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Paul R. Haddad | Authors

Articles

Electrophoretic Concentration — A Simple and Green Approach for Sample Preparation

Electrophoretic concentration (EC) is an electric field-driven and environmentally friendly off-line sample preparation for charged analytes. EC was demonstrated for the enrichment of either six anionic pollutants or five cationic drugs from purified, drinking, river, or waste- water samples. EC provided analyte enrichment in 15–50 min with concentration factors of 30–249 and 12–243 for the negatively and positively charged analytes, respectively. A modification of the EC device enabled simultaneous EC and separation (SECS) of six cationic and anionic herbicides with concentration factors of 18–337 in 30 min. The potential of SECS has also been evaluated for the determination of high mobility ions in urine and the results obtained have been compared to common acetonitrile treatment of urine. SECS provided an enrichment of high mobility ions and revealed more peaks compared to the acetonitrile treatment.

Retention Time Prediction Based on Molecular Structure in Pharmaceutical Method Development: A Perspective

The principal aim of this work was to provide a perspective with practical utility in streamlining the chromatographic method development in pharmaceutical industries based upon predicting the chromatographic retention times from molecular structures. Workflows were suggested with a focus on reversed-phase LC, IC, and HILIC as the three major techniques. Unlike HILIC, retention prediction in both reversed-phase LC and IC can benefit from the maturity of these techniques and the transparency of their retention mechanisms. In reversed-phase LC the solute coefficients in the hydrophobic subtraction model and in IC the a and b values in the linear solvent strength model can be the subject of modelling with their subsequent use in retention prediction. A workflow for HILIC can be based on the design of experiments approach, to account for all major contributors to the retention mechanism, and direct correlation of experimental retention times to the molecular descriptors.