Capillary Ion Chromatography at High Pressure and Temperature

Abstract

The application of high pressure and temperature in ion chromatography (IC) can significantly improve the efficiency and reduce the analysis time. In this work, the kinetic-performance limits of capillary IC columns with inner diameters of 400 μm packed with 4 and 7 μm macroporous anion-exchange particles were investigated employing a capillary ion-exchange instrument allowing column pressures up to 34 MPa and column temperatures up to 80 °C. Plate heights below 10 μm could be realized using capillary columns packed with 4 μm particles. Compared to conventional IC using 7 μm particles and pressures up to 21 MPa, a 40% improvement in plate number could be achieved when working at the kinetic performance limits at 34 MPa and using columns packed with 4 μm particles. Using coupled columns with a total length of 400 mm, a mixture of seven anions was separated within 7.5 min while yielding 20,000 plates. Increasing the temperature improved the performance limits when operating in the C-term region (for fast IC separation using columns <75 cm). Temperature also affected the retention properties and hence the selectivity. At higher temperature, retention for monovalent ions was mainly governed by ion diameter. An increase in retention with temperature was observed for small ions, and there was a decrease for ions having a larger diameter. The retention factor for divalent and trivalent anions increased with temperature.

Using contemporary liquid chromatography theory and technology to improve capillary gradient ion-exchange separations

“…Our group already demonstrated the possibility to successfully couple two capillary IC columns via zero-dead-volume connections and the experimental plate numbers matched the predicted kinetic performance limits [25]. In this study a column-coupling experiment was conducted by coupling seven 150 mm long capillary columns.…”

“…Only recently capillary columns with 4 m particles have become commercially available for IC separations [22,23]. To assess the performance limits of capillary IC in isocratic mode contemporary LC theory, originally proposed by Giddings [24], was applied to visualize the time required to obtain a specific number of plates (or peak capacity), while applying the maximum available operating pressure and taking into account both the separation efficiency and the column permeability [25,26]. In gradient mode, Causon et al predicted the gradient-performance limits based on isocratic data and an empirical peak-capacity calculation [27].…”

Capillary ion chromatography–mass spectrometry for simultaneous determination of glucosylglycerol and sucrose in intracellular extracts of cyanobacteria

“…Additionally, the split-flow is not needed when IC tandems MS detector with much smaller diameter columns and lower flow rate. Thus, this finding serves as a new foundation for the applicability of capillary IC in biological analysis [22].…”

“…Many recent reports demonstrated that capillary IC can significantly improve separation efficiency and sensitivity [18][19][20][21]. Additionally, the split-flow is not needed when IC tandems MS detector with much smaller diameter columns and lower flow rate.…”

Performance evaluation of ion-exchange chromatography in capillary format

“…For the sake of simplicity, the focus was put on one single anion that was arbitrarily selected as chloride (Fig. A) . The minimal plate‐height values ( h min ) were inspected for both systems.…”