Ludox solution

It can be advantageous to heat the chromatogram to 160 °C for 15 min before treating with nitrous fumes and to place it in the reagent chamber while still hot [1]. Heating to 260 °C has even been recommended for the purpose of reducing the fluorescent background [14], whereby the layer is previously immersed in 1 percent Ludox solution (silidc acid sol) to increase its stability [2]. The fluorescence of the substances detected usually remains stable for at least 2 weeks [2]. 

For absolute intensity measurements, apparatus calibration is necessary. In most equipment, it is difficult to calibrate against a pure liquid because of the low scattering power and low sensitivity of solid state apparatus associated with their high resolution. Consequently, calibration is often referred to a conventional apparatus using some more highly scattering medium such as a Ludox solution. 

Fig. 15.10 Fluorescence decays for a polythiophene derivative in toluene solution at 293 K and in thin film. The dashed lines in the decays are the pulse instrumental response functions in solution (obtained with a Ludox solution) and in the solid state (obtained with a blank sapphire disc inside the Horiba-Jobin-Yvon integrating sphere). Autocorrelation functions (AC.), weighted residuals and Chi square values (x ) are also present as insets. Reproduced with permission from Ref. [49], Copyright 2007, the American Chemical Society...

Figures 6 and 7 show the absorption spectra of colloidal CdS and ZnS at various times of illumination. The two colloids were prepared by adding an NaSH solution to solutions of Cd(C10j2 or Zn(C104)2, respectively, colloidal silicon dioxide (commercially available from Dupont Ludox HS30) being present at 6 x 10 M as stabilizer in both cases. The absorption starts in both cases close to the wavelengths that correspond to the photon energies (515 nm or 2.4 eV for CdS 340 nm or 3.7 eV for ZnS) at which the absorptions begin in the macrocrystalline materials. It is seen that illumination causes not only a decrease in the intensity of the absorption spectrum but also a change in the shape of the spectrum. The onset of light absorption is shifted towards...

Taramasso et al. (5) had originally reported two methods for the hydrothermal synthesis of TS-1. The first method (mixed alkoxide method) involves the preparation of a solution of mixed alkoxides of titanium and silica (preferably ethoxides) followed by hydrolysis with alkali-free solution of tetrapropylammonium hydroxide (TPAOH), distillation of the alcohol and crystallization of the resulting gel at 448 K. In the second method (dissolved or hydrolyzed titanium method) a soluble tetrapropylammonium peroxo-titanate species was prepared initially and then colloidal SiC>2 (Ludox AS-40) was added. This entire operation had to be carried out at 278 K. The TS-1 samples obtained by these two synthesis routes differed, particularly because of the presence of impurities such as Al3+ usually present in colloidal silica (33). 

When deconvolution is required, the time profile of the exciting pulse is recorded under the same conditions by replacing the sample with a scattering solution (Ludox (colloidal silica) or glycogen). 

Fig. 6.12. Data obtained by the single-photon wavelength 340 nm observation wavelength timing technique using a mode-locked ion- 390 nm. Reference scattering solution argon laser that synchronously pumps a cavity- (Ludox). Number of channels 900 channel dumped dye laser. Sample solution of POPOP width 4.68 ps. Result t = 1.05 + 0.01 ns in cyclohexane (undegassed). Excitation x = 1.055.

Instrumentation. The steady-state fluorescence spectra were measured with Perkin-Elmer MPF-44B fluorescence spectrophotometer. The single-photon counting instrument for fluorescence lifetime measurements was assembled in-house from components obtained from EG G ORTEC. A PRA-510B light pulser filled with gas was used as the excitation source. Instrument response function was obtained with DuPont Ludox scatter solution at the excitation wavelength. 

Zeolite rho was prepared from aluminosilicate hydrogels containing sodium and cesium cations. The procedure is entirely comparable with the synthesis of faujasite except for substitution of CsOH for about 10% of the NaOH in the faujasite synthesis gel. Alumina trihydrate (Alcoa C-33 grade) was dissolved in 50% NaOH solution at 100°. After cooling to ambient temperature, the required amount of CsOH solution was added, and the resulting liquor was blended into 30% silica sol (duPont Ludox LS-30) with vigorous mixing. After 3-7 days incubation at 25°, the synthesis gel was held at constant temperature, 80, 90, or 100°, until crystals formed maximum crystallinity was usually achieved in 2-4 days. 

Mesostructured molecular sieves such as Si-MCM-41 and Al-MCM-41 were synthesized using gels prepared by reacting colloidal silica (Ludox AS) with an Al(OH)3, solution in the presence of a surfactant. Al was incorporated in tetrahedral coordination inside the pristine crystals. However, as expected, dealumination occured upon calcination at 600°C/12h yielding materials having both tetrahedral and octahedral Al-species. 

The reactants used in this study were a colloidial silica, Ludox AS-40 (Dupont), reagent-grade tetrapropylammonium bromide (Aldrich Chemical Co.) and a 50wt% sodium hydroxide solution (Mallinckrodt Inc.). The reaction mixture had the oxide formula, 2.55Na20-5.0TPABr-100Si02-2800H20. The mole ratios of the... 

Zeolite ZSM-5. Zeolite samples were crystallized from a gel containing colloidal silica (Ludox AS-40), deionized water, aluminiumtriisopropylate (ATIP, Merck), as source of aluminium, and tetrapropylammonium bromide, (TPABr, Aldrich). Ammonia solutions were prepared by saturating a thermostated aqueous solution with... 

FIGURE 10J38 Gelation time versus Si02 concentratioa Two curves are shown (1) experimental observations are for Ludox SM silica particles (7 nm diameter) in 0.5 M NaCl solution, pH = 8.5, (2) predictions based upon equation 10.90 and [Pg.484]

Figure 2.31 Adsorption of non-lonlcs from aqueous solution. Comparison of data In semllogarlthmlc plots. X same data as In fig. 2.30, other data obtained by M.R. Bdhmer (loc. clt.) for C,-E- on Ludox. Methods of measurement. X. O via surface tension. molybdophosphorlc acid assay, A reflectometry (on oxidized silicon wafers). The arrows indicate c.m.c. s.

Figure 9-23. Densities yielded at 5°C from solutions of various materials used to form density gradients 9 indicates the density of a 30% solution of Ludox.

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