A gas chromatographic technique is described for obtaining ultra high purity 14(GH for use in biological studies. l4CHL purchased from commercial sources contained readily detectable impurities including radioactive acetylene. Following purification on two different columns, no impurities were detected by high sensitivity gas chromatographic analysis. However, shortly thereafter impurities were detected as a result of radiation decomposition. Trapping and immediately regenerating ultra high purity 14C24 from dilute, filtered Hg(CI04)2 solutions did not cause the formation of impurities, whereas additional impurities were formed when unpurified 14C2HI was used. Impurities were also formed when ultra high purity "GC-L was stored in such solutions prior to its regeneration or when it was trapped and immediately regenerated from more concentrated Hg(CI04) solutions.Surprisingly little is known about the metabolic fate of ethylene. In fact, it is not yet clear whether or not ethylene is incorporated into plant tissues, despite the fact that several studies (8-12, 14, 15) using radioactive ethylene have reported that a small but significant amount of label was incorporated by fruit and vegetative tissues. The present uncertainty, even in light of these reports, exists because of three major criticisms which have been raised (1, 2, 5) and the fact that other studies (4,6,7, 13) have failed to obtain any ethylene incorporation or metabolism. The first criticism is that adequate precautions were not taken to ensure that the label incorporated was derived from radioactive ethylene. Therefore, the reported incorporation may have been an artifact due to impurities originally present in the labeled ethylene or impurities derived from radiation decomposition (16). Second, several studies (8,14,15) was undertaken using ultra high purity "4C-labeled ethylene and aseptic conditions. This paper describes the GC' technique used throughout this study for obtaining ultra high purity "4C-labeled ethylene.Purchased samples of uniformly 14C-labeled ethylene with a reported radiochemical purity of 98% (22, 31, and 53 mCi/ mmole, Amersham/Searle) were purified twice by GC. All separations were performed on a Perkin-Elmer 900 GC connected to a Hewlett-Packard Model 7128A recorder and equipped with a fiame ionization detector and subambient accessory. Ultra high purity helium (Matheson Gas Products) served as the carrier gas while ultra high purity hydrogen (Elhygen H, generator) and oxygen (Matheson Gas Products) provided the flame. Routine ethylene analyses were performed isothermally at 110 C on a 1.83 m X 3.13 mm stainless steel activated alumina column (80-100 mesh) at a flow rate of 70 cc/ min. The sensitivity and stability of this instrument was such that 6 nl/l of ethylene could routinely be detected in a 1-cc gas sample producing a peak twice the baseline noise level with a retention time of 0.9 min.The "4C-labeled ethylene samples were purchased in 250-,4Ci lots and were shipped in small evacuated glass vials with a bre...