Including Current Best Practices for PFAS Sampling
Groundwater sampling is a core element of environmental investigations, compliance monitoring, and site remediation. Whether you’re testing for metals, VOCs, nutrients, or emerging contaminants like PFAS (per- and polyfluoroalkyl substances), the tubing you select plays a critical role in maintaining data integrity.
Choosing the wrong tubing can lead to analyte loss, cross-contamination, or regulatory non-compliance. In this guide, we’ll walk through how to select the right tubing for your groundwater sampling applications—especially for today’s increasingly strict PFAS sampling standards.
1. Define Your Sampling Objectives
Your tubing choice depends on your sampling goals:
- General water quality — broader material options.
- Metals analysis — tubing must not leach metals or interfere with results.
- Volatile Organic Compounds (VOCs) — low-sorption, low-off-gassing tubing is required.
- PFAS sampling — tubing must be free of fluoropolymer coatings (in most guidance) and PFAS-based lubricants; tubing should be chemically compatible and validated.
- Long-term monitoring — durable materials are key to minimizing maintenance and replacement.
2. Understand Your Water Chemistry
Always consider site-specific water chemistry:
- pH extremes
- Salinity
- Hydrocarbon presence
- Turbidity
- Dissolved organic carbon
- Known or suspected PFAS contamination
Tubing must be compatible with the sample matrix to avoid leaching or degradation.
3. Tubing Material Guide (Revised for PFAS Sampling)
| Material |
Pros |
Cons |
Best For |
| PTFE (Teflon®) | Chemically inert; great for VOCs | Often not recommended for PFAS unless validated; potential background interference | VOCs, critical metals |
| FEP | Flexible alternative to PTFE | Use with caution for PFAS—requires validation | VOCs |
| HDPE | Chemically resistant; widely recommended for PFAS | Less flexible than some tubing | PFAS, general water chemistry |
| Polypropylene | PFAS-compatible; non-fluoropolymer | May have limited size availability | PFAS sampling |
| Silicone | Accepted for peristaltic pump head tubing for PFAS sampling | Not recommended for full sample tubing due to permeability | Peristaltic pump head tubing for PFAS sampling |
| LDPE | Inexpensive; flexible | Not recommended for PFAS sampling due to potential sorption/leaching | General water chemistry (non-PFAS) |
| Polyurethane | Flexible; abrasion-resistant | Not suitable for VOCs or PFAS | Temporary purging |
| PVC | Low cost | Contains plasticizers and other leachable; avoid for PFAS and VOCs | Non-critical use |
4. Special Notes on PFAS Sampling
PFAS sampling requires extreme care due to ultra-trace target levels (ppt range) and the risk of cross-contamination. Tubing material must be chosen carefully:
Recommended materials for PFAS sampling:
- HDPE tubing
- Polypropylene tubing
- Silicone tubing for peristaltic pump head only (where needed for pump operation)
- PTFE/FEP only if explicitly validated and approved by regulator/project SOP
Avoid these materials for PFAS sampling:
- LDPE
- Polyurethane
- PVC
- Silicone as main tubing (other than in pump head use)
5. Sample Tubing Configuration for PFAS Sampling
Here is an example of a compliant tubing setup for PFAS sampling with a peristaltic pump:
[Well Water] → [HDPE or Polypropylene Drop Tube] → [Silicone Pump Head Tubing] → [HDPE or Polypropylene Discharge Tubing] → [Sample Bottle]
Key Points:
- Silicone is used only inside the pump head where required for flexible roller contact.
- HDPE or polypropylene tubing carries sample water before and after the pump head to prevent contact with permeable tubing.
- Use dedicated tubing and avoid re-use.
- Handle tubing with nitrile gloves, not PTFE-coated or latex gloves.
- Follow applicable EPA/state guidance documents for tubing selection and decontamination procedures.
6. Other Tubing Selection Considerations
- Inner diameter (ID): Must match pump or sampler specs.
- Wall thickness: Thicker walls resist kinking but reduce flexibility.
- Length: Minimize tubing length to reduce dead volume and analyte contact time.
- Deployment environment: Consider temperature, depth, exposure time, and flow rates.
7. Best Practices for Field Use
- Pre-clean tubing as required by project or regulatory SOPs.
- Store tubing in PFAS-free packaging—avoid PTFE tape, wax paper, and fluoropolymer-treated containers.
- Replace tubing frequently and use dedicated tubing for long-term PFAS monitoring wells.
- Document tubing material in your field forms and chain of custody records.
Summary: Match Tubing to Mission—Be Especially Careful with PFAS
In today’s regulatory environment, tubing selection is not an afterthought—it’s a critical QA/QC step in groundwater sampling.
For PFAS sampling:
Use HDPE or polypropylene tubing wherever possible. Use silicone only where necessary inside the peristaltic pump head. Do not use LDPE, PVC, polyurethane, or silicone for main sample tubing.
For VOCs and metals:
PTFE/FEP remains the gold standard (but verify for PFAS compatibility if multi-analyte sampling).
For general chemistry:
HDPE or polypropylene provides a safe and versatile choice.
Final Tip
Always check your project’s approved QAPP or regulator SOP—some agencies have specific tubing material requirements that vary slightly from national guidance (EPA 537.1, EPA 533, ITRC, various state PFAS SOPs).
When in doubt: consult your laboratory or equipment supplier before deploying tubing to the field.
