Analytical and confirmative techniques for dibenzo-p-dioxins based upon their cation radicals.

A large number of analytical methods for the detection of chlorinated dibenzo-p-dio-xins have been reported in the past few years (1-8) ; generally, these methods involve the use of gas-liquid chromatography (GLC) or GLC coupled with mass spectrometry (MS). Detection limits of about 1 ng have been reported for GLC-MS techniques with the demonstrated capability of detecting these compounds in the picogram range by use of special techniques. One of the disadvantages of such techniques, at least for confirmative purposes, appears to be the inability to distinguish between positional iso-mers by MS as well as the inaccessibility to many analysts of the expensive equipment involved. We were therefore interested in developing the potential of some new confirmative techniques for identification of the various chlorinated dibenzo-p-dioxins. To support this work we first synthesized a series of chlorinated dibenzo-p-dioxins (9). We then obtained the visible and electron spin resonance (ESR) spectra of the cation radicals of these materials, and finally we attempted to assess the usefulness of these data for confirmation of the presence of chlorinated di-benzo-p-dioxins. The results of these studies are described below. At the time we initiated these studies it was well known through the extensive and detailed published work of Tomita (10-12) and others (18, 14) that many substituted dibenzo-p-dioxins, when dissolved in strong acids such as H2SO4 or SbCl,, are converted into cations which form highly colored cat-ion radicals on oxidation by various oxidizing agents (KNO3, H202, etc.). This phenomenon was the basis for a proposed color test for the dibenzo-p-dioxin nucleus. Unfortunately certain highly chlorinated dibenzo-p-dioxins, for example, the octachloro derivative , were reported not to produce the colored cation radicals. It was our thesis at the time that this color reaction might be made the basis of a suitable screening and confirma-tive procedure for the chlorinated dibenzo-p-dioxins and that under the proper conditions , all of the substituted derivatives of dibenzo-p-dioxin would give the test. We quickly observed that the color reaction was quite specific; we found, for example , that no color was developed with chlorinated biphenyls, diphenyl ethers, di-benzofurans, xanthenes, or xanthones. In the case of the chlorinated dibenzo-p-dio-xins, the ease of formation of the colored species was highly dependent upon the total number and position of the chlorine atoms present, and upon the solvent and oxidizing agent used (15). We found that tri-September 1973 9