A comparative evaluation of HPLC, FTIR, Raman and NMR for analysis and monitoring of phosphatidylcholine to phosphatidylglycerol

In the enzymatic synthesis of phosphatidylglycerol (PG) from phosphatidylcholine (PC), the close structural similarity between these two phospholipids poses a major challenge for real-time monitoring and effective process control. In this work, we carried out a systematic comparative investigation of HPLC, FTIR, Raman and 31P NMR for their abilities of detecting and distinguishing PC from PG, where the HPLC is served as the baseline method. The results demonstrate that FTIR cannot detect PC or discriminate between PC and PG in this system. While Raman spectroscopy shows a linear correlation for PC concentrations between 700 and 1000 cm⁻¹, it similarly fails in differentiating PC from PG because of overlapping headgroup signals. By contrast, NMR offers high accuracy and reproducibility in quantifying both PC and PG, with minimal sample preparation and shorter analysis times in comparison to the HPLC. Applying the NMR in the real synthesis of PG from PC in an oscillatory baffled reactor, concentration profiles of PC decreasing and PG increasing with time are obtained.