Effect of Calibration and Environmental Condition on the Performance of Direct-Reading Organic Vapor Monitors

Abstract

The performance of three MIRAN SapphIRe Portable Infrared Ambient Air Analyzers and three Century Portable Toxic Vapor Analyzers equipped with photoionization (PID) and flame ionization (FID) detectors was compared with charcoal tube sampling. Relationships were investigated using two different calibration methods at four cyclohexane concentrations, three temperatures, and four relative humidities. For the first method, the TVA monitors were calibrated with a single concentration of methane for the FID, and isobutylene for the PID. The SapphIRe monitors were zeroed and the monitor's manufacturer-supplied library was used. For the second method, a five-point cyclohexane calibration curve was created for each monitor. Comparison of the monitor results of each calibration method (pooled data) indicated a significant difference between methods (t-test, p < 0.001), The SapphIRe group had results closer to the charcoal tubes with the second calibration method, while the PID and FID monitor groups performed better using the first calibration method. The PID monitor group's performance was affected only at the 90% relative humidity (RH) condition. Using the first method, the monitor readings were compared with the charcoal tube average using mixed linear model analyses of variance (ANOVAs) and regression. The ANOVA results showed there was a statistically significant difference among readings from all monitor types (p <0.0001). The regression results demonstrated that the SapphIRe (r² = 0.97) and FID (r² = 0.92) monitor groups correlated well with the charcoal tubes. The PID monitor group had a similar correlation when 90% RH was excluded (r² = 0.94) but had a weaker correlation when it was included (r² = 0.58). The operator should take care when using these monitors at high concentrations and the PID monitors at high humidities, consider the variability between units of the same monitor, and conduct performance verification of the monitor being used.

[Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resources: a program listing, schematic diagrams, and other design details for the test automation system.]

Keywords:

• direct-reading organic vapor monitors
• flame ionization detector
• photoionization detector
• SapphIRe
• toxic vapor analyzer

ACKNOWLEDGMENTS

The authors wish to acknowledge Michael Commodore and Judith Hudnall for conducting the environmental tests, Catherine Calvert for performing the charcoal tube analysis, and John Powers and Bradley Newbraugh for their assistance in the development of the LabView program and associated hardware.

The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Mention of commercial product or trade name does not constitute endorsement by the Centers for Disease Control and Prevention/National Institute for Occupational Safety and Health.

This work was supported by the National Institute for Occupational Safety and Health.