A review and a limited comparison of methods for measuring total volatile organic compounds in indoor air

Numerous methods attempt to measure the combined concentrations of volatile organic compounds (VOCs) in indoor air as total VOCs (TVOC). This paper reviews TVOC methods recently presented in the literature and at an international conference on indoor air quality, for the purpose of identifying common practices and of assessing the impacts that choices of sample collection media and analytical methods and instrumentation can have on TVOC results. The paper also presents the results of laboratory and field comparison of three TVOC methods. These are a flame-ionization-detector (FID) method a gas chromatography/mass spectrometry (GC/MS) method, and a method employing a photoacoustic infrared (IR) gas monitor. The laboratory experiments were conducted with eight different mixtures of VOCs. The FID method demonstrated an average accuracy of 93+/-18 percent when the measured values were calculated as concentrations of carbon. The FID and GC/MS methods demonstrated average accuracies of 77+/-37 and 75+/-22 percent, respectively, when the measured hydrocarbon-equivalent values were compared to the expected mass concentrations of the mixtures. The higher uncertainty for the FID was largely due to the low mass response of 27 percent for chlorinated compounds. The response of the IR gas monitor varied between 6 and 560 percent for different classes of compounds. Air samples from ten buildings were analyzed by both the FID and GC/MS methods. The results were highly correlated and similar, with the GC/MS values approximately 20 percent higher on average.