Alex von Bohlen

Relevance and analysis of traffic related platinum group metals (Pt, Pd, Rh) in the aquatic biosphere, with emphasis on palladium.

Following the introduction of automobile catalysts in the middle of the Eighties in Germany there is an increasing emission of the platinum-group-metals (PGM) platinum (Pt), palladium (Pd) and rhodium (Rh). Still, it remains unclear if these metals are bioavailable for aquatic animals and to which extent they accumulate in the aquatic biosphere. Zebra mussels (Dreissena polymorpha ) were maintained in water containing road dust at a concentration of 1 kg/10 l. Following an exposure period of 26 weeks, soft tissues of the mussels were analysed applying adsorptive cathodic stripping voltammetry (ACSV) for the determination of Pt and Rh and total-reflection X-ray fluorescence analysis after co-precipitation of Pd with mercury. This experiment revealed for the first time that all the three catalyst emitted metals were accumulated by mussels. The bioaccumulation increased in the following manner: Rh<Pt<Pd. Thus, the application of sentinel organisms in combination with modern trace analytical procedures in environmental impact studies does allow an assessment of the distribution and the degree of bioaccumulation of PGM in the environment, which is highly appreciated.

Investigation of pigments in medieval manuscripts by micro Raman spectroscopy and total reflection X-ray fluorescence spectrometry

Analytical pigment investigation can reveal important information for art-historians. The use of two micro-analytical techniques, micro Raman-spectroscopy and total reflection X-ray fluorescence, is shown to be very successful. These techniques give complementary information: Raman spectroscopy allows the identification of the different materials the pigment grains consist of, and total reflection X-ray fluorescence gives the average elemental composition of the sample.The latter is helpful to distinguish between the different palettes used by different artists or workshops. Samples can be taken with cotton wool swabs (Q-tips), which cause no visible alteration to the artefact. Such a sample allows both Raman-spectroscopy and total reflection X-ray fluorescence to be applied using less than 1 μg of material. This approach is illustrated with the pigment investigation of seven late-medieval Mercatellis manuscripts, kept in the Ghent University Library.

Pigment investigation of a late-medieval manuscript with total reflection X-ray fluorescence and micro-Raman spectroscopy

The use of micro-analytical techniques for the identification of artists’ pigments reveals a lot of information. Micro-Raman and total reflection X-ray fluorescence spectroscopy were applied to pigment investigations of several miniatures in the late-medieval Breviarium Mayer van den Bergh. The results demonstrate the possibility of distinguishing the different miniaturists who worked on this manuscript.

Survey of sampling techniques for solids suitable for microanalysis by total-reflection X-ray fluorescence spectrometry

A survey of solid sampling techniques is given, suitable for microanalysis or even ultramicroanalysis by total-reflection X-ray fluorescence (TXRF). A sample amount of 1 ng to 100 µg is placed on a clean, flat carrier usually made of quartz glass or Plexiglas ® . For quantification, a drop is added to the sample with a known amount of a single element serving as internal standard. Solid samples can be applied as small particles, fine powders, thin sections or deposits. Several techniques of solid sampling have been examined and one example of each technique is given demonstrating its suitability: direct placing of individual particles, suspension of powdered materials, collection of air dust by impaction, the touchstone technique for metals, laser ablation for local analysis, the Q-tip technique for paints and inks, freeze-cutting of organic materials and direct contamination control of wafers.

The influence of X-ray coherence length on TXRF and XSW and the characterization of nanoparticles observed under grazing incidence of X-rays

An approach to the chemical characterization and a study of the morphology of very fine fractions of nanoparticles on surfaces can be deduced from experiments using the grazing incidence X-ray Standing Waves (XSW) by means of Total Reflection X-ray Fluorescence (TXRF). Some theoretical aspects not considered until now for TXRF and XSW, e.g. the influence of coherence length of X-rays from different X-ray sources, the particle form, particle size and distribution, are presented and discussed. Results of numerical simulations of XSW-scans considering the modelling of particles are compared with the experimental data obtained from XSW experiments performed at a synchrotron radiation facility. Advantages and limitations of the applied techniques are discussed for the characterization of Au- and CdTe-nanoparticles.

X-ray standing waves : a method for thin layered systems

X-ray standing wave spectroscopy at grazing incidence (GI-XSW) is demonstrated to be a versatile method to characterize multilayer thin films and element distributions on a nanometre scale. In this work we present a measurement procedure and development of a computerized simulation tool to interpret measured intensities. Four different kinds of samples are investigated. First, thickness determination of a set of thin germanium layers on silicon ranging from 29 nm to 1 μm is presented, which demonstrates the wide dynamic range that is feasible and the limitations that occur. Second, analysis of a sample of gold clusters evaporated on an 80 nm polystyrene film on a silicon substrate is shown. Low contrast organic mono-, double or multilayers is the third kind of sample to be characterized by XSW. Finally, qualitative and quantitative characterization of a laser multilayer mirror utilizing XSW and a fast Fourier transform evaluation method are described. Measurement and simulation procedures for each kind of sample are outlined in this report as well as the possibilities and limits of this XSW method.

Element determination by total-reflection X-ray fluorescence spectrometry at the initial step of element speciation in biological matrices

Abstract Total-reflection X-ray fluorescence spectrometry (TXRF) is used for the simultaneous determination of Ca, Cu, Fe, K, Mn, Rb, Sr and Zn in 12 different vegetable foodstuffs and their cell fractions after mechanical cell breakdown. The vegetables are homogenized by liquid shearing (ultra-turrax treatment) in the presence of buffer. The homogenates are separated into cytosols (liquid fractions) and pellets (solid fractions) by centrifugation. The distribution of the elements between the fractions is determined. Before analyses all samples were digested with HNO3. The quick and simple method of cell breakdown as an initial step for speciation transfers Zn, Cu, Mn, Rb and K in significant percentages into the soluble form. Consequently, a large fraction of each of these elements is directly accessible to further analytical separation procedures. On average Sr, Ca and especially Fe are mainly bound to pellet components. TXRF proved to be an excellent analytical tool in these investigations. It requires only one internal standard and minute samples with simple preparation.

Determination of metals and their species in aquatic humic substances by using total-reflection X-ray fluorescence spectrometry

A combined analytical procedure, consisting of ligand exchange by ethylenediaminetetra-acetic acid (EDTA) off-line, size fractionation through multistage ultrafiltration (MS-UF) and metal determination using total-reflection X-ray fluorescence spectrometry (TXRF), has been developed for the speciation of heavy metals in selected aquatic humic substances (HS). Accordingly, natural HS/metal species somewhat preconcentrated by preparative ultrafiltration were reacted with equimolar amounts of dissolved EDTA as a function of time. Afterwards, a special MS-UF device was used for size fractionation of the HS under study and their metals species in the molecular mass range 1–100 kDa (six fractions), finally using TXRF (preferably with a Mo tube) for determination of the analytes (e.g. Cd, Cu, Fe, Mn, Ni, Pb and Zn) other than Al (determined by AAS). Thus, natural metal species in aquatic HS were revealed to be widely EDTA-inert, depending on the element, in contrast with those freshly formed. The TXRF measurements in HS were virtually unaffected by this matrix (up to 20 mg ml−1 HS) forming homogeneous “polymer” films on the sample carrier. Under routine TXRF conditions (10 μl sample, 300 s live time), detection limits in the lower ng ml−1 range and relative standard deviations between 4% and 7% (n=8) could be obtained in humic-rich water samples.

Choice of a suitable material for construction of a Battelle type impactor to minimize systematic errors in sampling of airborne dust

Systematic errors can occur when airborne dust is sampled with an impactor for subsequent element analysis. As could be shown, blank values, collection losses and memory effects are caused by the impactor and the material it is made of. Four different materials were chosen to build up a two-stage Battelle type impactor: Makrolon®, titanium, aluminium and stainless steel. The latter was applied without and with a coating of TiN. Air dust was collected on Vaseline® coated impaction plates and directly analyzed by total reflection X-ray fluorescence (TXRF). Up to 15 elements were determined simultaneously after internal standardization. Blank values arising from the impactor walls in contact with the gas flow were measured by sampling air from a clean bench. Relative collection losses were determined by sampling ambient air with two impactors in parallel and by comparing the two sets of results. Memory effects were measured by first collecting airborne particulates and then, after having replaced the impaction plates, pulling air through the impactor in a clean bench. The three effects led to relative systematic errors of a few % up to several 10% depending on element and impactor material. Stainless steel causing the largest errors has to be considered the least suitable material, even if coated with TiN. Aluminium led to moderate systematic deviations. Only titanium and Makrolon® were proven to be widely suitable impactor materials, the latter one, however, only when short sampling periods are applied.

Multielement analysis of biological reference materials by total-reflection X-ray fluorescence and inductively coupled plasma mass spectrometry in the semiquant mode

SummaryTotal-reflection X-ray fluorescence (TXRF) and inductively coupled plasma mass spectrometry (ICP-MS) were used for the analysis of two biological reference materials. The quantifications were carried out after addition of one single standard element which serves as an internal standard in both cases. The results of TXRF analysis were good to satisfactory. The method is therefore suitable for fast multielement analysis, because it needs no special calibration specimens. The results of ICP-MS analysis are at least in the order of magnitude of the certified values. In some cases recoveries fit very well. For quantitative analysis, however, the use of the standard addition method or the calibration with external standards is required.