Thermodynamic and QSRR Modeling of HPLC Retention on Modern Stationary Phases

Abstract

This paper investigates correlations between the standard chromatographic parameter, log k_w, obtained experimentally (classical thermodynamic) and obtained through the use of quantitative structure-retention relationships (QSRR) models (extrathermodynamic approach). QSRR models were created using descriptors from calculation chemistry, selected a priori on the basis of chemical intuition. Four modern analytical columns (packed with C18), often used in pharmaceutical analysis, were selected for the study. The simple extrathermodynamic model was demonstrated to be superior in terms of retention description with relation to rather complex models based on thermodynamic hermeneutics. However, all the QSRR equations derived are of limited predictive value as regards prediction of retention on the basis of the structure of the analyte. Nonetheless, they allow the differentiation of mechanism of separation operating on individual tested stationary phases. The descriptors, which are most significant in QSRR equations, appear to characterize better the net effect of interactions of the analytes with the stationary phases and the mobile phase containing acetonitrile as compared to the HPLC systems comprising methanol. These observations suggest that retention properties of new stationary phases studied in this work differ.

Keywords:

• liquid chromatography
• molecular descriptors
• QSRR
• retention modeling
• reversed-phase HPLC
• thermodynamics

Notes

Note: R, correlation coefficient; F, value of the F-test of significance; p, significance level. Numbers refer to individual HPLC systems. No. 1: MICRA NPS ODS I column, methanol-water eluent; No. 2: MICRA NPS ODS I column, acetonitrile-water eulent; No. 3: SUPELCO SUPELCOSIL LC-18 column, methanol-water eluent; No. 4: SUPELCO SUPELCOSIL LC-18 column, acetonitrile-water eulent; No. 5: Unison UK-C18 ODS column, methanol-water eluent; No. 6: Unison UK-C18 ODS column, acetonitrile-water eulent; No. 7: Zorbax SB-C18 column, methanol-water eluent; No. 8: Zorbax SB-C18 column, acetonitrile-water eulent).

Note: Numbers refer to individual HPLC systems. No. 1: MICRA NPS ODS I column; No. 2: MICRA NPS ODS I column; No. 3: SUPELCO SUPELCOSIL LC-18 column; No. 4: SUPELCO SUPELCOSIL LC-18 column; No. 5: Unison UK-C18 ODS column; No. 6: Unison UK-C18 ODS column; No. 7: Zorbax SB-C18 column; No. 8: Zorbax SB-C18 column.

Note: Number refer to individual HPLC systems. No. 1: MICRA NPS ODS I column; No. 2: MICRA NPS ODS I column; No. 3: SUPELCO SUPELCOSIL LC-18 column; No. 4: SUPELCO SUPELCOSIL LC-18 column; No. 5: Unison UK-C18 ODS column; No. 6: Unison UK-C18 ODS column; No. 7: Zorbax SB-C18 column; No. 8: Zorbax SB-C18 column.

Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/ljlc.