G. Schulze

Nitratbestimmung im Trinkwasser mit Hilfe der Ionen-Chromatographie

SummaryA comparison of the methods of ionchromatography and potentiometry shows that ionchromatography is suitable for the determination of nitrate in drinking water in a range between 1 and 100 mg/l. The standard deviation of this method in the upper range of 10–100 mg/l is between 2 and 0.5% and increases from 2 to 12% in the lower range of 1–10 mg/l. Regression in both ranges results in polynomials of the second degree. The analysis of drinking water by means of ion-chromatography covers, in addition to nitrate ions, the anions fluoride, chloride, phosphate, sulphate, bromide, and nitrite; the concentrations of the two last mentioned ions are generally below the detection limit.ZusammenfassungAnhand eines Methodenvergleichs zwischen Ionen-Chromatographie und Potentiometrie wird gezeigt, daß die Ionen-Chromatographie zur Nitratbestimmung im Trinkwasser in einem Bereich von 1–100 mg/l geeignet ist. Die Standardabweichung dieser Methode liegt in dem oberen Arbeitsbereich von 10–100 mg/l zwischen 2 und 0,5% und steigt in dem unteren Arbeitsbereich von 1–10 mg/l von 2 auf 12% an. Die Regression in beiden Bereichen führt zu Polynomen zweiten Grades. Neben dem Nitration werden bei der Analyse von Trinkwässern mit Hilfe der Ionen-Chromatographie auch noch die Anionen Fluorid, Chlorid, Phosphat und Sulfat simultan erfaßt, ferner Bromid und Nitrit, deren Konzentrationen jedoch im allgemeinen unterhalb der Nachweisgrenze liegen.

Trace element analysis of high-purity copper

SummaryIn copper samples trace impurities of the elements As, Bi, Cr, Fe, Pb, Sb, Se and Te in the low μg/g range were coprecipitated with lanthanum hydroxide and determined by flame AAS (Fe) and electrothermal AAS (other elements). Reduction of the sample weight results in a considerable saving of time compared to elder procedures and allows to apply centrifugation instead of filtration as separation technique, by which the risk of contamination is decreased. The completeness of separation was examined by analyzing standard solutions. Additionally radio tracer experiments were employed with Sb and Se. Based on recovery data, a classification scheme was set up with regard to adsorption behaviour. High-purity copper samples were analyzed by the procedure described; INAA and ICP-MS were used as comparison methods. Parameters affecting the precision were examined; the main influence was caused by the separation step. The procedure is well suitable for the determination of 2–10 μg/g As, Cr and Pb and 5–50 μg/g Fe in high-purity copper.

Matrix exchange technique for the simultaneous determination of several elements in flow injection potentiometric stripping analysis

ZusammenfassungZur Beseitigung von Störungen durch Potentialüberlappung bei der Bestimmung mehrerer Elemente im Spurenbereich durch Potentiometrische Stripping Analyse in Kombination mit der Fließinjektionstechnik werden einige allgemeine Gesichtspunkte erörtert. Unter Anwendung der Methode des Lösungswechsels werden die Strippingpotentiale von Cadmium, Blei, Thallium und Zinn in verschiedenen Grundelektrolyten gemessen. Die Werte dienen zur Optimierung der Zusammensetzung der Trägerlösung bei der Simultanbestimmung der Elemente. Der Zusatz von Komplexbildnern, wie Citrat, Tartrat oder Ammoniak, führt zu einer erheblichen Potentialverschiebung für die zweiwertigen Ionen, wodurch sich Einschränkungen bei Simultanbestimmungen aufheben lassen. Von den etwa 40 geprüften Trägerelektrolyten erwies sich als Strippinglösung das System NH3/KOH als am besten geeignet. Die Potentialauflösung ist so gut, daß die vier Elemente nebeneinander bestimmt werden können, auch wenn sich ihre Konzentrationen um eine Größenordnung unterscheiden.SummarySome general features of Flow Injection Potentiometric Stripping Analysis are outlined with special regard to the application of the matrix exchange technique. The stripping potentials of cadmium, lead, thallium, and tin in various supporting electrolytes are measured. The data are used to optimize the composition of the carrier solution for the simultaneous determination of mixtures of these elements. Complexing agents as citrate, tartrate, and ammonia lead to a drastic potential shift for bivalent ions, thus permitting the removal of limitations for the simultaneous determination. Among the nearly forty different supporting electrolytes tested, the NH3/KOH stripping solution was found to be unique. The resolution is so good that the four elements Cd, Tl, Pb, and Sn can be determined simultaneously even when they are present in concentrations differing by one order of magnitude.

Störeinflüsse durch Kupfer bei der potentiometrischen Stripping-Analyse von Zink und Cadmium

SummaryInterference problems in potentiometric stripping analysis due to intermetallic compound formation between copper and zinc as well as between copper and cadmium are examined. Different interference mechanisms are discussed. The possibility and limitation of eliminating the interference in the determination of zinc by addition of gallium is shown. If the amount of copper deposited at the mercury film exceeds its solubility in mercury, the determination of cadmium will be interfered with. The deposition of metal ions may be decreased without loss in sensitivity by using the stirrer-stop technique and/or by deaerating the sample. Thus, interference effects are diminished.ZusammenfassungDie bei der potentiometrischen Stripping-Analyse aufgrund intermetallischer Wechselwirkungen zwischen Kupfer und Zink sowie Kupfer und Cadmium auftretenden Interferenzen werden untersucht. Für die beiden Systeme werden unterschiedliche Mechanismen gefunden. Die Möglichkeit, durch Zugabe von Gallium die Kupfer-Zink-Interferenz zu eliminieren, wird dargestellt und die Grenzen werden ermittelt. Beim Überschreiten der Löslichkeit des abgeschiedenen Kupfers an der Quecksilberfilmelektrode tritt eine Störung der Cadmiumbestimmung auf. Eine verminderte Metallionenabscheidung bei gleichbleibender Empfindlichkeit der Methode wird durch die Rührerstop-Technik bzw. durch Entlüften der Probe erreicht, wodurch das Ausmaß der Störung verringert werden kann.

Nitrate in drinking water in the West German wine-growing areas of Baden and Württemberg.

Nitrate is regarded as a substance whose presence in drinking water is not considered as desirable. If reduced to nitrite it may cause methomoglobinemia in infants. Onward reaction with amines capable of coupling will result in the formatin of nitrosamins. Excessive use of fertilizers in agriculture is the most frequent cause of elevated nitrate contents of drinking water. To quantify this problem, drinking water was sampled at taps at 200 sites arranged on a grid covering the wine-growing areas of Baden and Württember. These samples were examined for their content of nitrate, chloride, and sulphate by means of ion chromatography. Clearly elevated nitrate contents were revealed by the resuls of measurements: 13% of samples showed values above the maximal concentration admissible under the EC Drinking Water Directive of 50 mg NO-3/l and 42% above the EC guide level. The excessive levels were mostly found in the regions of Kaiserstuhl-Tuniberg-Markgräflerland and Württembergisch Unterland. Many samples with an elevated nitrateacontent exhibited also elevated sulphate contents. The high nitrate levels are attributed to the use of nitrogen fertilizers in the vineyards.

Gas-liquid separator with integrated manifold as interface for HPLC-hydride AAS of organotin compounds

SummaryA gas-liquid separator is presented, which is adapted to the special conditions of metalorganic speciation analysis by HPLC-hydride AAS.

Untersuchungen zur Gleichwertigkeit von Analysenverfahren — Fließinjektionsanalyse und DIN-Verfahren bei der Orthophosphatbestimmung in Oberflächenwässern

SummaryThe German standard method for the determination of orthophosphate in water, waste water and sludge, laid down in the norm DIN 38405, part 11, is based on the absorbance measurement of the phosphormolybdic acid after reduction with ascorbic acid. In order to apply a more rapid method, flow injection analysis was used following a procedure published in the Tecator application note ASN 60/83. It is also based on the formation of molybdenum blue employing stannous chloride as reducing agent. The equivalence of both analytical methods is examined by statistical tests according to the norm DIN 38402, part 71. It is shown that no unequivocal assertion can be given because the examination is based on the selection of one sample only and the decision depends on the number of repeated determinations performed for the sample.

Untersuchungen zur Gleichwertigkeit von Analysenverfahren — Flie\injektionsanalyse und DIN-Verfahren bei der Chloridbestimmung in der Wasseranalytik

SummaryThe German standard method for the determination of chloride in water, waste water and sludge, laid down in the norm DIN 38405-D 1–2, is based on the titration with AgNO3 and potentiometric detection for the range 7–140 mg/l chloride. In order to investigate the equivalence of a more rapid method, flow injection analysis with different detection methods (photometric, potentiometric and by atomic absorption) is applied. Thirty samples of water of different types (waste, tap, surface and mineral water) are analysed and the results are examined by a statistical test, which, according to the norm DIN 38402, part 71, is based on orthogonal regression. The test shows that the results obtained with the FIA-methods are equivalent to those from the German standard method. The three flow injection systems mentioned have a 10–36-fold higher sample frequency and a lower (down to 1/1000) sample and reagent consumption. Therefore, these FIA-methods are superior to the actual German standard method.

Nitrat im Trinkwasser von Weinbaugebieten — eine ionen-chromatographische Studie

Wine-growing is one of the intensive cultures using extremely high doses of nitrogenous fertilizer, the washing out of which can have its influence on the quality of drinking water. To quantify the problem of burdening, drinking water was sampled from taps at 254 sites covering the wine-growing areas of Oberrhein, Main and Neckar. These samples were examined for their content of nitrate by means of ion-chromatography. The results reveal the following: 13 % of the samples exceed the maximal concentration admissible and 42 % are above guide level. For the regions of Wurzburg, Wurttembergisch Unterland and Kaiserstuhl-Tuniberg-Markgraflerland which are particularly loaded with nitrate it can be proved that artificial fertilizers do indeed influence the quality of drinking water. In these cases a dependence of nitrate concentration in drinking water on the local situation of the water catchment places — in view of areas used for wine-production — is given. A nitrate register for drinking water was established; it shows that parts of the population, who are particularly concerned, are additionally nitrate-burdened by drinking water by about a factor of four in comparison with other food. A critical examination of plainly immission-covering possibilities for the reduction of nitrate burdening leads to the necessity of regulations for limiting the emissions.

Potentiometrische Stripping-Analyse in fließenden Systemen

SummaryA thin-layer flow-through cell for the potentiometric stripping analysis at a glassy carbon electrode covered with a mercury film is introduced. The dependence of the signal height on the mercury concentration and the influence of the dissolved oxygen in the determination of lead and cadmium are investigated. A comparison is made between batch and continuous mode. The latter gives the possibility of achieving the oxidation step in a solution that is independent of the sample. Only this way is it possible to perform controlled oxidation in deaerated solutions containing small mercury concentrations. This leads to an increase in sensitivity by a factor of about one hundred.ZusammenfassungEine Dünnschicht-Durchflußzelle für die potentiometrische Stripping-Analyse an einer quecksilberbeschichteten Glaskohlenstoffelektrode wird vorgestellt. Die Einflüsse der Hg2+-Konzentration und des gelösten Sauerstoffs auf die Signalgröße bei der Bestimmung von Blei und Cadmium werden untersucht. Die diskontinuierliche Arbeitsweise wird mit der im fließenden System verglichen. Letztere bietet die Möglichkeit, den Oxidationsschritt in einer von der Probe unabhängigen Lösung vorzunehmen. Nur dadurch läßt sich in entlüfteten Proben bei kleinen Hg2+-Konzentrationen eine kontrollierte Oxidation durchführen. Dies führt zu einer Empfindlichkeitssteigerung um etwa den Faktor 100.