LCGC Europe-02-01-2008

This study evaluates the use of HPLC to estimate the log P (the octanol–water partition coefficient) of two compounds, apocynin and diapocynin. The paper will discuss the effects of an unexpected reversal of retention that occurred when these compounds were chromatographed with various amounts of methanol–water mobile phases.

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Screening for important factors during method optimization or in robustness testing involves two-level screening designs, such as fractional factorial and Plackett–Burman designs, as described in Part 1. This second part on screening designs discusses the experimental protocol for executing these designs and the data analysis of their results.

The use of dual polarization interferometry (DPI) to measure the behaviour of alkyl-modified surfaces under different solvent regimes is described. The empirically observed and modelled behaviour of grafted long alkyl chain adlayers on a silica surface were in good agreement. The empirical data was also compared with data using analogous systems and these also matched well. This approach has the potential to gain much greater insight into the behaviour of reversed-phase (RP) columns and could help to design column surfaces that are resistant to phase collapse.

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This month's column discusses the practicalities of detecting substitutions in counterfeit pharmaceuticals. The approaches used are practical "take home" lessons readers can apply to analyse unknowns in any mixture.