ISO 16000-4:2011 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 formaldehyde 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. 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.