Standardization in biological analyses of aluminum: what are the needs?

A review of the literature of aluminum (Al) levels in biological samples, particularly Alzheimer's disease (AD) brain, reveals a lack of interlaboratory agreement at both the bulk and microprobe levels. One possible reason for this controversy may be the methods chosen for quantitation and standardization. Currently, the major problem affecting quantitation of Al at the bulk level is the lack of low-Al-concentration, matrix-matched certified standards.

"Standardless" quantitative electron probe microanalysis with energy-dispersive X-ray spectrometry: is it worth the risk?

"Standardless" procedures for quantitative electron probe X-ray microanalysis attempt to eliminate the need for standardization through calculation of standard (pure element) intensities. Either "first principles" calculations, which account for all aspects of X-ray generation, propagation, and detection, or "fitted standards" calculations, which use mathematical fits to measured intensities from a limited set of pure standards, can form the basis for standardless analysis. The first principles standardless analysis procedure embedded in the National Institutes of Health/National Institute of Standards and Technology comprehensive X-ray calculation engine and database, Desktop Spectrum Analyzer, has been tested against spectra measured on NIST standard reference materials, research materials, and binary compounds.

Trypanosoma cruzi: elemental composition heterogeneity of cloned stocks.

Concentrates of the epimastigote stage of Trypanosoma cruzi stocks derived from single cell clones and cultured under identical conditions display a spectrum of 'colors' varying from dark brown to milk white. The color of the concentrate is reproducible for a parasite stock. An essential component of the culture medium for epimastigote growth is hemin, an iron-containing compound.

Quantitative X-ray mapping of biological cryosections.

The potential for applying X-ray mapping to the elemental microanalysis of biological cryosections is discussed. Methods are described for acquiring and processing data, including use of the top-hat digital filter to remove the average effects of the background contribution. Practical considerations for X-ray mapping are discussed in terms of typical counts per pixel and minimum detectability which depends on the number of pixels chosen to integrate the signal.

Separation of overlapping core edges in electron energy loss spectra by multiple-least-squares fitting.

A multiple-least-squares fitting procedure for quantitating electron energy loss spectra is demonstrated on some strongly overlapping core edges. The method, first applied by Shuman and Somlyo [Ultramicroscopy 21 (1987) 23], takes into account plural inelastic scattering and can be applied under conditions of non-uniform sample thickness where Fourier deconvolution techniques are invalid. By using appropriate reference spectra generated from pure compounds, quantitation of potassium and calcium (L23 edges) is possible in the presence of carbon (K edge), and sulfur in the presence of phosphorus (L23 edges).