Bestimmung von gelöstem Sauerstoff und Stickstoff in Wasser mittels Gaschromatographie

Zusammenfassung Es wird eine Methode zur gleichzeitigen Bestimmung von im Wasser gel?stem Sauerstoff und Stickstoff vorgeschlagen. Nach der Probenahme in Glasgef?ssen wird das Wasser teilweise durch Helium aus den Gef?ssen verdr?ngt. Die im Wasser gel?sten Gase treten ins Helium über, in welchem der Sauerstoff- und Stickstoffgehalt gaschromatographisch bestimmt wird. Die erhaltenen Messwerte werden mit Ergebnissen der Sauerstoffbestimmung nach Winkler verglichen.

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Summary A method is proposed for the concomitant determination of nitrogen and oxygen, dissolved in water. After sampling in glass flasks, the water is displaced partially by helium. Nitrogen and oxygen, dissolved in water, are then transferred into helium, in which the two gases are determined by gas chromatography. The results obtained are compared with those received by the Winkler method for determination of oxygen.

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Résumé Une méthode pour la détermination simultanée de l'oxygène et de l'azote dissous dans l'eau est proposée. Après le prélèvement d'échantillons dans des récipients en verre, l'eau est partiellement chassée hors des récipients au moyen d'hélium. Les gaz qui sont dissous dans l'eau passent dans l'hélium dont la teneur en oxygène et en azote est déterminée par chromatographie en phase gazeuse. Les valeurs de ces dosages sont comparées aux résultats obtenus par la détermination de l'oxygène d'après Winkler.

     

Die elektrochemische Bestimmung des im Wasser gelösten Sauerstoffs mit Hilfe einer modifizierten Membranelektrodentechnik

Zusammenfassung Die Anwendungsm?glichkeiten der elektrochemischen Sauerstoffbestimmung wurden durch die Einführung der Kurzzeitmessung erweitert. Diese Methode gibt eine gr?ssere Empfindlichkeit und erlaubt somit die Sauerstoffbestimmung im μg/l-Bereich. Ferner wurde ein System entwickelt, das von der Membrandicke und dem Membranmaterial unabh?ngig ist. Das ist ein Vorteil, der speziell für Sauerstoffmessungen in Kl?ranlagen interessant sein dürfte.

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Summary This paper presents a new electrochemical technique for DO measurements by means of membrane electrodes. In stead of the well-known steady state measurements, a transient technique which is more sensitive was used. This gives the possibility of measuring oxygen in the μl/l range. The system is independent of the membrane material and the membrane thickness. The stirring influence is considerably less than for steady state measurements. The independence of the membrane material will be especially useful for oxygen measurements in waste purification plants.

     

Die praktische Anwendung der elektrochemischen Sauerstoffbestimmung im Wasser

Zusammenfassung Zum Betrieb der früher beschriebenen Oxytester-Sonde [2] wurde ein Transistorger?t entwickelt zur Messung von Temperatur, Sauerstoffgehalt und Leitf?higkeit des Wassers. Die Stromversorgung erfolgt aus eingebauten Stahl-Akkus, welche mit einem ebenfalls eingebauten Gleichrichteraggregat immer wieder nachgeladen werden k?nnen. Das Ger?t kann gleichzeitig als vollwertiger Labor-Leitf?higkeitsmesser und als Labor-Fernthermometer eingesetzt werden. DieTemperaturmessung mit Thermistoren ist ausgebaut für Direktablesung der Temperatur an einem dreistelligen Z?hlwerk (Helipot-Digidial), ebenso die Messung deselektrischen Widerstandes. Diespezifische Leitf?higkeit kann direkt abgelesen werden; die Konstante der Messzelle wird in die Messbrücke eingeeicht. Kabelwiderstand und-kapazit?t sind kompensiert. Die Anzeige des Brückensignals wird zweistufig verst?rkt und ist hochempfindlich. DerSauerstoffgehalt kann wahlweise nach dem Verfahren vonT?dt (ohne extern zugeführte Hilfsspannung) oder polarometrisch (mit dem gleichen Elektrodenpaar aus Gold und Zink) gemessen werden.

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Summary In an earlier publication [2] we described a probe (oxytester) for the combined and remote measurement of temperature, conductivity and oxygen content of water. The present paper describes an improved instrument for the probe that is fully transistorized and powered by nickel-cadmium batteries which can be recharged with a built-in rectifier. Watertemperature is measured with the aid of thermistors and directly indicated on a 3-digit counter (Helipot Digidial). The same applies for theelectrical resistance. Specific conductivity can also be read directly from the instrument, because the circuits are precalibrated and resistance and capacity of the cable compensated. Amplification of the signal renders the instrument highly sensitive.Oxygen content of the water can be measured either by T?DT's method (without auxiliary voltage) or polarometrically (with the same zinc and gold electrodes). The instrument has been designed for routine use in limnological research, and for industrial control of water conditions. It is being manufactured in Switzerland.

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Herrn Prof. Dr. O. Jaag zum 60. Geburtstag herzlich zugeeignet!     

Untersuchungen zum Nachweis von Escherichia coli im Wasser

From river water there were isolated 21 species (mainly coliform bacteria) in 914 strains. Of the pure cultures of coliform bacteria (E. coli, Enterobacter, Klebsiella, Citrobacter) 74.1 % of E. coli and 23.2 % of the Klebsiella strains showed lactose decomposition with gas formation at 44 °C. More than 90 % of the isolated Klebsiella did not form indole. Therefore, the temperature test and the indole formation (at 44 °C) (TI-test) made a very specific detection of E. coli in water possible. 94.7 % of the cultures grown initially on endoagar after a positive TI-test proved to be E. coli. The detection of E. coli showed a very good agreement with the standard method and the TI-test, the detection with the standard method being considerably dependent on the number of checked coliform colonies.     

Überleben von Campylobacter jejuni im Wasser

The Campylobacter jejuni survival pattern was investigated in model experiments using drinking water and surface waters differing in organic contamination. Further conditions studied were two different temperature levels (4 °C and 20 °C, resp.) as well as several starting densities of the testing strain. In drinking water, i.e. relatively uncontaminated water, the starting density showed a direct influence on the interval of surviving. The same was noted for temperature, where higher levels (20 °C) resulted in a relative quick inactivation of the investigated agent. Mentioned influences played a similar role in the surface water medium, together with the level of organic contamination: An increase of the value of COD to about 15.4 mg/l O₂ halved the interval of surviving. No relation to the dissolved oxygen tension was found.     

Gaschromatographische Bestimmung von polychlorierten Biphenylen in Wasser nach Headspace-Festphasenmikroextraktion

Gas-chromatographic Determination of Polychlorinated Biphenyls in Water after Headspace Solid-phase Microextraction Headspace-analytical techniques are usually applied to the determination of easily volatile substances in water, whereas semivolatiles are generally isolated by liquid-liquid or solid-phase extraction. In the present paper, a method is presented for isolating high boiling polychlorinated biphenyls (PCB) using headspace solid-phase microextraction at elevated temperature. In spite of their low vapor pressure, the analytes are adsorbed very efficiently on a poly-dimethylsiloxane-coated fiber. Thus, in combination with GC/ECD, a very simple and sensitive solventless determination of PCB is accomplished. Using the simplest possible standard conditions, limits of determination in the lowest nanogram-per-liter range are achieved. Further increased sensitivity down to the ppq (parts per quadrillion) range is possible by stirring and increasing the sample volume and adsorption time. Moderate matrix effects have been observed in some surface and groundwaters.     

Bestimmung von Sulfid in Wasser mit einer ionenselektiven Elektrode

For the direct potentiometric measurement by means of a sulphidselective solidstate membrane electrode (as the reference electrode a calomel electrode with a salt bridge filled with 1M KNO₃-solution) there were mixed 25 ml sample with 25 ml sulphide-antioxidant buffer (0.2 M ascorbic acid in 2 M NaOH, Ag₂S-saturated). Calibration is done with thioacet-amide in the same buffer. This measuring arrangement determines sulphide concentrations of 1.5.10^?6… 10^?3 M. If the buffer is added to the samples in the ratio of 1 +1 immediately during sampling, the sulphide content will be stabilized by this for at least 24 h. The measuring method and its calibration are compared with other methods of calibration with Na₂S and the potentiometric titration, the iodometric titration and the photometric determination. The method having been developed proves to be very selective and requires a minimum expenditure of time.