Taylor Dispersion Analysis in Coiled Capillaries at High Flow Rates

Abstract

Taylor Dispersion Analysis (TDA) has been performed for analytes moving at high flow rates in long, coiled capillaries. A thin injection zone of the analyte is stretched by the flow and final distribution of concentration of the analyte at the end of the capillary has the gaussian shape. The high flow rates in coiled capillary generate vortices. They convectively mix the analyte across the capillary. This mixing reduces the width of the gaussian distribution several times in comparison to the width obtained in a straight capillary in standard TDA. We have determined an empirical, scaling equation for the width as a function of the flow rate, molecular diffusion coefficient of the analyte, viscosity of the carrier phase, internal radius of the cylindrical capillary, and external radius of the coiled capillary. This equation can be used for different sizes of capillaries in a wide range of parameters without an additional calibration procedure. Our experimental results of flow in the coiled capillary could not be explained by current models based on approximate solutions of the Navier-Stokes equation. We applied the technique to determine the diffusion coefficients of the following analytes: salts, drugs, single amino acids, peptides (from dipeptides to hexapeptides), and proteins.

A reduced‐order model for chemical species transport in a tube with a constant wall concentration

“…[1][2][3][4][5] Such characteristics can be presented in terms of the transport coefficients (including the effective advection coefficient, the dispersion coefficient, and the effective Sherwood number). The objectives of developing transport coefficients are first, to determine the important parameters that control the mass flux released from the chemical species source and second, to include the determined parameters in a transport sub-model in large-scale simulation, and design of optimal strategies.…”

A method for rapid screening of interactions of pharmacologically active compounds with albumin

“…The centrifugal force caused appearance of vortices which mixed additionally the analyte across the capillary and in this way relieved the condition L/u ) R 2 /D. Therefore, application of high flow rates and coiled capillaries shortened time of measurement from hours to minutes, improved accuracy of measurements and decreased the consumption of reagents [36,37].…”

“…2). These vortices additionally mix the analyte inside the capillary and reduce the width of the concentration distribution [36,37].…”

“…In our experiments we use high flow rates of the carrier phase (to shorten the time of measurements) and use the following scaling equation for the diffusion coefficient [36]:…”

“…where r is the density of the carrier phase, u is the average velocity of flow (averaged across the capillary), m is the viscosity of the carrier phase, R is the inner radius of the capillary and r is the radius of the curvature of the coiled capillary, s c is the dispersion coefficient (width of the concentration distribution) in a coiled capillary, Lambert W is the Lambert W function (see Supporting information), A = 0.87 AE 0.02 and B = À3.8 AE 0.2 are fitted parameters [36]. We use Eq.…”