| Ion chromatography (IC) is a method that has gained acceptance in industry for the separation and quantification of ions. Currently, analytical labs are faced with the challenge of increasing sample throughput. For this reason, high-speed separations are extremely sought after. This thesis investigates methods for reducing analysis time in IC. In particular, two approaches were examined: elevated temperature and monolithic columns.; IC separations are usually performed at room temperature, however, an increase in column temperature decreases eluent viscosity which in turn decreases the pressure necessary to achieve a given flow rate. Therefore, the flow rate can be further increased at elevated temperatures before the pressure maximum of the IC column is reached. However, elevated temperatures also affect the retention of ions. The first part of the thesis deals with the characterization and modeling of the effect of temperature on IC separations. It was found that increasing the column temperature results in significant changes in retention, and in particular, the retention of ions could decrease, increase or not be affected at all, depending on the type of stationary phase and eluent. These studies facilitated the implementation of elevated temperatures for high-speed cation separations. A 35% improvement in separation speed was obtained by operating at 60°C for a mixture of lithium, sodium, ammonium, potassium, rubidium, cesium, magnesium, calcium and strontium.; Alternatively, high-speed IC can be performed with monolithic columns. Monolithic columns result in a much lower resistance to flow than columns packed with particles since they contain large channels for eluent flow. Therefore, high flow rates can be used with modest pressure drops. Separations were performed on a reversed-phase monolith using either ion-interaction chromatography, or permanent coating of the monolith with a hydrophobic surfactant (didodecyldimethylammonium bromide, DDAB) to convert it into an ion exchanger. Both approaches resulted in the separation of anions in less than one minute, which represents about a ten-fold improvement in separation speed. Finally, this thesis shows that monoliths are better suited for high-speed IC than elevated temperature. |
