Design of a Total-Reflection X-Ray Fluorescence Spectrometer and Application to Periphyton Communities

Abstract: The work presented in this thesis deals with the use of total-reflection X-ray fluorescence (TXRF) spectrometry for trace element analysis of periphyton. A TXRF spectrometer was designed and its performance was evaluated with a plankton reference material. For 12 .my.-samples, the imprecision of the analysis is < 10 %, while the inaccuracy (which is mostly due to specimen error) is < 20 %.

Two methods of analysis were developed for periphyton grown on glass discs. The first method (for freshwater periphyton) uses only nitric acid and hydrogen peroxide to digest a batch of 10 samples in about two hours. For a small laboratory, however, a complete preparation may take up to two days. The method gives recovery rates of 70 to 130 % for the elements P, S, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Se, Rb, Sr and Pb. The relative standard deviations are <20 % for all of these elements except P and S.

The second method (for marine periphyton) uses the periphyton glass disc directly as sample reflector in TXRF. No sample preparation is required other than a quick wash in distilled water (to remove excess sea water) and the addition of an internal standard. A complete preparation of a batch of 10 samples takes about one hour. The method gives recovery rates of 60 to 140 % for the elements K, Ca, Mn, Fe, Ni, Cu, Zn, As, Rb and Sr. Relative standard deviations are < 10 % for most elements.

The two methods were applied in an ecotoxicological experiment and a baseline study. In the ecotoxicological experiment, the response of periphyton communities to an episode of tri-n-butyltin (TBT) exposure was investigated. Effects of exposure to light and TBT were observed in the trace element content of the communities. In the baseline study, the trace element content of periphyton communities at 13 locations in European rivers was determined.