Recent developments in HPLC methods have focused on various strategies in order to increase the speed of analysis. One area of impressive growing is column technology. Today, analytical methods that propose the use of short columns packed with sub-2 μm particles installed in ultra high-pressure LC instruments are not uncommon. Another strategy consisted of heating thermally resistant columns to temperatures well above of 100°C in order to reduce eluent viscosities and, therefore, column backpressure. We discuss experimental conditions for achieving high-throughput analysis using standard instruments with a few simple modifications. The chromatographic performance of two particulated and a silica-based monolithic column operated at moderate temperatures and flow rates are compared. The monolithic column proved to be stable over several thousands column volumes at 60°C. More important, its resistance to mass transfer at this temperature was significantly reduced. Very fast separations of two different mixtures of pharmaceutical compounds, anti-inflammatory drugs and β-blockers, were achieved with the three columns at 60°C by using ACN/buffer at 5 mL/min. Excellent peak shapes of basic solutes and quite reasonable resolutions were achieved in very short analysis times with columns operated at temperatures moderately higher than the usual room temperature.
A chiral anion-exchanger stationary phase based on cinchonidine (CD) was developed. Two columns were packed with and without endcapping (EC) treatment (CD-chiral stationary phase[CD-CSP(EC)] and [CD-CSP], respectively) and studied for their ability to separate N-2,4-dinitrophenyl α-amino acids (DNP-amino acids) enantiomers over a temperature range of 10-40 °C with a hydro-organic buffer mobile phase. The more hydrophobic, endcapped stationary phase showed significantly larger retentive capacity than the non-endcapped one. The apparent thermodynamic transfer parameters of the enantiomers from the mobile to both CSPs were estimated from van't Hoff plots within the cited temperature range. Similar studies with two natural quinine-based columns (QN-CSP and QN-CSP(EC)) were previously reported. In this work, a critical comparison in the chiral recognition ability to DNP-amino acids of these cinchonidine and QN-based chiral columns was drawn. It has been found that QN-based CSPs show greater chiral recognition capability towards these derivatives than CD-CSPs. The influence of the QN methoxy group on the equilibrium constants of the enantioselective interaction between these DNP-amino acids with these two cinchona CSPs could be assessed.
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