PCL Staff Use NALDI-MS to Analyze Phospholipid Components of Liposomes
In Matrix-Assisted Laser Desorption/Ionization (MALDI) mass spectrometry a chemical matrix is required to protect analyte molecules from being destroyed by the laser and to facilitate vaporization and ionization. The matrix gives rise to peaks in the low mass range (<800) which can obscure molecules of interest in this range. Nano-Assisted Laser Desorption/Ionization (NALDI), an innovative matrix-free approach, eliminates the problem of matrix peaks. The techniques can also provide quantitative data very rapidly (less than 2 minutes per sample). NALDI uses disposable nano-structured target plates. The nano-material on the target absorbs the laser energy and allows for the desorption/ionization process of the analyte. As a result of the absence of the matrix, mass spectra present very low chemical background and increased sensitivity. The method is fast and reproducible and may be applicable to other lipids and small molecules. This method was recently published in the journal, Lipids.
This study was designed to analyze and quantitate phospholipid components of liposomes. Here we have developed an assay to quantitate the DPPC and DC(8,9)PC in liposomes by NALDI following various treatments. To test our method we chose to analyze a liposome system composed of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) and DC(8,9)PC (1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine), as DC(8,9)PC is known to undergo cross-linking upon treatment with UV (254 nm) and this reaction converts the monomer into a polymer. First, calibration curves for pure lipids (DPPC and DC(8,9)PC) were created using DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) as an internal standard. The calibration curve for both DPPC and DC(8,9)PC showed an R(2) of 0.992, obtained using the intensity ratio of analyte and internal standard.
Calibration curves for DPPC and DC8,9PC. Concentration ranges for DPPC and DC8,9PC were respectively 10–200 ng/lL and 2.5–100 ng/lL.
Next, DPPC:DC(8,9)PC liposomes were treated with UV radiation (254 nm). Following this treatment, lipids were extracted from the liposomes and analyzed. The analysis of the lipids before and after UV exposure confirmed a decrease in the signal of DC(8,9)PC of about 90%. In contrast, there was no reduction in DPPC signal.
Mass spectra of phospholipids from liposome before (A) and after (B) UV treatment (254 nm)