Using molecular recognition of β-cyclodextrin to determine molecular weights of low-molecular-weight explosives by MALDI-TOF mass spectrometry

Abstract

This study presents a novel method for determining the molecular weights of low molecular weight (MW) energetic compounds through their complexes of ␤-cyclodextrin (␤-CD) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) in a mass range of 500 to 1700 Da, avoiding matrix interference. The MWs of one composite explosive composed of 2,6-DNT, TNT, and RDX, one propellant with unknown components, and 14 single-compound explosives (RDX, HMX, 3,4-DNT, 2,6-DNT, 2,5-DNT, 2,4,6-TNT, TNAZ, DNI, BTTN, NG, TO, NTO, NP, and 662) were measured. The molecular recognition and inclusion behavior of ␤-CD to energetic materials (EMs) were investigated. The results show that (1) the established method is sensitive, simple, accurate, and suitable for determining the MWs of low-MW single-compound explosives and energetic components in composite explosives and propellants; and (2) ␤-CD has good inclusion and modular recognition abilities to the above EMs. has become a powerful instrument for analyzing large synthetic polymers and biomacromolecules. However, for low-mass analytes-especially compounds that have a mass-to-charge of less than 500 Da-it has been a challenge. Because most of the molecular weights (MWs) of the currently used matrixes are less than 500 Da and because, during laser irradiation, they also act as their own matrixes, a variety of matrix-related ions are produced. Therefore, the use of MALDI-TOF-MS has been limited to the analysis of low-mass analytes. As a consequence, many analysts and experts of MALDI-TOF-MS have made considerable efforts and approaches to overcome this problem [1][2][3][4][5].Cyclodextrins are cyclic oligosaccharides that have ␣-d-glucose units that are connected through (1¡4) linkages. The most common forms of cyclodextrin are ␣-, ␤-, and ␥-cyclodextrin (cyclomaltohexa-, hepta-, and octaoses), which contain six, seven, and eight glucose units, respectively. The structures of these molecules are toroidal, containing an apolar cavity with primary hydroxyl groups lying on the outside and the secondary hydroxyl groups being located inside [6,7]. The guest molecules that have a suitable size and shape can be incorporated into the cyclodextrin cavity to form inclusion complexes. The formation of these complexes has been attributed to weak interactions, including van der Waals interactions, hydrophobic effects, and hydrogen bonding. The ability of cyclodextrins to form inclusion complexes with a variety of guest molecules has attracted widespread interest in academic research and industrial applications. Cyclodextrin complexes have been studied by using different physical methods and spectroscopic methods. However, the analysis of low-mass analytes by MALDI-TOF-MS, especially those in the mass range below 500 Da, has been a major challenge [8 -15].In this paper, a novel method of using the molecular recognition of ␤-cyclodextrin (␤-CD) to determine the mass of low-MW explosives by MALDI-TOF-MS is established.

Suppression of Matrix-related Ions Using Cyclodextrin in MALDI Mass Spectrometry

“…Recently, Zhang et al used b-cyclodextrin (bCD) to separate the mass number of analyte from matrix-related ions region. 19 They put an analyte molecule (RDX; hexahydro 1,3,5-trinitro-1,3,5-triazine) into bCD, and then they carried out MALDI mass measurements of bCD + RDX species in the presence of matrix molecule (SA; sinapinic acid). They clearly separated the mass number of analyte molecule from matrix-related fragment region.…”

The application of single particle aerosol mass spectrometry for the detection and identification of high explosives and chemical warfare agents

“…12 Explosives are commonly identified using colorimetry, 13 UV-absorption spectroscopy, 14,15 laser-induced fluorescence (LIF), 16,17 immunoassay, 18 ion mobility spectrometry (IMS), [19][20][21][22][23] and mass spectrometry (ion trap and time-of-flight (TOF)). [24][25][26][27][28][29][30][31][32][33] It should be noted that research into explosives detection is performed on gas, liquid, and/or solid phase explosives, and that the sampling methods and concepts of operation vary widely between the different techniques. The limits of detection for the various techniques are dependent on the sampling method and sample phase, and therefore prevent a direct comparison among the different techniques.…”

What Happens to Hydrophobic Interactions during Transfer from the Solution to the Gas Phase? The Case of Electrospray-Based Soft Ionization Methods

“…A number of studies report on more or less successful analyses of noncovalent complexes where hydrophobic forces are considered to play a dominant role for the stability [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Liu et al [19,20] showed the preservation of hydrophobically stabilized complex between bovine β-lactoglobulin and its natural ligands, fatty acids, for the fraction of ESI-generated ions.…”

“…CDs allow for the formation of inclusion complexes with various nonpolar molecules in polar solvents [34]. Several studies have reported on the detection of inclusion complexes between CDs and aromatic or aliphatic guests, amino acids, peptides, and drugs by ESI-MS [23][24][25][26][27][28][29][30][31][32][33]. However, in these studies, guest molecules bore at least one polar group that pointed out of the cavity and enabled hydrogen bonding or dipole-dipole interactions with hydroxyls of the CD rim.…”