If you're a project manager, field leader, or environmental consultant relying on high-quality data, here are five missteps you don't want to make.

1. Improper Sample Canister Preparation or Handling

The foundation of air testing using TO-15 lies in the sample canister—and poor handling here creates risk before the sample is even collected.

• Inadequate cleaning or certification: All canisters must be certified clean to below method detection limits. Reusing uncertified or improperly cleaned canisters can introduce background contamination.
• Vacuum level not confirmed: Canisters must be fully evacuated to the required vacuum level prior to sampling. Skipping this step results in insufficient sample volume or skewed concentrations.
• Inappropriate regulator settings: Using the wrong flow controller or failing to verify the intended sampling interval (e.g., grab vs. 8-hour integrated) leads to incorrect sample collection profiles.
• Canister damage or leaks: Dents, loose fittings or cracked seals may cause leaks that compromise sample integrity—often going unnoticed until after lab analysis.

Best practice: Confirm that each canister is leak-checked, certified, properly vacuumed, and matched with the correct flow control hardware before arriving on-site.

2. Inaccurate or Incomplete Field Documentation 

TO-15 isn’t just about chemical analysis—it’s also about defensibility. And poor documentation can jeopardize your data’s credibility.

• Missing or incomplete chain-of-custody (COC) forms: Labs rely on this paperwork to match canisters to samples. Missing times, locations or initials can cause analytical delays or unusable results.
• Incorrect sample times or flow rates: Accurate timestamps and flow duration are essential for determining total sample volume and interpreting results.
• Lack of field notes on conditions: Weather, wind, temperature, or nearby activities can influence VOC concentrations. If these aren’t logged, anomalous results may go unexplained.

Best practice: Use pre-filled documents when possible, and have field staff trained on every required field for documentation. Audit the forms on-site, not afterward.

3. Overlooking Ambient Conditions That Affect VOC Integrity

Even a well-prepared canister can deliver flawed data if ambient conditions during sampling aren’t accounted for.

• Humidity and condensation: Moisture can interfere with preconcentration and gas chromatography, reducing sensitivity or masking analytes. Dry-air purging and proper canister materials help mitigate this.
• Extreme temperatures: Both heat and cold can affect canister pressure and VOC behavior. Temperature logs help validate unexpected concentrations.
• Proximity to sources or barriers: Sampling too close to temporary emission sources (e.g., idling vehicles, HVAC intakes) or shielding structures can skew the representativeness of results.

Best practice: Record environmental parameters during every sampling event, and note anything that may influence air composition—planned or otherwise.

4. Misunderstanding SIM Mode vs. SCAN Mode Reporting

A subtle but critical distinction lies in how TO-15 data is acquired and reported by the environmental lab.

• SCAN Mode (Full Spectrum): The instrument collects mass spectral data across a wide range of ions. This allows for broad detection, including Tentatively Identified Compounds (TICs), but at higher detection limits.
• SIM Mode (Selected Ion Monitoring): The instrument targets specific ions for selected VOCs. This significantly improves sensitivity, often by an order of magnitude, enabling detection at much lower concentrations.

Pitfall: If your sampling goal is risk assessment or regulatory compliance at ultra-trace levels, relying on SCAN mode results may be insufficient. Requesting SIM mode in advance ensures detection of low-level targets relevant to health-based decision making.

Best practice: Clarify your data use case—screening vs. compliance vs. litigation—and confirm with the lab whether SIM or SCAN mode will be used. The choice has major implications for reporting limits and defensibility.

5. Assuming the Lab Will Catch Mistakes 

TO-15 is a performance-based method—meaning it’s up to the field sampling team, not just the lab, to ensure accuracy.

• Labs won’t know if regulators were calibrated correctly or if a leak occurred in the field.
• They may not question a form missing ambient temperature or barometric pressure.
• They will analyze whatever they receive—whether or not the sample was collected according to best practices.

Best practice: Treat the field team as the first line of quality control. Empower them with checklists, train them on the method, and create feedback loops with the lab to catch patterns in problematic samples.

Final Notes: Precision Matters at Every Step

TO-15 is a powerful analytical method—but its reliability depends on careful execution, especially in the field. From sample canister prep to documentation to analysis, there are multiple points where errors can compromise data integrity.

The most common TO-15 pitfalls are entirely preventable:

• Skipping leak checks or not vacuuming canisters properly.
• Recording inaccurate sampling times or flow rates.
• Neglecting ambient conditions that affect sample validity.
• Filling out chain-of-custody forms incompletely or incorrectly.
• Misunderstanding the difference between SCAN and SIM mass spectrometry modes.

Each of these issues might seem small in isolation, but together they can jeopardize compliance, delay decisions, or undermine confidence in your data. For high-stakes projects—like vapor intrusion investigations, Superfund site assessments, or air quality permitting—there’s no margin for error.

Take Action

If you’re unsure whether your TO-15 sampling plan meets current best practices, or if recent lab reports have raised red flags about documentation or detection limits, it may be time to get expert input.

And here’s where to get it…at Metiri, you can talk directly to our experts.

Contact Lori Near (lori.near@metirigroup.com) or Douglas Duncan (douglas.duncan@metirigroup.com) to discuss your project, any TO-15 concerns you have, or to clarify sampling and reporting best practices.

You’ll get answers from a team that’s worked through hundreds of TO-15 programs—and can help you avoid the most common (and costly) TO-15 pitfalls.