The ubiquitous nature of PFAS in the environment makes ensuring a contaminant-free workflow essential. In this application note, we demonstrate that Resprep S-DVB SPE cartridges and related sample preparation products are consistently free of background interferences. In addition, a PFAS delay column effectively removes any contamination that may be present in the instrument. Using the materials and procedure presented here, EPA Method 537.1 requirements for cleanliness, accuracy, and precision were reliably met.<\/p>\n\n\n\n
Per- and polyfluoroalkyl substances (PFAS) are being analyzed more now than ever before due to growing concern about human exposure and potential adverse health effects. Their persistent nature and widespread use across many industries and in diverse products, ranging from non-stick kitchenware, weatherproof clothes, and aqueous film-forming foam (AFFF) to food packaging coatings, has made them essentially ubiquitous contaminants worldwide. Accordingly, testing of soils, wastewater, drinking water, and other environmental matrices, along with PFAS testing in foods, continues to increase.<\/p>\n\n\n\n
In 2020, the U.S. EPA released Method 537.1 revision 2 [1] for PFAS analysis in drinking water. The method specifies that sample preparation must be performed using styrene-divinylbenzene (S-DVB) SPE cartridges and that deviation in the extraction procedure is not allowed. Because background PFAS contaminants can leach out of materials anywhere in the sample pathway and interfere with target compound analysis, labs must demonstrate acceptable background, accuracy, and precision results each time a new lot of supplies is used. In addition to this initial qualification, routine blank and QC sample analysis is required to ensure continued performance.<\/p>\n\n\n\n
In a typical workflow, the sample comes in contact with multiple surfaces and substances, each of which can be possible sources of PFAS contamination or retention. These include collection vessels, chemicals (Trizma base, solvents, mobile phases, etc.), pipettes, SPE products, manifolds or automated systems, tubing, filters, vials, vial caps, and components within the LC. Even when care is taken to avoid materials known to leach PFAS, such as PTFE, or to which target analytes may adhere, such as glass, the use of clean, high-quality consumables will help prevent downtime due to system suitability failures.<\/p>\n\n\n\n
Here, we followed U.S. EPA Method 537.1 and demonstrated a contaminant-free workflow that meets the stringent method requirements. While this data set is based on Method 537.1, similar testing to determine if background PFAS are present is strongly recommended for other PFAS methods [2] due to the pervasiveness of PFAS contamination.<\/p>\n\n\n\n
PFAS analytical, internal, and surrogate standards were used to create calibration standards and laboratory fortified blanks as directed by EPA 537.1. Eight calibration standards were created from 0.2\u201350 ppb corresponding to 0.8\u2013200 ppt in drinking water prior to 250-fold concentration, which occurs during sample preparation. Laboratory reagent blanks (LRB) and laboratory fortified blanks (LFB) were used as per EPA 537.1, sections 9.2.2\u20139.2.4. LFBs spiked at 40 ppt were used to determine the accuracy and precision of the method.<\/p>\n\n\n\n
Analytical and surrogate standards were added to 250 mL 18.3 M\u03a9\u2022cm (megohm) ultrapure reagent water for the LFB samples. The LFB samples were kept in polypropylene containers prior to extraction. The materials used for this workflow are detailed in Table I.<\/p>\n\n\n\n
PFAS were extracted by using Resprep S-DVB SPE cartridges (6 mL, 500 mg) attached to a Resprep vacuum manifold. Cartridges were first conditioned using 15 mL methanol followed by 18 mL reagent water, never allowing the bed to dry. Reservoirs were affixed to the SPE cartridges with adaptors to avoid the use of PTFE transfer lines. Use of reservoirs, as set up in Figure 1, made the addition of the samples more convenient. The full sample preparation procedure is described below and in Figure 2.<\/p>\n\n\n\n
For extraction, a flow rate of approximately 10\u201315 mL\/min was established, and care was taken to never allow the particle bed to dry throughout the extraction process. After the samples had passed through the cartridges, we rinsed each sample bottle with two 7.5 mL aliquots of reagent water. After rinsing the sample bottles, the aliquot was used to rinse each sample reservoir as well to ensure that no PFAS of interest in the sample were left behind.<\/p>\n\n\n\n
Following extraction, we dried the SPE cartridges by drawing air through them while they were still attached to the vacuum manifold. After drying, collection tubes were placed in the manifold and two 4 mL aliquots of methanol were passed through each SPE cartridge and collected. The collection tubes were removed from the manifold, and the extract was concentrated to dryness under nitrogen flow while heating the samples at 65 \u00b0C.<\/p>\n\n\n\n
Once the samples were dry, we added 1 mL 96:4 methanol:water solution and internal standard and then vortexed to ensure proper mixing. After vortexing, aliquots of the concentrated solution were transferred to polypropylene sample vials and capped with polyethylene caps. Samples were then analyzed via an LC-MS\/MS equipped with a PFAS delay column (cat.# 27854) and a Raptor C18 LC column (50 mm x 2.1 mm, 2.7 \u00b5m; cat.# 9304A52). Method conditions can be found in Figures 3 and 4.<\/p>\n\n\n