Metal-organic frameworks as superior media for thermal desorption-gas chromatography application: A critical assessment of MOF-5 for the quantitation of airborne formaldehyde

Abstract

In this study, formaldehyde (FA) in the air was collected and analyzed using metal-organic framework-5 (MOP-5) as the sorbent material (for both sorbent tube (ST) sampling and thermal desorption (TD) analysis) in gas chromatography-mass spectrometry (GC-MS) detection. A series of experiments was carried out to determine the optimal analytical conditions for maximum recovery of FA by TD-GC-MS. Optimal TD conditions for adsorption and desorption of MOF-5 were determined to be - 25 degrees C and 100 degrees C, respectively. These conditions yielded good linearity (R-2 = 0.9975), precision (mean 1.79 +/- 1.17%), and high sensitivity. The method detection limit (MDL) of 0.1 ng was attained to determine 0.82 ppb of FA in 100 mL of air (limit of detection (LOD) of 8 pg (0.06 ppb)). The concentration of FA, when measured from ambient air samples using MOF-5, averaged 9.67 ppb (n = 3, RSE = 239%). FA samples, when analyzed in parallel using the DNPH cartridge-HPLC-UV system recommended by the US EPA, yielded similar results (mean of 10.5 ppb) to the MOF-5 dataset In addition, trace quantities of FA (0.25 ng) were also detected from samples of as little as 20 mL of air. Our results suggest that MOF-5 is a suitable sorbent media for thermal desorption analysis and in fact surpasses the performance of commercial sorbents used for VOC analysis. As such, a GC-based detection method for FA comprising simple thermal desorption without complicated procedures, such as a derivatization step, was realized.