Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization.
In a study of the metal-related ion generation mechanism in matrix-assisted laser desorption ionization (MALDI), crystals of matrix used in MALDI were grown from matrix- and salt-containing solutions. The intensities of metal ion and metal adducts of the matrix ion obtained from unwashed crystals were higher than those from crystals washed with deionized water, indicating that metal ions and metal adducts of the matrix ions are mainly generated from the surface of crystals. The contributions of preformed metal ions and metal adducts of the matrix ions inside the matrix crystals were minor. Metal adducts of the matrix and analyte ion intensities generated from a mixture of dried matrix, salt, and analyte powders were similar to or higher than those generated from the powder of dried droplet crystals, indicating that the contributions of the preformed metal adducts of the matrix and analyte ions were insignificant. Correlation between metal-related ion intensity fluctuation and protonated ion intensity fluctuation was observed, indicating that the generation mechanism of the metal-related ions is similar to that of the protonated ions. Because the thermally induced proton transfer model effectively describes the generation of the protonated ions, we suggest that metal-related ions are mainly generated from the salt dissolution in the matrix melted by the laser. Graphical Abstract ᅟ.
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.|Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Chuping
C
Lee
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
I-Chung
IC
Lu
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
Hsu Chen
HC
Hsu
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.|Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Hou-Yu
HY
Lin
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.
Sheng-Ping
SP
Liang
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan.|Department of Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
Yuan-Tseh
YT
Lee
Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan. ckni@po.iams.sinica.edu.tw.|Department of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan. ckni@po.iams.sinica.edu.tw.
Chi-Kung
CK
Ni
Ionization mechanism; MALDI; Metal ion; Thermal model; Thermally induced dissolution