Twenty one (two unidentified) and 14 impurities were detected and identified in the bottom parts of the zone refined ingots of commercially available ex-coal tar acenaphthene and pyrene, respectively. with the help of Hewlett-Packard 1 as chromatographs type 6890 GC System and 5890 series 11 equipped with fused silica capillary columns and the FID and MS detectors. The result of quantitative determination have shown that naphthalene, 2-methylnaphthalene and 9H-fluorene, and 7-methylanthracene, 1-phenylnaphthalene, fluoranthene and unknown compound with the molecular weight of 208 may be treated as the major impurities of the above hydrocarbons. respectively. These results have also shown that with the exception of methyldibenzofuran present as impurity in acenaphthene, the segregation coefficients of all the remaining detected impurities are lower than unity. Moreover, it was found that the final distribution of the major impurities after 100 passes of the melting zone may be described with high accuracy by a third-order equation. The purification procedure worked out on the basis of the determined impurity segregation behaviour enabled the preparation of the hydrocarbons with purity greater than or equal to 99.999 mass% from which high quality crystals were grown. (C) 2002 Elsevier Science B.V. All rights reserved.