Kubische Berechnung der Retentionsindices ohne Kenntnis der Totzeit tm

Zusammenfassung In der vorliegenden Arbeit wird eine Methode zur Retentionsindex-Bestimmung beschrieben, die von einem kubischen Zusammenhang zwischen Bruttoretentionszeit-Differenzen der Referenzhomologen und der Kohlenstoffzahl ausgeht. Hieraus ergeben sich direkt die Nettoretentionszeiten. Der Fehler der Totzeitbestimmung entfällt bei dieser Methode. Mit den so gewonnenen Nettoretentionszeiten erhält man über einen kubischen Zusammenhang zwischen 1g t_s=f(C) die Retentionsindices. Extrapolationen und Interpolationen sind über 300 Retentionsindexeinheiten mit einem mittleren Fehler von ±0,02 Retentionsindexeinheiten möglich. Das Verfahren bietet sich für eine automatische Berechnung der I-Werte mittels on-line-Datenverarbeitung an.

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Cubic calculation of retention indices without determining the dead-time t_m

Summary The method for the calculation of retention indices described here is based on a third order relationship between the logarithm of differences of unadjusted retention times of homologues and the carbon number. From this adjusted retention times are directly calculated. A determination of the dead-time is not necessary thus avoiding the errors connected with this factor. A cubic equation for the logarithm of the adjusted retention time lg t_s as a function of carbon number C_n is used for the retention index calculation. Extrapolations and interpolations can be done over a range of 300 index units with an average deviation of ±0.02 i.u.. The method offers the possibility of an automated on-line calculation of retention indices by computer merely on the basis of unadjusted retention times.

     

Almost constant sequences and well-distribution in compact groups

We study the properties of sequences (c _n ) in a compact groupG such that (x _n ) being (weakly) well-distributed implies (c _n x _n ) being (weakly) well-distributed and give a complete characterisation in terms of almost constant sequences as well as a generalisation to non-compact locally compact groups.     

The determination of chlorinated biphenyls,chlorinated dibenzodioxins,and chlorinated dibenzofurans by GC-MS

High resolution gas chromatography, with mass selective detection, has been used for the analysis of PCB on methyl 50 % octyl polysiloxane (SB 50 Octyl), methyl octadecyl polysiloxane, and a smectic polysiloxane (SB Smectic); and for the analysis of polychlorodibenzodioxins and polychlorodibenzofurans with 1 to 8 chlorine substituents on 100 % cyanopropyl siloxane (SP 2331), smectic polysiloxane (SB Smectic), a new polar stationary phase (DB-Dioxin). The analysis has also been performed by column coupling.     

Eine globalanalytische Behandlung des Douglas'schen Problems

In this paper we consider the Douglas problem of genus O. Starting point is the global analysis for minimal surfaces of the type of the disc which was developed by A.J. Tromba. The set of all k-connected minimal surfaces of genus O has a product structure, which is a consequence of the variation of the conformal type. The base space is the space of domain parameters and the fibres are the manifolds of k-connected minimal surfaces of constant conformal type (cf.[7]). It is possible to develop a global analysis also for the more general situation considered here with the following results:

-The map which assigns to every minimal surface its boundary curve (in the sense of the Douglas problem) is a Fredholm operator. The index depends on the number and the total order of the branch points.

-The analysis allows to prove isolatedness and stability results in a relatively simple way.

     

LIQUID-CRYSTALLINE PHASE TRANSITION OF MONOMOLECULAR LAYERS OF CHLOROPHYLL a*

Monomolecular layers of chlorophyll a at the air-water interface were investigated by absorption spectroscopy and simultaneous thermodynamic measurements. Whereas at temperatures near 20°C at all pressures, only a liquid phase exists, at a temperature of 4°C, a liquid-crystalline phase transition is observed at a surface pressure of 5 dynes/cm. Pressure-induced changes in the chlorophyll arrangement become evident from a drastic change in the absorption spectra, accompanying the phase transition. The crystalline phase exhibits an extremely narrow absorption band (halfwidth below 9 nm) centered at 698 nm, indicative of a coplanar chlorophyll arrangement in a well-ordered environment. It is highly probable that in these model membranes a chlorophyll arrrangement could be established that is equivalent to the one proposed for the reaction center P700.     

Transport and Fate of Organic Compounds in the Global Environment

The role of chemistry in our soon-to-be global industrial society requires a global perspective for the discussion of the uptake, transport, and conversion of chemical compounds in the environment. The fate of organic compounds in the volume flow of the atmosphere and hydrosphere can be categorized into transport pathways and adjustments of equilibria in the multiphase system atmosphere-oceans-land surface. The global volume flow in the atmosphere (wind, areas of high and low pressure) and in the hydrosphere (rivers, circulation of water in lakes, ocean currents) alone would account for the transport of organic compounds if they were stable and if all these compounds were molecularly distributed in these phases. However, this particular case is observed only for volatile chlorofluorocarbons and tetrachloromethane. For most organic compounds, complex adsorption/desorption processes on finely dispersed particle phases in the air and water as well as abiotic and biotic transformations determine the transport behavior. The global fate of a compound includes its accumulation as well as its decomposition in defined environmental compartments. Both phenomenon may have long-term consequences in the af-fected areas; this is indicated by the accumulation of polychlorobiphenyls and analogous compounds in marine mammals and deep-sea fauna, and is evident in the decomposition of chlorofluorocarbons in the stratosphere. The accepted definition of the level of a risk, the product of the probability of an event and the potential amount of damage, takes on a new dimension when viewed from a global perspective-especially when one further connects the extent of the damage to the possible means of correction. It is the responsibility of scientists to point out the irreparable regional to global consequences directly and indirectly connected to the production of chemicals and to provide suggestions for prevention. Politicians can only react by applying their methods to limit the damage; however, they cannot generate any solutions based on science.     

Isolierung und Anreicherung von Chlorphenoxyessigsäuren aus Wasser mit makroretikulären Adsorberharzen XAD-2 und XAD-7

Herbicide chlorophenoxy acetic acids can be isolated by the macroreticular adsorbing resins Dowex Amberlite XAD-2, XAD-4, XAD-7 and XAD-8. The adsorption of phenoxy acetic acids reaches an optimum at pH 2 and flow rates of about 5 bed-volumes per minute. Elution depends on the polarity and contact time of the eluent. A quantitative isolation of chlorophenoxy acids in the 25 ppb range in water can be achieved by adsorption at the divinylstyrolresin XAD-2 following elution with acetone. Further concentration of the eluate is possible by standard methods.     

Quantitation of camphechlor/toxaphene in cod-liver oil by integration of the HRGC/ECD-pattern

Summary Quantitation of camphechlor/toxaphene in biological matrices like cod-liver oil or fish is difficult because it is a very complex mixture of alicyclic polychlorinated compounds. Furthermore, many toxaphene components are biotransformed and photodegraded and the complex mass spectral fragmentation pattern of HRGC/MSD (electron impact (EI)) cannot be used for quantitation at the g/g-level or below. The use of several indicator-peaks after ECD-detection using the technical standard mixture for calibration does not characterize the entire pattern in a biological sample. Two averaging integration methods that are based on the entire HRGC/ECD-pattern of toxaphene compounds after separation from the PCB congeneres by adsorption chromatography on silicagel, allow a fast and accurate quantitation of the mixture in biological samples, e.g. cod-liver oil. Biological degradation does not disturb the determination because the whole pattern of the complex mixture is considered instead of only a few compounds of the parent mixture which could be degraded or not.