Organic modifier effect

T. Hanai, Quantitative in silica analysis of organic modifier effect on retention in reversed-phase liquid chromatography,/. Chramatagr. Set, 2014, 52, 75-80. 

Fig. 2-14. The effect of organic modifier on retention, selectivity and resolution of methionine on teicoplanin CSP (250 x 4.6 mm). The flow rate was 1.0 mL min at ambient temperature (23 °C).

Some advice can be formulated for the choice of organic modifier, (i) Acetonitrile as an aprotic solvent cannot interact with residual silanols, whereas the protic methanol can. Thus, when measuring retention factors, methanol is the cosolvent of choice, as it reduces the secondary interactions between the solutes and the free silanol groups, (ii) For the study of the performance of new stationary phases one should use acetonitrile, as the effects of free silanol groups are fuUy expressed [35]. (iri) Acetonitrile with its better elution capacity can be considered as the best organic modifier for Hpophilicity measurements of highly Hpophihc compounds with adequate stationary phases [36]. 

Note that the interfacing of LC techniques with MS puts significant constraints on the solvents that can be used i.e., they must be volatile, with a low salt concentration, for MS compatibility. Narrow-bore columns, which use much smaller amounts of salt and organic modifier, appear to have potential for facilitating IEC-MS applications.40 Despite the excellent sensitivity of MS detection for most elements, however, there are cases where matrix effects can interfere. In this situation, combination of IEC with atomic emission spectrometry (AES) or atomic absorption spectrometry (AAS) may be preferable, and can also provide better precision.21 32 4142 Other types of... 

Table 2-6. The effects of organic modifier on the separation of amino acids on teicoplanin CSP.a ...

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