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Influence of variation in mobile phase pH and solute pKa with the change of organic modifier fraction on QSRRs of hydrophobicity and RP-HPLC retention of weakly acidic compounds
- Source :
- Talanta. 101:64-70
- Publication Year :
- 2012
- Publisher :
- Elsevier BV, 2012.
-
Abstract
- The variation in mobile phase pH and ionizable solute dissociation constant (pK(a)) with the change of organic modifier fraction in hydroorganic mobile phase has seemingly been a troublesome problem in studies and applications of reversed phase high performance liquid chromatography (RP-HPLC). Most of the early studies regarding the RP-HPLC of acid-base compounds have to measure the actual pH of the mixed mobile phase rigorously, sometimes bringing difficulties in the practices of liquid chromatographic separation. In this paper, the effect of this variation on the apparent n-octanol/water partition coefficient (K(ow)″) and the related quantitative structure-retention relationship (QSRR) of logK(ow)″ vs. logk(w), the logarithm of retention factor of analytes in neat aqueous mobile phases, was investigated for weakly acidic compounds. This QSRR is commonly used as a classical method for K(ow) measurement by RP-HPLC. The theoretical and experimental derivation revealed that the variation in mobile phase pH and solute pK(a) will not affect the QSRRs of acidic compounds. This conclusion is proved to be suitable for various types of ion-suppressors, i.e., strong acid (perchloric acid), weak acid (acetic acid) and buffer salt (potassium dihydrogen phosphate/phosphoric acid, PBS). The QSRRs of logK(ow)″ vs. logk(w) were modeled by 11 substituted benzoic acids using different types of ion-suppressors in a binary methanol-water mobile phase to confirm our deduction. Although different types of ion-suppressor all can be used as mobile phase pH modifiers, the QSRR model obtained by using perchloric acid as the ion-suppressor was found to have the best result, and the slightly inferior QSRRs were obtained by using acetic acid or PBS as the ion-suppressor.
- Subjects :
- Aqueous solution
Chromatography
Quantitative Structure-Activity Relationship
Hydrogen-Ion Concentration
Models, Theoretical
High-performance liquid chromatography
Analytical Chemistry
Dissociation constant
Partition coefficient
Acetic acid
chemistry.chemical_compound
chemistry
Phase (matter)
Perchloric acid
Organic Chemicals
Acids
Hydrophobic and Hydrophilic Interactions
Phosphoric acid
Chromatography, High Pressure Liquid
Subjects
Details
- ISSN :
- 00399140
- Volume :
- 101
- Database :
- OpenAIRE
- Journal :
- Talanta
- Accession number :
- edsair.doi.dedup.....70e4a54493060d3d6ac3d09813ec8d16