Retention Indices as the Most Reproducible Retention Parameters in Reversed Phase HPLC. Calculation for Hydrophilic Phenolic Compounds Using Reference n‐Alkyl Phenyl Ketones

Abstract

A comparison of various presentation forms of retention parameters measured in multi‐step gradient elution regimes in reversed phase HPLC indicates that retention indices in the scale of n‐alkyl phenyl ketones (so‐called Smith′s RI system) have the maximal reproducibility. However, the determination of these parameters for most hydrophilic compounds eluted before the first reference acetophenone (RI=800) implies their calculation by extrapolation, that can lead to the high irreproducibility of results, especially in regimes with initial isocratic stages followed by fast gradient elution. This fact explains the necessity of elaboration of a new calculation method based on the extrapolation of retention concentrations, which provides the appropriate interlaboratory coincidence of RI values at least within the range 600–800 i.u. Using this algorithm, retention indices for about 60 phenolic compounds have been determined, that permits us to identify them in complex mixtures of natural plant's extractive substances using HPLC without corresponding reference samples.

Keywords:

• Organic compounds of phenol series
• Reversed‐phase HPLC
• Retention indices
• Reference n‐alkyl aryl ketones
• Extrapolation
• Interlaboratory reproducibility