A methodology for determination of phospholipids.

A simple method for the determination of phospholipids in an aqueous dispersion and in amniotic fluid was developed. The procedure is based on the observation that dispersed phospholipids promoted the solubilization of an insoluble dye--detergent complex. The solubilization of the complex between the negatively charged dye, Coomassie brilliant blue (CBB), and a positively charged detergent, cetyltrimethylammonium bromide (CTAB), produced a blue solution having a visible absorbance maximum above 600 nm. A linear increase in absorbance intensity occurs with an increase in phospholipid concentration. An assay using the CBB-CTAB reagent adsorbed on 3-mm glass beads is used to estimate total dispersed phospholipids between 2 and 25 micrograms/ml. Thereby, a two-phase water-methanol-chloroform system is formed. The products of zwitterionic phospholipids (such as phosphatidylcholine and phosphatidylethanolamine) partition to the organic phase while the dye complex solubilized in anionic phospholipids (such as phosphatidylglycerol and phosphatidylinositol) partitions to the aqueous phase. This procedure results in a convenient, sensitive, and rapid method for the simultaneous determination of the total phospholipid, zwitterionic phospholipid, and anionic phospholipid concentrations. Application of the new assay for determination of phospholipids in amniotic fluid is described.