Automated Solid Phase Extraction of PFAs from Tap Water

Perfluorinated compounds (PFAs) are a family of molecules that include various lengths of fluorocarbon chains with an attached functional group. They are typically used to make products and coatings that resist heat, stains, grease, and oil, such as furniture, clothing, non-stick cooking utensils, and wire insulation.

The CDC reports that exposure to large amounts of PFAs can negatively impact human growth and reproduction, among other ill effects. The concentration limit for PFAs in tap water is defined by the EU Water Framework Directive and the EPA.

To achieve a Low Limit of Detection (LOD) and Low Limit of Quantification (LOQ) requirements, experts recommend isolating and concentrating these perfluorinated compounds from a large volume of water (e.g., 500 ml) using Solid Phase Extraction (SPE) before mass spectrometry analysis. This method is widely used for other contaminants (e.g., pesticides, drug residues, etc.). However, obtaining reliable, accurate, and precise results requires overcoming numerous challenges.

Using full automated SPE systems under positive pressure, such as our Gilson ASPEC family systems, reduces this human dependency and improves reproducibility with precise control of SPE key parameters, such as volumes, flow rates, and drying or not drying control.

The majority of manual SPE methods are performed using a vacuum manifold. While this type of system appears relatively simple, it is highly technician-dependent with considerable expertise required in practice. The chemist must watch for vacuum fluctuation and unevenness and must be vigilant to avoid cartridge drying during condition steps or channeling while executing the SPE method.

Using full automated SPE systems under positive pressure, such as our Gilson ASPEC family systems, reduces this human dependency and improves reproducibility with precise control of SPE key parameters, such as volumes, flow rates, and drying or not drying control. In addition, a full SPE automation saves considerable time, especially when a long and tedious SPE protocol is performed with the percolation of a large volume of samples. Laboratory personnel can focus their efforts and time on other projects while the automated SPE instrument is operating, which helps increase overall productivity.

To achieve an accurate SPE protocol means obtaining high recoveries of analytes of interest at the end of the process and efficient removal of interference to limit matrix effects during the analysis itself. While the choice of the SPE cartridge and its associated method is crucial, accuracy can also be strongly impacted by other criteria, such as external contamination from the sampling up to the analysis.

Precautions for Automated PFAs Analysis Process

Unfortunately, PFAs are used in many components found in analytical systems, which can make obtaining accurate results challenging. The presence of PFAs in HPLC systems (PTFE, FEP elements), solvents, sampling bottles, valves, transfer tubing, and so forth can lead to a significant chance of sample contamination and high PFAs background. This contamination can mask trace levels of PFAs from detection or lead to false positives.

To prevent external contamination, some precautions were implemented based on not using fluoropolymers, including the use of:

• Nitrile Gloves
• HDPE Gilson 700 ML bottles both for samples and SPE solvents
• ASPEC 274 Large Volume system equipped with PEEK tubing kit
• AFFINISEP Free-PFAs SPE cartridges
• Gilson PIPETMAN® DIAMOND Tips for sample handling and for standard preparation
• Gilson Polypropylene tubes to collect elution

The analysis was directly performed after SPE, using an LC-MS/MS system step. To solve the risk of potential contamination sources from LC pumps, a simple and economical solution was adopted with the implementation of a delay column between the LC pumps and the injector.

Figure 1: ASPEC 274 Large Volume System