By using the SPE cartridge connector, the SPE cartridge to be tested is connected to an LC system where it acts as the column. Although it is not common in SPE to run a linear gradient, an initial scouting gradient, as is common in HPLCmethod development [22], can provide a lot of information about retention behaviour and selectivity. Based on a scouting gradient, a choice for the sorbent type can be made by scanning different types of stationary phases. Once a suitable sorbent was chosen, the elution behaviour of the analytes under isocratic conditions can be determined.
With the cartridge connected to the LC system, different isocratic chromatograms should be recorded at different modifier concentrations. For each type of mobile phase (acidic or basic) the obtained retention times will be related to the modifier concentration by Eq.  Also, from the isocratic chromatograms, information about the peak shape can be obtained and by performing a few measurements as described in Section 2.3, this peak shape can be approximated. It was assumed that the peak shape parameters can be kept constant, regardless of the used solvent. Variations in these parameters may result in a discrepancy between the predicted shape of the eluted band and the real shape resulting in a variable recovery prediction.
However, SPE cartridges were not expected to perform as analytical columns and therefore some variation in recovery was considered acceptable. The SPE model can now be used as a simulator for the real system. The strategy to use this model is to start with the sample application and to find the conditions that favour retention.
Do you want to know more about this easy way of using the right SPE cartridge? We organize Our State of The Art symposia, were the focus is on how to use functionalized Silica, like the Practicle Hands-on SPE day, send an e-mail to us!
New practical algorithm for modelling analyte recovery in bioanalytical  reversed phase and mixed-mode solid phase extraction
G. Hendriks,
a,, D.R.A. Uges b, J.P. Franke
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