Abstract
The reduction in sensitivity of the Photoyae TIP, TIP-1, and the H-NU101 total organic vapor analyzers equipped with photoi-onization detectors (PID) to toluene and gasoline in the presence of methane (0.5–5.0% v/v) was examined. The results showed an exponential decrease in detector sensitivity, with a reduction of about 30% for 03% methane and 90% for 5% methane. A Photovac TIP (PID), a Century OVA equipped with a flame ionization detector (FID), and a Photovac 10S50 portable gas chromatograph (PID) were used in a soil gas survey to map the areal extent of gasoline contamination. The survey area was paved, and comparison of FID and PID response showed that methane was widespread under the asphalt, including areas where gas chromatography showed no gasoline contamination. Two soil gas samples analyzed in the laboratory showed concentrations of 0.23% and 0.99% methane by volume. Because high concentrations of biogenic methane are found in the environment, this loss of sensitivity may be important when PID organic vapor analyzers are used in the field.