Method TO-15 Requirements - Part I: "There's more than one way to skin a cat"

Over the past several months, I have had several inquiries on the requirements of the U.S. EPA’s Compendium Method TO-15 (Determination of Volatile Organic Compounds (VOCs) In Air Collected In Specially-Prepared Canisters And Analyzed By Gas Chromatography/Mass Spectrometry (GC/MS)). So I thought it might be useful for potential end users of said method to be aware of the following excerpts (paying careful attention to the underlined and italicized text) I have copied from the Foreword and Project Summary of the Compendium of Methods for the Determination of Toxic Organic Compounds in Ambient Air - Second Edition (which may be found here):

“As with the previous Compendia of methods, these methods are provided only for consideration by the user for whatever potential applications for which they may be deemed appropriate. In particular, these methods are not intended to be associated with any specific regulatory monitoring purpose and are specifically offered with no endorsement for fitness or recommendation for any particular application.”

“Consequently, this treatment allows the user flexibility in selecting alternatives to complement his or her background and laboratory capability.”

“This Second Edition has been prepared to provide regional, state and local environmental regulatory agencies, as well as other interested parties, with specific guidance on the determination of selected toxic organic compounds in ambient air.”

 

So what do I want you to take away from all that and what does it mean for you? Well… first off Method TO-15 is a “guidance document.” This means that if you are looking to analyze VOCs in canisters with a GC-MS, you may refer to TO-15 for “guidance” on how you may go about doing so. This does not mean you need to adhere to what is written in the TO-15 in order to be method “compliant.” Compliant is in quotations, because there really is nothing to “comply” with.

It is also important to know that Method TO-15 is considered a “performance-based method” (PBM). See back around 1997 the U.S. EPA shifted their methods from “agency approved procedure-based methods (APBM) to PBMs. Why??? I speculate the agency got sick and tired of various contractors, local and state agencies, etc. submitting countless and varying methods for approval, all of which were aimed at tackling the same goals. So in the end, they said “hey… we don’t care how you get it done, so long as your method meets said criteria.” (This is not a real quote… just how I envision someone at the agency talking.)

So… please take a look at the following excerpts from Method TO-15 for a specific example of the PBM guidance (again… paying careful attention to the underlined/italicized text):

3.1, Bullet 3: “In addition, Compendium Method TO-15 establishes method performance criteria for acceptance of data, allowing the use of alternate but equivalent sampling and analytical equipment.”

“7.2.2.2 Chromatographic Columns. 100% methyl silicone or 5% phenyl, 95% methyl silicone fused silica capillary columns of 0.25- to 0.53-mm I.D. of varying lengths are recommended for separation of many of the possible subsets of target compounds involving nonpolar compounds. However, considering the diversity of the target list, the choice is left to the operator subject to the performance standards given in Section 11.”

Note that Method TO-15 does not tell you what column you must use. I personally suggest a 30 m column, which I will blog about more in the future. It does state however “performance standards”; hence, the PBM. So I have gone ahead and done the legwork for you and scoured TO-15 to elucidate what are the main performance criteria you should be aware of and it goes something like this: Section 11.1.1 of TO-15 identifies three performance criteria, which should be met for a system to qualify. These criteria are: a method detection limit of ≤0.5 ppbv, replicate precision within 25 percent, and audit accuracy within 30 percent for concentrations normally expected in contaminated ambient air (0.5 to 25 ppbv). However, I would be remiss if I were not to point out that TO-15 does go on to list additional quality control measures laboratories should follow in order for their data to be considered acceptable. For example: Section 8.4.1 (Canister Cleaning and Certification) of TO-15 stipulates that any canister that has not tested clean (compared to direct analysis of humidified zero air of less than 0.2 ppbv of targeted VOCs) should not be used. In addition, section 10.5.5 (Technical Acceptance Criteria for the Initial Calibration) of TO-15 states that for the initial calibration the calculated percent relative standard deviation (%RSD) for the relative response factor (RRF) for each compound in the calibration table must be less than 30% with at most two exceptions up to a limit of 40%. These are just two examples of quality control measures outlined in TO-15… stay tuned for part II, which will list the remainder of the quality control measures.

So in the end, Method TO-15 has 3 major performance criteria (see the aforementioned) and several quality control measures you should be aware of. How you go about accomplishing this is entirely up to you. This holds true for the other TO Compendium Methods (e.g., 11A, 17, 13A, etc…). Of course… TO-15 can give you some insight into how, but bottom line… the method is there to help you get an idea of how to skin a cat. As we know, “there's more than one way to skin a cat.”