Chromatographic evaluation using basic solutes of the silanol activity of stationary phases based on poly(methyloctylsiloxane) immobilized onto silica

J of Separation Science

2011

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Complex analyses of polar compounds, especially basic ones, require more selective stationary phases. The present paper describes a stationary phase prepared by thermal immobilization of poly(methyltetradecylsiloxane) onto chromatographic silica (PMTDS-SiO(2)). This stationary phase presents hydrophobic and ion-exchange interactions that confer both high retention and unique selectivities for basic solutes. The influence of ion-exchange interactions is confirmed by the increase in retention factors of basic solutes when the mobile-phase pH changes from acidic to neutral and by the decrease in retention factors when the mobile-phase pH changes from neutral to alkaline. The ion-exchange properties of the stationary phase are enriched in neutral mobile phase (pH 7-7.5) using soft Lewis bases such as tricine and tris as buffers but are suppressed in both acidic (pH 2.5-6) and highly alkaline mobile phases (pH≤10). Increasing both temperature and flow rate permits more rapid separations while maintaining the selectivity. The stability of the stationary phase is evaluated with acid, neutral and alkaline mobile phases.

Section: Effect Of Mobile-phase Ph and Buffer Type On Retention And Asupporting

confidence: 90%

Section: Introductionsupporting

confidence: 60%

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Selectivity of some basic solutes on a poly(methyltetradecylsiloxane)‐silica stationary phase

J of Separation Science

2011

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Characterization of a mixed-mode reversed-phase/cation-exchange stationary phase prepared by thermal immobilization of poly(dimethylsiloxane) onto the surface of silica

Euerby²

2012

Anal Bioanal Chem

A novel stationary phase prepared by the thermal immobilization of poly(dimethylsiloxane) onto the surface of silica (PDMS-SiO(2)) has been described, evaluated and compared with 229 commercially available RP-LC stationary phases using the Tanaka column classification protocol. The phase exhibited many unique chromatographic properties and, based on the phases in the database, was most similar to the fluoroalkylated phases (aside from the obvious lack of fluoro selectivity imposed by the C-F dipole). The phase exhibited classic reversed-phase behaviour in acid mobile phase conditions and mixed-mode reversed-phase/cation-exchange retention behaviour in neutral mobile phase conditions. The phase exhibited acceptable stability at both low and intermediate pH, conditions which should impart optimum chromatographic selectivity to the phase. Retention of basic analytes was shown to occur by a "three site model" as proposed by Neue. This new PDMS-SiO(2) stationary phase is extremely interesting in that the dominancy of its hydrophobic and ion-exchange interactions can be controlled by the influence of mobile phase pH, buffer type and concentration. The PDMS-SiO(2) stationary phase may provide a complementary tool to reversed-phase and HILIC stationary phases. The present results highlight the fact that the type of buffer, its concentration and pH can not only affect peak shape but also retention, selectivity and hence chromatographic resolution. Therefore, in method development and optimization strategies it is suggested that more emphasis should be given to the evaluation of these mobile phase operating parameters especially when basic solutes are involved.

Comparison of classical chromatographic tests with a chromatographic test applied to stationary phases prepared by thermal immobilization of poly(methyloctylsiloxane) onto silica

Euerby²

2012

Anal Bioanal Chem

Stationary-phase evaluation in reversed-phase liquid chromatography (RP-LC) is not a straightforward process. A number of tests to characterize and classify stationary phases have been suggested. The results of these various tests, however, do not always describe the real properties of the stationary phase. This study critically compares several tests for RP-LC stationary phases, including the Engelhardt, Tanaka, and SRM 870 tests, as well as an in-house test, with emphasis on the stationary-phase descriptors of hydrophobicity and silanol activity. The stationary phases were prepared by thermal immobilization of poly(methyloctylsiloxane) onto silica. Hydrophobicity data from the tests were generally good and interchangeable between the several tests. In contrast, the silanol activity results of the various tests differ significantly. As a consequence, stationary phase classification with respect to silanol activity depends considerably on the test method applied. A new classification method for silanol activity is proposed.