Results are presented of an interlaboratory round-robin study of the application of timeResolved Emission Spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media. This involved 13 independent laboratories, using various instrumental adevices and data 2 analysis methods. In some cases, experimental data from a laboratory were analysed using different softwares. Samples were prepared based on appropriate speciation diagrams and in general were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (i) acidic medium where UO 2 2+ aq is the single emitting species, (ii) uranyl in the presence of fluoride ions, (iii) uranyl in the presence of sulfate ions, and (iv) uranyl in aqueous solutions under various pH conditions, promoting hydrolysed species. Results between the laboratories are compared in terms of number of decay components, luminescence lifetimes and spectral band positions. The potentials and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.
The fluorescence spectra and lifetimes of diluted beer have been explored and found not to report on protein removal either by silica or tannic acid, nor polyphenol uptake by PVPP. Comparing the fluorescence spectra of beer with that of tea and hops, it seems that proteins, complex polyphenols and iso-a-acids can contribute to the intrinsic fluorescence of beer, although the contribution from polyphenols must be minimal since treatment with PVPP does not dramatically change the background fluorescence. To eliminate the problem of background fluorescence haze-active protein was isolated. Steady-state and time-resolved fluorescence techniques were used to characterise these and to monitor their uptake by different silica gels as a function of pH. Heat treated large pore volume, small surface area silicas were the more effective adsorbers for the proteins under study, with pH 4 being optimum. Using both intrinsic amino acid fluorescence and the extrinsic fluorophore fluorescamine, the timeresolved fluorescence anisotropy has been measured and the radius of the isolated haze protein found to be ~ 35 Å. Comparisons have been made with proteins of known size and structure such as human and bovine serum albumins (HSA and BSA).
Key words:Beer, fluorescence, haze-active protein, polyphenols, silica adsorption.
-2863(9'8-32The intrinsic fluorescence characteristics of beer are expected to be complex due to the overlap of emissions from numerous species. Nevertheless once the different origins of the fluorescence have been identified, by comparison with the isolated species, new insights may be found into the brewing and stabilisation processes. With this goal in mind, various constituents in beer have been studied and compared using steady-state and time-resolved fluorescence techniques.The interaction of protein with amorphous silicas, eg., silica hydrogels, silica xerogels, is of interest to the beverage industry. Of importance is its role in the prevention of chill haze, and subsequent risk to permanent haze formation in fruit-based beverages or cereal based beverages, such as beer. Chill haze forms as a result of the interaction of haze-active proteins with polyphenols. In order to maintain the clarity of beer and to extend colloidal shelf life, the brewing industry selectively removes these proteins from beer by adsorption onto and into amorphous silicas. Information regarding the detailed structure and amino acid sequence of these haze-active proteins is limited. In general terms, there are two types of protein present in beer: hydrophilic and hydrophobic. The hydrophilic proteins are responsible for haze formation and need to be removed whereas the hydrophobic proteins provide foam stability and must remain 16 . Bentonite removes both hazeactive and foam-active protein whereas silica gel offers specificity for haze-active proteins 20 . This specificity is a result of the proline residues in the haze-active proteins. These proline rich proteins are known to originate from malt and have an isoelectric point in the re...
Ultraviolet and x-ray excited luminescence of fluorescein and rhodamine-6G doped sol-gel glasses were studied at room temperature with the aim of characterizing and understanding the scintillation performance of such materials. Fast energy transfer from the glass host to the dye luminescent centers was found. While the overall radioluminescence efficiency was rather low due to nonradiative losses in the glass host, our results demonstrate the potential of sol-gel technology as a versatile tool in controlling the spectral and time response of such unusual organic-inorganic scintillators
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