Silica gel thin-layer chromatography of acidic phospholipids. II. Chromatographic behaviour of phosphatidylserine and phosphatidic acid applied with different cation composition on adsorbents either free of metal ions or containing a surplus of divalent metal ions.

Different salt forms of phosphatidylserine and phosphatidic acid (two acidic phospholipids) have been subjected to thin-layer chromatography on two commonly used silica adsorbents, one of which (silica gel HR) is practically free of metal ions and the other (silica gel G) contains 13% of calcium sulphate as binder. The chromatographic behaviour was studied in an acidic, a neutral and a basic solvent. Both adsorbents provided usable systems for phosphatidylserine with each of the three solvents, except for silica gel G with the neutral solvent, in which system tailing was prominent. The inclusion of calcium sulphate in the silica gel tended to impair chromatography of phosphatidylserine in acidic and neutral solvents, but improved its chromatography in the basic solvent. In all the systems, the migration was independent of the cation composition of the applied phosphatidylserine samples. For the chromatography of phosphatidic acid, only three of the systems tested were usable, and in those three, the chromatographic behaviour was independent of the cation composition of the samples. The calcium sulphate in an adsorbent increased tailing of phosphatidic acid in acidic and neutral solvents, as it did for phosphatidylserine, whereas with the basic solvent, calcium sulphate in the adsorbent caused phosphatidic acid to remain at the origin. Two one-dimensional thin-layer chromatographic systems previously recommended for the chromatography of acidic phospholipids were unsuitable for the chromatography of phosphatidic acid under the conditions used here. For both phosphatidylserine and phosphatidic acid chromatographed in acidic systems, the solvent must contain water in addition to acetic acid if excessive tailing is to be avoided.