Rapid perfluorinated alkyl acid analysis

17th January 2017

Posted By Paul Boughton

Longer lists of targeted perfluorinated alkyl acids can be analysed in eight minutes (10 minute total cycle time) on a 5 μm Raptor C18 SPP column using LC-MS/MS
Labs reporting PFOA and PFOS alone can increase sample throughput with a <2 minute analysis (4.5 minute total cycle time)

Dr Shun-Hsin Liang presents some recent research using LC-MS/MS

Perfluorinated alkyl acids are manmade fluorochemicals that are used as surface-active agents in the manufacture of a variety of products, such as firefighting foams, coating additives, textiles and cleaning products. They have been detected in the environment globally and are used in very large quantities around the world.

These fluorochemicals are extremely persistent and resistant to typical environmental degradation processes. As a result, they are widely distributed across the higher trophic levels and are found in soil, air, groundwater, municipal refuse and landfill leachates. The toxicity, mobility and bioaccumulation potential of perfluorooctanesulphonic acid (PFOS) and perfluorooctanoic acid (PFOA), in particular, pose considerable potential adverse effects for the environment and human health. Such effects include carcinogenicity, toxicity, hormonal effects, immunological effects and endocrine disruption.

Due to exposure risk and the likelihood of these detrimental impacts, PFOS and PFOA have both come under regulatory scrutiny and many countries have restricted their use and are establishing threshold levels in drinking water and other matrices. In Directive 2013/39/ EU (an amendment to the Water Framework Directive), PFOS is named as a “Priority Substance” with very challenging environmental quality standards. PFOS was also listed in the Stockholm Convention on Persistent Organic Pollutants in 2009, and PFOA is currently being considered for inclusion in this international treaty, which is aimed at global protection of human and environmental health. In addition, EU Directive 2006/122/ECOF now prohibits the manufacture and use of PFOS in the EU, and this directive also considers PFOA to present a risk profile that is comparable to PFOS. Similarly, PFOS is already regulated under the European Chemicals Agency’s REACH regulation EC No. 1907/2006, and PFOA is currently identified as a “Substance of Very High Concern” and has been placed on the REACH candidate list.

Challenging analysis

Perfluorinated alkyl acid analysis can be challenging because these compounds are chemically different from most other environmental contaminants. They are difficult to quantify because some are more volatile than others, and they also tend to be more hydrophilic and somewhat reactive. In addition, fluorochemicals are present in polytetrafluoroethylene (PTFE) materials, so excluding the use of any PTFE labware throughout the sampling and analytical processes (including HPLC solvent inlet tubing) is essential for accurate analysis.

Typically, perfluorinated alkyl acids are analysed by LC-MS/ MS methods, but some methods (e.g. ISO 25101 or DIN 38407- 42) require long analysis times (>20 min) that can greatly limit sample throughput.

The method developed here offers a fast analysis that still ensures sufficient resolution for the MS dwell time for all compounds within a specific retention time window. In the chromatogram shown in Fig.1, all target perfluorinated alkyl acids were analysed on a Raptor C18 column in under eight minutes with a total cycle time of 10 minutes. In addition to providing a fast analysis that supports sample throughput, there is no sacrifice in peak resolution or selectivity, meaning all fluorochemicals are easily identified and they elute as highly symmetrical peaks that can be accurately integrated and quantified by MS/MS. If PFOA and PFOS are the only target fluorochemicals of concern,  the analysis can be further optimised, which results in a fast, <two-minute separation with a total cycle time of just 4.5 minutes, as shown in the Fig.2 chromatogram.

The Raptor C18 5μm particle column used here offers excellent resolution for fluorochemicals with short total cycle times in part because it is a superficially porous particle (SPP) column. These particles, which are also commonly known as “core-shell” particles, have been proven to produce faster, more efficient separations than fully porous particles (FPP).

This is due to the shorter diffusion path and reduced peak dispersion that result from the solid core that is characteristic of SPP particles and that differentiates them from FPP particles. If desired, even faster analysis times could be obtained by using a Raptor C18 SPP column with 2.7 μm core-shell particles.

Whether labs conducting perfluorinated alkyl acid analysis by LC use longer target analyte lists or focus just on PFOA and PFOS, the excellent peak shapes and separations achieved here result in consistent, accurate quantification with much shorter analysis times. As increased regulatory interest and human health and environmental concerns drive up demand for efficient, effective perfluorinated alkyl acid analyses, methods such as the one presented here can help labs report results quickly and accurately.

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Dr Shun-Hsin Liang is senior LC applications chemist with Restek.  





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