Negative Ion Laser Desorption/Ionization Time-of-Flight Mass Spectrometric Analysis of Small Molecules Using Graphitic Carbon Nitride Nanosheet Matrix

Abstract

Ultrathin graphitic carbon nitride (g-C 3 N 4 ) nanosheets served as a novel matrix for the detection of small molecules by negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was described for the first time. In comparison with conventional organic matrices and graphene matrix, the use of g-C 3 N 4 nanosheet matrix showed free matrix background interference and increased signal intensity in the analysis of amino acids, nucleobases, peptides, bisphenols (BPs), and nitropolycyclic aromatic hydrocarbons (nitro-PAHs). A systematic comparison of g-C 3 N 4 nanosheets with positive and negative ion modes revealed that mass spectra produced by g-C 3 N 4 nanosheets in negative ion mode were featured by singly deprotonated ion without matrix interference, which was rather different from the complicated alkali metal complexes in positive ion mode. Good salt tolerance and reproducibility allowed the determination of 1-nitropyrene (1-NP) in sewage, and its corresponding detection limit was lowered to 1 pmol. In addition, the ionization mechanism of the g-C 3 N 4 nanosheets as matrix was also discussed. The work expands its application scope of g-C 3 N 4 nanosheets and provides an alternative approach for small molecules. M atrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has been widely applied to the analysis of synthetic polymers and proteins over the past two decades. 1,2 Although some remarkable achievements have been made, analysis of low-molecular-weight compounds (m/z < 500 Da) by MALDI-TOF MS using conventional organic matrices (e.g., α-cyano-4-hydroxycinnamic acid, CHCA) remains a great challenge due to the strong matrix-derived interference in the low mass region. 3 Furthermore, the inhomogeneous co-crystallization of analytes with an organic matrix often requires sweet-spot searching, which results in low shot-to-shot reproducibility. 4 To solve these problems, great efforts have been made recently. One strategy is to exploit new organic matrices with low background. 5,6 Another one is the development of surfaceassisted laser desorption/ionization mass spectrometry (SALDI-MS) 7 by using inorganic nanomaterials as matrices. At present, a diversity of inorganic nanomaterials including porous silicon, 8,9 metal/metal oxide nanoparticles, 10−13 inorganic carbon-based materials, 7,14−16 and metal−organic frameworks 17,18 have been introduced as SALDI matrices. In particular, using inorganic carbon-based nanomaterials like fullerene, 19 graphite, 15 carbon nanotubes, 14,20 graphene, 16,21,22 and carbon nanodots 23,24 appears to be an attractive ionization method due to the merits of remarkable charge mobility and universal optical adsorption property. However, most of the carbon material matrices showed poor solubility and water dispersibility, which usually leads to the inhomogeneous crystallization with the analytes and, thus, decreases the sensitivity of SALDI MS and shot-to-shot reproducibility. 23 On the other hand, altho...

Simultaneous and direct analysis of multiple types of organic contaminants in water based on a MOF decorated with a suitable quantity of Au nanoparticles, using SALDI-TOF MS

“…S4-S7 and Table S3, ESI †). This meant that the LODs for most of the analytes achieved in the present study were comparable to, or better than, those reported in the literature, 8,13,17 indicating the high sensitivity of the established method. Moreover, the perfect homogeneity of the UiO-66-NH 2 @Au matrix results in good reproducibility.…”

Nanomaterials as Assisted Matrix of Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for the Analysis of Small Molecules

“…Recently, Lin et al [50] used g-C 3 N 4 nanosheets as an assisted matrix of LDI for analyzing various different low molecular weight compounds. Mass spectra with free background interference and improved signal intensity were obtained for analyzing a series of small molecules including amino acids, nucleobases, peptides, bisphenols, and nitro-polycyclic aromatic hydrocarbons (nitro-PAHs) in the negative mode.…”

Negative ion laser desorption/ionization time‐of‐flight mass spectrometric analysis of small molecules by using nanostructured substrate as matrices

“…In particular, g‐C 3 N 4 nanosheets with nanoscale and atomic‐scale thickness possess of lamellar graphite structure, and strong UV adsorption capability, it is believed that the g‐C 3 N 4 nanosheets can satisfy the criteria to serve as a matrix for LDI‐TOF MS . Inspired by its exceptional properties, our group recently prepared ultrathin g‐C 3 N 4 nanosheets by ultrasonication‐assisted liquid exfoliation of bulk g‐C 3 N 4 in water and first applied it as matrix for LDI‐TOF MS. As shown in Figure , the obtained nanosheets were dispersed stably in water, even upon standing for 2 months. Besides, the transmission electron microscopy (TEM) and atomic force microscopy (AFM) images confirmed that the nanosheets were well separated from each other with the thickness of 2 nm and the diameter of ∼200 nm, respectively.…”

“…E, UV‐visible spectrum of bulk g‐C 3 N 4 and nanosheets. Reprinted with permission from Lin et al Copyright 2015 American Chemical Society…”