Simultaneous and direct analysis of multiple types of organic contaminants in water based on a MOF decorated with a suitable quantity of Au nanoparticles, using SALDI-TOF MS

Abstract

Due to intensive industrial growth, water has become more and more polluted with toxic organic contaminants, which pose a great threat to human health and water ecosystems. Developing advanced multi-residue methodologies can provide broad and realistic information about water pollution in a rapid, sensitive and selective way. Mass spectrometry (MS) coupled with gas chromatography (GC) or liquid chromatography (LC) has been successfully applied for identifying and analyzing multiple types of analytes in different elds. 1-3However, these methods usually involve complicated sample treatment procedures and require professional staff to operate the instruments; this is cost-intensive, labor-intensive and time-consuming.Recently, the surface-assisted laser desorption/ionization time-of-ight mass spectrometry (SALDI-TOF MS) technique using nanoparticles as the laser desorption/ionization (LDI)-assisting matrix for the determination of toxic organic contaminants has been developed. The advantages of SALDI-TOF MS over other methodologies include high throughput and analysis speed, good tolerance toward contaminants, the ability to analyze complex mixtures, and easy operation. 4,5Various kinds of environmental organic and inorganic pollutants have been analyzed using SALDI-TOF MS including dioxin, 6 peruorinated chemicals (PFCs), 7-10 brominated ame retardants, 10-12polycyclic aromatic hydrocarbons (PAHs), However, multi-residue methodology has not been successfully established and applied based on the SALDI-TOF MS technique. This could be very informative for the simultaneous measurement of the above mentioned pollutants to monitor the concurrences of organic contaminants in water samples. To achieve this, nanomaterials should exhibit very high efficiencies for the detection of various small molecules, and very low background interference in the region of 200-800 Da. Gold nanoparticles (Au NPs) offer a powerful SALDI matrix for small biomolecules.25-31 However, the Au NP matrix oen produces many Au cluster peaks in the mass spectrum that tend to suppress the actual sample ion peaks; moreover, the Au colloids may become inhomogeneously distributed aer being dried on the target plate, thus leading to poor reproducibility. To solve this problem, in our work, the Au NPs are loaded onto zirconium based metal-organic frameworks modied with amino groups (UiO-66-NH 2 ) via an impregnation method which takes advantage of the electrostatic attraction between AuCl 4 À and the amino groups on the MOF. The content of Au NPs in the nanocomposites is 0.3 atomic% according to X-ray photoelectron spectroscopy (XPS) analysis (Table S1, ESI †), which both guarantees excellent assistance for the LDI of the analytes and avoids intense Au cluster peak interference in the mass spectrum. MOFs have also been reported to have matrix effects for the detection of low-mass molecules. 9,16,18 Therefore, a synergistic effect on the LDI of the analytes in SALDI-TOF can be expected from the combination of the Au NPs and the MOF itself. Detailed i...

Highly Defective UiO-66 Materials for the Adsorptive Removal of Perfluorooctanesulfonate

“…Multiple mechanisms are possible for PFOS adsorption to UiO-66, including Lewis acid–base complexation or electrostatic adsorption of the sulfonate headgroup of PFOS to the Zr 4+ CUS in defective UiO-66, ion-exchange between the charge compensating Cl – and the sulfonate headgroup, hydrophobic interactions between PFOS and the bdc linker molecules, and hydrogen bonding between PFOS and Zr-coordinated water. , In this system, we hypothesize that electrostatic interactions with Zr 4+ and/or hydrophobic interactions are most likely. Lewis acid–base complexation (i.e., chemisorption) between the Zr 4+ CUS and the sulfonate headgroup of PFOS was ruled out via the FTIR spectra of the MOFs after adsorption (Figure S3b).…”

“…The TGA and pore size distribution data implicate that UiO-66-25 is missing more linkers than UiO-66-10 (Figure S2, Figure d), and therefore is likely more hydrophilic. Increased framework hydrophobicity has been demonstrated to be beneficial for the adsorption of PFASs onto UiO-66-based materials, indicating that the right balance between increased amount of Zr CUS sites and decreased hydrophobicity (as functions of structural defectiveness) can improve the adsorption properties for PFOS and other perfluorinated compounds. , …”

Nanomaterials as Assisted Matrix of Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for the Analysis of Small Molecules

“…To overcome the interference from Au cluster peaks and poor reproducibility, Niu et al [ 115 ] synthesized an Au NP-loaded Zr based MOF by using functionalized amino groups (UiO-66-NH 2 @Au) and used as adsorbent of solid phase extraction (SPE) as well as matrix for LDI-TOF MS. Since the strong affinity to organic pollutants of UiO-66-NH 2 @Au, perfluorinated chemicals including perfluorobutane sulfonate, perfluorohexane sulfonate and PFOS, the endocrine disrupting chemical bisphenol A (BPA), halogenated flame retardants including TBBPA, pentabromophenol and tetrachlorobisphenol A, the pesticide PCP, and hormones including l -thyronine, l -thyroxine and 17-aethynylestradiol at different levels were successfully identified by LDI-TOF MS in negative mode with the assistance of UiO-66-NH 2 @Au.…”

Rapid and selective adsorption of a typical aromatic organophosphorus flame retardant on MIL-101-based metal–organic frameworks

“…Besides, the benzene structures in such MOFs can form p-p interactions with aromatic substances. 20 It have been reported that some ame retardants can be encapsulated in MOFs, 21,22 but the amount of relevant studies is still limited. Li et al 23 found that MIL-based MOFs showed the effective adsorption of a typical brominated ame retardant, hexabromocyclododecane, from aquatic environment via hydrophobic interactions.…”