Isocratic Resolution of Fluoroquinolone-Based Antibiotics on the Phenylethyl-Bonded Phase under Nonaqueous Elution: A Consideration of the Separation Mechanism

This paper reports the isocratic resolution of 10 fluoroquinolone-based antibiotics and their precursors on the phenylethyl-bonded phase under the elution of the nonaqueous mobile phase composed of acetonitrile, methanol, acetic acid, and triethylamine. Most of the analytes were baseline resolved within 10 minutes. The interaction simulation and Fourier-transform infrared spectroscopy (FTIR) data indicated that the carbonyl-containing group, a secondary or tertiary amine of an analyte, was heavily involved in the retention, resulting in retention with residual silanol groups on the stationary phase. In some cases, the elution reversal or resolution enhancement of analytes was observed when the volume of acidic or basic additive in the mobile phase was dominant. However, the π-π complexation interaction between the fluorine-attached phenyl group of the analyte and the phenylethyl moiety on the stationary phase was not observed. Consequently, the resolution could not be reproduced either on the other stationary phase modified with C18, phenyl, or phenylhexyl moiety under the same chromatographic conditions or under the aqueous elution.

Deposition and Integration of a Novel Ultra-Low k (2.2) Material

Increasing demands for faster chip speed and reduced power consumption are driving the semiconductor industry to develop insulating layers with lower dielectric constants. As the dielectric constant of a material is reduced, however, it becomes increasingly difficult to achieve the mechanical strength required to manufacture a multilevel interconnect. A new route to the synthesis of mesoporous silica has been demonstrated on 200 mm wafers. Silicate precursors dissolved in supercritical CO2 are infused into a block copolymer film. The polymer is then removed, but the resulting porous SiO2 replicates its ordered structure, enhancing the strength of the network. Incorporation of alkyl silicates further improves the film properties. Post-treatment to cap residual silanol groups renders the surface of the film hydrophobic and stabilizes it to air exposure. By appropriate choice of the block copolymer and other process parameters, the pore size and density can be varied and k values as low as 1.8 can be achieved. For a film with a dielectric constant of 2.25, the pore size is ∼4 nm. The hardness and modulus are 1.1 GPa and 7.8 GPa, respectively, as measured by nanoindentation. Four-point bend measurements yield fracture energies of 9.8 J/m2. More importantly, the film can withstand chemical mechanical planarization (CMP) using standard oxide polishing conditions.