Application of reverse‐phase h.p.l.c. for the determination of partition coefficients

Abstract

AbstractReverse‐phase high performance liquid chromatography (h.p.l.c.), using a C18 analytical column, has been applied to the determination of partition coefficients for a range of agrochemicals and industrial chemicals. Using a correlation plot of the logarithm of the capacity factor (k) with the logarithm of the n‐octanol/water partition coefficient (Pow), partition coefficients were predicted with a 95% tolerance interval of ± log 0.80 of the literature ‘shake flask’ value for compounds of random structure over the log Pow range 0–6. Individual regression lines were fitted for compounds of comparable size and functional grouping, which reduced any bias and thereby enabled more accurate predictions to be made. The reverse‐phase h.p.l.c. method has a number of advantages over the traditional ‘shake‐flask’ method. Quantitative methods are not required or do not have to be developed and only the determination of the retention time is necessary. Quick and precise determinations of retention times are facilitated by h.p.l.c. and further improvement can be obtained by automation of solvent mixing, solute injection and data processing. H.p.l.c. was used to generate partition coefficient data for highly hydrophobic materials and, because of its resolving power, data for mixtures and solvent fractions. Dual detection, using u.v. and r.i. in series, was necessary for some compounds, particularly unknown mixtures and impure compounds. Calculations of log Pow based on the fragment‐addition method using the structural data file, MACCS, was of considerable value in confirming experimentally derived values. In certain cases, calculated log Pow values were considered more trustworthy than experimental values.