Suggestions for the quantitative X-ray microanalysis of thin sections of frozen-dried and embedded biological tissues

When a microregion in a thin section of frozen-dried and embedded tissue is analysed by the conventional electron-probe X-ray continuum-normalization method, the measured quantity is in mmol of element per kg of embedded specimen. As each microregion contains an unknown amount of embedding medium, this quantity generally lies indeterminately somewhere within the wide range between mmol of element per kg of hydrated tissue and mmol of element per kg of dehydrated tissue. However, if a ‘tag’ element is incorporated in the embedding medium, the contribution of the medium to the local continuum count in each probed field should be measurable, and the X-ray data may then unambiguously yield mmol of element per kg of dehydrated tissue. This result should not be affected by shrinkage on freeze-drying or by incomplete replacement of water by embedding medium. The same X-ray data can additionally provide estimates of mmol of element per unit volume, mmol of element per kg of hydrated tissue and local dry-mass fraction. However, these estimates are subject to errors due to tissue shrinkage, incomplete replacement of water and beam damage.     

盐及盐卤中微量铁铝钙镁的连续测定

介绍了用ＥＤＴＡ络合滴定法连续测定盐及盐卤中微量铁铝钙镁的原理和步骤。回收率在９８．５％～１０３．９％之间，方法简便，具有连续快速的特点。     

激光探针等离子体质谱测定NIST硅酸盐玻璃标样中痕量元素

采用激光探针等离子体质谱技术 ,以 42 Ca为内标 ,经预熔样处理 ,获得 NIST硅酸盐玻璃标样中 2 4种痕量元素 (Rb、Sr、REE、Th、U等 )的含量。结果表明 :方法的检出限在取样孔径 5 0 μm条件下可达 <1 0 -7(U、Th)～ <1 0 -6(REE) ,以 NIST61 2的一点为标准测定其它点 ,大多数元素的精密度优于± 1 0 % ;以NIST61 2为标准测定 NIST61 0 ,大多数元素的准确度优于± 1 0 %。     

The cryopuncher: A pneumatic cryofixation device for X-ray microanalysis of tissue specimens

A cryopunching device is described which allows cryofixation of tissue specimens by quick contact with a precooled copper surface during excision. The advantage of the cryopuncher for analytical electron microscopy of cells and tissues in defined functional states is illustrated by electron probe X-ray microanalysis of freeze-dried cryosections from rat liver and dogfish kidney. In comparison with results obtained from specimens plunged into liquid propane, cryopunching in situ results in similar preservation of morphology and remarkably improved intracellular K/Na ratio.     

The influence of oxide surface layers on bulk electron probe microanalysis of oxygen—application to Ti-Si-O compounds

This paper discusses a generalized method to measure with the electron probe microanalyzer (EPMA) the oxygen in a material containing a surface oxide layer. The continuum background is the most difficult to measure, particularly for materials in which oxygen-free samples cannot be produced. The method depends on the preparation of either oxygen-free samples or well characterized oxygen-containing samples. Specific application of the method to the Ti-Si-O system is discussed. In addition, measurements of oxide surface-layer thickness of 3.6–8.0 nm on Ti and Ti-Si compounds were obtained using EPMA and a scanning Auger microprobe (SAM). The nature of the oxide surface layers was shown using x-ray photoelectron spectroscopy (XPS).     

A generalization of atom location by channelling enhanced microanalysis

The technique of atom location by channelling enhanced microanalysis (ALCHEMI), has limitations in practical application. A generalization of this technique, with the underlying idea that additional relationships can be generated by performing these experiments at an appropriate number of orientations depending upon the stoichiometry of the original compound has been developed. The precise number of orientations required to solve the distributions in a whole class of related compounds is expressed in terms of the stoichiometry of the original compound along with the alloying additions.     

A section press and low elemental support for enhanced preparation of freeze-dried cryosections

A press- and specimen holder system is described, whereby thin, freeze-dried cryosections can be obtained more conveniently and with greater protection against contamination and harmful temperature fluctuations. The use of a grid and retainer assembly as the basic working unit, greatly facilitates low temperature work particularly when delicate grids are preferable from an analytical point of view. A new press has been constructed in order to keep the sections permanently pressed during freeze-drying and rewarming. The press also protects the sections during transfer to an external freeze-dryer.     

Analytical electron microscopy of aluminium alloys

X-ray microanalysis and electron energy loss spectroscopy of thin foils constitute the important techniques of high resolution chemical analysis using the electron microscope. The technique of x-ray microanalysis is discussed in this paper with particular emphasis on the study of aluminium alloys using a dedicated scanning transmission electron microscope (stem). The principle of determining chemical composition from observed x-ray peak intensities including the absorption of x-rays and beam broadening in thin foils are considered. The accuracy of peak intensity measurement and detection limits in x-ray microanalysis are illustrated with reference to Al-Mn alloys. The Cliff-Lorimer (k) factors for manganese, iron and copper with respect to aluminium were obtained from standard samples. Identification of phases in 1100 and 1200 aluminium and 3008 (Al-Mn-Zr) alloy were carried out from measured intensities of x-ray peaks. The experimental results emphasize the value of developing techniques for extracting the particles from the aluminium matrix. The transition phases formed in Al-6%Zn-3%Mg and Al-4% Cu were investigated by micro-diffraction and x-ray microanalysis.     

Chemical cryoprotection for structural studies

With the ascendency of techniques for ultrarapid cooling and the successful control of ice crystal damage by purely physical means, it has become necessary to make a case for the continued use of chemical antifreeze agents in any circumstances. These circumstances include the need to explore tissues deeper than those superficial layers, whose morphology can be preserved by ultrarapid cooling, the avoidance of superficial areas of damage inflicted by dissection and tissue slicing, and situations where the growth of ice crystals must be controlled throughout the specimen, as for example for the cutting of frozen sections. The control of ice crystal damage would ideally be by the avoidance of any freezing at all but in practice can be seen in terms of the control of ice crystal size, which in turn depends on the density of nuclei that develop in the specimen and the rate of accretion of water molecules to the crystallites that form on these nuclei. Chemical antifreeze agents act in a variety of ways to increase the density of nuclei and/or to reduce the rate of growth of ice crystals: by promoting nucleation, by enhancing subcooling and by increasing the viscosity of the extracellular medium. In this way, large numbers of small ice crystals are produced. The different types of cryofixative agent each have their own advocates, advantages, special applications and drawbacks and these must be taken into account when considering the range of methods available for the analysis of cryofixed material.     

聚冠醚的合成与性质Ⅳ.：微量镉的分离,富集与测定

报道了以新的双酚Ａ型聚冠醚为交换柱的固定相，分离、富集并测定微量镉离子的方便而满意的方法。