Flow‐rate dependence of gel permeation chromatography

Abstract

synopsisAnalysis of polystyrene xttriidards by gel permeation chromatography over B wide range of flow ratev revealed two sources of error in volume measurement. These errors arise from solvent evaporation in the xiphon chamber and from solvent continuing to flow into the siphon during discharge. Appropriate corrections are discussed, and a vapor feedback loop to eliminate the solvent evaporation error is described. The flow rate dependence of the GPC calibration curve, expressed in the corrected elution volumes, a p pears different from that reported in the literature. The corrected flow rate dependence of peak elution volumes is in agreement with the expectation of ditrusion and exclusion theories.

Evaluating dispersion in gel permeation chromatography. Axial dispersion of polymer molecules in packed beds of nonporous glass beads

“…It has been established (1-5) that the gel permeation chromatography (GPC) separation is dependent upon the volumes of the solute molecules, but relatively little is known about the detailed mechanisms controlling the permeation process itself. Various models for predicting elution times in GPC have been proposed (5)(6)(7)(8)(9)(10)(11)(12), and several approaches (4,(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) have been taken to evaluate peak broadening, which is probably the major factor limiting the accuracy with which molecular-size distributions can be determined by GPC at the present time. Our own approach (14) proposes that broadening during flow through a GPC column arises from free-stream dispersion effects plus mass transfer of solute molecules into and out of the pores (the permeation process).…”

Experimental Variables and Techniques

“…columns. The variations in elution volume with changes in flow rate that have been reported [18][19][20] can be attributed to the apparent shifting of peak maxima because of degradation-induced changes in peak shape at high flow rates. No change in retention volume occurs for either large molecules (polystyrene M = 411,000 g/mol; diffusion coefficient, D s = 22 × 10 −8 cm 2 /s) or small molecules (acetonitrile, M = 41 g/mol; D s = 1 × 10 −5 cm 2 /s).…”

Retention

“…As seen in Figure 2.4, flow rate has little effect on SEC retention. Experimental results indicate that the kinetic or mass transfer process does not influence the retention mechanism in the SEC separation [14,15], a fact recognized by John Moore in his original publication on gel permeation chromatography [9]. For skewed SEC peaks at very high flow rates, the values of V R at the center of mass, not the maximum, of each peak should be used in studying the effects of flow rate on SEC retention.…”

“…14 Dimensionless exclusion parameter as a function of dimensionless polymer size for spheres, rods, and Gaussian chains. Exclusion parameter V d is for a dilute array of cylinders with radius a.…”