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

Abstract

Studies of the sorption and desorption processes in microparticle systems are significant for understanding the microscopic mechanisms of solid-phase extraction, liquid chromatography, mass transport in soil, and so forth. [1][2][3][4][5][6][7][8] Because the sorption and desorption processes of a solute in octadecylsilyl (ODS)-silica gel systems are highly dependent on the volume ratio of an organic solvent to water in a mixture solvent, measurements of the microscopic polarity of an ODS phase are necessary for analyses of the separation processes. In liquid chromatography, a solute in a mobile phase distributes into an ODS phase, dependent on the flow rate of the mobile phase, the adsorption/desorption rates, the intraparticle diffusion rate, and so on. Therefore, direct measurements of the sorption rates in ODS-silica gel systems are indispensable for analyzing the separation mechanism. 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. ExperimentalAfter spherical ODS-silica gel (Wako Pure Chemical, Wakosil 40C18: particle diameter (d), 20 -60 µm; surface area, 330 cm 2 /g; pore diameter (dp), 12 nm; pore volume (Vp), 1.0 cm 3 /g) was soaked in acetonitrile, the solvent was repeatedly replaced with acetonitrile-water (percentage by volume of acetonitrile, 0 -15 vol%) containing KCl (0.01 mol/dm 3 ). Single microparticle measurements were performed at 298 ± 0.5 K by microcapillary manipulation and microabsorption methods (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. Figure 2 shows the absorption spectra of PB sorbed into single ODS-silica gel microparticles for 0 and 15 vol% of acetonitrile. The absorbance of PB increased with time and became saturated. Both the ratio of a saturated absorbance value (Aeq) to the PB concentration in an acetonitrile-water solution (Ca-w) and the time to saturation significantly increased with the decreasing percentage of acetonitrile. The absorption spectrum of PB is highly dependent on the solvent polarity and hydrogen bonding. 9 In water, acetonitrile (20 vol%)-water, methanol, or acetonitrile, the absorption maximum of PB (λmax) Intraparticle mass transfer processes of Phenol Blue (PB) in single octadecylsilyl (ODS)-silica gel microparticles in acetonitrile-water were analyzed by microcapillary manipulation and microabsorption methods...

Mass transfer of weak acid in nanometer-sized pores of octadecylsilyl-silica gel

“…In a silica gel/water system, we reported the relationship between the intraparticle diffusion coefficient and isotherm parameters, and nanometer pore size dependence of the intraparticle diffusion for the sorption of a cationic dye [13,14]. In an octadecylsilyl (ODS)-silica gel/organic solventwater system, the microscopic polarity near the ODS/solution interface has been reported for the sorption of a neutral solute [15,16]. In the present article, the sorption of a weak acid into single ODS-silica gel microparticles, used as a separation medium in liquid chromatography and solid-phase extraction, was analyzed using the microcapillary injection-manipulation and absorption microspectroscopy.…”

Release Mechanism from a Microsphere of a Silkworm Chitin Derivative Studied by Single Microparticle Injection and Absorption Microspectroscopy

“…17 The lmax of the dye adsorbed on ODS groups on the mesopore walls of the ODSsilica gel in water was 626 nm. 18 As can be seen in Fig. 1, lmax of the dye in the microsphere was 635 nm.…”

“…The molar extinction coefficient of the dye at 635 nm (e) in the microsphere was assumed to be equal to that in water at the peak wavelength (658 nm). 18 The distribution ratio of phenol blue (R) was determined from R = Cp,eq/Cw,eq. As shown in Fig.…”

“…Previously, we reported that the contribution of pore diffusion of a solute with a ~1 nm is much greater than that of the surface diffusion in silica gel (dp = 3 -30 nm) and ODSsilica gel (dp = 12 nm) based on single microparticle measurement analysis. 11,12,18 In these systems, Do increased with decreasing R, and was directly proportional to 1/(1 + R). In the present system, however, Do was independent of R. Therefore, diffusion in the dibutyrylchitin microsphere is limited by the surface diffusion, and the contribution of the pore diffusion is negligibly small.…”

Diffusivities of Tris(2,2′-bipyridyl)ruthenium inside Silica- Nanochannels Modified with Alkylsilanes

“…200 nm in diameter from the aqueous phases (10 -8 to 10 -6 cm 2 s -1 ) 12 and Phenol Blue extracted in octadecylsilyl-modified silica gel (pore diameter, 12 nm) from the water/acetonitrile mixtures (10 -11 to 10 -8 cm 2 s -1 ). 37 These values are also smaller than those in the bulk solution phases. These slow diffusivities are important aspects to consider in applications of a nanopore membrane modified with an alkylsilane as a nanofluidic system.…”