Fig. 5. Analytical HPLC comparison of the natural attractant and a synthetic tryptophan standard. Samples were reacted with o-phthalaldehyde (OPA) prior to injection, producing derivatives that were identified by RP-HPLC with fluorescence detection at 400 nm (Em₄₀₀). (A) A sample of the purified natural sperm attractant corresponding to 0.25 nmoll^-1, showing the diagnostic retention time and purity of the sample. (B) Co-injection of the previous sample with 0.25 nmoll^-1 of a synthetic standard of L-tryptophan, showing co-elution as a single peak.