Accurate quantification of multiple sulfur compounds in natural gas: Preparation and evaluation of a thioether-functionalized covalent organic framework-based gas chromatography capillary column

Accurate quantification of sulfur compounds, such as hydrogen sulfide and mercaptans, is crucial for natural gas quality control and ensuring the safe supply of energy sources, given their high reactivity and corrosiveness toward gas pipelines and equipment. In this study, a thioether-functionalized covalent organic framework (COF-LZU8) was selected for its potential specific interactions with sulfur compounds via thioether groups and straight channels, and was synthesized and uniformly immobilized onto the inner surface of a capillary column via in-situ growth. This column was employed as a stationary phase for gas chromatography (GC) to qualitatively separate and quantitatively detecte several sulfur compounds in natural gas. The key findings are as follows: (1) The column exhibited high separation efficiency and good linearity over two orders of magnitude, attributed primarily to S–S and hydrogen bonding interactions between COF-LZU8 and the sulfur compounds, as indicated by simulation results. (2) The limits of detections (LODs) for the seven sulfur compounds ranged from 0.017 mg/m 3 (methyl mercaptan) to 0.746 mg/m 3 (methyl sulfide). (3) At a concentration of 10.1 mg/m 3 , the relative standard deviations for peak area and retention time, determined from replicate injections, were 0.01%–1.43% and 0–0.14% for intra-day precision (n = 5), and 1.29%–3.37% and 0.05%–0.23% for inter-day precision (n = 5), respectively. Satisfactory accuracy was further confirmed by the small absolute errors observed for standard gases. (4) The determined concentrations of sulfur compounds obtained with the COF-LZU8-coated capillary column were consistent with those of multiple commercial columns for standard gases with small absolute errors and analysis of an actual natural gas sample also showed agreement between the COF-LZU8-coated capillary column and a commercial GC column (DB-SULFUR) within 0.5 mg/m 3 . This study presents a competitive GC capillary column that shows potential as an alternative to commercial stationary phases, providing a promising platform for applying covalent organic frameworks (COFs) as GC stationary phases for the simultaneous detection of multiple sulfur compounds in the natural gas industry.