Effect of feed zone width on product purity in preparative-scale, continuous free-flow isoelectric focusing separation of enantiomers

The effects of the increased width of the sample feed stream upon the purity of the collected fractions were examined in the continuous free-flow isoelectric focusing separation of the enantiomers of dansyl-tryptophan. Compared to the reference separation obtained with a narrow feed stream introduced through the central sample feed port of the continuous free-flow isoelectric focusing separation unit, the final pH gradient, the position of the enantiomer band centroids and the values of the cumulative product recoveries and cumulative product purities remained essentially identical as the width of the feed band of the racemic sample dissolved in the carrier ampholyte was increased up to the full width of the separation chamber suggesting that the current, limiting practice of narrow, central feed bands can be safely abandoned and dilute feedstock solutions can be utilized in preparative-scale isoelectric focusing enantiomer separations.