Mineral borates, the primary industrial source of boron, are found in a large variety of compositions. One such source, kernite (Na2B4O6(OH)2·3H2O), offers an array of challenges for traditional electron-probe microanalysis (EPMA)—it is hygroscopic, an electrical insulator, composed entirely of light elements, and sensitive to both low pressures and the electron beam. However, the approximate stoichiometric composition of kernite can be analyzed with careful preparation, proper selection of reference materials, and attention to the details of quantification procedures, including correction for the time dependency of the sodium X-ray signal. Moreover, a reasonable estimation of the mineral's water content can also be made by comparing the measured oxygen to the calculated stoichiometric oxygen content. X-ray diffraction, variable-pressure electron imaging, and visual inspection elucidate the structural consequences of high vacuum treatment of kernite, while Auger electron spectroscopy and X-ray photoelectron spectroscopy confirm electron beam-driven migration of sodium and oxygen out of the near-surface region (sampling depth ≈ 2 nm). These surface effects are insufficiently large to significantly affect the EPMA results (sampling depth ≈ 400 nm at 5 keV).

The intracellular distribution of the elements carbon, nitrogen, and oxygen was measured in cultured rat hepatocytes by energy dispersive electron probe X-ray microanalysis of 100-nm-thick freeze-dried cryosections. Electron irradiation with a dose up to 106 e/nm2 caused no or merely negligible mass loss in mitochondria and in cytoplasm. Cell nuclei lost carbon, nitrogen, and—to a clearly higher extent—oxygen with increasing electron irradiation. Therefore, electron doses less than 3 × 105 e/nm2 were used to measure the subcellular compartmentation of carbon, nitrogen, and oxygen in cytoplasm, mitochondria, and nuclei of the cells. The subcellular distribution of carbon, nitrogen, and oxygen reflects the intracellular compartmentation of various biomolecules. Cells exposed to inorganic mercury before cryofixation showed an increase of oxygen in nuclei and cytoplasm. Concomitantly the phosphorus/nitrogen ratio decreased in mitochondria. The data suggest mercury-induced production of ribonucleic acid (RNA) and decrease of adenosine triphosphate (ATP). Although biomolecules cannot be identified by X-ray microanalysis, measurements of the whole element spectrum including the light elements carbon, nitrogen, and oxygen can be useful to study specific biomolecular activity in cellular compartments depending on the functional state of the cell.

Low-voltage energy-dispersive X-ray microanalysis has a number of distinct advantages for measuring the concentration of light elements (Z = 11−20) in a largely organic matrix. Between 10 and 4 kV, there is a 50-fold decrease in the size of the incident beam-specimen interaction volume which enables discrete subcel-lular compartments to be analyzed. Experiments with mineral and organic samples of known chemical composition show that two of the most widely used analytical algorithms are capable of providing quantitative data at accelerating voltages as low as 5 kV. This technique is used at 5 kV to analyze frozen hydrated fracture faces of leaves of the tea plant which are known to contain aluminium. Higher levels of aluminium are found in the cell walls and are associated with increased levels of silicon and magnesium. The advantages and disadvantages of the experimental approach are discussed in relation to analysis carried out at higher voltages.