pH-Dependent Solid-Phase Extraction for Enhanced Detection of Persistent Toxic Substances in Consumer Products by High-Resolution Mass Spectrometry

Abstract

Consumer products (CPs) represent a significant source of persistent toxic substances (PTS) due to their widespread use and complex chemical compositions. While some ingredients are disclosed on product labels or in public databases, numerous compounds remain unidentified, raising concerns about human and environmental exposure. While high-resolution mass spectrometry (HRMS) offers comprehensive screening for unknown compounds, its sensitivity and accuracy are frequently hampered by severe ion suppression from matrix components like surfactants and salts. To overcome this, we developed a novel pH-dependent solid-phase extraction (SPE) method specifically optimized for CP analysis. This approach effectively removes matrix interferences and significantly improves analytical signal quality, offering a promising platform for enhanced PTS detection in CPs. Five CPs were selected to establish sampling and sample preparation protocols based on their formulations: washing machine cleaner and fabric softener dryer sheets (solid CPs), and laundry detergent, bug spray, and sanitizer tissues (liquid CPs). Lower organic phase extracts were prepared for water-insoluble CPs via liquid-liquid extraction, followed by pH-dependent SPE for both water-insoluble and water-soluble CPs. SPE was performed under four solution conditions: 1% formic acid (acidic; pH 2.0), HPLC-grade water (neutral; pH 6.2), 2% ammonium hydroxide (basic; pH 10.0), and sequential acidic-to-basic conditions. Extracted samples were analyzed using UHPLC-Q-TOF MS. Ten target surfactants showed distinct pH-dependent extraction behaviours. Anionic surfactants (linear alkylbenzene sulfonates, sodium lauryl sulfate, and sodium laureth sulfate) were more effectively removed under acidic conditions compared to basic conditions. Cationic quaternary ammonium compounds were efficiently removed under both basic and acidic-basic conditions. Poor retention under basic conditions was attributed to ion pairing between permanently charged quaternary ammonium cations and hydroxide anions, forming hydrophilic complexes with reduced affinity for the hydrophobic HLB sorbent. These results demonstrate that selective pH adjustment is essential for efficiently removing specific matrix interferences, highlighting the necessity of analyte-specific pH optimization based on interfering substance characteristics in CP analysis. This pH-dependent SPE method provides a promising platform for PTS detection in CPs, though further optimization is needed to achieve broader applicability across various environmental matrices.