Abstract
We report a multi adsorbent-based method using combinations of metal-organic frameworks (MOFs) and a commercial sorbent Tenax-TA for sampling and thermal desorption (TD) gas chromatography-mass spectrometry (GC-MS) quantification of mixtures of six (C1 to C5) aldehydes. The feasibility of this approach was demonstrated along with the optical analytical conditions for maximum recovery. Optimal TD conditions for adsorption and desorption of aldehydes using MOF-5 (Zn-based MOF)+ Tenax-TA were determined as −25 °C and 150 °C, respectively (purge volume: 100 ml). These conditions yielded good linearity (R2 = 0.997), precision, and high sensitivity. Analysis of the aldehyde mixtures yielded slightly smaller R2 values than the analysis of single species. Additionally, the performance of MOF-5+ Tenax-TA was compared with other combinations comprising of Cu-based MOF-199 and Zr-based MOF of UiO-66 topology. The results of the theoretical modelling analyses propose simultaneous interaction of the C=O group of aldehydes with open metal sites of the studied MOFs and van der Waals interaction of hydrocarbon “tail” of aldehydes with linkers of MOFs. The combined interactions significantly increased the enthalpy (eV/molecule) of formaldehyde adsorption on MOF. Our findings unravel a potential way to extend the application of GC-based detection toward concurrent analysis of organic molecules of variable sizes.
Highlights
Metal organic frameworks (MOFs) are hybrid nanoporous materials comprised of metal ion or metal ion clusters and bridging organic linkers
The outcomes of our experiments were discussed in light of theoretical interactions between metal-organic frameworks (MOFs) and the main active site of aldehyde (C=O group) molecules based on density functional theory (DFT)
This study reveals for the first time the use of MOF-based multi-adsorbents in sorbent tubes and thermal desorption-based analysis of a mixture of carbonyl compounds with varying molecular weights
Summary
Metal organic frameworks (MOFs) are hybrid nanoporous materials comprised of metal ion or metal ion clusters and bridging organic linkers. Thermal desorption (TD)-gas chromatography (GC) is one of the most important tools for the quantitative analysis of volatile organic compounds (VOCs) This analysis can be effectively carried out for light VOCs like carbonyl compounds (CCs) using a high performance liquid chromatography (HPLC)-UV system in the context of a derivatization technique. The limitations of the poor adsorptivity of commercial adsorbents can be overcome by replacing the commercial sorbents or by combining them with materials with large surface area and high thermal stability. Carbonyl compounds (except FA) are most commonly analyzed by trapping the compounds onto commercial sorbents and transferring them into a thermal desorption unit connected to a GC or GC-MS system[19]. This study reveals for the first time the use of MOF-based multi-adsorbents in sorbent tubes (at room temperature) and thermal desorption-based analysis of a mixture of carbonyl compounds with varying molecular weights
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