Single-element separation

Single-element Separation Extraction of Cs + ion is fairly difficult due to the small charge density of the atomic surface. Thus, calix-crowns were preferentially used for the extraction, because they trap Cs + ion not only by coordinating with the crown ring, but also by interaction with the n-electrons of the phenyl rings of the calixarene (382, 383). On the other hand, many reports appeared concerning extraction of Sr2+ from acidic solutions by crown ethers (384). 

An additional material based on the extractant octyl-phenyl-N,N-diisobutyl-carbamoylmethylphosphine oxide, or CMPO, (marketed under the name TRU-Spec) has also been widely utilized for separations of transuranic actinides (Horwitz et al. 1993a) but is also useful for uranium-series separations (e.g., Burnett and Yeh 1995 Luo et al. 1997 Bourdon et al. 1999 Layne and Sims 2000). This material has even greater distribution coefficients for the uranium-series elements U (>1000), Th (>10000), and Pa. As shown in Figure 1, use of this material allows for sequential separations of Ra, Th, U, and Pa from a single aliquot on a single column. Separations of protactinium using this material (Bourdon et al. 1999) provide an alternative to liquid-liquid extractions documented in Pickett et al. (1994). 

It was once believed that air was a single element, but by the fifteenth century ce, scientists began to question whether it was possibly at least two separate gases. Leonardo da Vinci was one of the first to suggest the air consisted of at least two gases. He even determined that one of them would support hfe and fire. 

J, J, Berzelius and his collaborator Wilheim Hisinger, isolated from a heavy mineral found in 1781 in a mine at Bastnas, Sweden, another similar and yet somewhat different "earth". This one was named ceria and the mineral cerite after the then recently discovered planetoid Ceres, It was believed at the time, that both yttria and ceria were single elements, but subsequent study showed each to be a mixture of oxides, the complete separation and identification of which required more than a century of effort. 

A gene expression profile consists of a single description line, starting with > , followed by one or more data lines. The data consist of elements, separated by a space or a new line. Each element consists of a UniGene identifier and an expression value separated by a colon. 

The response of an atom to the strength of the external magnetic field is different for different elements, and for different isotopes of the same element. The resonance frequencies of most nuclei are sufficiently different that an NMR experiment is sensitive only to a particular isotope of a single element. The frequency for H is 200 MHz at 4.7 T, but that of l3C is 50.4 MHz. Thus, when recording the NMR spectrum of an organic compound, we see signals only for H or 13C, but not both H and l3C NMR spectra are recorded in separate experiments with different instrument settings. 

Native elements are minerals composed of a single element. This group also includes natural alloys, which are mixtures of two metals. Based on their physical properties, the native elements can be separated into three divisions metals (such as Ag, Au, Cu, Fe, Hg, Pb, Pt, Sn), semi-metals (such as As, Bi, Sb, Te), and non-metals (C, S, Se). 

Mixed Elements. Clearly, it would be advantageous from a nomenclature point of view to have elements composed by combinations of operations via Og, Oc, and Ob. These can be easily introduced but are also subject to reactivity restrictions, leading to a third rule. Rule 3 binary element combinations formed by operations not part of the ring under consideration behave as single elements and cannot be separated into jnore simple elements. Togther with Rules 1 and 2, this Rule 3 eliminates ambiguous reactions in most of the cases of interest. There may be more complex combinations that Rules 1, 2, and 3 do not completely define. In each case, isomorphic or homomorphic elements may exist but can be reached as per discussion above. 

Before the 1960 s, the analysis of toxic elements in airborne materials employed separations and colorimetric determination for single-element problems, or spectrographic methods for multielement, multisample studies. Variable matrices in most aerosols sampled had prevented sensitive, but interference-prone, flame-emission methods from attaining much usage. The increased concern over the environmental effects of toxic elements in the late 1960 s resulted in a need for greater sensitivity and ease of operation in measurements of these elements. The many laboratories with increased responsibilities found AAS most useful because of its accuracy, sensitivity, and relative lack of matrix effects, plus the low cost of the equipment. 

---