Isocratic methods surfaces

Methods applying LC—MS—MS for the quantitative determination of APEO were seldom reported. Houde et al. [29] recently described a LC(ESI)—MS—MS method for the determination of NPEO and nonylphenoxy carboxylates (NPEC) in surface and drinking water using a reversed-phase column (Cg) with isocratic elution. Transitions from the [M + NH4]+ ions to different product ions (m/z 127, 183, 227, 271, 315, 359 for NPEO reEO = 1-6 and m/z 291 for reEO = 7-17) were monitored, yielding detection limits from 10 to 50 ng L-1. 

The VERSE method was extended to describe the consequences of protein denat-uration on breakthrough curves in frontal analysis and on elution band profiles in nonlinear isocratic and gradient elution chromatography [69]. These authors assumed that a unimolecular and irreversible reaction taking place in the adsorbed phase accoimts properly for the denaturation. The choice of this reaction was based on numerous literature observations of the irreversible adsorption of proteins on hydrophobic surfaces [70]. This model (VERSE-LC) was verified using... 

In ideal SEC, no interactions between the sample and the support should occur only the pore dimension and the pore size distribution and therefore the volumes related to the porosity and to the interparticle volume can influence the separation. This makes SEC an easy and quick method to handle and to optimize in comparison with other chromatographic techniques such as ion-exchange chromatography or reversed-phase chromatography. Analyses of proteins in SEC are in fact carried out in the isocratic mode and the choice of the mobile phase is only directed to minimize the interactions between the sample and the support surface it does not influence the retention of the analyte when ideal conditions... 

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