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Investigation of the use of large pore size stationary phases in micellar liquid chromatography

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Description: One of the limitations that has restricted the applicability of micellar liquid chromatography (MLC) is the weak eluting power of micellar mobile phases compared to conventional hydro-organic mobile phases used in reversed phase liquid chromatography (RPLC). This may be the result of Donnan or steric exclusion of the micelles from the pores of conventional small pore size (∼100 Å) stationary phases, within which nearly all (≥99%) of the stationary phase resides and the analytes spend most of their time. To determine if large pore size stationary phases would overcome this limitation in MLC, several C 8 and C 18 stationary phases ranging from 100-4000 Å were investigated using a diverse set of test solutes and micellar solutions of anionic, neutral, and cationic surfactants as mobile phases. With the larger pore size stationary phases, the eluting power of the MLC mobile phases were enhanced with all surfactant types, the greatest effect being with the neutral surfactant. Thus, the weak eluting power of micellar mobile phases can be overcome by the use of large pore size stationary phases. The critical pore diameter--the diameter at which exclusion effects become negligible--was found to be ∼300 Å and ∼1000 Å for the C 8 and C 18 columns, respectively. Partitioning behavior of representative nonpolar and polar solutes on both the small and large pore size C 8 and C 18 columns was shown to follow the three-phase partitioning model for MLC. Methylene group selectivity data showed that there were significant differences in the stationary phase characteristics between the small and large pore size C 8 columns whereas the C 18 columns only showed minor differences. The large-pore (1000 Å) C 18 stationary phases were found to be very effective in eluting highly hydrophobic compounds such as alkylphenones which are strongly retained on the conventional small-pore (∼100 Å) stationary phases typically used in MLC. In addition, the usefulness of large-pore C 18 stationary phases in such important MLC applications as rapid gradient re-equilibration and direct sample injection of drugs in plasma was also demonstrated.
Language: English
Format: Degree Work