The effect of temperature on the retention of analytes with different volatility in RP HPLC with a low content of acetonitrile in the eluent
Abstract
It is known that an increase of temperature in RP HPLC can significantly improve the efficiency of the chromatographic process and reduce the content of the organic modifier in the eluent or even use pure water as the latter. However, an increase of the water content in the eluent, the wettability of the hydrophobic silica gel C18 inevitably deteriorates and, as a consequence, the formation of a stationary gas phase (SGP) in the pores of this sorbent occurs. Obviously, the existence of SGF, first of all, will influence the behavior of volatile analytes. The purpose of this work is to study the effect of temperature on the retention of analytes with different volatility at low acetonitrile levels in the eluent, taking into account the possible existence of a gas phase in the pores of the sorbent.
Based on the results of the studies performed, it was established that an increase in temperature allows several times to reduce the value of HETP in RP HPLC, regardless of the volatility of the analytes. The negative influence of the high volatility of the analytes begins to appear only at high temperatures and a low rate of elution in the case of a low content of acetonitrile in it or its absence. Such an effect can be explained by the longitudinal diffusion of the analytes in the SGP located in the pores of the hydrophobic sorbent. The existence of SGP is confirmed by temperature dependences of retention parameters of analytes with different volatility: potassium nitrate, dimethylformamide, acetone and acetylene. An increase in temperature is accompanied by an improvement in the wettability of the hydrophobic octadecylsilicagel, an increase in the volatility of the analytes, and a decrease in their adsorption. The listed processes in various ways affect the retention parameters of these analytes. As the temperature rises, the volume of retention of the non-adsorbing non-volatile potassium nitrate increases, in the case of practically non-adsorbing highly volatile acetone, this volume remains practically unchanged, and in the case of less volatile acetone and dimethylformamide adsorbed, the retention volume decreases, but to different degrees.
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