R.D. Vis

Incorporation routes of elements into human hair; implications for hair analysis used for monitoring

A study has been made on the incorporation of some trace elements and minerals into human hair by measuring their distributions across hair diameters. For this study the Particle Induced X-ray Emission (PIXE) technique using the proton microbeam of the Vrije Universiteit of Amsterdam has been applied. Results of measurements on single hair strands at different positions in the root and outside the skin provide evidence that the elements not only can enter the cortex via the matrix but also via the hair root sheaths. Moreover, there are indications that the distribution of an endogenous element is not always homogeneously spread over a cross section of the hair. Endogenous Fe and Pb seem to be peaked on the periphery of the hair by natural means, while the elements S,Zn and Cu of the samples measured are found to be distributed homogeneously across the hair diameter. The consequences for hair analysis in use for monitoring the trace elements status of an individual are discussed.

Experimental comparison of synchrotron radiation with other modes of excitation of X rays for trace element analysis

Abstract Monochromated synchrotron radiation (SXRF), 17.5 keV photons from an X-ray tube (XRF) with Mo anode and 3 MeV protons (PIXE) were used to excite X-ray spectra from thin samples of standard reference materials. Relative detection limits derived from these X-ray spectra were calculated to compare the different excitation modes. XRF shows the highest detection limits, while protons and synchrotron radiation monochromated to 16.5 keV are comparable. Much lower detection limits (down to 0.1 ppm) are experimentally shown with synchrotron radiation monochromated to 9.1 keV. Results are in agreement with theoretical predictions. The advantage of the polarization of the synchrotron radiation has been discussed theoretically and shown experimentally.

The effect of dietary zinc deficiency on the mossy fiber zinc content of the rat hippocampus

SummaryThe effect of dietary zinc deficiency on the mossy fiber zinc content of the rat hippocampus was investigated using PIXE (Particle Induced X-Ray Emission) spectroscopy. Using the proton microbeam (60×60 μm), 2 mm linescans were made on hippocampal sections and the data were expressed as absolute zinc concentrations. Values of 55 and 136 ppm (dry weight) were found for the mean background zinc level and the maximum mossy fiber zinc level, respectively, in animals fed a control diet containing 50 ppm zinc. Treatment of these animals with dithizone caused about 50% reduction in the maximum mossy fiber zinc level. Feeding a zinc-deficient diet for 28 days did not cause a decrease in the mossy fiber zinc level, however, feeding the zinc-deficient diet for 90 days reduced the maximum mossy fiber zinc level by about 30%. The results are discussed in relation to the behavioral abnormalities that have been observed in zinc-deficient animals.

TTPIXAN — A package of computer programs for quantitative thick target PIXE analysis

Abstract We present the computer program TTPIXAN, developed recently in our group as a tool for quantitative thick target PIXE analysis. Our intention was to develop an accurate and general computer code which could be useful in all aspects of PIXE analysis, i.e. either for choosing optimal working conditions when planning an experiment, or afterwards, when performing quantitative analysis for a wide range of sample types and thicknesses. The program is suitable for proton excitation as well as for deuterons and He ions in the common range of excitation energies (0.5–4 MeV).

Ellipsoid X-ray focussing for synchrotron-radiation microprobe analysis at the SRS, Daresbury, UK

Abstract A focussing monochromator for synchrotron-radiation microprobe analysis has been made by bending and fixation of a Si(111) crystal onto an ellipsoidal mould produced by numerically controlled diamond cutting. Experiments were performed using 15 keV radiation from the SRS dipole line. Measured beam profiles, topograms and fluxes are compared with the results of a ray-tracing program. In the experiment the spot size has been reduced, if compared with a flat monochromator, by a factor of 1000 horizontally and by a factor of 15 vertically, in agreement with the calculations. The measured photon-flux density is 104 photons/(s mA μm2), suited for detecting trace elements of sub-ppm concentration in an organic matrix with a detection volume of the order of 10 μm diameter.

On the incorporation of trace elements into human hair measured with micro-PIXE

Abstract A study has been made on the incorporation of trace elements into human hair by measuring concentration distributions across hair diameters of selected samples using the Amsterdam proton microbeam. Because hair is considered as a recording filament, reflecting metabolic changes over a period of time, a hair of a young mother was plucked 4 months after delivery of her first child. No change in the Zn and Cu concentrations correlated with the period of gestation was observed. A strong increase of Ca in the distal end must be attributed to outside contamination. From a study of a hair root, including the root sheaths, it is found that the method of incorporation of sulfur (minor element) differs strikingly from the behaviour of the trace elements Zn, Cu, Fe and Ca. The Zn and Cu distributions provide evidence of a, not yet reported, transversal transcellular input route, in which the root sheaths play an important role. From the results it is deduced that Zn and Cu seem to be distributed homogeneously by nature, while Fe, present at a high level in the root sheaths, seems to be peaked by nature on the periphery. The results are discussed against the background of the range of values of concentrations of certain elements found in the literature.

A proton microbeam under construction

Abstract A proton microbeam is presently being assembled in our laboratory. A description of the various components and systems will be given, such as slit systems, magnetic lenses and the target chamber, including detectors, microscope and target scanning intruments. The figure of 2 μm is a critical lower limit in every respect. It represents both the accuracy of the positioning of the target and the resolving power of the microscope. It is therefore also a practical lower limit to the useful beam spot size.

The measurement of position dependent trace element concentrations with micro-proton induced X-ray emission

Abstract The extension of the Proton Induced X-Ray Emission (PIXE) technique to micro-PIXE is described here. This development involves the possibility of measuring trace element distributions on the ppm level with spatial resolution on the μm scale. The possible applications of the proton microprobe at our institute are described on the basis of measurements of element distributions across the diameter of human scalp hair.

Elemental trace analysis in serum using proton-induced X-ray flourescence

Abstract In order to perform a study of changes in concentrations of trace elements into the sera of nephritic patients, PIXE is applied to this type of samples. For six elements calibration curves are measured using distilled water solutions and also using the technique of standard addition to show the influence of matrix effects. To calculate these matrix effects a computer code is developed. A comparison is made between results obtained with protons, deuterons and alpha-particles of 2.5, 5.0 and 10.0 MeV respectively. In most samples more than ten elements are quantitatively determined. For two elements the results are compared with results of other analytical techniques such as atomic absorption sctroscopy.

RBS-PIXE analysis on μm scale on thin film high-Tc superconductors

Abstract To determine the stoichiometry of thin films of YBaCuO high- T c superconductors on a μm scale, a beam of 3.045 MeV αs was used. The RBS signal has been used to determine the metal concentrations and the 16 O(α, α) 16 O resonance reaction for the oxygen concentration determination. The metal concentrations were calculated by fitting the RBS spectra with the computer program RUMP. The oxygen concentration was calculated by comparing the resonance oxygen yield of the film with that induced in a pure MgAl 2 O 4 crystal as a standard. The YBaCuO film thickness was determined in the lateral direction in order to see whether there was a lateral gradient in the film thickness. The films were prepared in sets of two by electron gun evaporation, one on an Al 2 O 3 substrate and the other on a SrTiO 3 substrate. The latter sample has been annealed to get the required perovskite crystal structure. PIXE was used to check the films for contamination.