Sensitive and background-free determination of thiols from wastewater samples by MOF-5 extraction coupled with high-performance liquid chromatography with fluorescence detection using a novel fluorescence probe of carbazole-9-ethyl-2-maleimide

• A novel background-free fluorescence probe was synthesized for thiols determination.
• The MOF-5 was utilized for the extraction of thiols from wastewater.
• The derivatization could be finished in just 10 min under a mild condition.
• The developed method exhibited low LOD in the range of 8–17.1 pmol/L.

A sensitive and background-free pre-column derivatization method for the determination of thiol compounds using metal-organic framework material (MOF-5) as dispersive solid-phase extraction (DSPE) adsorbent followed by high-performance liquid chromatography fluorescence detection (HPLC-FLD) has been developed. In this paper, a novel labeling reagent, carbazole-9-ethyl-2-maleimide(CAEM), was synthesized and reacted with thiols at 40 °C for 10 min in the presence of PBS buffer (0.02 mol/L, pH 7.5). Interestingly, CAEM itself had no fluorescence, while its derivatives exhibited intense fluorescence with an excitation maximum at λex 274 nm and an emission maximum at λem 363 nm, which greatly reduced the background interference and improved the sensitivity of the method. Furthermore, the MOF-5 was prepared and used as DSPE adsorbent for the selective adsorption of thiols from wastewater sample. Under the optimized experimental conditions, an excellent linearity for all analytes over their concentration ranges of 0.01–1.0 μmol/L (R2>0.9986)were obtained with the limit of detection (LOD) ranging from 8 to 17.1 pmol/L for nine tested thiols. The feasibility of this method for the determination of thiols in wastewater samples had been evaluated and satisfactory average recoveries (n=3) were achieved with the range of 86.6–98.5%.

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