Supplementary Information
Direct Analysis of Triacylglycerols from Crude Lipid Mixtures by Gold Nanoparticle-Assisted Laser Desorption/Ionization Mass Spectrometry
Running Title:AuNP-LDI MS of TAGs from Crude Extracts
Jeongjin Son, Gwangbin Lee, and Sangwon Cha*
Department of Chemistry, Hankuk University of Foreign Studies,Yongin, 449-791, Korea.
Correspondence to:Sangwon Cha; e-mail:
Supplementary Results and Discussion
Selection of Alternative Matrixes for TAGs
Our criteria for choosing candidate matrixes for selective TAG analysis were as follows: 1) the ability to ionize molecules through cationization because TAGs were detected as sodiated ions ([M + Na]+), 2) the ability to suppress ions from PCs, and 3) compatibility with highly saline samples such as crude extracts and biological tissues. We chose AuNP and GO as candidate matrixes since both showed a good cationizing ability, PC signal suppression, and high salt tolerance in previous studies [1-3].
Among AuNPs with various sizes and capping agents, we found that 12-nm citrate-capped AuNPsperform the best for TAG analysis. We first tested bare AuNPs with no capping agent because a previous report [4] showed the superior performance of bare AuNPs over other capped AuNPs in the analysis of small carbohydrates. However, under our experimental conditions, bare AuNPs aggregate frequently such that the shelf life was short and the resultant mass spectra were poorly reproducible. Therefore, only AuNPs with a stabilizer were further investigated, and the citrate-capped AuNP matrix was finally chosen because of its high salt tolerance[2] and wide commercial availability. Finally, 12-nm AuNPs were chosen because Chiang et al. reported that small (<10 nm) AuNPsare more efficient for LDI, but are unstable and irreproducible; therefore, they claimed that about 14 nm nanoparticlesas optimal species for LDI MS [5].
Supplementary Table S1.Mass peak assignments for lipids in beef lipid extract.
m/z a / Possible Ions Assignedb742 / [PE 36:3 + H]+
760 / [PC 34:1+ H]+
766 / [PE 36:3 + Na]+
771 / [TAG44:1 + Na]+
782 / [PC 34:1 + Na]+
798 / [PC 34:1 + K]+
799 / [TAG46:1 + Na]+
808 / [PC 36:2 + Na]+
825 / [TAG48:2 + Na]+
827 / [TAG48:1 + Na]+
841 / [TAG49:1 + Na]+
853 / [TAG50:2 + Na]+
855 / [TAG50:1 + Na]+
867 / [TAG51:2 + Na]+
879 / [TAG52:3 + Na]+
881 / [TAG52:2 + Na]+
895 / [TAG53:2 + Na]+
907 / [TAG54:3 + Na]+
909 / [TAG 54:2 + Na]+
aIndicatedm/zs are nominal m/zs.
Supplementary Table S2.Mass peak assignments for lipids in brain lipid extract.
m/z a / Possible Ions Assignedb734 / [PC 32:0 + H]+
750 / [Cer d18:1/18:0c+ Na]+
756 / [PC 32:0 + Na]+
760 / [PC 34:1 + H]+
762 / [PC 34:0 + H]+
766 / [Cer d18:1/18:0hd+ Na]+, [Cer d18:1/18:0+ K]+
772 / [PC 32:0 + K]+
782 / [PC 34:1 + Na]+
784 / [PC 34:0 + Na]+
786 / [PC 36:2 + H]+
788 / [PC 36:1 + H]+
798 / [PC34:1 + K] +
804 / [Cer d18:1/22:1 + Na]+
806 / [PC 38:6 + H]+, [Cer d18:1/22:0 + Na]+
808 / [PC 36:2 + Na]+, [Cer d18:0/22:0 + Na]+
810 / [PC 36:1 + Na]+, [PC 38:4 + H]+
820 / [Cer d18:1/23:0 + Na]+, [Cer d18:1/22:1 + K]+
822 / [Cer d18:1/22:0h + Na]+, [Cer d18:1/22:0 + K]+
824 / [Cer d18:0/22:0h + Na]+, [Cer d18:0/22:0 + K]+
832 / [PC 38:4 + Na]+ , [Cer d18:1/24:1 + Na]+
836 / [PC 38:2 + Na] + , [Cer d18:1/23:0h + Na]+, [Cer d18:1/23:0 + K]+
838 / [Cer d18:0/23:0h + Na]+, [Cer d18:1/22:0h + K]+
848 / [Cer d18:1/24:1h + Na]+, [Cer d18:1/25:0 + Na]+, [Cer d18:1/24:1 + K]+
850 / [Cer d18:1/24:0h + Na]+
852 / [Cer d18:0/24:0h + Na]+, [Cer d18:1/23:0h + Na]+
860 / [Cer d18:1/26:1 + Na]+
862 / [Cer d18:1/25:1h + Na]+
864 / [Cer d18:1/25:0h + Na]+, [Cer d18:1/24:1h + K]+, [Cer d18:1/25:0 + K]+
866 / [Cer d18:0/25:0h + Na]+, [Cer d18:1/24:0h + K]+
876 / [Cer d18:1/26:1h + Na]+, [Cer d18:1/26:1 + K]+
878 / [Cer d18:1/26:0h + Na]+, [Cer d18:1/25:1h + K]+
880 / [Cer d18:0/26:0h + Na]+, [Cer d18:1/25:0h + K]+
881 / [TAG 52:2 + Na]+
883 / [TAG 52:1 + Na]+
903 / [TAG 54:5 + Na]+
905 / [TAG 54:4 + Na]+
907 / [TAG 54:3 + Na]+
909 / [TAG 54:2 + Na]+
aIndicatedm/zs are nominal m/zs.bPeak assignments were based on previously reported identifications [3, 6] and/or MALDI MS/MS experiments. cCer A/B corresponds to galactosylceramidesphingoid long chain base (A)/amide-linked fatty acid (B). dh corresponds to the hydroxyl group at the C2 position of the amide-linked fatty acid.
Supplementary Figure S1.Properties of the aqueous gold nanoparticle solution used in this study. This information was provided by the manufacturer, CNVision Co. (Seoul, Korea).
Supplementary Figure S2.LDI mass spectra of a total brain lipid extract (500 ng per spot) with DHB as a matrix.See the SupplementaryTable S2 for the detailed peak assignments.
Supplementary Figure S3.AuNP-assisted LDI TOF/TOF mass spectrum of ions detected at m/z881.8 ([TAG 52:2 + Na]+) in Figure 3(b).Fragment ion assignment (B- and C- type ions) was based on the reference [7].
References for Supplementary Information
1.Jackson, S.N., Ugarov, M., Egan, T., Post, J.D., Langlais, D., Schultz, J.A., Woods, A.S.: MALDI-ion mobility-TOFMS imaging of lipids in rat brain tissue. J. Mass Spectrom. 42,1093-1098 (2007)
2.Wu, H.-P., Yu, C.-J., Lin, C.-Y., Lin, Y.-H., Tseng, W.-L.: Gold Nanoparticles as Assisted Matrices for the Detection of Biomolecules in a High-Salt Solution through Laser Desorption/Ionization Mass Spectrometry. J. Am. Soc. Mass Spectrom. 20,875-882 (2009)
3.Lee, G., Son, J., Cha, S.: Selective or Class-wide Mass Fingerprinting of Phosphatidylcholines and Cerebrosides from Lipid Mixtures by MALDI Mass Spectrometry. B. Korean Chem Soc. 34,2143-2147 (2013)
4.Su, C.-L., Tseng, W.-L.: Gold nanoparticles as assisted matrix for determining neutral small carbohydrates through laser desorption/ionization time-of-flight mass spectrometry. Anal. Chem. 79,1626-1633 (2007)
5.Chiang, C.-K., Chen, W.-T., Chang, H.-T.: Nanoparticle-based mass spectrometry for the analysis of biomolecules. Chem. Soc. Rev. 40,1269-1281 (2011)
6.Cha, S.W., Yeung, E.S.: Colloidal graphite-assisted laser desorption/ionization mass spectrometry and MSn of small molecules. 1. Imaging of cerebrosides directly from rat brain tissue. Anal. Chem. 79,2373-2385 (2007)
7.Pittenauer, E., Allmaier, G.: The renaissance of high-energy CID for structural elucidation of complex lipids: MALDI-TOF/RTOF-MS of alkali cationized triacylglycerols. J. Am. Soc. Mass Spectrom. 20,1037-1047 (2009)
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