Key words: TXRF, Daphnia magna, trace elements


This internship took place at the XMI group of the department Analytical Chemistry at Ghent University. As a result of an internal UGent collaboration between the Department of Archaeology and Analytical chemistry a new total reflectance X-ray fluorescence spectrometer, the TX2000 of GNR, has been installed. By applying the total reflection X-ray fluorescence methodology, this instrument should be capable of achieving very low detection limits, possibly reaching the level of only few tenths of ppb for an element such as zinc. The primary goal of my internship was to study the methodological parameters that may influence the performance of this new spectrometer.

However, in order to have a practical example, the TXRF methodology was studied and optimized by applying it to investigate Daphnia Magna. These crustaceans live in fresh water systems all over the world and are the lowest level of the food guide pyramid. The Laboratory for Environmental Toxicology and Aquatic Ecology (ecotox) of UGent studies the mechanisms of uptake (intake) of metals by these minuscule organisms, which are used as environmental bio-indicating monitoring systems. Until now, the ecotox laboratory determines the metal concentration using atomic absorption spectrometry (AAS). Because this technique requires a certain amount of sample, ten daphnids are digested at the same time and measured all together. Afterwards the average concentrations of the elements are calculated. Since the TXRF methodology promises detection of very low amounts of material, this particular example of investigating single daphnids was chosen in order to study the performance of the GNR TX2000 spectrometer. During this internship there will be worked with differently adapted daphnids which were cultivated in control medium, medium contaminated with zinc, medium contaminated with cadmium and a medium contaminated with both zinc + cadmium.


As a final conclusion there can be stated the TXRF technique gives promising results for the elemental analysis of daphnids. The quantification of the element cadmium with the TX2000 is difficult since the cadmium Lα-line is heavily interfered from the potassium Kα-line. Because each daphnid is an individual organism and the results sometimes shown high standard deviations, only trends can be discussed. To confirm these trends at least thirty daphnids per treatment should be analysed.