Determination of free gossypol in chemically treated cottonseed meals containing dianilinogossypol

Summary A method is proposed for the determination of free gossypol in chemically treated cottonseed meals containing dianilinogossypol. The procedure includes a rapid qualitative test for detecting the presence of dianilinogossypol in cottonseed meals. Investigation of the properties of dianilinogossypol showed that it was appreciably soluble in water‐free solvents, such as acetone, methyl ethyl ketone, or chloroform, but only slightly soluble in 70% acetone, an efficient solvent for the extraction of free gossypol. Both 70% acetone extracts of chemically treated meals and pure dianilinogossypol in the same solvent exhibited significant changes in optical density due to slow hydrolysis of dianilinogossypol. Dilution of aqueous acetone extracts with 80% isopropyl alcohol produced changes in optical density even greater than those occurring in undiluted extracts, introducing serious errors in the free gossypol determination. The addition of a small amount of aniline to the aqueous acetone for extraction stabilized the extract against changes in optical density and yielded constant values for free gossypol over a period of several hours. Use of aqueous acetone without aniline gave values which increased with the time interval between extraction and analysis. Extrapolation of these values to zero time gave results in good agreement with those obtained by the use of aqueous acetone containing aniline. The intense background color in extracts of chemically treated meals introduces a source of error when photoelectric colorimeters yielding non‐linear calibration curves are used for analysis. A modification in the customary method of calculation eliminates this source of error.