Fluorescence with isooctane

Dunn and Stich [78] and Dunn [79] have described a monitoring procedure for polyaromatic hydrocarbons, particularly benzo[a]pyrene in marine sediments. The procedures involve extraction and purification of hydrocarbon fractions from the sediments and determination of compounds by thin layer chromatography and fluorometry, or gas chromatography. In this procedure, the sediment was refluxed with ethanolic potassium hydroxide, then filtered and the filtrate extracted with isooctane. The isooctane extract was cleaned up on a florisil column, then the polyaromatic hydrocarbons were extracted from the isoactive extract with pure dimethyl sulphoxide. The latter phase was contacted with water, then extracted with isooctane to recover polyaromatic hydrocarbons. The overall recovery of polyaromatic hydrocarbons in this extract by fluorescence spectroscopy was 50-70%. 

Lamparczyk (1992) provided detailed methods for the sample preparation and TLC determination of fecal bile acids (cholic, chenodeoxycholic, deoxy-cholic, lithocholic, and ursideoxycholic acids). After the sample is cleaned up by liquid-liquid extraction, from 2 to 20 a1 of purified fecal bile solution (no more than 20 p,g of bile acids) is spotted in the preadsorbent zone of a 20 X 20-cm silica gel plate. The plate is developed in isooctane-2-propanol-acetic acid (30 10 1) for 40 min, dried, and developed again with isooctane-ethyl acetate-acetic acid (10 10 2) for 65 min. For quantitative analysis, the plate is dipped for 2 sec into a 0.2%, 2,7-dichlorofluorscein ethanol solution. Bile acid fluorescence is measured with a TLC scanner and the results calculated by the peak-height method. Rivas-Nass (1994) evaluated the influence of temperature, ionic strength, mobile-phase pH, and addition of modifiers to the solvent system on the silica gel TLC of bile acids. 

The experimentally obtained values show larger divergence based on alkane fluorescence measurement. Walter et al. [148] and Luthjens et al. [65,128] published 0.8-0.9. Later the latter authors modified their value to 0.65 [149]. In solutions of isooctane, cyclohexane, or -hexane with naphthalene, Sauer and Jonah established this value as 0.5 0.1 this singlet formation probability is approximately constant during the decay of charged species up to 70 nsec [150]. In final product experiments/ = 0.34 [151], 0.53, and 0.47 [84] was estimated for cyclohexane, cix-decalin, and trans-6eca m, respectively. The low value for cyclohexane is due to the ionic reactions before recombination. 

In the presence of excess of cadmium ions, [Cd2+]/[S2-] = 2, Figures 3.4.3A and 3.4.3B show the fluorescence spectra at various water content. The unchanged spectra with the excitation wavelengths indicate a lower size distribution of the particles formed in mixed reverse micelles than that obtained in the case of the Cd(N03)2/ HMP/AOT/isooctane/water reverse micellar system. The shift of the emission maximum with the water content, w, can be related to the increase of the average size of the particles. For a sample synthesized for a given experimental... 

FIGURE 5-52. Examples of normal phase separations, (a) Corn-oil tocopherols. Sample 10 /xL of corn oil in 100 /xL of mobile phase. Column Nova Pak Silica (4 jam), 3.9 mm ID x 150 mm. Mobile phase 0.3% isopropyl alcohol in isooctane. Flow rate 1.0 mL/min. Detection fluorescence 290 nm excitation and 335 nm emission. (b) Separation of vitamin E from vitamin A. Mobile phase 0.5% isopropyl alcohol in isooctane. Other conditions are the same as those in a with the exception that retinol was detected with 365 nm excitation and 510 nm emission, (c) Structures of compounds. 

Fluorescence (, 3, 247 nm in neat p-dioxane) occurs with a quantum yield of 0.029 (184) in the liquid state only (183). Addition of water effects a diminution and a red shift while isooctane causes a blue shift, as well as a reduction in intensity. O2 (183) and N2O (187) are quenchers. It is thought that the fluorescence is from some form of excited aggregate whose composition varies with dilution, and that monomeric p-dioxane does not fluoresce (183). It has also been suggested that photodetachment of an electron might occur, and fluorescence might be a consequence of charge recombination (187). 

P>MA Particles. PIB-stabilized PbWA particles were prepared containing naphthalene [N] groups covalently attached to the fTWA chains. This was effected quite simply by adding l naphthylmethyl methacrylate to the NWA polymerization step of the particle synthesis. From reactivity ratios, one knows that the N groups are randomly distributed along the P>MA chains. The particles were purified by repeated centrifugation, replacement of the supernatant serum with fresh solvent (isooctane) and redispersion. A fluorescence spectrum of the dispersion was typical of that of a 1-alkyl-naphthalene. Chemical analysis indicated a particle composition IB/NWA/N of 13/100/10. 

Figure I. Fluorescence decay profile of N (lower curve, measured at 337 nm) and Ant (upper curve, 450 nm) for dispersions of PIB-stabilized F MA particles, labelled with N in the F MA phase, in isooctane containing 2 x 10 M Ant.

Even more important are reactions of radiolytic products with the precursors of these excited states. Results from recent experiments in which the solute luminescence and magnetic field effect were compared for radiolysis of cyclohexane or isooctane with 0.5-2.2 MeV electrons, 1-5 MeV protons, and 2-20 MeV a-particles suggested that the decrease in the solute luminescence and the magnetic field effect was due to both the increasing importance of crossrecombination and the "intervention of radicals or other transient species with the precursors" with the fluorescent states [63]. The effects of spin relaxation and ion-radical reactions in dense spurs were identified as likely causes for reduced magnetic field effects, fluorescence yields, and probabilities 0 in spurs from 17-40 keV x-rays as compared to the spurs from fast electrons [80]. 

Structural dependence on temperature is now best illustrated by example. Optically inactive poly(hexyl-2-methylpropylsilane) has an a parameter of 1.29 in THF indicating a rigid rod-like structure. Furthermore, in isooctane solution at ambient temperature the peaks of the UV absorption and fluorescence spectra are narrow, they mirror each other, and the Stokes shift is only 3 nm. These are indicative of an almost homogeneous photoexcited energy state with minimal structural variation in the main chain. Notwithstanding this conclusion, when the solution is cooled to -80 °C, the absorptivity increases, the peaks narrow, and the Stokes shift drops to 2.2 nm. It is thus assumed that the polymer attains a perfectly extended rod shape at this temperature. ... 

Tocopherols are analy2ed in their vmesterified form and separations are very easy by HPLC. The use of fluorescence detection provides very accmate results. The oil is diluted with eluent (3% tetrahydrofuran in isooctane) to 10 mg ml Pure standards are analy-... 

Tetrahydrofuran extracts of the PVC were mixed with methyl alcohol to reprecipitate the polymer or diethyl ether Soxhlet extractions of PVC were applied to a Merck fluorescent silica Gel G plate which was developed with ethyl acetate-isooctane (15 85 v/v) or methylene chloride or diethyl ether - petroleum ether (40-60). After development the plate was sprayed with 2% ethanolic resorcinol, then 4 N sulfuric acid. The plates were then heated to 135 °G and sprayed with 25% sodium hydroxide to locate the plasticisers. 

The emission decays of 9Phen in isooctane at room temperature can be analyzed as two exponential with decay times of respectively 2.71 ns and 32.27 ns. Based on a identiflability study [32] a set of decay data of 9Phen was measured at three different emission wavelength and five different concentrations of the quencher 1,4-dibromobenzene at each wavelength. Two time increments were used for each set of quencher and emission wavelength. The fluorescence decay of 9-ethylphenantrene in absence and in presence of quencher was studied and the obtained values were used in the analysis. The set of data were analyzed according to the global compartmental scheme 1 and the results are reported in table 1. 

Only information about the photophysical properties of meso A5 has been reported. The fluorescence spectrum of meso A5 in isooctane at room temperature shows predominant broad excimer emission with maximum at 480 nm (Ijv/Ij =23). Lowering the temperature de creases the excimer emission (Ij /Im 0.08 at 183 K). The fluorescence decay curves of meso A5 in the monomer region (377 nm) are analyzed as the sum of a two exponential function. The decay curves in the excimer region are fitted to a triple exponential function. One of the exponents has a negative preexponential factor. The complex photophysical behaviour of meso A5 cannot be interpreted with the one ground state conformation present if one does not include the possibility of aryl rotamers and consequently the existence of partial overlap excimers. The existence of more than one excimer is confirmed when fluorescence decay curves in function of wavelength of detection in the excimer region were analyzed. The shorter... 

Degraded butyl rubber (PIB of N 40,000 containing IX unsaturation) (10 g), methyl methacrylate (M4A, 90 g), azobisisobutyronitrile (0.1 g) are heated at 90 for 8 hours, under nitrogen, in a hydrocarbon solvent such as isooctane. Spherical particles form. Labelled particles are obtained by adding a methyl methacrylate derivative of a fluorescent dye [e.g., dye-CIbQ2C(CH3)C=CH2]. Particles are purified of all soluble reactants and by products by repeated centrifugation, decanting, and redispersion in fresh solvent. Our dye-labelled particles had a coi osition with an IB/methacrylate mole ratio close to 1/9. Particle diameters varied fr[Pg.614]

X 10 for cyclohexene, 2.3 x 10 for 1,3-cyclooctadiene, 2.0 x 10 for cyclohexane all in M- s" from Ref. [288]. Rate constant for 2,5-dimethyl-2,4-hexadiene refers to cumyloxyl in benzene. From Table 3.9. From Ref. [215] in acetonitrile. From Ref. [256] in acetonitrile for cyclohexene see also Refs. [258,259]. From Ref. [33] see also Ref. [72] in isooctane. Calculated from fluorescence lifetime in neat ethanol based on a lifetime in gas phase of 1030 ns. "From Ref. [230] in benzene/di-tert-butoxyperoxide (1/2). "From Ref. [289] in benzene. °From Ref. [288] in chlorobenzene Ref. [290] in benzene/di-ferf-butoxyperoxide (1/2). Values for cumyloxyl radicals can be found in Refs. [288,291,292]. PFrom Ref. [74] in benzene. From Ref. [291] in benzene see also Refs. [74,293]. From Ref. [232] in benzene at 37°C. Value for diethylsulfide. From Ref. [294] in benzene." From Ref. [70] in neat acetone. For quenching of triplet acetone by n-propylamine and triethylamine in acetonitrile see also Refs. [172,271]. In the case of alkoxyl radicals the values for cumyloxyl radicals are reported. From Refs. [29,231] reaction with fert-butoxyl radicals in benzene/di-tert-butoxyperoxide (1/2). Values not reported in table n-propylamine 1.6 x 10 M s, diethylamine ... 

Although the very existence of CMC of surfactant dissolved in nonpolar has been questioned, the UV absorption and fluorescence emission measurements of AOT-solubilized solubilizates, such as tert-butylphenol, pyrene, and hemi-Mg salt of 8-anilino-l-naphthalenesulfonic acid, in isooctane provided evidence for the existence of CMC at different values of R = [H20]/[A0T] (with R < 3) and CMC value increases with increase in R. The values of CMC, obtained at different temperatures, were used to calculate standard enthalpy of micellization (AH j°) from Equation 1.13 and standard entropy of micellization (AS j ) from Equation 1.14, and these respective values vary from 38.07 to 44.81 kJ mol and 184.60 to 202.60 JK moE with increase in temperature from 20 to 45°C. The positive AH j values arise mainly from the dismantling of hydrated ions in the quasi-lattice of AOT interior. 

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