Selectivity of solid phase extraction for dissolved organic matter in the hypersaline Da Qaidam Lake, China

Abstract

Dissolved organic matter (DOM) was isolated from the hypersaline Da Qaidam Lake using solid-phase extraction (SPE) methods with five different adsorbents: ENVI-Carb (non-porous graphitized carbon), HLB, PPL, and XAD-8 (polymer based), and ENVI-18 (silica based). Structure-selective assessments of SPE-DOM isolated using the different adsorbents were conducted using a combination of complementary analysis techniques, including dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) analysis, as well as elemental analysis, Fourier transformed infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). The results indicated that the modified polymer based adsorbents (PPL and HLB) exhibited higher DOC recoveries than the others. The PPL and ENVI-Carb cartridges can recover representative nitrogen-containing organic components from the hypersaline lake. The SPE-DOM isolates obtained using ENVI-18 and XAD-8 adsorbents contained higher proportions of purely aliphatic, alkene, and aromatic compounds; the ENVI-Carb and PPL adsorbents showed higher affinity for polar functionalized aliphatic and nitrogen-containing compounds; HLB isolate was enriched with oxygen-rich organic compounds and sulphur-bearing components. The structural and compositional features of SPE-DOM from the hypersaline Da Qaidam Lake indicated the predominately autochthonous sources of organic matter in the lake.