Silica fluorescent

Ow H, Larson DR, Srivastava M, Baird BA, Webb WW, Wiesner U (2005) Bright and stable core-shell silica fluorescent nanoparticles. Nanoletters 5(1) 113-117... 

At r = 6 min, 5 p,L of serum were injected. As it flowed through the column, free phenytoin displaced some fluores-cently labeled phenytoin from the silica. Fluorescence was measured at 820 nm with laser excitation at 785 nm. 

Silica-fluorescent dye beads have not been utilized as much as the PS-based ones. As pointed out recently in our efforts these are easily prepared in abundance, and have optical and chemical features that lend them suitable for flow cytometry applications. The limiting feature—concentration quenching—of any fluorophore-bead system is illustrated in Fig. 11 for rhodamine 6G in silica. Here, successively higher concentrations of R6G in a layer of silica-R6G around the same core silica showed quenching of R6G emission from the increase to a maximum at S and then decrease in intensity for samples S-1 to S-6 shown in Fig. 11. 

Bele, M., Siiman, 0. and Matijevic, E. (2002) Preparation and flow cytometry of uniform silica-fluorescent dye microspheres. Journal of Colloid and Interface Science, 254, 274-82. 

Hydrocarbon groups (FIA method) NF M 07-024 ISO/DIS 3837 ASTM D 1319 Chromatography on silica gel with fluorescent indicators... 

In addition to tire standard model systems described above, more exotic particles have been prepared witli certain unusual properties, of which we will mention a few. For instance, using seeded growtli teclmiques, particles have been developed witli a silica shell which surrounds a core of a different composition, such as particles witli magnetic [12], fluorescent [13] or gold cores [14]. Anotlier example is tliat of spheres of polytetrafluoroetliylene (PTFE), which are optically anisotropic because tire core is crystalline [15]. 

Figure C2.6.2. CSLM image of near hard-sphere silica particles of diameter d = 1050 nm witli a fluorescent core of diameter 400 nm, showing fee stacking (top), hep stacking (bottom middle) and amoriDhous areas (image size 16.3 pm X 16.3 pm, courtesy of Professor A van Blaaderen)...

The analysis of cigarette smoke for 16 different polyaromatic hydrocarbons is described in this experiment. Separations are carried out using a polymeric bonded silica column with a mobile phase of 50% v/v water, 40% v/v acetonitrile, and 10% v/v tetrahydrofuran. A notable feature of this experiment is the evaluation of two means of detection. The ability to improve sensitivity by selecting the optimum excitation and emission wavelengths when using a fluorescence detector is demonstrated. A comparison of fluorescence detection with absorbance detection shows that better detection limits are obtained when using fluorescence. 

SORBTION-X-RAY-FLUORESCENCE DETERMINATION OE TOXIC METALS WITH THEIR PRECONCENTRATION ON COMPLEXING CHEMICAL MODIEIED SILICA... 

In this work the results of reseai ch common sorbtion-X-Ray-fluorescence analysis of Pb(II), Cd(II), Zn(II) and Mo(VI) with preconcentration on complexing chemical silica gel modified with mercaptane groups and modified with 8-hydroxyquinoline were described. The conditions and limits of determination of the X-Ray-fluorescence method in the thin lawyers ai e discussion. 

It was shown that X-Ray-fluorescence method do possible to separate metals in the multycomponents samples by different methods of synthesis chemical modified silica and different ways of coordination of ion metals on the surface. 

Organic fluorescence indicators for aluminium oxide, silica gel and cellulose layers (code F366, UV366) include ... 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

It is known that not all reactions proceed in the same manner on all adsorbent layers because the material in the layer may promote or retard the reaction. Thus, Ganshirt [209] was able to show that caffeine and codeine phosphate could be detected on aluminium oxide by chlorination and treatment with benzidine, but that there was no reaction with the same reagent on silica gel. Again the detection of amino acids and peptides by ninhydrin is more sensitive on pure cellulose than it is on layers containing fluorescence indicators [210]. The NBP reagent (. v.) cannot be employed on Nano-Sil-Ci8-100-UV2S4 plates because the whole of the plate background becomes colored. 

The reasons for the above phenomena are to be found in differing configurations of hydrogen bonds, the effect of pH, differences in the structures of fluorescence indicators and binders and differences in surface area. For example, silica gel 60 possesses a surface area of 500 m /g [211] while that of Si 50 000 lies below 5 m /g [212],... 

In the case of substances whose structures are pH-dependent (e.g. phenols, carboxylic and sulfonic acids, amines etc.) it is possible to produce fluorescences or make them disappear by the deliberate manipulation of the pH [213] (Table 20). Shifts of the positions of the absorption and emission bands have also been reported. This is particularly to be observed in the case of modified silica gels, some of which are markedly acidic or basic in reaction (Table 25). 

Hydrophilic liquids can also cause stabilization and amplification of fluorescence Thus, Dunphy et al employed water or ethanol vapor to intensify the emissions of their chromatograms after treatment with 2, 7 dichlorofluorescein [260] Some groups of workers have pointed out that the layer matenal itself can affect the yield of fluorescent energy [261 —263] Thus, polyamide and cellulose layers were employed m addition to silica gel ones [245] The fluorescence yield was generally increased by a factor of 5 to 10 [264], but the increase can reach 100-fold [234, 265]... 

The reagent can be employed on silica gel, kieselguhr and Si 50 000 layers and, if necessary, on RP-2 and RP-8 phases. It cannot be used on RP-18 layers [9] because here the whole plate is fluorescent. )... 

Note The reagent can be employed on silica gel, kieselguhr. Si 50 000 and RP layers [6]. The fluorescence intensities of the chromatogram zones can be increased by dipping in a solution of liquid paraffin in hexane or chloroform [8,11]. 

Detection and result The chromatogram was dried in a stream of warm air for 10 min, immersed in the reagent solution for 3 s and then subjected to intense UV radiation (high pressure lamp, A = 365 nm) for up to 10 min. Terephthalic (hRf 0 - 5), pimelic (hRf 55), suberic (hRf 60), sebacic (hRf 65 — 70) and benzoic acids (hRf 70 — 75) together with sorbic, malic, adipic, citric, tartaric, lactic and fumaric acids only exhibited a reaction on silica gel layers at higher concentrations. 4-Hydroxybenzoic, salicylic and acetylsalicylic acids fluoresced light blue after irradiation. The detection limit per chromatogram zone was 0.5 pg for salicylic acid and more than 5 pg for benzoic acid. 

Since the fluorescence intensity of the zones on silica gel layers is reduced after a few minutes the determination of aromatic amino acids is usually performed on... 

It is often possible to increase the detection sensitivity in visible light by exposing the dipped or sprayed chromatogram to ammonia vapors it can also be sprayed with caustic soda or potash solution. When this is done the fluorescence intensity is reduced on silica gel layers and increased on RP ones. 

Thin-layer plates were made with silica gel-calcium sulfate and each contained a mixture of zinc silicate and zinc cadmium sulfide as phosphors. Separated components are generally visible under ultraviolet light by fluorescence quenching. This was true, in part, for the pyrethrins, except that some of the separated components possessed a natural fluorescence under the ultraviolet lamps. 

A three-step nitration process of toluene is described. The advantages of the modified process are reduced waste, less hazardous operation, reduced oleum requirement, partial replacement of coned HN03 with dil HN03, and higher rate of toluene flow into the reactor (Ref 86) The continuous process of H.C. Prime (Ref 73) for preparing TNT was studied by thin-layer chromatography on silica gel with a starch binder and a fluorescent indicator. The nitration... 

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