A Comparison of Methods for the Determination of Dead Time in a Reversed-Phase High-Performance Liquid Chromatography System Used for the Measurement of Lipophilicity

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Abstract
The dead time (void volume) of a reversed-phase system utilizing a column containing the divinylbenzene-styrene copolymer packing (PRP-1) was determined using candidate dead time markers, and two series of homologues, n-alkanols and n-alkyl benzenes. The retention data from the homologous series were subjected to several mathematical treatments. The retention data for n-alkanols gave consistent values for the dead time (1.24–1.27 minutes) provided that data from MeOH and EtOH were not included. Data from the n-alkyl benzene series did not provide a reliable value for system dead time. Of the candidate void volume markers examined, sodium nitrate and water (1.26 minutes) had retention times which were consistent with dead times calculated from the n-alkanol series. As nitrate is readily detected by both UV and RI at low concentrations, it is the preferred dead time marker for this HPLC system. The homologous series of compounds were used to calibrate the system for the determination of lipophilicity. The alkyl benzenes and alkanols provided two different calibration lines on plotting log k' vs log P (octanol). The calibration lines were not statistically different when plotting log k' vs log P (hexadecane).

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