Closer look at the operating definition of protein recovery in CE

Analyte recovery is an important figure to assess protein adsorption on fused-silica capillaries. In 1991, Regnier et al. estimated recovery by assuming the loss of analyte from adsorption and thus the decrease in peak area measured by two detectors to be proportional to the length of the capillary section between them. In this report, we closely examine this concept and its adaptation to commercial CE instruments to determine protein recovery. We hypothesize that, once a steady-state migration is reached, protein adsorption is a first-order process with respect to protein concentration and surface density of adsorbing sites. This hypothesis is shown to be valid over a reasonably wide range of capillary effective length and, as a result, protein recovery decreases exponentially with the migrated distance. However, unlike the traditional recovery figure obtained through a conventional spike process, protein recovery measured by this approach does not have the same merit since it is strongly dependent from capillary dimensions and applied electric field. Nevertheless, protein recovery and the slope of the logarithmic protein peak area versus length plot are useful figures to compare protein adsorption on different capillary surfaces. Several literature reports dealing with the application of Regnier concept to calculate protein recovery are discussed.