Evaluation of thermally pretreated silica stationary phases under hydrophilic interaction chromatography conditions

Three novel hydrophilic interaction chromatography columns packed with bare silica 2.6 mu m superficially porous particles were evaluated. These stationary phases undergo a different pretreatment temperature (400, 525, and 900 degrees C) that might influence their kinetic performance and thermodynamic properties. In the first instance, we demonstrated that the performance of these columns was inferior to the commercial ones in the low plate count range (10 000 plates), but was more favorable for N values beyond 40 000 plates. Thanks to its high permeability and reasonable flow resistance (phi = 695), together with a minimum reduced heights equivalent to a theoretical plate value of only 2.4, the stationary phase pretreated at 400 degrees C was particularly attractive for N > 70 000 plates with a remarkably low impedance value (E = 2488). In a second step, the impact of pretreatment temperature was evaluated using two mixtures of polar substances, namely nucleobases and derivatives, as well as nicotine and derivatives. Retentions and selectivities achieved on the tested stationary phases were appropriate, but selectivity differences were minor when modifying pretreatment temperature from 400 to 525 degrees C. When we increased the pretreatment temperature up to 900 degrees C, the surface chemistry was more seriously modified. Finally, the columns presented a good stability even at high temperature (70 degrees C), especially for the phases pretreated at 400 and 525 degrees C.