Extraction enhancement factor

Three methods for trace metal preconcentration were examined liquid-liquid extraction aided by a chelating agent, concentration on a synthetic chelating resin and reductive precipitation with NaBTLt. The latter method gave 1000-fold preconcentration factors with total recovery of Pb and other elements17. Preconcentration of nanogram amounts of lead can be carried out with a resin incorporating quinolin-8-ol (3)18. Enhancement factors of 50-100 can be achieved by such preconcentration procedures followed by determination in a FLA (flow injection analysis) system limits of detection are a few pg Pb/L19. 

A similar procedure is followed in the determination of Fe(II) with 2-nitroso-5-diethylaminophenol using ion pair extraction into chloroform. The enhancement factor achieved experimentally is 47. The detection limit for Fe(II) is 8 x 10 moll which is three to four times better than that obtained by conventional absorption spectrometry. The detection limit is governed by the background signal originating from the impurity of Fe(II) contained in the reagent. 

Despite these mechanistic intricacies and uncertainties, it is possible to extract considerable information from the electrochemical behavior. When two separate redox couples are observed, it is possible to determine the ratio KJKi, the factor of electrochemically-enhanced cation binding that occurs upon electrochemical switching. The enhancements observed always follow the trend Li >Na >K. This result is expected in view of coulombic considerations. Factors as high as 10 were observed for Li cation and lower values, typically 10 were observed for K [7]. Although these enhancement factors exhibit a clear selectivity, the overall binding... 

Lastly, Jakasa et al. [102] observed a threefold increase in the absorption of polyethylene glycols through skin eroded by 5 % SLS, as opposed to Ortiz et al. s decrease [101], seemingly attributable to a more severe barrier damage secondary to heightened SLS concentration. Nonetheless, enhancement factors for penetration extracted from these few studies with chemical damage are modest to none. 

Evidence for a diffusible or extractable hormonal factor in embryos and axes has been mentioned above with respect to three seeds—C. maxima, Ricinus communis, and P, ponderosa. If these promotive factors were gibberellins one would expect applied GA to substitute for the embryo or axis. In Cucurbita and Pinus the axis and embryo cannot be replaced by GA and thus the stimulatory factor in the embryo is not likely to be GA alone. Isolated endosperm of Ricinus, however, does respond to GA by showing enhanced activity of fructose-1,6-diphosphatase, as it does to embryonic extracts. 

Thermionic, thermal-field, and FE zone boundary for an emitter with the WS of 4.5 eV. In addition, FE zones with WSs of 4.0 and 5.0 eV are presented. The down arrow on the x axis indicates the field at which the I-T curve was measured. (Reprinted from Carbon, 43(13), Lim, S.C. et al.. Extracting independently the work function and field enhancement factor from thermal-field emission of multi-walled carbon nanotube tips, 2801-2807, copyright (2005), with permission from Elsevier.)... 

Lim SC, Jeong HJ. et al., Extracting independently the work function and field enhancement factor from thermal-field emission of multi-walled carbon nanotube tips. Carbon, 2005.43(13) 2801—2807. 

The first example of the utilization of MOFs for solid-phase extraction (SPE) was reported by Yan s group in 2006. Copper(II) isonicotinate [Cu(4-C5Fl4N- 00)2(1320)4] MOF was dry-packed in a precolumn for flow injection SPE on-line coupled with high-performance liquid chromatography (FIPLC) for the determination of trace polycyclic aromatic hydrocarbons (PAFIs) in coal fly ash and local water samples. Enhancement factors from 200 to 2337 for the studied PAFIs ranged were achieved, depending on the shape, size, and hydrophobic property of the PAHs. Recently, Zn(BTA)2 (BTA = benzotriazole) and MOF-5 were also explored as novel sorbents for the SPE of trace benzo[a]pyrene in edible oils and PAFIs in environmental matrices, respectively. 

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