Measurement of the ratio of lecithin to sphingomyelin in amniotic fluid by fast atom bombardment mass spectrometry.

We describe a fast atom bombardment mass spectrometric method to determine the ratio of lecithin to sphingomyelin in amniotic fluid. Between m/z 400 and 1000, amniotic fluid extracts showed clear peaks for only sphingomyelin and lecithin. The molecular species of fatty acid in the phospholipids were analyzed quantitatively and quickly in a small volume of the extracts. The dipalmitoyllecithin/palmitoylsphingomelin ratio, determined by the proposed method, showed a reasonable correlation to the lecithin/sphingomyelin ratio measured by thin-layer chromatography. This method allows rapid and sensitive measurement of these phospholipids.