Evaluation of Column Test Methods to Study Inactivation of Chemically Bonded Silica Gels

The silanol activity and trace metal detection methods for chemically bonded silica gels were evaluated in silico. Test compounds with large molecular sizes may demonstrate negative results because of the possibility of indirect hydrogen bonding via short alkyl groups or siloxane of the silica gels. This hypothesis was based on the observation of weak hydrogen bonding energy values similar to those observed in the study of the alkyl group effect on the hydrogen bonding of alkanols. Consequently, smaller molecules may be a better choice for the analysis of bonded-phase quality.

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.

Pentafluorophenyl bonded phase separation: the assay of Australian antioxidant formulation of ascorbic acid, rutin and hesperidin

This work describes two novel validated HPLC methods for the separation and determination of potent antioxidant formulation.

Modified mortar pad behavior in the transfer of compressive stresses

ABSTRACT This research aims to analyze the compressive stress transfer between precast concrete elements using cement mortar pads modified with polypropylene fibers, styrene-butadiene latex and heat-expanded vermiculite. The stress transfer analyses are performed interleaving a cementbearing pad between two concrete blocks, subjecting the entire specimen to different compressive load tests. The parameters analyzed in the tests are: surface roughness (using bosses on the bonded phase of different thicknesses), compressive strength with monotonic and cyclic loadings. The main results obtained in this study are: a) the presence of pad increased the strength in 24% for thicknesses of imperfections of 0.5 mm and approximately 12% for smooth faces blocks; b) gain of effectiveness of the bearing pad when the concrete strength was reduced; c) for cyclic loading, the bearing pad increased in 48% the connections strength.