Mixed-mode stationary phase

The recent development of mixed-mode stationary phases may provide new approaches for the separation of neuroactive steroids from biological matrices. These stationary phases typically embed a charged functional group within the nonpolar carbon chains typically employed in RP separations, and as such separations based on both RP and ion-exchange characteristics can be designed. Examples of this column type are the Primesep line of columns from SIELC Technologies. This separation approach maybe quite useful for the separation of steroid sulfates from complex mixtures. 

Ohyama, K., Fujimoto, E., Wada, M., Kishikawa, N., Ohba, Y., Akiyama, S., Nakashima, K., and Kuroda, N. (2005). Investigation of a novel mixed-mode stationary phase for capillary electrochromatography. Part III separation of nucleosides and nucleic acid bases on sulfonated naphthalimido-modified silyl silica gel.. Sep. Sci. 28, 767—773. 

CF1, N02 1, BF1, N03 1, P04 3, Se03 2, S04 2, lactate, acetate, propionate, butyrate, isobutyrate Mixed mode stationary phase Careful control of eluent pH and ionic strength - [62]... 

A new type of mixed-mode stationary phase which incorporates both strong anion-exchange (triehtylammonium methylstyrene) moieties and C18 (octadecylacrylate) ligands was used by Scherer et al. to separate acetylsalicylic acid and three of its metabolites in less than 2 min [42], A rapid reversed EOF (1.8 mm/s) was generated over a wide range of pH, from 3 to 9. It was found that EOF velocity shows variation with pH, the magnitude of which is a function of the content of SAX versus C18 moieties. 

Fig. 4.6. Dependence of EOF linear velocity on pH of the mobile phase using a CEC column packed with a Mixed Mode stationary phase. Column 25 cm Hypersil Mixed Mode packed capillary. Mobile phase 75Q McCN-.50 mM Na2HP04. Voltage 20 kV. Marker thiourea.

JT Eleveld, HA Claessens, JL Ammerdorfer, AM van Herk, CA Cramers. Evaluation of mixed-mode stationary phases in liquid chromatography for the separation of charged and unchaiged oligomer-like model compounds. J Chromatogr A 677 211-227, 1994. 

While lome sutionaiy phases are dominated a single nu mecha alsm, and subsequently can be placed near one of the apices of the triangle, other stationary phases function via two or more mqjor retention mecha nisms. These multimodal phases, henceforth referred to as mixed-interaction or mixed-mode stationary phases, have historically bMn successful in separating such biomolecules as nucleic adds and protdns. Most often, phases of these types have been used in low- to medium-pressure chromatography, and have often been of polymeric base. 

The fundamental difference between conventional stationary phases and mixed-mode stationary phases is that in synthesizing mixed-mode supports heterogeneity is a goal rather than a side-product. Subsequently the design of heterogeneous stationary phases should allow for a considerable d ree of variability. 

One of the key aspects of using the multiligand approach for synthesizing mixed-mode stationary phases has been the reproducibility of the bonding chemistry. In most phases produced a kinetic approach has been taken. Two or more ligands of the appropriate starting silane are simultaneously co-... 

Fio. 9. Simultaneous separation of deoxynudeotides and deoxynudeosides on a series of mixed-mode stationary phases. Mobile phase was 10% methanol and 0.05 M KH,P04, pH 4.9. [Courtesy of Crowther (111).]... 

CEC-MS is used as an analytical tool for pharmaceutical analysis. The CEC-ESl-MS analysis and quantification of a potential drug candidate from 13 structurally related compounds in extracted plasma were reported by Paterson et al. [26]. The CEC column was packed with an experimental mixed-mode stationary phase containing both Cig and sulfonic acid ligands. These phases promote stable electroosmotic flow across a wide range of pH values and allow a greater choice of buffer pH values. The mobile phase was acetonitrile/25 mM ammonium acetate (75 25) at pH 3.5 adjusted with... 

Chromatographic determination of surfactants can be performed by utilizing different separation modes, such as reversed-phase, ion-exchange and size-exclusion techniques. However, a mixed-mode stationary phase has been developed that is suitable for analyzing anionic, nonanionic and cationic surfactants in a single run [51]. The packing material of the commercially available column consists of 5-p,m particles with a pore size of 120 A and a specific surface area of 300 m g . ... 

Applications of ion Chromatography on Mixed-Mode Stationary Phases... 

Applications of Ion Chromatography on Mixed-Mode Stationary Phases 643 Table 6.2 Structural and technical properties of the OmniPac separator columns. 

Liu, X. and Pohl, CA. (2011) HlLlC behavior of reversed-phase/ion-exchange mixed-mode stationary phases and their applications, in Hydrophilic Interaction Liquid Chromatography (HILIC) and Advanced Applications (eds P.G. 

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