Measurement of Desorption Rates from Octadecylsilyl Bonded-Phase HPLC Particles and Its Characterization in Terms of Pore, Surface, and Film Diffusion

Abstract

An instrument is developed to measure rates of desorption of solutes from particulate HPLC packing materials for processes that are quantitatively complete in a few tenths of a second. The instrument is a modified, pressure-driven, stopped-flow device. The major modifications include positioning a very short (0.6 mm) bed of the particles just upstream of the detector cell, eliminating the mixing chamber, and adding high-speed switching valves in order to allow sequential continuous flow of individual solutions. Instantaneous rate curves are measured for the desorption of 1,2-dimethyl-4-nitrobenzene (DMNB) from 12-microm-diameter porous particles of the bonded-phase packing Luna C-18 employing high linear velocities of the eluting solvent. The same experiment is performed for the nonsorbed compound phloroglucinol (PG) The PG rate curve is used in two ways (i.e., subtraction and deconvolution) in order to correct the observed rate curve of DMNB for experimental artifacts such as bed hold-up volume and instrument band broadening. The cumulative desorption rate curve of DMNB is obtained by integration. It is accurately described (R2 > 0.999) by a theoretical model that invokes both intraparticle diffusion (including both hindered pore diffusion and surface diffusion) and external film diffusion. The surface diffusion coefficient is (3.2 +/- 0.8) x 10(-6) cm(2)/s and the diffusion film thickness is 0.5 microm. The validity, of both the experimental technique and the theoretical model, is demonstrated by excellent agreement between a predicted and an observed chromatographic elution peak for DMNB on a 25-cm-long commercial column of Luna C-18.

Analysis of Distribution and Intraparticle Diffusion of a Fluorescent Dye in Mesoporous Silica Gel by Confocal Fluorescence Microspectroscopy

“…According to the pore and surface diffusion model proposed by Ruthven et al, Dp is given by the equation: Dp = DwH/ {τw(1 + R)} + DsR/{τs(1 + R)}, 3,20 where Ds and H are the surface diffusion coefficient and the hindrance parameter dependent on the molecular diameter of the solute (a) and dp, respectively. τw or τs is the tortuosity for the pore or surface diffusion, respectively, and was reported to be 1.5 -2.3 for silica gel.…”

“…In ODS-silica gel/solution systems, intraparticle diffusion of a solute has been reported to be governed by the surface diffusion. 20,23,24 In the ODS-silica gel system, the distance between the adjacent octadecylsilyl groups as the adsorption sites is short due to the long alkyl group, so the surface diffusion will effectively proceed.…”

External and Intraparticle Diffusion of Coumarin 102 with Surfactant in the ODS-silica Gel/water System by Single Microparticle Injection and Confocal Fluorescence Microspectroscopy

“…As Ke = 5 × 10 3 , Dp is estimated to be much greater than 2 × 10 -9 cm 2 s -1 . According to the pore and surface diffusion model, on the other hand, Dp is given by the equation for Ke >> 1: Dp = DwH/{τp(1+Ke)}+Ds/τs, 14,30 where H is the hindrance parameter and estimated to be 0.69 by the Renkin equation as the coumarin 102 diameter is 1 nm. 31 Ds is the surface diffusion coefficient of coumarin 102.…”

Mass Transfer of Water-insoluble Organic Compound from Octadecylsilyl-silica Gel into Water in the Presence of a Nonionic Surfactant

“…Therefore, the intraparticle diffusion, such as the surface diffusion of perylene, will be fast. 4,9 On the other hand, since the micelle formation and dissolution rates for Triton X-100 are much faster than the release rate in the present system, 22 they are also not the ratedetermining step for the release of perylene.…”

“…In chromatography, solid phase extraction, drug delivery systems, and soil remediation, kinetic analyses of the sorption and release processes are important. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Surfactants are frequently used in porous material systems. For example, the dissolution of water-insoluble organic compounds from a soil or porous medium has been demonstrated on the basis of the characteristic behavior of surfactants.…”