Rapid determination of small molecule pollutants using metal-organic frameworks as adsorbent and matrix of MALDI-TOF-MS

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has been commonly used for the determination of macromolecules owing to the high sensitivity and convenience. However, the direct analysis of small molecule with MALDI-TOF-MS remains a challenge due to the matrix interference in the low mass region. In this paper, metal-organic frameworks (MOFs: MOF-5, MOF-235, Cu-btc MOFs and Uio-66(Zr)-2OH) were successfully used as both adsorbent and significant matrix of MALDI-TOF-MS method for the analysis of small molecule pollutants. Benzo(a)pyrene (BaP) and perfluorinated compounds (PFCs) were chosen as model analytes to investigate the matrix function of MOFs with LDI measurement in positive and negative reflection mode, respectively. As a result, MOFs exhibit high laser desorption/ionization efficiency and function well in both positive-ion and negative-ion modes. Compared to the MS spectra with conventional matrices, MS spectra obtained on MOFs matrix are only featured by deprotonated molecule ion peaks without background interference. Furthermore, MOFs, with large surface area and π-π stacking structure, can also enrich trace amounts of small molecule pollutants from solution efficiently and quickly. According to these, we developed a simple method in which MOFs-solid-phase extraction (SPE) enrichment was combined with MALDI-TOF-MS to realize the direct analysis of perfluorooctanesulfonate (PFOS) in real water samples.