Unsaturation index

Biodiesel is normally produced by starting from vegetable oils having an IV of <130, that is, having a low unsaturation index, such as rapeseed oil (IV = 110-115), sunflower oil (IV = 120-130) and soybean oil (IV = 125-135). 

Effects of Water-column Recycling and Sediment Diagenesis on the Alkenone Unsaturation Index... 

Several investigators have conducted laboratory studies of the effects of degradation on the alkenone unsaturation index. In the early history of the development of the UI7 index. 

Nearly all culture calibration studies predict higher growth temperatures for the same unsaturation index than postulated by the Prahl et al. (1988) regression, although several (Conte et al. (1998a) and G. oceanica cultures of Sawada et al. 

It should be possible to test the fidelity of alkenone SST reconstructions with an independent paleothermometer such as 5 0. There are a number of reasons why this comparison is not straightforward, however. First, many planktonic foraminifera live below the mixed layer for part or all of their life cycle. Comparing their isotopic temperatures with the unsaturation index of the alkenone producers, which must live in the photic zone, may not yield consistent estimates of past temperature changes. Many foraminifera have seasonal cycles of production far more pronounced... 

Villanueva J., Grimalt J. O., Cortijo E., Vidal L., and Labeyrie L. (1998) Assessment of sea surface temperature variations in the central North Atlantic using the alkenone unsaturation index (U37). Geochim. Cosmochim. Acta 62, 2421—2427. 

The unsaturation index UN can be expressed by a more general form, called multiple bond count, as... 

Unsat index multiple bond descriptors Unsat-p index multiple bond descriptors unsaturation index multiple bond descriptors unsaturation number multiple bond descriptors unsaturated bonds multiple bond descriptors... 

CoccoUthophores produce long-chain alkenones that have proved particularly useful for palaeo-temperature reconstruction they can be found in almost all marine sediments from the present day back to at least 140 million years, and are remarkably unaffected during sedimentation and burial. It turns out that in order to maintain the flexibility of their cell membranes, coccolithophores alter the number of double bonds in the alkenone chain in response to temperature. Laboratory experiments using cultures of Emiliani huxleyi have shown that the relative abundance of alkenones containing 37 carbon atoms and two double bonds (C37 2) is higher in cooler waters, while the relative abundance of alkenones containing 37 carbon atoms and three double bonds (C37-3) is higher in warmer waters (Prahl Wakeham 1987). The alkenone unsaturation index, Ul, is thus defined as ... 

A number of research groups now utilise such techniques for palaeoceanographic studies, so comparability of data between laboratories is crucial. In a recent study, twenty four laboratories were provided with eight test samples and asked to measure U 7, the alkenone unsaturation index, and alkenone concentrations (RoseU-Mele et al. 2001). The interlaboratory difference in Uk temperature estimates was <2.1 °C, which is slightly higher than the... 

It was found from the analysis of laboratory cultures and field samples that the extent of unsaturation (number of double bonds) in these long-chain ketones varies linearly with growth temperature of the algae over a wide temperature range (Brassell et al. 1986 Prahl and Wakeham 1987). To describe this, an unsaturation index was suggested, which in its simplified form is defined by the concentration ratio of the two... 

Calibration was then made with the growth temperatures of laboratory cultures of different hapto-phyte species and with ocean water temperatures at which plankton samples had been collected. From these data sets, a number of different calibration curves evolved for different species and different parts of the world ocean so that some doubts arose as to the universal applicability of the unsaturation index. In a major analytical effort, Muller etal. (1998) resolved the complications and arrived at a uniform cahbration for the global ocean from 60°N to 60°S. The resulting relationship. 

The index of hydrogen deficiency (sometimes called the unsaturation index) is the number of K bonds and/or rings a molecule contains. It is determined from an examination of the molecular formula of an unknown substance and from a comparison of that formula with a formula for a corresponding acyclic, saturated compound. The difference in the numbers of hydrogens between these formulas, when divided by 2, gives the index of hydrogen deficiency. 

The index of hydrogen deficiency (unsaturation index), U, that corresponds to the preceding formula is calculated easily by applying the relationship... 

These are very simple examples, but provide a plan of attack for the problems at the end of the chapter. It is highly unlikely that an analyst can identify a complete unknown by its IR spectrum alone (especially without the help of a spectral library database and computerized search). For most molecules, not only the molecular weight, but also the elemental composition (empirical formula) from combustion analysis and other classical analysis methods, the mass spectrum, proton and C NMR spectra, possibly heteroatom NMR spectra (P, Si, and F), the UV spectrum, and other pieces of information may be required for identification. From this data and calculations such as the unsaturation index, likely possible structures can be worked out. 

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