Untersuchungen zur HPLC-Bestimmung von Pesticiden mit amperometrisch detektierbaren Hydroxylgruppen

Summary For the sensitive determination of pesticides in soil and water samples, the possibility of using h.p.l.c. with amperometric detection was investigated. The polarographic and voltammetric behaviour of some selected compounds (bromofenoxim, bromoxynil, dimethirimol, dinoseb, dinoterb, DNOC, ethirimol, ioxynil, maleic hydrazide, pentachlorophenol) was tested.After separation by h.p.l.c. the detection of all these pesticides may be done in the voltammetric cell by the anodic signal of their hydroxyl group. The sensitivity of the determination lies in all cases in the pg-range.The simultaneous determination of the metabolites in presence of the pesticide is shown with the example of bromofenoxim and its photolytic decomposition products.

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Herrn Prof. Dr. Rolf Neeb zum 60. Geburtstag gewidmet     

Determination of zinc, cadmium, lead and copper in soils and sewage sludges by microprocessor-controlled voltammetry in comparison with atomic absorption spectrometry

Summary Information on the heavy metal contents in soils and sewage sludges is of strong ecological interest. For control of the maximum allowed concentrations photometric and atomic absorption spectrometric methods have been developed for the determination of the single elements; sample digestion is carried out using hydrochloric acid and nitric acid.Differential pulse polarography and differential pulse anodic stripping voltammetry allow the simultaneous determination of different heavy metals in one digestion solution according to their electrochemical behaviour. This possibility is given, for instance, for zinc, cadmium, lead and copper. The adequate procedure was tested with a microprocessor-controlled polarograph. Flame atomic absorption spectrometry was used as reference method.

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Bestimmung von Zink, Cadmium, Blei und Kupfer in Böden und Klärschlämmen durch mikroprozessorgesteuerte Voltammetrie im Vergleich mit der Atomabsorptionsspektrometrie

     

Voltammetric speciation of butyltin compounds

A sensitive and selective procedure for the determination of tributyltin chloride (TBT), dibutyltin dichloride (DBT) and monobutyltin trichloride (MBT) based on solid phase extraction (SPE) with ENVI-Carb non-porous carbon as column material followed by adsorptive cathodic stripping voltammetry (AdSV) in the presence of tropolone is reported. The determination limits achieved using a 500 mL water sample were 210 ng L^–1 (as Sn) for TBT, 30 ng L^–1 (as Sn) for DBT and 40 ng L^–1 (as Sn) for MBT. The method was used to determine the levels of butyltin species in surface water from the yacht harbour at Zewen on the Mosel River and in the tap water supply in Trier.Dedicated to Professor Dr. K. Doerffel and Professor Dr. H. Kriegsmann on the occasion of their 70th birthdays     

Dimethyl- and bis[(trimethylsilyl)methyl]cuprates show aggregates higher than dimers in diethyl ether: molecular diffusion studies by PFG NMR and aggregation-reactivity correlations

The molecular sizes of higher aggregates of dimethylcuprates (Me(2)CuLi (1), 1.LiI, and 1.LiCN) and bis[(trimethylsilyl)methyl]cuprates ((Me(3)SiCH(2))(2)CuLi (2), 2.LiI, and 2.LiCN) in diethyl ether (Et(2)O) were determined by pulsed field gradient (PFG) NMR diffusion measurements. The obtained diffusion coefficients show molecular sizes larger than those of dimers for all systems. In these higher aggregates, steric hindrance and dilution reduce aggregation, whereas LiCN increases it. The molecular sizes were first determined by a spherical model-free approach and then refined by structure models of higher aggregates. These models were built by a combination of diffusion results, known NMR studies, and crystal structures. Thus, polymeric chains with homodimeric cores connected by solvent (salt-free case) or solvent and salt (salt-containing case) were proposed. These models were confirmed by a solvation analysis, whereby the number of solvent molecules attached to the aggregates was determined by a weighted average study. On the basis of these structure models, the number of repetition units (length index) was determined to be between 1.3 and 5.2, with the general trends in aggregation independent of the structure model used. A combined analysis of the determined length indices and known relative reactivities led for the first time to a correlation between higher aggregation and reactivity of dimethylcuprates in the addition reaction with enones: aggregates higher than dimers reduce the reactivity. Consequently, despite their consistent homodimeric core structures, for the first time the remaining reactivity differences between iodo- and cyanodimethylcuprates in Et(2)O are explained by the difference in their aggregation.     

Dielectric relaxation measurements on aerosol-OT/water/cyclohexane-solutions at low water content

The complex relative dieletric permittivity of aerosol-OT(AOT)/water/cyclohexane solutions has been measured within the frequency range 5 kHz-10 GHz. The investigated solutions were of oil-rich type with varying AOT- and water content. A marked dielectric relaxation has been found. The dielectric increment as well as the conductivity steeply increase with the water content, while the relaxation time decreases. Theoretical models of heterogeneous dielectrics consisting of polar, highly conductive inclusions in a nonpolar solvent with low conductivity have been applied to the results, allowing conclusions with regard to the inclusions, shape and conductivity.     

Determination of toxic elements by cathodic-stripping-voltammetry

Summary The DPCSV determination of arsenic, selenium and tellurium in the sub-ng/ml range is discussed. After electrolytic deposition of the elements as intermetallic compounds with copper on the electrode surface, the determination is carried out by cathodic stripping. The simultaneous determination of selenium and tellurium or of selenium and arsenic is possible. Problems which occur in the application of these methods are discussed.

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Bestimmung toxischer Elemente durch CSV

Zusammenfassung Es werden Verfahren zur Bestimmung von Arsen, Selen und Tellur im sub-ppb-Bereich durch DPCSV beschrieben. Nach elektrolytischer Anreicherung der Elemente als intermetallische Verbindungen mit Kupfer auf der Elektrodenoberfläche erfolgt die Bestimmung auf der Grundlage der kathodischen Auflösung. Sowohl für Selen und Tellur als auch für Selen und Arsen ist die simultane Bestimmung möglich. Probleme bei der Anwendung dieser Bestimmungsverfahren werden diskutiert.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Organocuprate conjugate addition: structural features of diastereomeric and supramolecular pi-intermediates

In the reaction pathway of conjugate additions with organocuprate reagents, Cu(I) pi-complexes and Cu(III) sigma-complexes have been identified as central, NMR-detectable intermediate species. However, no experimental evidence for the structures of pi-intermediates with extensive chiral enones or the principal aggregation level and aggregate structure of pi-complexes in diethyl ether has been available so far. Furthermore, the structural characteristics of pi-complexes which are essential for their high reactivities and diastereoselectivities have not yet been rationalized experimentally. Therefore, the pi-intermediates of 4,4a,5,6,7,8-hexahydro-4a-methyl-naphthalen-2(3H)-one and Me2CuLi or Me2CuLi x LiX (X = I, CN) in diethyl ether are investigated in detail. For the first time, the formation of two intermediate cuprate enone pi-complexes on both sides of the double bond is observed. In addition, the conformation of the enone adopted in the major beta-face pi-complex rationalizes the exclusive syn addition observed in the synthetic product. For the investigation of the aggregation level and structure, a NMR screening of pi-complexes with Me2CuLi x LiX (X = I, CN) and three achiral enones is performed, which simplifies the spectra by the generation of enantiotopic pi-complexes. Thus, NMR diffusion experiments on cuprate intermediates and the detection of scalar couplings across copper without isotope labeling are possible for the first time. Extensive NMR studies, including those of cyclohexanone complexes, show that, in principle, salt-free dimethylcuprate is able to complex the carbonyl group. However, in the presence of salt, the carbonyl-complexing aggregates are composed of salt and cuprate moieties. These mixed aggregates cause the formation of large supramolecular pi-intermediate structures which control their reactivity. The pi-complexing cuprate units show a bent geometry as a general structural feature that is unaffected by the presence or kind of salt and the type of enone. Thus, the high diastereoselectivity and the reactivity of organocuprate 1,4-addition reactions are for the first time rationalized on the basis of structural characteristics of selected pi-intermediates.