Chemical fractions

Boyle, E. A. (1988). The role of vertical chemical fractionation in controlling late Quaternary atmospheric carbon dioxide. /. Geophys. Res. 93, 701-715. 

Desbrow, C., Routledge, E.J., and Brighty, G.C. et al. (1998). Identification of estrogenic chemicals in STW effluent. 1. Chemical fractionation and in vitro biological screening. Environmental Science and Technology 32, 1549-1558. 

U and Th concentrations in secondary deposits precipitated from solution generally reflect relative abundances in the hydrosphere. Uranium is co-precipitated with CaCOs in subaerial environments on exsolution of CO2 (or evaporation), while the immediate daughter products are essentially absent. This represents extreme chemical fractionation of parent and daughter isotopes within the hydrosphere. 

The experimental studies cited below have isolated and tested the impact of caffeine, different methods of preparation, and different chemical fractions of coffee beans on serum cholesterol levels over a varied range of time periods. 

Gupta S.K., Chen K.Y. Partitioning of trace metals in selective chemical fractions of nearshore sediments. Environ Lett 1975 10 129-158. 

Jin Q., Wang Z., Shan X., Tu Q., Wen B., Chen B. Evaluation of plant availability of soil trace metals by chemical fractionation and multiple regression analysis. Environ Pollut 1996 91 309-315. 

Ma, L.Q. and Rao, G.N., Chemical fractionation of cadmium, copper, nickel and zinc in contaminated soils. J Environ Qual 1997a 26 259-264. 

Nissenbaum A. Distribution of several metals in chemical fractions of sediment core from the sea of Okhotsk. Israel J Earth Sci 1972 21 143-154. 

Huang QY, Chen WL, Guo XJ (2004) Chemical fractionation of Cu, Zn and Cd in two Chinese soils as influenced by Rhizobia. Commun Soil Sci Plant Anal 35(7-8) 947-960... 

During the past several years exciting advances have taken place in radioactive dating techniques—advances which have made it possible to determine unusually small isotope ratios and to determine the radioisotopic composition of individual chemical fractions and particle size fractions of extremely small samples. 

The basic idea in radioactive age-dating of rocks (from the Earth, Moon and meteorites) is to find the ratio of daughter to parent in an isolated system. Thus the age inferred is usually the solidification age which is the time since the last occasion when chemical fractionation was halted by solidification. (K-Ar dating gives a gas-retention age which can be slightly shorter.)... 

Spaccini R, Piccolo A (2007) Molecular characterization of compost at increasing stages of maturity. 1. Chemical fractionation and infrared spectroscopy. J Agric Food Chem 55(6) 2293-2302... 

Food odors are also important as attractants for traps both on their own or in combination with pheromone lures as synergists or additive attractants. Food odors can be used to improve the capture of species that do not have commercially available pheromone lures, of females that do not respond to traps with sex pheromones, and of immature stages. In a number of situations, pheromones combined with food odor are more attractive then either alone (Landolt and Phillips, 1997 Phillips et al., 1993 Trematerra and Girgenti, 1989). Food odor has an advantage over food bait packs because typically the insect is unable to develop on the chemical fraction containing the attractant in contrast to food bait packs. The effectiveness of food attractants can be diminished in environments that contain other food odors. 

The sample is usually ablated using a Nd-YAG ultraviolet laser (k = 266 nm the theory of laser light is given in Section 4.1). Earlier systems used an infrared laser, but chemical fractionation was found to be a problem (Jeffries et al. 1996). A movable stage and integral optical microscope allow... 

Jeffries, T. E., Pearce, N. J. G., Perkins, W.T., and Raith, A. (1996). Chemical fractionation during infrared and ultraviolet laser ablation inductively coupled plasma mass spectrometry - implications for mineral micro analysis. Analytical Communications 33 35-39. 

At steady-state, solid and liquid far from the interface tend to have the same concentration. Kinetic partitioning therefore brings solid-liquid partition coefficients close to unity and decreases chemical fractionation. The concentration profile in the liquid at distance x from the interface also reads... 

Since the denominator falls in the range Dt to 1, concentration in the solid is closer to that of the liquid away from the interface than equilibrium fractionation would require. Again, disequilibrium partitioning during crystal growth decreases solid-liquid chemical fractionation. 

Langmuir, C. H., Vocke, R. D., Hanson, G. N. Hart, S. R. (1978). A general mixing equation with applications to Icelandic basalts. Earth Planet. Sci. Letters, 37, 380-92. Larimer, J. W. (1967). Chemical fractionations in meteorites - I. Condensation of the elements. Geochim. Cosmochim. Acta, 31, 1215-38. 

After the labeling experiment, the biomass is harvested, chemically fractionated, derivatized, and, finally, in most cases analyzed by GC-MS (see below and Section IV.C). Electron impact ionization is used, which leads to fragmentation of the metabolite, so that not only the molecular ion is measured but also several fragments, a circumstance that makes the measured information more valuable for subsequent data evaluation. 

---