Lab Science News

Background

Total Volatile Organic Compounds (TVOC) may be evaluated when building designers/managers are pursuing the Leadership in Energy and Environmental Design Green Building Rating System for New Construction (LEED-NC) EQ Credit 3.2. The latest LEED-NC guidance document specifies that the maximum allowed concentration of TVOC measured in a building (post construction, pre-occupancy) is 500 µg/m³; the guidance also mentions using the sampling/analytical methods in the US EPA Compendium of Methods for the Determination of Air Pollutants in Indoor Air. However, none of these sampling and analytical methods address TVOC in particular, and thus the existing methods must be modified. In addition, TVOC is not defined (in terms of boiling point range, etc.) in the latest LEED-NC guidance and therefore is left open for interpretation; historically, many definitions of “TVOC” exist in literature.

For TVOC measurement, the analytical technique used must always reference one compound for calibration purposes. All compounds detected are then assumed to have the same response factor as the calibration compound. For instance, handheld instruments are most often calibrated using isobutylene or methane, and laboratory-based methods may reference TVOC as hexane (C6), toluene, or some other chemical species.

In practice, indoor air quality practitioners may use several different techniques for evaluating TVOC in buildings. Each sampling & analytical method has its own benefits and drawbacks, cost implications, and applicability.

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The Massachusetts Department of Environmental Protection (MassDEP) recently updated and finalized their Air-Phase Petroleum Hydrocarbons (APH) analytical method. The APH method, which had been in draft format since February 2000, was completed last year by a MassDEP Workgroup and approved after a month long public comment period in December 2008. The committee was comprised of MassDEP personnel, laboratory experts and data users.

The most significant updates to the APH method include:

• Analyte List Revisions - 2-Methylnaphthalene was removed from the target analyte list and is no longer considered an air-phase petroleum hydrocarbon. In addition, laboratories will no longer report the “unadjusted” hydrocarbon ranges.
• Calibration Standards Revisions - Indene, hexylcyclohexane and 1-methynaphthalene were removed as hydrocarbon range calibration standards/retention time markers, due to poor performance and stability in the whole air matrix.
• Standard Preparation – The newly revised method will only allow vapor phase standards to be used for calibration. (Previously, in the draft method, methanol based standards were allowed.)
• Calibration & Quality Control Requirements, Holding Time and Performance Standards – Many small changes were made in order to make the APH method consistent with EPA Method TO-15.

The MassDEP APH method is currently the only existing method to look at vapor phase hydrocarbons in a risk based corrective action approach (i.e. with fractionated aliphatic and aromatic ranges). Going beyond EPA Method TO-15 or a traditional total petroleum hydrocarbons (TPH) approach, this method provides more specific information about the type of hydrocarbon contamination at a site.

As an example of the utility of the APH method, Figure 1 shows the total ion chromatogram for a soil gas sample collected at a site impacted by historical subsurface petroleum product contamination. For this example, all the APH target compounds (1,3-butadiene, benzene, toluene, ethylbenzene, xylenes, MTBE, and naphthalene) as well as several other petroleum indicator species (1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, n-nonane, n-decane, n-dodecane, n-undecane) were not present above the laboratory reporting limit. However, as is visually evident, there was still a strong weathered petroleum pattern present in the sample. The hydrocarbon ranges reported in the APH method were able to capture this information which otherwise might have been overlooked in a basic review of the numerical results.

Figure 1. - Total Ion Chromatogram of Real-World APH Sample

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References (Current as of December 2008)

1. MassDEP Method for the Determination of Air-Phase Petroleum Hydrocarbons (APH), December 2008. Available at: http://www.mass.gov/dep/cleanup/laws/qaqcdocs.htm#IV

2. MassDEP Standard Operating Procedure for Indoor Air Contamination, SOP-BWSC-07-01, August 2007 (made available April 2008). Available at: http://www.mass.gov/dep/cleanup/laws/policies.htm#iasop

3. MassDEP Indoor Air Sampling & Evaluation Guide, WSC Policy #02-430, April 2002. Available at: http://www.mass.gov/dep/cleanup/laws/policies.htm#indair

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View the APH method flyer (PDF file)

Read about testing for petroleum hydrocarbon contaminations

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