Reinhold Klockenkämper

Determination of the critical thickness and the sensitivity for thin-film analysis by total reflection X-ray fluorescence spectrometry

Total reflection X-ray fluorescence is a new powerful tool for simultaneous multielement determinations of relatively rough and thin films. For the excitation with a Mo-tube the critical thickness of “infinitely” thin films was estimated to be about 4 μn for biological tissues, 50 nm for mineral powders and 2 nm for metal smears. Moreover, for 75 elements the relative sensitivities of their K- or L-lines were calculated theoretically by means of fundamental parameters. The relative sensitivities for 25 elements were also measured in three kinds of samples: a nearly matrix-free type, a mineral and an organic type. They were found to be equal within a margin of 8% showing the absence of matrix effects. They correspond to the theoretical values, to within 9%, which demonstrates the validity of theory and fundamental data. With the aid of these relative sensitivities, a simple calibration is possible by means of a single internal standard element.

Elemental analysis of environmental samples by total reflection x-ray fluorescence : a review

A review of total reflection x-ray fluorescence (TXRF) as an effective excitation mode for energy-dispersive x-ray spectral analysis is presented. The instrumental conditions of excitation under grazing incidence (ψ < 0.1°) are emphasized and the analytical features of powerful detection and simple and reliable quantification are characterized. The applicability of TXRF to environmental analyses is illustrated by some typical examples. The analysis of pure water samples leads to detection limits at the ppt (ng/l) level. A special matrix separation is only needed for river, sea and waste waters. The analysis of air dust is directly possible with a sampling volume of 1 m 3 and a sampling time of 1 h. Organ tissue can be analysed down to the lower ppm range after freeze-cutting of μm thick sections. Plant material has to be pulverized and digested prior to analysis, e.g. with nitric acid In combination with a chromatographic separation, speciation is made possible for small 0.5 ml fractions, e.g. for vegetable foodstuffs. For all these applications a multi-element determination can be carried out, for about 20-25 elements simultaneously. Simple and reliable quantification is effected by internal standardization. The reliability of the method has been proved by intercomparison tests. Second-generation instruments that are compact and user-friendly are now commercially available.

Analysis of pigments and inks on oil paintings and historical manuscripts using total reflection X-ray fluorescence spectrometry

Old oil paintings and illuminated historical manuscripts are valuable objects of cultural heritage. Pigments and inks once used for these artefacts today allow insights of art historical or archaeological relevance. For their identification, a number of non-destructive spectroanalytical methods can be applied. This paper first gives a historical review and describes fundamentals of optical and x-ray fluorescence spectrometry including instrumentation and analytical characteristics. The variant of total reflection x-ray fluorescence (TXRF) is shown to be a highly convenient tool for the characterization of inorganic pigments and inks. Since only micro-samples are needed, a very gentle sampling technique can be applied. It consists of rubbing a dry cotton-wool bud (Q-tip) over the painted surface without causing any visible damage. Only a minute amount of a few micrograms is removed from the object, transferred to a glass carrier and analyzed by TXRF. Some remarkable examples of TXRF analysis of old paintings and illuminated manuscripts are given. Rather than emphasizing the analytical details, the archaeometric potential of the method is illustrated. Copyright

Separation and enrichment of palladium and gold in biological and environmental samples, adapted to the determination by total reflection X-ray fluorescence

The reductive co-precipitation of trace and ultra-trace elements together with mercury followed by complete evaporation of the mercury makes it possible to determine palladium and gold by total reflection X-ray fluorescence. Both elements can be detected without interferences at optimal sensitivity in the pg range. Thus, detection limits of, e.g., 2.5 ng L-1 for palladium and 2.0 ng L-1 for gold, in urine, were obtained. The precision was determined to 0.04 at a palladium concentration of about 200 ng L-1 urine and to 0.19 at a gold concentration of only 18 ng L-1. The recovery for a urine sample spiked with known amounts of palladium and gold amounted to > 95%. Results of the combined procedure are given for the determination of palladium and gold in the urine of non-exposed and occupationally exposed persons and in some other environmentally relevant samples.

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.

Atomic emission and atomic absorption spectrometric analysis of high-purity powders for the production of ceramics

SummaryDirect analysis methods and multistage combined analytical procedures for the determination of impurities at the μg/g level and the upper ng/g level in high-purity powders of Al2O3, AlN, Si3N4 and SiC are described. Results obtained with a novel direct slurry-atomization technique using a Babington nebulizer and inductively coupled plasma optical emission spectrometry (ICP-OES) are presented. A comparison of analysis results of combined analytical procedures including wet chemical decomposition and determinations with graphite furnace atomic absorption spectrometry (ETAAS) or ICP-OES with those of slurry-atomization ICP-OES show the capabilities of this technique for routine analysis in production control. Detection limits for Al, B, Ca, Co, Cu, Fe, Mg, Mn, Si, Ti, W, V, and Zn in the matrices mentioned are between 0.03 and 2.5 μg/g. For elemental concentrations ⩾ 10 μg/g relative standard deviations of the measurements are generally below 10%. The technique is shown to be a powerful tool for trace determinations in powder samples. This is shown by its use for analysis of a series of the ceramic powders mentioned and comparative results of other direct techniques such as total reflection X-ray fluorescence spectrometry and instrumental neutron activation analysis.

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.

Total-reflection X-ray fluorescence moving towards nanoanalysis: a survey ☆

Abstract Within the last 20 years, total-reflection X-ray fluorescence (TXRF) has been applied to solve a lot of analytical problems. It turned out that TXRF gives an actual approach to nanoanalysis in three different fields: (i) for tiny samples with only nanogram sample amounts; (ii) for low traces with concentrations down to ng/l; (iii) for surfaces and shallow layers with some nanometer thickness. After a short tutorial on total-reflection of X-rays and the formation of standing waves, several selected examples are given for each of the three fields of nanoanalysis. Finally, a critical evaluation of TXRF and its future prospects are given in this survey article.

Quantification in total reflection X-ray fluorescence analysis of microtome sections

Abstract Thin sections of biological materials were prepared by means of a freezing microtome (10 μm thick, 10 mm in diameter; 200 μg), placed on quartz-glass carriers and analyzed by total reflection X-ray fluorescence (TXRF). Numerous element traces of physiological relevance were determined simultaneously. The quantification was based on spiking the sections with an internal standard element (gallium); standard reference materials were analyzed with 10% accuracy in the μg g -region. The easy and fast micro and trace analytical method is very suitable for screening and monitoring tasks in biology and medicine.

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.