl while the analysis of zinc requires an electrode activation procedure. The electrode activation is performed by stripping zinc in an electrolyte containing 0.1 mol/L HCl and 2 μg/g Zn2+ and electrolysis at −1400 mV (SCE). The concentration range of linear response occurs where the electrode is not fully covered by metal clusters during the electrolysis step. The influence of mercury is investigated and a model is proposed which explains the co-deposition of mercury and test metals in the electrolysis step in terms of a charge-distribution parameter. The model explains that the decrease of stripping peak area, as a function of concentration, is entirely due to mercury ions being simultaneously reduced together with the ions of the test metal in the electrolysis step. The influence of hydrogen evolution and oxygen reduction together with possible improvements of the method are discussed.
Determination of cadmium in indium phosphide by electrothermal atomic absorption spectrometry and ion-selective electrode potentiometry by M. Taddia; Dario Ranno; Roberto Fornari (pp. 533-537).
Two independent methods for the determination of cadmium in cadmium-doped indium phosphide have been developed. Electrothermal atomic absorption spectrometry (ETAAS) utilized both platform atomization and a chemical modifier composed of magnesium nitrate and orthophosphoric acid. As the matrix mass was found to influence the cadmium sensitivity, matrix matched calibration standards were necessary. The detection limit (3sB) is 0.20 μg/g for a 100 mg sample. The electrochemical method employed a solid-state cadmium sulfide-silver sulfide electrode as potentiometric sensor. An excess of indium (III) influenced the electrode response. A preliminary chelation-extraction of indium with acetylacetone at pH 5.0 in acetate buffer overcame the interference. The detection limit of the ISE-potentiometric method is 10 μg/g for a 200 mg sample. Two indium phosphide single crystals grown from melts doped with cadmium sulfide or cadmium telluride were analyzed for their cadmium content.
Ligand-exchange chromatographic separation of polycyclic aromatic hydrocarbons and polycyclic aromatic sulfur heterocycles on a chelating silica gel loaded with palladium (II) or silver (I) cations by U. Pyell; S. Schober; G. Stork (pp. 538-541).
2-Amino-1-cyclopentene-1-dithiocarboxylic acid silica gel (ACDA-SG) loaded with Ag(I) or Pd(II) ions has been examined for the group fractionation of polycyclic aromatic sulfur heterocycles (PASH) from polycyclic aromatic hydrocarbons (PAH) via ligand-exchange chromatography in the normal phase mode. It is shown that metal loading has a great impact on the selectivity of ACDA-SG for PASH and PAH. Pd(II) loaded ACDA-SG proved to be suitable for the group isolation of PASH from the aromatic fractions of petroleum mixtures (number of condensed rings?3).
Development of an amperometric detector for the determination of phenolic compounds by Hong-yuan Chen; Ai-min Yu; Dan-ke Xu (pp. 542-545).
Polyhistidine chemically modified electrode is shown to greatly improve the voltammetric waves and increase the current response of phenolic compounds (such as dopamine (DA), epinephrine (E) and catechol (CC)) for their cation-selective quality. When used as amperometric detector, the detection limits are 6×10-9 mol/L for DA, 8×10-9 mol/L for E and 2×10-8 mol/L for CC. The modified electrode has also been used as electrochemical detector for capillary electrophoresis (CE) and the phenolic compounds were successfully separated and detected with high resolution. The electrode has a good stability; 80% of the original response was obtained after being used in CE for one month.
Occurrence and distribution of polycyclic aromatic hydrocarbons (PAHs) in an agricultural ecosystem by D. Martens; J. Maguhn; P. Spitzauer; A. Kettrup (pp. 546-554).
The concentration and distribution of PAHs were determined in soil, surface water, sediments, and groundwater of the experimental farm of the research network “Forschungsverbund Agrarökosysteme München” (FAM), part of a rural region in Bavaria, Germany. Analytical procedures include ultrasonication, solid phase extraction, liquid-liquid extraction, HPLC and fluorescence detection. Fifteen common PAHs were usually found in low concentrations in the examined compartments. The distribution of total PAHs in surface soils of 15 sampling sites in the area was not uniform. It could be demonstrated that there were high concentrations in valleys and low concentrations on top of the hills, due to long-term transport of PAHs to the valleys by surface run-off. Subsurface soil was found to contain lower amounts. Tetra- to hexacyclic PAHs showed similar profiles in the subsurface soil and in the top soil, while profiles of bi- and tricyclic PAHs deviated significantly. Additionally, tetra- to hexacyclic PAHs were enriched in distinct zones in the subsurface soil and exhibited similar patterns in groundwater and aquifer material. These results indicate a transport of bi- and tricyclic PAHs mainly in the dissolved or gaseous state and a predominant particle-associated transport of tetra- to hexacyclic PAHs. This particle-bound transport increases the migration velocity of hydrophobic pollutants through the vadose zone and enhances the mobility in groundwater.
Extraction of humic acids from a natural matrix by alkaline pyrophosphate. Evaluation of the molecular weight of fractions obtained by ultrafiltration by D. Tonelli; Renato Seeber; Claudio Ciavatta; Carlo Gessa (pp. 555-560).
Fractions of humic acids, resolved by ultrafiltration of extracts from a sample of peat treated with alkaline pyrophosphate solution, have been submitted to high-performance size-exclusion chromatography, with the aim of determining the molecular weight distributions. Anomalous peaks, located at retention volumes higher than those corresponding to the main signal, are present in the elution profiles relative to the lightest fractions. These peaks are more intense when using a refractive index detector rather than a UV detector. Elemental analysis data for the lightest fractions suggested that the spurious peaks are due to the presence of inorganic material. The hypothesis that pyrophosphate interacts with humic acids in the course of the extraction has been confirmed by colorimetric determination of the phosphorus content in the different fractions. As a consequence, the extraction procedure has been modified by using 0.1 mol/L NaOH as extractant.The average molecular weights of the various fractions, following NaOH extraction, result in substantial agreement with those obtained following pyrophosphate solution extraction (if the ‘pyrophosphate peaks’ present in the chromatographic profile are discarded in the calculations).
Capillary gas chromatography of polychlorinated benzonitriles (PCBN) by Bernhard Mittermaier; Karlheinz Ballschmiter (pp. 561-564).
Polychlorinated benzonitriles (PCBN) are products of combustion chemistry and can be emitted from municipal waste incinerators. Their possible relevance to environmental chemistry has not previously been described, with the exception of the herbicide 2,6-dichlorobenzonitrile. The isomer-specific separation and detection of the 19 PCBN congeners is performed by HRGC-ECD and HRGC-MSD. Commercially unavailable congeners were synthesized from chlorinated anilines and benzaldehydes. Retention data on three different stationary phases are given. Structure-retention relationships are discussed. A structure-specific systematic numbering of the 19 PCBN congeners is suggested.