In the first phase of this project, methods for analyzing PXAs were developed using liquid chromatography-electrospray ionization-Orbitrap-high resolution mass spectrometry (LC-ESI-Orbitrap-HRMS) and a novel CP-Seeker integration software package for homologue detection and integration. A prototype PXA-C14 standard was used to validate sample extraction procedures for indoor dust and the subsequent analysis and integration steps. The confirmed method was then applied to 59 indoor dust samples from six countries including Australia (n=10), Belgium (n=10), Colombia (n=10), Japan (n=10), Thailand (n=10) and the United States of America (USA, n=9). PXAs were detected in seven samples from the USA, with carbon chain lengths of C8, C10, C12, C14, C16, C18, C24 to C28, C30 and C31 observed overall, but not detected in samples from any other countries.
In the second phase of this project, a full series of 16 PXA mixture standards ranging C10 to C17, each at low and high halogenation degrees, were synthesized at the University of Hohenheim by bromination and chlorination of n-alkanes. The custom synthesized standards were characterized LC-Orbitrap-HRMS and used to assess the applicability of pattern deconvolution quantification strategies for PXAs in indoor dust. PXAs of Br1-9 and Cl1-8 were detected as [M + Cl]- adduct ions among the C10 to C17 standards as well as substantial proportions of PCAs.
A quantification procedure was developed for PXAs using pattern deconvolution strategies previously applied for the measurement of PCAs. Triplicate fortification experiments were performed using varied halogenation compositions prepared from mixtures of the 16 PXA standards to assess the accuracy and precision of the quantification method. The pattern deconvolution method showed an average measurement accuracy of 82 % across the studied carbon chain lengths and coefficient of variance ≤ 20% between replicates. Overall, >90 % of quantified ΣPXA concentrations in the fortification trials met the European Union Reference Laboratory’s accuracy acceptability criteria of 50 to 150%.
The PXA pattern deconvolution quantification procedure was also applied to the seven indoor dust samples from the United States of America in which PXAs were detected. The results revealed poor correlations between the homologue distribution in samples and the prototype standards (R2 ≤ 0.40) which prevented reliable quantification for PXAs of most carbon chain lengths. The findings of this study indicates that the modified pattern deconvolution procedure is a suitable strategy for the quantification of PXAs in environmental samples, but that standards with diverse halogenation profiles more closely matching those found in indoor dust will be required before reliable PXA measurement can be achieved in indoor dust.
