Deactivation of fused silica capillary columns with phenylhydrosiloxanes

Abstract

A method is described for surfacedeactivation and modification of fused silica capillary columns with a cyanopropyl-containing reagent. The deactivation procedure involved a dehydrocondensation reaction between a bis(cyanopropy1)methylhydropoIysiloxane reagent and surface silanol groups at an optimum temperature of only 25OOC. Actual critical surface tension measurements were made using the capillary rise method. Excellent deactivation for acidic and basic compounds at the low ng level, and wettability for nonpolar and polar polysiloxane stationary phases were obtained. A procedure was developed to remove acidic impurities that are present in polar stationary phases.

Force and flux relations for flows of ionic solutions between parallel plates with porous and charged layers

“…The functional form connecting the Donnan potential to the fixed-charge distribution depends upon the form of the freeand fixed-charge densities. For a fixed charge density that is independent of the local potential, and a free charge determined by (11),…”

“…The porous layer exhibits a resistance beyond the viscous retardation of the fluid alone; this effect is captured in the −ku term. Below, we solve for the velocity in the channel and then describe the hydraulic conductance, χ (soft) 11 . For convenience and clarity, we work in the dimensionless variable y * = y/δ and define β = h/δ, which is the half-height of the channel normalized by the porous layer thickness.…”

“…For values of β approaching unity, nearly all nonvanishing values of α will have some effect on the velocity profiles. For the one-dimensional geometry considered, we compute χ (soft) 11 from Eq. (13).…”

“…Describing transport within the porous membrane layer requires an understanding of the interplay between chemical and physical attributes of the porous layer. Fuel cells [7], filtration assemblies [8], and electrophoretic [9,10] and chromatography systems with coated surfaces [11] use membranes or membranelike layers to some extent. Contemporary workers use anionic and cationic exchange membranes in through-flow configuration for the purification of brackish solutions [12], where transport across exchange membranes is essential to solution treatment [8].…”

Avaliação dos processos de pré-tratamento da superfície da sílica fundida no preparo de colunas capilares inertes para cromatografia gasosa

“…Tríska e colaboradores realizaram a reação de silanização a 350 °C por um período de 24 horas, mas Markides descreve que a melhor desativação alcançada foi a 350 °C por um período de apenas 10 horas [17,18] .…”