Revisiting the dependence of retention factor on the content of organic component in the mobile phase in reversed‐phase HPLC
Serban C. Moldoveanu, Elena Bacalum, Toma Galaon, Victor David
Abstract
In high‐performance liquid chromatography, the dependence of retention factor k on volumetric fraction ϕ of organic phase is expressed by log k = F( ϕ ) with F( ϕ ) obtained by measuring log k at different ϕ values. From F( ϕ ), a value k w is calculated by taking ϕ = 0. The equation log k = F( ϕ ) is applied for predicting k , and k w is a descriptor of hydrophobic character of solutes and stationary phases. Calculated k w should not depend on the nature of organic component of mobile phase but extrapolation procedure leads to different k w for different organic components. The present study shows that the expression of F( ϕ ) changes depending on the range of ϕ and the same function F( ϕ ) cannot be used for the full range of ϕ from 0 to 1. Consequently, k w obtained by extrapolation of ϕ to zero is not correct because the expression of F( ϕ ) was generated by fitting the data using ϕ with higher values. The present study shows the proper way to obtain the value of k w .