VOC Canister Sampling and GC/MS Analysis
EPA TO-15 VOC Air Testing: Canister Sampling, GC/MS and TIC Analysis
EPA Method TO-15 and the updated TO-15A approach use specially prepared whole-air canisters followed by laboratory preconcentration and gas chromatography/mass spectrometry (GC/MS) to identify and quantify selected volatile organic compounds in air.
EPA whole-air VOC methods
What Are EPA Method TO-15 and TO-15A?
EPA Compendium Method TO-15 was published in 1999 for measurement of selected volatile organic compounds in air collected in specially prepared canisters and analyzed by GC/MS. EPA published Method TO-15A in 2019 as an updated method that incorporates current canister-sampling and analytical technologies, more detailed quality-control procedures, and defined performance criteria.
TO-15A describes measurement of a subset of the 97 volatile organic hazardous air pollutants identified in the Clean Air Act Amendments. EPA also states that the method may be used for additional VOCs and for applications including indoor-air investigations when the required method-performance criteria are met.
In practice, environmental laboratories often offer a defined TO-15 or TO-15A target list. The exact analytes, reporting limits, and accreditation status vary by laboratory and project, so the laboratory scope should be confirmed before sampling.
From the room to the chromatogram
How TO-15 VOC Air Sampling Works
Prepare the Canister
The laboratory cleans, qualifies, and evacuates a specially prepared stainless-steel canister before field use.
Collect the Whole-Air Sample
Air enters the evacuated canister through the sampling inlet. Depending on the investigation, the sample may be collected as a grab sample or over a defined time period using a flow controller.
Preconcentrate the VOCs
At the laboratory, a measured portion of the collected air is concentrated before instrumental analysis so trace-level VOCs can be measured.
Separate Compounds by Gas Chromatography
The gas chromatograph separates compounds as they travel through the analytical column, producing individual chromatographic peaks.
Identify and Quantify by Mass Spectrometry
The mass spectrometer evaluates the mass spectrum associated with each peak. Target compounds are identified and quantified using laboratory calibration, retention information, and method quality-control criteria.
Calibrated compounds come first
What Does the TO-15 Target List Include?
There is no single laboratory target list that should be assumed for every project. EPA TO-15 and TO-15A cover selected VOCs, while individual laboratories may calibrate additional compounds when method performance can be demonstrated.
Aromatic VOCs
Common laboratory lists may include compounds such as benzene, toluene, ethylbenzene, and xylenes.
Halogenated VOCs
Chlorinated and other halogenated solvents may be included where supported by the laboratory's calibration and reporting limits.
Solvents and Industrial VOCs
The method may be useful for selected solvent-related compounds associated with coatings, cleaning products, fuels, or industrial materials.
Laboratory-Specific Additions
Some laboratories offer expanded calibrated analyte lists beyond the core compounds commonly associated with standard TO-15 reporting.
Confirm the target list before the canister is deployed.
The suspected source should drive the analyte list. If a client is concerned about a particular chemical, the laboratory should confirm that the compound is included, that the reporting limit is suitable, and that the compound performs adequately using the selected method.
Extending the investigation beyond the calibrated list
What Are Tentatively Identified Compounds (TICs)?
During GC/MS analysis, the instrument may produce chromatographic peaks that do not correspond to compounds on the laboratory's calibrated target list. When TIC review is requested and offered by the laboratory, selected non-target peaks may be compared with a computerized mass-spectral reference library to develop a presumptive compound identification.
EPA data-review guidance distinguishes TICs from calibrated target compounds. A TIC identification is tentative, and the associated concentration is generally approximate or estimated rather than a fully calibrated quantitative result.
Why TIC Review Can Be Valuable in an Odor Investigation
TIC review can flag significant non-target peaks that would otherwise be absent from a standard target-analyte table.
It may help generate leads when the building has a chemical odor but the suspected compound is not known before sampling.
Spectral-library similarity is presumptive. A TIC name should not be reported as if it were confirmed by an authentic calibration standard.
TIC concentrations are typically estimates and may require follow-up analysis if a specific compound becomes important to the investigation.
TIC analysis should be requested before the laboratory analysis whenever possible.
Laboratories differ in whether they offer TIC searches, how many peaks are reviewed, the spectral-library criteria used, and how estimated concentrations are reported. These details should be established in the project scope rather than assumed after the report is issued.
Building and indoor-air applications
When TO-15 VOC Testing May Be Useful
Unexplained Chemical Odors
Canister sampling may help evaluate a range of VOCs when the odor source is unclear and several chemical categories are plausible.
Renovation and New Materials
Paints, coatings, adhesives, flooring, furnishings, and other new products may contribute VOCs to occupied spaces after construction or fit-out.
Source Comparison
Samples from an affected room may be compared with another indoor location or outdoor air when the comparison is useful to the investigation.
Pre-Occupancy Documentation
VOC sampling may document selected indoor-air conditions before occupancy after construction, furnishing, or major renovation.
Vapor Intrusion Investigations
EPA identifies indoor-air and vapor-intrusion investigations as applications where TO-15A may be used when method performance criteria are met.
Unknown-Compound Screening
Optional TIC review may provide additional investigative information when a standard target list does not fully explain the observed odor or source history.
A separate analytical issue
TO-15 Should Not Be Assumed to Be the Best Formaldehyde Method
Formaldehyde is a reactive carbonyl compound and presents analytical challenges in canister methods. EPA's original TO-15 method specifically notes that calibration of formaldehyde can be challenging.
When formaldehyde is the principal concern, Angstrom generally treats it as a separate target and can use formaldehyde-specific sampling such as NIOSH Method 2016, which collects formaldehyde on DNPH-treated media followed by HPLC analysis.
A combined investigation can therefore include a TO-15 or TO-15A canister for broader VOCs together with a separate formaldehyde-specific sample.
Know what the data do and do not establish
Important Limitations of TO-15 and TIC Results
A Sample Represents a Defined Period
VOC concentrations can change with ventilation, HVAC operation, occupancy, product use, temperature, outdoor air, and source activity.
The Target List Is Finite
A compound absent from the calibrated analyte list should not automatically be interpreted as absent from the air.
TICs Are Screening-Level Evidence
TIC names are tentative and concentrations are estimated. Important findings may require confirmation with a compound-specific calibrated method.
Laboratory data should be interpreted with the building investigation.
A useful VOC assessment considers suspected sources, sample locations, ventilation, temperature, recent activities, comparison locations, reporting limits, and whether the compounds of interest were actually included in the analytical scope.
Related Angstrom resources
Formaldehyde, VOC & Indoor Air Quality Resources
These Angstrom resources provide additional information about formaldehyde-specific sampling, formaldehyde from cabinets and engineered wood, and broader indoor air quality investigations.
Commercial service information for formaldehyde-specific sampling, TO-15/TO-15A VOC testing, chemical-odor investigations, and interpretation.
View service Formaldehyde From Cabinets, MDF & Engineered WoodLearn how cabinets, composite wood, MDF, particleboard, furniture, and built-ins may contribute formaldehyde to indoor air.
Read guide Indoor Air Quality TestingBroader indoor air quality assessment for VOCs, chemical odors, ventilation, particles, mold, and other building-related concerns.
View servicePrimary EPA technical sources
Official EPA TO-15 and TO-15A Resources
EPA's current index for TO-15, TO-15A, and other standardized toxic-organic air-sampling methods.
Open EPA compendium EPA Method TO-15AEPA's 2019 method for VOCs collected in specially prepared canisters and analyzed by GC/MS.
Open Method TO-15A EPA Compendium Method TO-15EPA's original 1999 whole-air canister and GC/MS method for selected VOCs.
Open Method TO-15 EPA TO-15 Data Review GuidanceEPA technical-review guidance addressing target-compound identification, quality-control review, and tentatively identified compounds.
Open EPA data-review guidanceTO-15 VOC testing questions
Frequently Asked Questions
What is EPA Method TO-15?
TO-15 is an EPA method for collecting whole-air samples in specially prepared canisters and analyzing selected VOCs by gas chromatography/mass spectrometry.
What is the difference between TO-15 and TO-15A?
TO-15 was published in 1999. TO-15A was published in 2019 and provides updated guidance for canister sampling, current analytical technologies, quality control, and method-performance criteria. EPA's compendium currently lists both methods.
Can TO-15 identify an unknown chemical odor?
It can quantify compounds on the laboratory's target list and may provide additional investigative information through TIC review when offered. It cannot guarantee identification of every chemical contributing to an odor.
What is a TIC?
A tentatively identified compound is a non-target peak that is given a presumptive identity based primarily on its mass spectrum and library comparison. The identification is tentative and the concentration is generally estimated.
Does TIC analysis expand the TO-15 target list?
It expands the investigative information available from the GC/MS data, but it does not convert non-target compounds into calibrated target analytes. TIC results remain tentative and estimated unless confirmed by an appropriate follow-up method.
Can TO-15 reliably measure formaldehyde?
Formaldehyde presents canister-analysis challenges and should not automatically be treated like a routine TO-15 target. When formaldehyde is the main concern, a formaldehyde-specific DNPH method such as NIOSH Method 2016 is generally more appropriate unless the laboratory demonstrates suitable canister performance.
Can a TO-15 sample be collected over several hours?
Yes. EPA TO-15A allows whole-air samples to be collected as grab samples or as time-integrated samples. The flow controller and sampling duration should be selected for the project objective and coordinated with the laboratory.
Should I request TIC analysis before sampling?
Preferably yes. Laboratories differ in whether they offer TIC review, how many peaks they search, their reporting criteria, and how estimated concentrations are calculated. The requested deliverable should be defined in advance.
Need VOC or Chemical-Odor Air Testing?
Angstrom provides independent formaldehyde and VOC air sampling for residences, offices, schools, and commercial buildings, including TO-15/TO-15A canister sampling, laboratory GC/MS analysis, and TIC review when appropriate and available.
