Graphite/Liquid Mixed Matrices for Laser Desorption/Ionization Mass Spectrometry

Abstract

A combination of liquid matrix and graphite particulates (2 μm) has been proposed as a method suitable for the laser desorption/ionization mass spectrometry of peptides and proteins (Sunner, J.; et al. Anal. Chem. 1995, 67, 4335). Here we demonstrate the potential of this approach as a straightforward, and very general, method of achieving the ultraviolet laser desorption/ionization of a broad range of intermediate weight analytes. The desorption/ionization mechanism, the influence of preparative procedures, and the breadth of application of this methodology have been investigated. A simple and robust preparative procedure is presented for the analysis of proteins, oligosaccharides, and synthetic polymers. Detection sensitivities are in the femtomole region for lower molecular weight peptides and oligosaccharides. The graphite acts as an energy transfer medium by absorbing the UV radiation, leading to thermal desorption of the liquid matrix and analyte. The liquid matrix was observed to fulfill several important roles. In the case of peptides and proteins, which preferentially form protonated molecular ions, it acts as a protonating agent. It also enhances the signal intensities of cationized species (e.g., polysaccharides and polar polymers) by assisting their desorption. An excess of liquid matrix serves to cool the analyte during the desorption step and minimize decomposition. The presence of liquid matrices increases the sample lifetime at a particular desorption spot, minimizing the time-consuming search for "hot spots". The addition of cationizing salts has been shown to improve the quality of mass spectra obtained for polar polymers and extend the range of materials that can be investigated to include apolar synthetic polymers.

Ion soft-landing into liquids: Protein identification, separation, and purification with retention of biological activity

“…Glycerol and carbohydrates themselves are not good matrices for UV-MALDI applications; however, addition of various UV absorbing chromophores (including traditional MALDI matrices) produces adequate liquid MALDI matrices and soft-landing can be performed directly into these matrices [42]. Soft-landing followed by MALDI detection using ␣-cyano-4-hydroxycinnamic acid and p-nitroaniline doped glycerol surfaces gave the results shown in Figure 6.…”

A novel laser desorption/ionization method using through hole porous alumina membranes

“…To date a number of ionization techniques that belong to SALDI have been proposed,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, ...…”

“…nanoparticles as typical, in treatable forms such as suspension liquids in order to ensure that the photon energies of the laser can act to desorp and ionize analytes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45. Indeed, the soft ionization laser method such as the original form of MALDI also belongs to this category 1.…”

2B or not 2B, that is the question: further investigations into the use of pencil as a matrix for matrix‐assisted laser desorption/ionisation

“…More recently, the use of ionic liquid matrices has become widespread 9 and the conditions required for the effective use of the matrix suppression effect (MSE) have been investigated. 10 The use of graphite as a matrix [11][12][13] and the utilisation of graphite target plates, without the addition of a standard crystalline matrix, 14 was discussed in our earlier publication, 15 where graphite powder and graphite rod were investigated as possible matrices for the analysis of actinides. Difficulties in handling and deposition of the graphite were highlighted and a simplified method utilising pencil lead (PL) as a new MALDI matrix was developed in this laboratory to address these problems.…”