1. Maggi Tebrake– Early Pharmaceutics & Technology, 3M Health Care Ltd, Loughborough Lindsey Gunby– Industrial Placement Student (EP&T 2004-05), 3M Health Care Ltd, Loughborough The popularity of silica as the back bone to reversed phase materials is due to its mechanical stability and the ability to readily modify its particle shape and size and chemically modify its surface. The drawbacks of silica lie in its limited pH range and the presence of un- reacted, acidic silanol groups resulting in tailing of basic compounds. However, exactly these secondary interactions of API (active pharmaceutical ingredient) and silica surface can be vital to achieve sufficient separation of polar compounds in reversed phase HPLC. Various approaches have been taken to classify the overwhelming number of columns available in order to give a guide for chromatographers during method development. This study investigates an approach to classify a number of reversed phase materials with regards to their capability to provide selectivity for polar compounds while maintaining symmetrical peaks for basic compounds and showing retention for uncharged species. Introduction Conclusion Experimental An Investigation Into LC Column Classification Enabling your success Basic Compounds The following API’s were employed as probes in a test mixture: Propranolol Ibuprofen Caffeine BDP The resulting separations were optimised for the current standard column, YMC AQ pack ODS, using DryLab TM. The performance of the columns listed in Table 1 was then tested using the previously optimised conditions for each pH range and the quality of the separations compared to the quality of the separation achieved using the YMC column. Table 1: Columns tested including reference column YMC AQ pack 3M Drug Delivery Systems Results Figure 1: Chromatograms of the test mix on the test columns listed in table 1 run at low (left), neutral (middle) and high (right) pH conditions The YMC column was used as the reference point against which the performance of all other columns was measured. The uncharged BDP shows a similar retention time on all columns. However, there are significant differences in retention, selectivity and peak shape for the charged compounds in the test mix. There is generally good peak shape for all compounds at low pH of the mobile phase. However, significant differences in selectivity for the charged compounds could be observed. At high pH the acidic silanol groups on the surface of the silica back bone are charged and a deterioration in peak shape is an indication how easily accessible these acidic silanol groups are. Particularly the Nucleodur Pyramid shows dramatic degradation in peak shape for Propranolol. Gradients (Tg = 15 min and 10 min) covering 0 % to 100 % acetonitrile were performed at 30ºC and 50ºC column temperature. The gradients were run in acidic, basic and uncontrolled pH conditions. The flow rates and injection volume were l ml/min and 10 mcl respectively. Figure 1 shows the chromatograms of the test mix run on the six different test columns. The test mix and conditions developed in this study proved a quick and simple method to compare column performance at various pH conditions. BDP retention time can be used as an indicator for the columns hydrophobicity. Propranolol peak shape can be used to indicate silanol activity. The resolution of caffeine and propranolol at low pH can be used as an indication for selectivity towards polar compounds. The same is true for Ibuprofen and caffeine at high pH.