The QED ionization mechanism in MALDI

PITTSBURGH - Aug. 10, 2015 - PRLog -- .
Introduction
MALDI standing for Matrix- Assisted Laser Desorption Ionization is a soft ionization technique in mass spectrometry for analyte molecules that otherwise fragment when ionized by more conventional ionization methods. In 1988, MALDI began when Tanaka and co-workers [1] used what they called the “ultra-fine metal plus liquid matrix method”, specifically a matrix of 30 nm cobalt NPs that upon irradiation with a 337 nm nitrogen laser ionized large proteins from 1 to 35 kDa. NPs stand for nanoparticles. Tanaka received the 2002 Nobel in Chemistry for demonstrating the mass spectrometry with protein analytes upon ionization in a matrix of NPs with a nitrogen laser as illustrated in the thumbnail.

However, MALDI research in 2006 shifted [2] from Tanaka’s simple NP matrix to complex organics. Then as now, the problem is to explain MALDI ionization of analytes having IPs > 8 eV with nitrogen UV lasers having single photon energy of only 3.68 eV. IP stands for ionization potential. Since multi 2 photon and even 3 photon processes necessary to reach 8 eV ionization levels are highly unlikely, there is yet no rational mechanism known to explain how analytes ionize in MALDI.

Proposal
Analytes are proposed to ionize in MALDI as NP matrices convert the nitrogen laser energy to the emission of non-thermal QED induced EM radiation at EUV levels. QED stands for quantum electrodynamics, EM for electromagnetic, and EUV for extreme ultraviolet. QED is a consequence of QM that denies atoms in NPs the heat capacity to conserve absorbed EM energy by an increase in temperature. QM stands for quantum mechanics. Instead, the absorbed laser energy is conserved by QED producing EM radiation at the frequency of waves standing across the NP that ionize the analytes. See diverse QED applications at http://www.nanoqed.org/, 2010 – 2015.

Analysis
In NP assisted MALDI, the absorbed UV laser energy is almost totally confined in the NP surfaces because of their high surface to volume ratios. Hence, NP atoms are spontaneously placed under temporary, but high EM confinement. Since the temperature cannot increase by QM, QED converts the surface energy into standing EM waves having half-wavelength λ/2 equal to the NP diameter.  Because the NP diameter is of nanometer dimensions, the QED radiation wavelength λ has Planck energy E = hν in the EUV to exceed the ionization potential of the analytes, where h is Planck’s constant and ν is frequency. Here, ν = (c/n)/λ with λ = 2d, where c is the velocity of light, with n and d being the refractive index and diameter of the NPs.

Discussion
In applying QED radiation theory to Tanaka’s NPs, the refractive index n of cobalt in the UV is, n = 1.5. Hence, the QED radiation produced from d = 30 nm NPs has wavelength λ = 90 nm giving Planck energy E = 13.8 eV thereby exceeding analyte IPs > 8 eV. Today, Tanaka's MALDI is performed [3] with NP diameters from < 5 to 35 nm suggesting NP matrices are producing QED radiation at EUV levels thereby explaining how analytes are routinely ionized in MALDI with nitrogen lasers.

Conclusions
QED induced EM radiation of 13.8 eV from 30 nm cobalt NPs ionized the analytes in Tanaka’s MALDI experiment, although with smaller NPs, QED produces EUV radiation by simply irradiating the NP matrix with a nitrogen laser. There is no need in MALDI for mass spectrometry based on organic matrices.

References
[1] K. Tanaka, et al. "Protein and Polymer Analyses up to m/z 100 000 by Laser Ionization Time-of flight Mass Spectrometry," 2 (20), 151–3, 1998.
[2] R. Knochenmuss, “Ion formation mechanisms in UV-MALDI,” Analyst, 131, 966–986, 2006.
[3] S. K. Kailasa, et al., “Semiconductor Nanomaterials-Based Fluorescence Spectroscopic and Matrix-Assisted Laser Desorption/Ionization (MALDI) Mass Spectrometric Approaches to Proteome Analysis,” Materials, 6, 5763-5795, 2013.