This part of ISO 16000 specifies a determination of formaldehyde in indoor air using a diffusive sampler with solvent desorption and high performance liquid chromatography (HPLC). The test method is applicable to the measurement of formaldehyde1) in indoor air over the range from 0,001 mg/m3 to 1,0 mg/m3 for a sampling period of between 24 h and 72 h. For sampling periods of 24 h, the applicable concentration range is 0,003 mg/m3 to 1 mg/m3, and for 72 h it is 0,001 mg/m3 to 0,33 mg/m3. NOTE Confirmed samplers with respect to measurement sensitivity and precision can apply to short-term sampling (less than 24 h). The method is suitable for measurements in atmospheres with conventional indoor air relative humidity and for monitoring at air velocities as low as 0,02 m/s. The chromatographic step in the method is designed to eliminate potential interferences, including those due to the presence of other carbonyl compounds. The sampling method gives a time-weighted average result. NOTE There are several diffusive samplers with various designs and shapes commercially available. They are all based on the reaction of 2,4-dinitrophenylhydrazine with formaldehyde. They are not specifically described in this part of ISO 16000 to avoid any impression that ISO favours one model over another.