Simultaneous reversed-phase extraction of lipoxygenase and cyclooxygenase metabolites of arachidonic acid in nasal secretions: methodological aspects.

An improved analytical method for the simultaneous solid-phase extraction of arachidonic acid metabolites in biological samples is described. The major aim of the work was to define the cause of the different recoveries reported in the literature for leukotrienes and hydroxyeicosatetraenoic acids. We used nasal lavages to carry out a comparative study of solid-phase extraction parameters of practical importance in securing good recoveries of leukotrienes and hydroxyeicosatetraenoic acids from biological samples. We evaluated the influence of the pH of the sample, the pH of the water used to wash the extraction cartridge before elution of the adsorbed analytes, the comparative behaviour of commercially available octadecyl adsorbents and the influence of the concentration-evaporation step on final recoveries. Data thus obtained show that there is no significant difference in results when the samples and the water used to wash the cartridge before analyte elution are adjusted to pH values ranging between 4.0 and 7.4. Below pH 4.0, losses may be significant. Furthermore, recoveries can be very much dependent on the type of solid-phase cartridge material and on the eluent evaporation method, especially with regard to aqueous phase removal.