Margit B. Müller

Use of fluorescence fingerprints for the estimation of bloom formation and toxin production of Microcystis aeruginosa

The development of methods facilitating the detection of cyanobacterial blooms in drinking water reservoirs at an early stage is of great importance. Fluorescence spectroscopy could meet these requirements. The study contains the examination of possible correlations between the different maxima of a fluorescence excitation-emission matrix and the amount of produced and excreted toxins of a lab culture of Microcystis aeruginosa at different stages of growth. Various fluorescence signals (protein-like and humic-like substances, pigments) are suited for an estimation of cell density and actual intra- and extracellular toxin concentration. One signal at 315nm/396nm presumably originating from protein-like substances might be useful as a tool for the prediction of increasing cyanobacterial toxin concentrations. As the measurement of fluorescence matrices is still time consuming, synchronous scans with Deltalambda=80nm were tested as a potential alternative. They accurately depict the course of protein-like and humic-like fluorescence during the different stages of growth although especially the latter one is not captured at its maximum. However, due to insufficient separation of chlorophyll a and phycocyanin, the image of the matrix maxima by synchronous scans with Deltalambda=80nm can only be used with minor restrictions. Nevertheless, fluorescence spectroscopy seems to be a powerful tool for the evaluation of cyanobacterial blooms.

Metal Distribution in Different Size Fractions of Natural Organic Matter

In this paper, size-exclusion chromatography (SEC) was used to determine the metal concentration in different size fractions of a bog lake water. Two methods were applied: (a) preparative SEC with off-line metal concentration analysis and (b) direct coupling of an analytical SEC system on-line with an inductively-coupled plasma mass spectrometer (ICP-MS). In the preparative SEC measurements, maximum concentrations were found for different metal ions in different size fractions of the natural organic matter (NOM). Normalization of metal concentrations to dissolved organic carbon concentration (DOC) yielded two maxima in the high and in the very low molecular-weight fractions. Whereas good recoveries were found for Al, Fe, and Ni, only 40% were obtained for Pb. This indicates that Pb formed labile complexes with NOM, and hence could strongly interact with the column material. In the experiments with the analytical SEC-ICP-MS system, the same trends were observed, but with even lower recoveries than in the preparative system. Sample preconcentration and storage were also investigated with respect to decrease in metal concentration. During the ultrafiltration preconcentration step Al and Fe were removed only to a small extent, whereas about half of the initial Pb was lost. This indicates that Al and Fe were mainly bound to high molecular-weight fractions of NOM. In contrast to that, Al and in particular Fe were removed from solution more than proportionally with respect to DOC because of aggregation of the NOM during storage, whereas Pb and Ni were concentrated relative to the DOC. Metallverteilung in verschiedenen Grosenfraktionen naturlicher geloster organischer Wasserinhaltsstoffe In dieser Arbeit wurde die Grosenausschlusschromatographie (SEC) genutzt, um die Verteilung von Metallen in unterschiedlichen Grosenfraktionen von gelosten organischen Wasserinhaltsstoffen (NOM) eines Moorsees zu bestimmen. Dazu wurden zwei verschiedene Methoden angewandt: (a) eine praparative SEC-Methode (die Fraktionen wurden gesammelt und die Metallkonzentrationen wurden off-line gemessen); (b) die direkte Kopplung der SEC mit einem Massenspektrometer mit induktiv gekoppeltem Plasma (ICP-MS). Mit dem praparativen System wurden fur verschiedene Metalle maximale Konzentrationen in unterschiedlichen Grosenfraktionen der NOM gefunden. Wurden die Metallsignale auf die Konzentration an gelostem organisch gebundenem Kohlenstoff (DOC) normiert, so ergaben sich zwei Maxima: in der hochmolekularen Fraktion und in der sehr niedrigmolekularen Fraktion. Gute Wiederfindungen bei der chromatographischen Trennung wurden fur die Elemente Al, Fe und Ni erhalten. Fur Pb wurden lediglich 40% wiedergefunden. Das deutet darauf hin, dass Pb labile Komplexe mit NOM ausbildet und so mit der stationaren Phase der chromatographischen Saule wechselwirken kann. In den Experimenten mit der direkten SEC-ICP-MS-Kopplung wurden die gleichen Trends wie mit dem praparativen System gefunden. Allerdings wurden schlechtere Wiederfindungen erhalten. Die Probenaufkonzentrierung und -lagerung wurde ebenfalls bezuglich der Veranderung der Metallkonzentration untersucht. Bei der Ultrafiltration, die zur Aufkonzentrierung der Probe angewandt wurde, wurde nur ein kleiner Teil von Al und Fe entfernt, wahrend etwa die Halfte des Pb durch die Membran abgetrennt wurde. Das bedeutet, dass Al und Fe hauptsachlich an die hochmolekulare Fraktion der NOM gebunden waren. Bei der Lagerung der Probe bildeten sich Aggregate, die durch Filtration der Probe vor ihrem Gebrauch fur die SEC-Experimente abgetrennt wurden. Dabei wurden Al und Fe bezogen auf die DOC-Konzentration uberproportional entfernt. Ni und Pb wurden relativ zur DOC-Konzentration angereichert.

Reconsidering the quantitative analysis of organic carbon concentrations in size exclusion chromatography.

The evaluation of the molecular size distribution of natural organic matter (NOM) in aquatic environments via size exclusion chromatography (SEC) is important for the understanding of environmental processes such as nutrient cycling and pollutant transport as well as of technical water treatment processes. The use of organic carbon (OC) detectors has become popular in recent studies due to improved availability and quantification possibilities, which supposedly are superior to those of ultraviolet (UV) detectors. A set of 12 NOM samples was used to demonstrate the limitations of online OC detection (OCD) when analyzing complex aquatic organic matter. A novel evaluation approach for SEC data is introduced by combining the information from UV absorbance (UVA) and OCD chromatograms as well as offline total OC (t-OC) and dissolved OC-specific UVA (SUVA) measurements. It could be shown that about 70% of certain OC components were not detected with the OCD system used in this study. For the investigated samples, these types of carbon accounted for up to 72% of the t-OC, i.e. for such NOM samples quantification by OCD is not possible or at least highly questionable. The addition of an oxidant improved the overall oxidation efficiency only slightly. Most likely NOM that predominantly consists of polysaccharides and features a nominal molecular weight of 150kg/mol or more was responsible for low OCD yields. For future applications, a further improvement of the OCD system would be worthwhile so that quantitative analytical data on the molecular size distribution of NOM and its structural characteristics such as the SUVA distribution can be obtained.

A new concept for the fractionation of DOM as a basis for its combined chemical and biological characterization

To overcome the problem of non-specific interactions during the preparative fractionation of dissolved organic matter (DOM) for its combined chemical and biological characterization, the concept of standardized fractions (SFs) was developed. The concept is based on the calibration of the fractionation systems with suitable standards for the experimental definition of SFs, and the subsequent preparative fractionation of DOM samples according to the predefined SFs. Undesired non-specific interactions can thus be minimized experimentally. It was applied to the fractionation methods size exclusion chromatography (SEC) and multistage ultrafiltration (mst-UF). A brownwater sample and an effluent from a sewage treatment plant were fractionated. The two methods performed rather differently which was evidenced both by the polydispersity of the resulting fractions as well as sum parameter fractionation patterns. Consequently, the interpretation of data obtained from the chemical-physical as well as biological analysis must always consider the limitations and particularities of the fractionation method employed.

Sample cleanup and reversed-phase high-performance liquid chromatographic analysis of polar aromatic compounds in groundwater samples from a former gas plant.

A method for the analysis of the polar aromatic compounds 1H-quinolin-4-one (Q), 10H-acridin-9-one (A), 5H-phenanthridin-6-one (P) and 9H-fluoren-9-one (F) in aqueous solutions has been developed. The method comprises steps for sample preparation (solid-phase extraction, cleanup) and analytical determination by means of reversed-phase high-performance liquid chromatography (RP-HPLC). For the cleanup step the suitability of two different sorbents (alternative A: silica gel, alternative B: LiChrolut EN) was investigated. Alternative B depicted several advantages, in particular higher sorbent capacity, faster and less complicated handling, higher recovery and better reproducibility. For Q, A and P, reproducibility of all method steps is better than 13%, with recovery rates ranging from 76% to 105% (n=3). Alternative B was applied to groundwater samples from a former gas plant. The analytes A and P could be detected at concentrations in the micro/l range.