Salt-induced matrix effects on PFAS quantification in online SPE-LC-MS/MS analysis
Aleum Lee1, Soo Min Song1,2, Hee Sun Moon3,4
1Groundwater Environment Research Center, Geo-Environment Research Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, 34132, Korea.
Residual inorganic ions in water significantly impact perfluoroalkyl substances (PFAS) quantification using online SPE-LC-MS/MS. Salt addition improves detection limits for short-chain PFAS but complicates accurate measurement due to incomplete internal standard correction.
Area of Science:
- Environmental Chemistry
- Analytical Chemistry
- Mass Spectrometry
Background:
- Automated online solid-phase extraction (SPE) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) is crucial for quantifying perfluoroalkyl substances (PFAS) in environmental waters.
- Residual inorganic ions from water matrices can interfere with electrospray ionization (ESI), potentially biasing PFAS quantification.
- Understanding the impact of common ions like sodium chloride (NaCl) and calcium chloride (CaCl2) on PFAS analytical response is vital for method accuracy.
Purpose of the Study:
- To evaluate the influence of environmentally relevant salt concentrations (10-30 mg/L NaCl or CaCl2) on PFAS analytical response in an online SPE-LC-MS/MS system.
- To assess the matrix effects and internal standardization efficiency for various PFAS compounds under varying ionic conditions.
- To determine the implications of salt-induced response alterations for method validation and data interpretation in PFAS analysis.
Main Methods:
- Utilized an automated online SPE-LC-MS/MS system operating in negative ESI-MRM mode.
- Tested modest salt concentrations (10-30 mg/L NaCl and CaCl2) in environmental water samples.
- Analyzed perfluorobutanoic acid (PFBA) and a suite of other PFAS compounds, including isotopically labeled internal standards.
Main Results:
- Salt addition improved the detectability of PFBA, lowering detection limits (LOD) to 0.17-0.22 ng/L and quantification limits (LOQ) to 0.57-0.74 ng/L.
- Isotope dilution provided incomplete compensation for salt-dependent response changes, with PFBA/13C4-PFBA area ratios increasing significantly.
- Matrix effects ranged widely (-74% to +1005%), with short-chain PFAS (e.g., PFPeA) showing the strongest signal enhancement (up to tenfold), while longer-chain PFAS exhibited weaker or negative effects. NaCl amplified these effects more than CaCl2.
Conclusions:
- Environmentally relevant salt concentrations substantially alter PFAS response patterns in automated online SPE-LC-MS/MS, impacting method validation and data interpretation.
- Short-chain PFAS are particularly susceptible to salt-induced signal enhancement, and isotope dilution offers incomplete correction for these effects.
- Ionic composition of water matrices must be explicitly considered when quantifying PFAS, especially short-chain compounds, to ensure accurate analytical results.
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