Colorimetric determination of phospholipids by use of molybdophosphate, and its application to amniotic fluid

We studied the reaction between molybdophosphoric acid and lecithin. The resulting complex was isolated and shown to contain molybdophosphate and lecithin in the molar ratio 1/3. It is insoluble in water but soluble in chloroform, and the reaction is specific for molecules containing electrophilic nitrogen, indicating good specificity in biological fluids for nitrogen-containing phospholipids. In solution the complex may be reduced, yielding molybdenum blue. We applied the reaction to the measurement of phospholipid concentrations in amniotic fluid. As compared with procedures involving either digestion or the determination of lecithin/sphingomyelin ratio, the present technique is faster and its analytical precision exceeds that of the lecithin/sphingomyelin ratio determination. Although results by the three methods do not correlate well, the predictive value of the present method appears to be comparable with the other two.