Prism Analytical Technologies, Inc. (PATI)
Chief Technical Officer
Before getting into the technical aspects of Total Volatile
Organic Compounds (TVOCs), it is important to understand what is really meant
by the term. A TVOC value is not simply the sum of the volatile organic
compounds detected in an analysis. For example, consider a radio signal
received on a car stereo. Suppose the station is playing a flute solo.
An analysis of the radio signal at any specific moment in time would show
a single note or “peak” in the signal (apologies are extended to musically
astute for ignoring the harmonics, timbre, etc. here). If the station
were coming in clearly, that single tone would be overwhelming relative to the
magnitude of the rest of the tones. If the same station is playing an
organ solo, there might be six clear, distinct tones. If the station were
playing rock music, there would be a distorted conglomerate of discordant
tones. For the last example, now consider a station that is coming in
poorly and is playing rock music. The static or “white noise” would
nearly overwhelm the already complex signal. In each and every case, the
radio volume might be the same, but the tonal makeup and complexity would be
vastly different. Such is the case with a TVOC value. The value
includes all of the indistinguishable “chemical noise” as well as the
recognizable compounds. As in the radio analogy, without a significant
“total signal”, there is no radio reception; however, a high total signal could
be anything from one pure tone to nothing but loud static. So it is with
TVOC, a low TVOC usually indicates that there is no VOC problem (unless, of
course, the TVOC value is due to only a small number of compounds); however, a
high TVOC value may result from a high level on one single compound or it may
be a vast collection of low compound levels from a chemical “soup”, or it may
be anything in between.
Note in the following chromatogram the difference in TVOC makeup as compared to the identifiable compounds.
The “hump” in the chromatogram is a collection of undifferentiated hydrocarbons. Even though many of the individual compounds are not discernable, collectively, they contribute heavily to the TVOC load.
Currently there is no
The recognized symptoms above 3000 ng/L generally include drowsiness, eye and respiratory irritation, general malaise, headache, nausea, and exacerbation of symptoms of respiratory ailments. Some data suggests that high TVOC levels amplify the hazardous effects of specific, harmful VOCs. In addition, there is some empirical information from IH consultants who perform medically driven environmental investigations, which indicates that typically acceptable levels are too high by a factor of two or more for chemically sensitive individuals.
Prism Analytical Technologies, Inc. (PATI) has worked with the available literature, large chemical companies, and many IH consultants active in the IAQ field as well as using our own consultative data correlating symptoms to TVOC levels to establish the following table defining the limits and effects of TVOC concentrations:
Measuring TVOC and How PATI Measures and Reports TVOC
Several devices are available that do an acceptable job estimating TVOC including PID (Photoionization Detectors), AirCuity monitors, XXXX, and several others. These are especially useful for continuous monitoring or for obtaining real-time data. However, the use of GC-FID (Gas Chromatography-Flame Ionization Detector) or GC-MS (Gas Chromatography-Mass Spectrometry) will provide the most accurate and useful data although GC-FID has the drawback of not providing secondary verification of compound identity. PATI uses GC-MS in determining the TVOC value because, should a question arise as to the identity of the specific compounds.