Effect of relative humidity on the determination of formaldehyde with the NIOSH 3500 method (chromatropic acid method)

Abstract

The relative humidity of a formaldehyde test atmosphere was found to be a factor in formaldehyde determination using the chromatropic acid (CTA) method; also known as the NIOSH 3500 method.Formaldehyde recovery efficiencies of 100% were obtained when the relative humidity was below 0.1% at temperatures across the range 22–27 °C. Relative humidity levels of 50% and then >95% gave reduced efficiencies of 66 and 36%, respectively, across the temperature range 22–27 °C. Multiple linear regression yielded a correction algorithm for the CTA method that accounted for the influence of water at all the concentrations, masses and relative humidities studied: