Simultaneous Determination by Selective Esterification of Trimellitic, Phthalic, and Maleic Anhydrides in the Presence of Respective Acids

Trimellitic, phthalic, and maleic anhydrides are important building blocks to produce polymers and additives, such as plasticizers. In humans, the exposure to these compounds can cause several health issues. In European Union and USA, their presence in substances and mixtures is restricted by CLP Regulation (no. 1272/2008) and HCS/HazCom 2012, respectively, but no information about the corresponding acids is reported. For this reason, a selective method to determine anhydrides in mixtures, in the presence of acids, could be interesting. Nowadays, methods in the literature are either not selective or use explosive and toxic reagents (as diazomethane). In this work, an innovative, greener, and safer method for the simultaneous recognition and quantification of anhydrides and acids, via direct injection gas chromatography-mass spectrometry, is developed. The sample pretreatment consists in selective esterification with absolute ethanol on the anhydride, followed by a treatment with boron trifluoride-methanol for the methylation of remaining carboxylic groups. The optimization of the functionalization, a crucial step of the method, was optimized by experimental design. The limit of detection-limit of quantification (LOD-LOQ) values for trimellitic, phthalic, and maleic anhydrides are 0.31-0.93, 0.47-1.41, and 0.06-0.18 μg/mL, respectively.