Modified silica-containing matrices towards the MALDI-TOF-MS detection of small molecules

The new silica-based matrices were designed to demonstrate the concept of using silica to immobilize classic MALDI matrix materials for the analysis of small molecules (<600 Da). The matrices were synthesized by covalently attaching a precursor of ionic liquids (a silylated amine) to the silica and then reacting it with the anion of a conventional MALDI matrix material such as alpha-cyano-4-hydroxy cinnamic acid (CHCA) to form an ionic macro-complex. This new matrix material displayed at least two advantages. First, the immobilization of the CHCA did not impact the chromophore region of CHCA molecule, which retained its original maximum absorption band at 328 nm. This made the new matrix material compatible with standard MALDI-TOF mass spectrometers equipped with nitrogen lasers. Second, by covalently immobilizing the cationic portion of the ionic liquid moiety on the silica, it was possible to avoid low-mass chemical noise arising from the matrix in the positive-ion mode. The new matrix materials were based on silica gel and mesoporous silica, SBA-15. Their small molecule utility was investigated using two neurotransmitters, dopamine (153.08 Da) and serotonin (176.09 Da). The MALDI-TOF-MS analysis of the neurotransmitters demonstrated that the matrix material based on the modified mesoporous silica ([SBA-15-Si-NH(3)(+)][CHC(-)]) yielded spectra with minimal chemical noise and good analyte signal intensity. This was hypothesized to be due to the more efficient ionization facilitated by the larger surface area and spot uniformity of such a matrix material. (C) 2011 Elsevier B.V. All rights reserved.