Determination of xanthoxin by immunoassay

2‐ Cis (‐)xanthoxin (XA) was linked to bovine serum albumin through a Schiff's base and the adduct stabilized by sodium borohydride reduction. The conjugate (molar coupling ratio: 3 mol XA per mol protein) was highly immunogenic in rabbits. Antisera contained antibodies binding XA with high affinity (K a = 1.8 × 10 8 M −1 ). [ 3 H]‐XA (2.2 × 10 14 Bq mol −1 ) was synthesized by oxidation of [ 3 H]‐XA alcohol with MnO 2 and used to set up a radioimmunoassay [RIA, detection limit, 1 pmol; measuring range, 1 to 200 pmol (0.3 to 60 ng) XA]. The sera were also suitable for enzyme‐linked‐immunosorbent assay (ELISA) using XA‐alkaline phosphatase conjugates. The technique was more sensitive [detection limit, 0.1 pmol; measuring range, 0.1 to 50 pmol (0.05 to 15 ng) XA] than the radioimmunoassay, but less precise.