The thin layer chromatographic separation of lipids on Chromarods, followed by measurement of organic carbon in the latroscan TH-10 Mark II Analyser, normally leaves the Chromarods ready for immediate reuse. However, a polar lipid fraction derived from rapeseeds included a component that resisted complete combustion on the Chromarod-S (silicic acid), although sterols, triglycerides, and phospholipids left no detectable residue. The component was mobile in organic/water solvent systems containing acids and contained magnesium and zinc. By comparison with authentic standards it was shown to be phytin, a salt of phytic acid, which is found in several commercially important oilseeds. The incomplete combustion is attributed to formation of oxides or carbonates of magnesium, calcium, or zinc. © 1979, Oxford University Press. All rights reserved.