The compound-independent calibration of alkyl organophosphorus flame retardants in rice using GC-ICP-MS

Organophosphorus flame retardants (OPFRs) are widespread environmental contaminants with bioaccumulative potential and associated human health risks. The lack of commercial reference standards for many OPFRs limits the accuracy of their quantification. In this study, a compound-independent calibration (CIC) method using gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) was developed for the simultaneous quantification of seven alkyl OPFRs, with tripropyl phosphate (TnPP) as a single universal calibrant. Key parameters were optimized: a DB-5MS column (15 m × 0.25 mm × 0.10 μm) with pulsed splitless injection (70 psi, 280 °C), and ICP-MS settings including an RF power of 1600 W, sampling depth of 7.5 mm, dilution gas flow rate of 0.5 mL/min, and octopole voltage of - 5 V. The method exhibited excellent linearity (R² = 0.9994 to 0.9999) over the range of 0.01-1.0 μg/mL. Limits of detection and quantification were 0.22 to 0.91 ng/mL and 0.75 to 3.02 ng/mL, respectively. For six of the seven OPFRs (excluding TEHP), the relative P response ratios compared to TnPP ranged from 0.91 to 1.01, confirming effective structure-independent calibration. The matrix effect in rice was moderate (enhancement factors 1.13-1.35). Quantitative results obtained by the CIC method agreed well with those from an external standard approach, with relative deviations within -8.54% to +7.78%. This work demonstrates that CIC-GC-ICP-MS using a single, readily available calibrant provides a reliable, practical solution for quantifying alkyl OPFRs in complex food matrices, effectively overcoming the challenge posed by the scarcity of compound-specific reference standards.