Theoretical investigation of low detection sensitivity for underivatized carbohydrates in ESI and MALDI.
Electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mainly generate protonated ions from peptides and proteins but sodiated (or potassiated) ions from carbohydrates. The ion intensities of sodiated (or potassiated) carbohydrates generated by ESI and MALDI are generally lower than those of protonated peptides and proteins. Ab initio calculations and transition state theory were used to investigate the reasons for the low detection sensitivity for underivatized carbohydrates. We used glucose and cellobiose as examples and showed that the low detection sensitivity is partly attributable to the following factors. First, glucose exhibits a low proton affinity. Most protons generated by ESI or MALDI attach to water clusters and matrix molecules. Second, protonated glucose and cellobiose can easily undergo dehydration reactions. Third, the sodiation affinities of glucose and cellobiose are small. Some sodiated glucose and cellobiose dissociate into the sodium cations and neutral carbohydrates during ESI or MALDI process. The increase of detection sensitivity of carbohydrates in mass spectrometry by various methods can be rationalized according to these factors. Copyright © 2016 John Wiley & Sons, Ltd.
Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.
Jien-Lian
JL
Chen
Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.|Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Chuping
C
Lee
Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.
I-Chung
IC
Lu
Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.
Chia-Lung
CL
Chien
Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.|Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Yuan-Tseh
YT
Lee
Department of Chemistry and Biochemistry, National Chung Cheng University, Chia-Yi, 62102, Taiwan.
Wei-Ping
WP
Hu
Institute of Atomic and Molecular Sciences, Academia Sinica, P. O. Box 23-166, Taipei, 10617, Taiwan.|Department of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan.
Chi-Kung
CK
Ni
D002241:Carbohydrates / Q000032:analysis* / Q000737:chemistry*; D002412:Cations; D057230:Limit of Detection; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
D002241:Carbohydrates; D002412:Cations
ESI; MALDI; carbohydrate; low detection sensitivity