Xian-Yong Wei

Rapid analysis of carboxylic acids and esters with a direct analysis in real time ion source

RATIONALEnCoal oxidation produces carboxylic acids (CAs), including aliphatic acids, benzoic acids, and benzenepolycarboxylic acids, which are important fine chemicals and could be used for understanding the structural features of coals. However, detecting CAs usually faces great challenges due to extremely troublesome pretreatments. Therefore, it is essential to develop an analytical method for rapidly detecting CAs from coal oxidation.nnnMETHODSnA series of model compounds (MCs) of oxidation products and 2 practical samples were investigated by direct analysis in real time/time-of-flight mass spectrometer (DART/TOF-MS) under 3 different analytical conditions (ionizing gas temperature, organic solvent, and MC concentration).nnnRESULTSnIonizing methyl benzoate, dimethyl phthalate, and dimethyl adipate produces typical ions of methyl esters, including [M - OCH3 ]+ , [M + H]+ , and [M + NH4 ]+ . In contrast, the characteristic ions generated from CAs are polymer ions, such as [2M + NH4 ]+ , [3M + NH4 ]+ , [4M + NH4 ]+ , and [5M + NH4 ]+ , indicating the strong intermolecular hydrogen-bond interaction among CAs.nnnCONCLUSIONSnResults suggest that DART/TOF-MS could rapidly analyze CAs or esters in coal oxidation products according to their typical ions for further facilitating deep insight into the coal structure.