Direct Analysis of Intraparticle Mass Transfer in Silica Gel Using Single-Microparticle Injection and Microabsorption Methods

Abstract

Sorption and desorption processes of cationic dyes occurring in single silica gel microparticles in an aqueous solution were kinetically studied by microcapillary manipulation/injection and microabsorption methods. The sorption and desorption rates of rhodamine 6G were limited by diffusion of the dye in the particle interior. For methylene blue, the desorption rate was slow compared with the sorption rate, and the rate-determining step was not the diffusion of the dye. The sorption and desorption processes of the dyes were discussed in terms of intraparticle diffusion as well as of that accompanied by slow desorption.

Analysis of Sorption into Single ODS-Silica Gel Microparticles in Acetonitrile-Water

“…1). 11 If PB is adsorbed only on the particle surface, Aeq is independent of d, as previously reported. 12 This result indicates that water molecules enter the pores having hydrophobic walls in the ODS-silica gel, and PB is sorbed into the particle interior.…”

“…For a spherical particle, the time dependence of the radial concentration profile of a solute in the particle (Cp(r,t)) is given by the equation ∂Cp(r,t)/∂t = Do{∂ 2 Cp(r,t)/∂r 2 + (2/r)∂Cp(r,t)/∂r}, where Do and r are the apparent diffusion coefficient of the solute in the particle interior and the radially directed spatial coordinate, respectively. 11,13 Under the conditions Cp(r,0) = 0, Cp(d/2,t) = Cp,eq and ∂Cp(0,t)/∂r = 0, A(t) (= 2ε∫0 d/2 Cp(r,t)dr) was simulated for various Do values. The simulated A(t) curves of single microparticles for 0 vol% of acetonitrile are shown in Fig.…”

“…1). 10,11 A single ODS-silica gel in a KCl/acetonitrile-water solution was sucked into a microcapillary and injected into a KCl (0.01 mol/dm 3 )/acetonitrile-water solution containing PB using the microcapillary manipulation method. The time dependence of the absorption spectrum for a single microparticle was measured by the microabsorption method.…”

“…In this article, the sorption of Phenol Blue (PB), known as a solvatochromic dye, 9 into single ODSsilica gel microparticles in acetonitrile-water was analyzed using microcapillary manipulation and microabsorption methods, by which a single microparticle can be injected into a solution and the absorption spectrum of the single microparticle is measured with time. 10,11 We discuss the microscopic polarity in the ODS-silica gel system and diffusion of PB in the pores of the microparticles.…”

Kinetic Analysis of Distribution of Weak Acid in an Oil-Gelatin Microcapsule/Water System Studied by Microcapillary Injection and Microabsorption Methods

“…6,7 In order to measure an absorption spectrum greater than 350 nm, a light beam from a Xe lamp (Hamamatsu Photonics, LC5, L8253) was used as an ultraviolet-visible light source. The light beam was introduced to an optical microscope (Olympus, IX-70) through a pinhole of 100 µm diameter and focused by an objective lens (Olympus, LUMPlanFl).…”