Unraveling the structural composition of commercial Polyoxyethylene alkyl ether carboxylic acid via HPLC-ESI-MS: from active ingredients to byproducts

Polyoxyethylene alkyl ether carboxylic acid (AEC) is a high-performance surfactant widely used in personal care and industrial applications. Existing analytical frameworks often struggle with low sensitivity and the inability to simultaneously quantify active ingredients alongside residual raw materials. This study describes the development and validation of an HPLC-ESI-MS method for the comprehensive characterization of AEC products. Chromatographic separation was achieved on an XBridge® C18 column using a mobile phase consisting of methanol and 25 mmol/L ammonium formate (containing 0.2% formic acid) (80:20, v/v). The method enables the accurate quantification of residual AEO and the semi-quantitative estimation of the key byproduct polyethylene glycol ether carboxylic acid (PEG-CH2COOH). For C12-14 AEO and PEG-CH2COOH, the LODs were 0.2 and 0.5 μg/mL, and the LOQs were 0.6 and 1.5 μg/mL, respectively. Excellent linearity was observed (r ≥ 0.998), with mean recoveries ranging from 95.9% to 106.0%. Furthermore, mass spectrometric characterization facilitated the structural elucidation of PEG-CH2COOH. Based on these analytical findings, potential formation pathways involve the covalent incorporation of carboxymethyl groups through the oxidation or carboxymethylation of PEG terminal hydroxyl groups. This method provides a critical analytical tool for the quality control, safety assessment, and formulation optimization of AEC products.