Novel ultra stable silica-based stationary phases for reversed phase liquid chromatography—Study of a hydrophobically assisted weak acid cation exchange phase

Abstract

A mixed-mode reversed-phase/weak cation exchange (RP/WCX) phase has been developed by introducing a small amount of carboxylate functionality into a hydrophobic hyper-crosslinked (HC) platform. This silica based HC-platform was designed to form an extensive polystyrene network completely confined to the particle's surface. The fully connected polymer network prevents the loss of bonded phase, which leads to superior hydrolytic stability of the new phase when compared to conventional silica based phases. Compared to previously introduced HC phases the added carboxylic groups impart a new weak cation exchange selectivity to the base hydrophobic HC platform. The phase thus prepared shows a mixed-mode retention mechanism, allowing for both neutral organic compounds and bases of a wide polarity range to be simultaneously separated on the same phase under the same conditions. In addition, the new phase offers the flexibility that gradients in organic modifier, pH or ionic competitors can be used to affect the separation of a wide range of solutes. Moreover, the inherent weak acid cation exchange groups allow formic and acetic acid buffers to be used as eluents thereby avoiding the mass spectrometric ionization suppression problems concomitant to the use of non-volatile additives such as strong amine modifiers (e.g. triethylamine) or salts (e.g. NaCl) to elute basic solutes from the strong cation exchange phase which was previously developed in this lab. The use of the new phase for achieving strong retention of rather hydrophilic neurotransmitters and drugs of abuse without the need for ion pairing agents is demonstrated.

Optimization of the synthesis of a hyper‐crosslinked stationary phases: A new generation of highly efficient, acid‐stable hyper‐crosslinked materials for HPLC

“…This agrees well with our previous studies of all the other HC phases [43,44,71], suggesting the two solutes (i.e. trans-chalcone and cis-chalcone), which are the major determinants of S Ã , are also more strongly retained on the HC-T phase than on conventional RPLC phases.…”

Strong cation exchange column allow for symmetrical peak shape and increased sample loading in the separation of basic compounds

“…Compared with the separation made on the XBridge C18 column, the peaks on the SCX column were "clustered". A narrow wash window, especially for similarly charged analytes, is often encountered on SCX columns [17]. However, with good peak shapes, a considerable sample amount could still be acceptable within limited resolution spacing.…”

“…The dominant SCX materials typically feature sulfonic acid functionalities with different "spacers" attached to supports. According to their supports, SCXs can be mainly classified into organic polymer-based SCXs [15,16] and silica-based SCXs [17,18]. Polymeric materials are used mostly in ion-exchange chromatography, with a high chemical stability within a very wide pH range.…”

Retention mechanism of hypercrosslinked polystyrene silica hybrid phase in normal phase chromatography

“…The Carr group developed these polymer-silica hybrid phases as acid and thermal stable phases for RPLC [15][16][17][18][19][20][21][22]. The highly crosslinked aromatic network prevents loss of stationary phase under extreme conditions.…”

“…Normal phase HPLC separations have been performed with fully polymeric hypercrosslinked polystyrene [5,8] and with silica particles possessing a thin layer of highly crosslinked aromatic network [15][16][17][18][19][20][21][22]. The Carr group developed these polymer-silica hybrid phases as acid and thermal stable phases for RPLC [15][16][17][18][19][20][21][22].…”