Effect of oxalic acid impregnation of chromarods on the separation of phospholipids for determination by the latroscan TLC/FID

Phospholipid separations were carried out using Chromarods-SII impregnated with oxalic acid without interfering with Iatroscan TLC/FID detection and measurement. The resolutions were compared with untreated rods. Oxalic acid impregnated Chromarods gave better resolution of phospholipids, and the separations were more reproducible on a day to day basis compared to untreated Chromarods. A concentration of 0.25 M oxalic acid in acetonitrile, with 15 min of impregnation, followed by 60 min of activation at 110 C, provided the ideal conditions for coating. Three solvent mixtures, viz. CHCl₃:MeOH:HAc:H₂O (50∶30∶8∶4, v/v/v/v), CHCl₃:MeOH:H₂O (65∶35∶4, v/v/v), and CHCl₃:MeOH:28% NH₄OH (70∶30∶2, v/v/v) were tested as developing solvents. CHCl₃:MeOH:H₂O (65∶35∶4) was found to be the best solvent system. Double development (initially in acetone, followed by CHCl₃:MeOH:H₂O 65∶35∶4]) is of minor value in improving separations. All the above solvent systems are capable of separating most of the commonly occurring plant phospholipids, except phosphatidylinositol and phosphatidylserine. Both of these phospholipids eluted together on Chromarods-SII, giving a single peak on the Chromarod, regardless of whether the rods were impregnated with oxalic acid.