Two-Phase Flow in Liquid Chromatography, Part 1: Experimental Investigation and Theoretical Description

Abstract

Two-phase flow is investigated in the context of liquid chromatography. In order to describe the column behavior in the presence of multiple convective phases, an equilibrium theory model is established, accounting for both adsorption and multiphase flow. The validity of this model is studied specifically for the experimental system phenetole−methanol−water on a Zorbax 300SB-C18 column. For this purpose, the experimental system is characterized in terms of thermodynamic liquid−liquid equilibria, adsorption behavior, and hydrodynamic properties by independent experimental campaigns. Mathematical relationships are established, describing the investigated effects. Implementation of these relationships in the equilibrium theory model and application of the model to calculate elution profiles provides a quantitative description of experimental data from dynamic column experiments. The good agreement validates the model, its assumptions, and the established relationships. This study provides a thorough insight on the implications of multiple convective phases in the context of liquid chromatography.

Description of Adsorption in Liquid Chromatography under Nonideal Conditions

“…Compositions of the mixtures are given in mass fractions w i or were transformed into concentrations c i in mass of component per volume of the mixture. For the conversion of mass to volume, the mixture density ρ mix was determined from the component densities ρ i assuming additivity of volumes All dynamic column experiments and HPLC analyses were performed with the stationary phase Zorbax 300SB-C18 using a prepacked stainless steel column (150 × 4.6 mm) from Agilent Technologies (for single-component adsorption experiments of PNT, a column of 50 mm length was used). Total (inter- and intraparticle) porosities of the columns were determined through pulse injections of an analytical tracer (Uracil, purity >99%, Sigma-Aldrich), yielding porosities ϵ ref of 0.611 and 0.615 for the 15 and 5 cm columns, respectively.…”

“…The adsorbed-phase concentration n i F in equilibrium with the feed concentration c i F can be determined from the measured elution profile, applying the integral component mass balance (for a detailed explanation, see ref )­ with Frontal analysis experiments were performed for different solute (TBP) concentrations at the same eluent composition, to obtain an experimental data set. Series of frontal analysis experiments were performed at different eluent compositions.…”

“…Series of frontal analysis experiments were performed at different eluent compositions. Frontal analysis for PNT has been carried out previously and reported elsewhere …”

“…However, operating at high solute concentrations may result in considerable nonidealities in the liquid and/or adsorbed phases such that models based on the assumption of ideality might fail outside a very limited range of operating conditions. , In this work, we apply thermodynamic concepts to describe adsorption in an experimental system in a thermodynamically consistent manner and over a broad range of operating conditions, accounting for nonidealities in both liquid and adsorbed phases. The system under investigation involves the adsorbent Zorbax 300SB-C18, two adsorbing components phenetole (PNT) and 4- tert -butylphenol (TBP), and the solvent components water and methanol (both assumed to be nonadsorbable).…”

“…In this work, with the eluent being a binary mixture of methanol and water, single-component isotherms based on liquid-phase activities are applied to a broad range of eluent compositions, in which the solubility of the solutes and thus the investigated concentration range change considerably. An isotherm based on liquid-phase activities established for PNT (in the same experimental system as discussed here) has been recently shown to be applicable even beyond the solubility limits, i.e., in the presence of two convective, liquid phases in thermodynamic equilibrium …”