Abstract
Aqueous formaldehyde was stabilized in pH 7 phosphate buffer with excess sodium bisulfite of fixed and known concentration. The 5,5' -dithiobis(2-nitrobenzoic acid) (DTNB) procedure described previously was used to determine excess bisulfite colorimetrically. The slope of the calibration line (absorbance at 412 nm vs. formaldehyde concentration) is −0.350 A.U./ug CH2O/mL (correlation coefficient: 0.9995). The precision of the method at the 95% confidence level is indicated by the mean percentage relative error (1.81±1.67) and mean percentage standard error (0.42±0.39). Gaseous formaldehyde of known concentrations (ppm) in air was absorbed from air samples in pH 7 buffer and determined by the DTNB method. For the determination of formaldehyde in air, the precision and accuracy were demonstrated at the 95% confidence level by the mean percentage relative error (5.04±3.2), the mean percentage standard error (1.72±1.0), the mean percentage recovery (99.9±2.7), and the mean percentage absolute error (1.86±1.6). The graphic comparison of air concentration found vs. air concentration calculated shows a slope of 0.993 ppmfound/ppmcalcd (correlation coefficient: 0.9993).