Improved cleanup of large lipid samples for electron capture gas chromatographic quantitation and gas chromatographic-mass spectrometric confirmation of organochlorine residues.

A new cleanup method for large lipid samples is described for the analysis of organochlorine traces. The method allows both electron capture gas chromatographic (GC) quantitation of sub-ppb levels and confirmation by GC-mass spectrometry. The lipid is extracted with concentrated sulfuric acid from a 2-5% solution of light petroleum ether. The method has been scaled up without increasing the petroleum volume by the alternate addition of lipids and sulfuric acid. Recovery studies were performed with 11 common organochlorine contaminants spiked in butterfat and in vegetable oils at the ppb level. The method is characterized by low lipid carryover of 0.02% by minimal use of solvent (about 2-3 mL/g lipid), and by its simplicity. A 50-200 g sample can be cleaned up in one day. Five micrograms of incurred p,p'-DDE has been cleaned up from a 50 g butterfat sample and purified by one TLC run. The eluted compound was analyzed by GC-MS and showed one peak (flame photometric detector) with a mass spectrum identical to authentic p,p'-DDE.