Comparative study of solid phase extraction techniques for isolation of leukotrienes from plasma.

We have compared five commercially available absorbent materials (i.e. C18 Sep-Pak, C18 J.T. Baker, Amberlites XAD-7, XAD-2 and XAD-4) for their applicability as effective tools for extraction of leukotrienes from plasma samples. Leukotriene C4 (LTC4) and B4 (LTB4) were selected as representatives of peptidic and non-peptidic leukotrienes, respectively. These leukotrienes were added to 1 ml of plasma and passed through columns containing the above described adsorbent materials. The recovery was determined for each material using different combinations of solvents. XAD-4 gave the highest recovery for LTB4 (90%), whereas XAD-4 and XAD-2 gave identical recoveries for LTC4 (90%) when an eluting solvent mixture of pyridine-water--dimethylformamide (50:45:5) was used. The efficiency of the other three solid adsorbent materials for leukotriene extraction were in order of decreasing magnitude, C18 J.T. Baker greater than XAD-7 greater than C18 Sep-Pak. XAD-7 was shown to be more efficient for LTB4 than for LTC4, whereas the octadecylsilane C18 materials gave approximately similar recoveries for both of the leukotrienes. In addition to very good extraction properties of XAD-4 and XAD-2 as compared to octadecylsilane silica, these solid adsorbent materials retained less plasma impurities than the C18 materials, giving cleaner chromatograms for leukotrienes extracted from plasma. Therefore, XAD-4 or XAD-2 are the best overall choice for extraction of leukotrienes from plasma for reversed-phase high-performance liquid chromatographic analysis.