There are commercial ELISA kits available to assay Resolvin E1 but whether the answer they give is valid or not will have to be determined by you on your samples.  While antibodies generally have a high degree of specificity there may be a cross-reactivities with structurally similar components in your matrix.  You will need to put your samples through some sort of purification process (eg SPE, HPLC, TLC) and compare the answer you get at each stage with the answer you determined at the previous step.  When these are the same you will know that you have achieved sufficient purification.  If you are lucky, you might get away with assaying a crude sample but you will need to prove the validity of the answer by doing at least one step of purification.

Dear Charles H Hocart Thank you very much for your answer.