A method and apparatus for isolation of a barely volatile organic compound in a sample suspected to contain the same, e.g. a dioxin, which includes continuously adding superheated steam and a volatile and hardly water-soluble/water-insoluble solvent to a liquid or solid sample suspected to contain said organic compound to be isolated, a solid sample being dissolved in said solvent which can dissolve said organic compound to be isolated, distilling off an azeotropic mixture of said organic compound and said solvent by steam distillation, separating a solvent phase of said solvent dissolving said organic compound and said water phase, and recovering quantitatively said organic compound from said solvent. The dioxins are then further subjected to analysis, for example, GC, HRGC-MS and the like.