Correction of Matrix Effects for Reliable Non-target Screening LC–ESI–MS Analysis of Wastewater

Matrix
effects are well-known challenges for accurate and comparable
measurements with liquid chromatography (LC) electrospray ionization
mass spectrometry (ESI–MS). This study describes a three-step
method to evaluate and compensate for matrix effects in enriched wastewater
extracts using LC ESI-high-resolution MS (HRMS). As a first step,
the “dilute and shoot” approach was used to determine
the optimal relative enrichment factor (REF) for a direct comparison
between wastewater influent (REF 10) and effluent (REF 50) extracts.
However, the rapid decrease in the number of non-target compounds
detected with increasing dilution leads to the need for a correction
of the matrix effect for analyzing samples with higher REFs. As a
second step, the observed matrix effect at higher REFs was corrected
by the retention time-dependent matrix effect. A new scaling (TiChri
scale) of the matrix effect was introduced, which demonstrates that
the total ion chromatogram (TIC) predicts the matrix effect as effectively
as post-column infusion (PCI) approaches; thus, the average median
matrix effect was improved from −65 to 1% for influent (REF
100) and from −46 to −2% for effluent extracts (REF
250). The TIC traces for concentrated (REF 250) influent and effluent
samples were successfully used to correct the matrix effects and allowed
the extent of micropollutant degradation in three WWTPs to be quantified.
As a final step, the residual structure-specific matrix effect was
predicted and corrected by quantitative structure–property
relationships (QSPR), which led to a further correction of the matrix
effect to 0 ± 7% for 65 compounds.