IR-MALDI-MS analysis of HPTLC - Separated phospholipid mixtures directly from the TLC plate

The application of a recently developed direct coupling of high-performance thin-layer chromatography (HPTLC) and infrared matrix-assisted laser desorption/ionization orthogonal extracting time-of-flight mass spectrometry (Dreisewerd, K.; Muthing, J.; Rohlfing, A.; Meisen, L; Vukelic, Z.; Peter-Katalinic, J.; Hillenkamp, F.; Berken-kamp, S. Anal Chem. 2005, 77, 4098-4107) to the analysis of phospholipid mixtures is demonstrated. Mixtures of six phospholipid types were exemplarily analyzed. The sensitivity was found to be in the range between about 10 and 150 pmol of material spotted for HPTLC, depending on phospholipid acidity, R-f value, and ion polarity. The lateral resolution of the analysis is on the order of the laser focus diameter of about 220 x 300 mu m(2), allowing differentiation between phospholipid species of different acyl chain composition within one single HPTLU band, which were undistiguishable by a mere visual assessment. Analyte diffusion due to the addition of glycerol to the HPTLC plate was found to be-if at all notable-of only minor importance.