Development of formaldehyde standard gas generator based on gravitational dispensing-vaporization and its application to breath formaldehyde determination

A new formaldehyde (HCHO) standard gas generation method based on gravitational dispensing-vaporization was developed, and an automated flow injection analysis (FIA) system coupled with a porous membrane-based diffusion scrubber (DS) is proposed for the determination of gaseous HCHO in human breath. An HCHO standard solution in a 2-mL Terumo (R) syringe was dispensed gravitationally via a fused-silica capillary tip through a perpendicular arm of a tee heated at 40 C. The HCHO standard Solution was delivered at a flow rate of 39.5 nL/min and completely vaporized by airflow through the tee-arm. The gaseous HCHO was collected into a water absorber in the DS. The solution dissolved sample gas was injected into the FIA system. The fluorescent derivative was produced by merging HCHO and 5,5-dimethylcyclohexane-1,3-dione at pH 5.0. The intensity was recorded at the excitation wavelength of 395 run and the emission wavelength, 463 nm. In this manner, reliable instrument calibration of the FIA system could be carried Out. Under the optimum condition, a linear calibration curve for HCHO was obtained in the range of 3.68 to 147 ppbv. The limit of detection (S/N = 3) was 0.16 ppbv The collection of a gaseous sample and HCHO detection were automatically operated with a home-made protocol. The proposed method was applied to the determination of HCHO in exhaled human breath. The concentration range in 4 healthy volunteer subjects (nonsmoker) ranged from 5.8 to 11.8 ppbv. We also found that for another subject (smoker) smoking increased the breath HCHO concentration to approximately 1.5-fold, and then the concentration later returned to the initial level 30 min after the smoking.