Availability of elements

Recently, some hght was shed on these and other compounds as well as on their structures and properties. Today it may be considered that some of the mistakes made earher could have been avoided by the availability of elements or compounds of higher purity, and thereby have prevented the incorporation of unexpected impurities. In this context it is important to note some experimental principles of solid-state synthesis that should be considered In solid-state synthesis, great attention should be always dedicated to the purity of the starting materials, the purity of the container material (and gas atmosphere) used in the reaction, and the control and adjustment of the reaction conditions in order to finally obtain a high yield product... 

Que Hee SS. 1994. Availability of elements in leaded/unleaded automobile exhausts, a leaded paint, a soil, and some mixtures. Arch Environ Contain Toxicol 27 145-153. 

Organochlorine pesticides and OPPs have been determined mainly using GC, because of the stability and volatility that most of them show under chromatographic conditions and, particularly, the availability of element-selective detectors that display high selectivity for OCPs (electron-capture detector, ECD), and OPPs (flame photometric detector, FPD, and nitrogen phosphorus detector, NPD). Mass spectrometry-based detection is also more popular in GC than in HPLC (1,2,12,16). 

Information on the abundance of elements comes from diverse sources. Most elements are obtained from minerals in the Earth s crust. The availability of elements therefore depends on the crustal abundance, which can be estimated by analyzing representative samples of minerals. The abundances of elements vary enormously, from common ones such as oxygen and silicon... 

Forest chemistry appears to be related to climate (mainly amounts of precipitation), geographical location (e.g. maritime influences) and the availability of elements in the soil (Jayasekera, 1993). Furthermore organisms are quite diverse and highly adaptive in element requirements and particularly in their tolerances. Due to the specific environment in an ecosystem without marked seasonal variations, predominantly poor soils and factors like high levels of precipitation, humidity or temperature, trees from tropical rain forests might have a rather dilferent chemistry from trees of the Northern Hemisphere. In order to understand the chemistry of heavy metals particularly in tropical forests more information is needed. 

A further, erueial parameter that must be considered is that of elemental sustainability. This eoncept relates to the availability of elements, and combines the reserves available with the (current) rate of use to provide an estimate of the time the reserves will last. Obviously, this will reduce if a new technology emerges that utilises the element in question - for relatively scarce elements, this could be quite a drastic reduction. 

The thermal cluster model is a complicated variant of percolation theory, assuming molecular mobility availability of elements, forming percolation cluster (in the polymers case - statistical segments). In this case the relationship is true [19] ... 

The composition of the soil and the availability of elements from it to plants are determined by the parent rock type, climatic actions, living organisms in the soil, soil management practices, and environmental pollution. The specific chemistry of lead in the soil is affected by... 

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