Are PFAS sticking in your system?16 Apr 2020
Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in our society and can be found in a wide range of consumer products; hence they are widely present in the environment, people and animals. They are persistent chemicals that have the potential to accumulate. Therefore, they are evaluated and monitored using a variety of methods and controlled by numerous regulations. Due to its every-where presence, it is no wonder they end up in our samples, systems or chemicals elevating our results and making us waste numerous hours searching for contamination to get the analysis to pass. Where do they come from? What are some of the most overlooked sources of contamination? How to avoid those false positives?
To abate the cross-contamination with PFAS, follow your sample journey from the sampling to the chromatogram on your screen. Just assure the samples never come in contact with material made or, coated with PFAS, which can be often easier said than done.
- Avoid LDPE bottles, clothing containing polytetrafluoroethylene (such as water-resistant coats or stain repellent clothing), waterproof notebooks, plastic clipboards, stick it note pads, permanent markers, or reusable ice packs (blue ice).
Instead, for sampling use HDPE (high-density polyethylene) and polypropylene bottles and label the sample after the sampling. Some labs offer pre-screened sampling bottles.
- Avoid glass transfer pipettes, vial caps with PTFE seals and even some glass HPLC vials (PFAS has been known to absorb to glass when it has been in contact for an extended period of time. Glass bottles or containers can be used if they are known to be PFAS-free). Who would have thought aluminum foil has a nonstick coat? Avoid wearing sunscreens/insect repellents, fabric softener, moisturizers and lab coats (stain-resistant). Avoid washing glassware with detergents that haven’t been tested for PFAS presence.
Instead, handle samples with materials that are made from rubber, polyvinyl chloride (PVC) plastics, and polyurethane. Wear lab coats made from cotton and nitrile gloves. Use polypropylene HPLC vials (Cat.#: 23242), caps (Cat.#: 23244) and disposable pipette tips (polypropylene). Hand wash all glassware.
An effective tip for all methods using SPE manifold is after analyzing SPE samples, all reusable parts should be washed with acetonitrile and sonicated for ~10 minutes to avoid cross-contamination.
- Avoid all PTFE tubing, PTFE frits, and sample valves with certain rotor seal or stator face. Be aware that when your LC-MS/MS system has been sitting overnight or extended time frame the first few injections will show a high level of PFAS due to the buildup of residual PFAS in the system.
Instead, replace all tubing with PEEK tubing or stainless steel in your system to avoid system-related interferences. You can find kits specifically designed for PFAS analysis from individual instrument companies (sometimes this can be costly and not feasible). A great option is to add a PFAS Delay Column (Cat.#: 27857) after the mixing chamber to trap system-related PFAS. See references listed at the bottom of this blog for PFAS Delay column video and another blog explaining it in greater detail. Before starting the analysis condition your analytical column (Raptor C18, (Cat.#: 9304A52) for methods such as US EPA 533, US EPA 537.1, ISO 21675:2019, ASTM D7968-17A, ASTM D7979-19, DIN 38407-42 and many more) with 20-30 column volumes. Refer to our PFAS column selection guide listed in the reference for additional dimensions. Execute 3-4 injections of high organic solvent (acetonitrile) while running your method to flush out any residual PFAS in your injector.
- A part of the system that is often overlooked when searching for PFAS contamination is the mobile phase. Many HPLC and LC-MS/MS grade mobile phases (water, acetonitrile, and methanol) use PTFE filters before they are bottled by the company. Bottle caps could have PTFE lining.
If contamination is found in the brand new solvent bottles, filter all the HPLC or LC-MS/MS grade water with a PFAS Delay column (Cat.#: 27857) before you make the buffer. Lot check all solvents and stick with a lot that works.
The most influential part to avoid contamination in PFAS analysis is to have a designated system, mobile phase, and materials that you know are PFAS-free. Any time you introduce a new part/solvent to the analysis test to make sure it is clean of PFAS. Good lab practice is always your friend.