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

The dead time (void volume) of a reversed-phase system utilizing a col umn containing the divinylbenzene-styrene copolymer packing (PRP-1) wa s determined using candidate dead time markers, and two series of homo logues, n-alkanols and n-alkyl benzenes. The retention data from the h omologous series were subjected to several mathematical treatments. Th e retention data for n-alkanols gave consistent values for the dead ti me (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 relia ble value for system dead time. Of the candidate void volume markers e xamined, sodium nitrate and water (1.26 minutes) had retention times w hich were consistent with dead times calculated from the n-alkanol ser ies. As nitrate is readily detected by both UV and RI at low concentra tions, it is the preferred dead time marker for this HPLC system. The homologous series of compounds were used to calibrate the system for t he determination of lipophilicity. The alkyl benzenes and alkanols pro vided two different calibration lines on plotting log k' vs log P (oct anol). The calibration lines were not statistically different when plo tting log k' vs log P (hexadecane).