Environmental Laboratory 29
tubing assemblies that contain known PFAS and separating any unavoidable interference from sources such as mobile phase by delaying their signal from the sample using an isolator column.
Improve detection and sensitivity with the Xevo TQ Absolute or switching to the UniSpray TM
Ion Source The direct injection approach for PFAS analysis requires a highly sensitive mass spectrometer to reach necessary performance criteria. The enhanced negative ion sensitivity of the Xevo TQ Absolute tandem quadrupole mass spectrometer allows for utilization of the direct injection method for PFAS analysis with a reduced sample injection volume of 10 µL without compromise to method performance. Figure 2 shows some chromatograms to illustrate the detection of PFOS and its branched isomers in wastewater at 0.7 ng/L.
An alternative option is to switch from electrospray to the novel UniSpray source. UniSpray or impactor ionization is a novel atmospheric ionization technique that makes use of a high-velocity spray, created from a grounded nebulizer impacting on a high-voltage target (stainless steel rod), to ionize analytes in a similar fashion to electrospray but promotes extra droplet break-up and desolvation via additional Coanda and vortex effects. A direct comparison was carried out to evaluate the relative sensitivity of each ionization source for PFAS analysis. The UniSpray ion source displayed consistent gains in sensitivity for all compounds, measured by comparing peak area, peak height, and signal to noise (see Figure 3). Although PFAS respond well using electrospray ionization in negative ion mode, UniSpray was shown to exhibit consistent gains in sensitivity for all twenty PFAS and offers a practical alternative to check compliance with water regulations for PFAS.
Method performance
We have previously reported the development of a direct injection method for PFAS suitable for checking compliance with the 2020 EU Drinking Water Directive.4
A limit of quantitation (LOQ) of 0.001 μg/L was achieved
Figure 3. Signal to noise and peak response comparison between UniSpray Ion Source (red) and Electrospray (blue) ionization techniques demonstrated at 2 ng/L in hard water (average S/N).
for each individual PFAS to be confi dent of implementing the 0.1 μg/L sum of the twenty PFAS limit, without the need for any pre-concentration steps. The method used an ACQUITY Premier BEH™ Shield RP18 Column on an ACQUITY TM UPLC I-Class PLUS System with Xevo TQ-XS Tandem Quadrupole Mass Spectrometer and the unique UniSpray ion source. In addition, the novel MaxPeak™ High Performance Surfaces (HPS) technology of the ACQUITY Premier UPLC Column provided an increase in sensitivity for the longer-chain PFAS. Subsequently, we reported the results of an interlaboratory study to assess the ease of implementation of the method and to further evaluate the performance of the method.5
Each
Figure 4. Bracketed matrix-matched calibration curves for a selection of PFAS at 1 ng/L to 200 ng/L (0.6 ng/L to 120 ng/L in vial concentration), including chromatograms for the quantitative transitions at 1 ng/L. All residuals are within 20% of nominal values.
laboratory successfully implemented the method, including installation of the ACQUITY UPLC PFAS Kit, using the start-up guide, and demonstrated stable chromatography and satisfactory sensitivity. Participants demonstrated good accuracy for the quantifi cation of the PFAS except PFBA in a water. Trueness was shown to be between 96 and 100%, and values for repeatability within each laboratory and reproducibility between laboratories were all <20%. All but three laboratories experienced issues relating to contamination with PFBA. This study confi rms that this direct injection UPLC-MS/MS method can be implemented in multiple laboratories and is suitable for checking drinking water supplies for compliance with various regulatory and advisory limits globally. Figure 4 also shows typical calibration graphs and Figure 5 chromatograms for compounds injected at 1 ng/L concentration in water.
Conclusions
Detection requirements for per- and polyfl uorinated alkyl substances (PFAS) have been getting more challenging as regulations to protect consumers and preserve the environment continue to be created and updated. The demand for sensitive solutions for direct injection to determine PFAS has also increased, since time-consuming sample preparation with SPE and the risk of contamination can be avoided. Using ACQUITY UPLC fi tted with the PFAS Installation Kit and the novel UniSpray ion source or the performance of the new Xevo TQ Absolute, it is possible to obtain suffi cient performance using direct injection of water samples to check compliance with regulations for PFAS in water.
References,
1. Directive (EU) 2020/2184 of the European Parliament and of the Council of 16 December 2020 on the quality of water intended for human consumption. OJ L 435, 23.12.2020, p. 1–62
2. Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the fi eld of water policy. OJ L327, 22.12.2000, p. 0001-0073
Figure 5: Typical chromatograms for the 20 PFAS listed in EU 2020/2184 Part B of Annex III at 1 ng/L in water.
Author Contact Details Janitha De Alwis • Waters Corporation • Address: Altrincham Rd, Wilmslow, SK9 4AX, Cheshire, UK • Tel: +44 0161 946 2400 • Email:
Janitha_de-alwis@waters.com • Web:
www.waters.com
3. Directive 2013/39/EU of the European Parliament and of the Council of 12 August 2013 amending Directives 2000/60/EC and 2008/105/EC as regards priority substances in the fi eld of water policy Text with EEA relevance. OJ L226, 24.8.2013,p. 1-17
4. Willmer H, Organtini K, Adams S. Routine Determination of Per- and Polyfl uorinated Alkyl Substances (PFAS) in Drinking Water by Direct Injection Using UPLC-MS/MS to Meet the EU Drinking Water Directive 2020/2184 Requirements. Waters application note, 720007413, 2022.
5. Hird S, Adams S, Willmer H, Organtini K, Williams J. Evaluation of the Performance of a UPLC-MS/MS Method for the Determination of PFAS in Drinking Water, for Checking Compliance with the EU Drinking Water Directive, Using an Interlaboratory Study. Waters application note, 720007538, 2022
List of Trademarks used in publication are trademarks of Waters Corporation. © 2022 Waters Corporation
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