This standard describes the procedure and equipment for the determination of formaldehyde in the airborne at the workplace through the active sampling on an appropriate collection substrate coated with 2,4-DNPH and analysis by high performance liquid chromatography (HPLC). The range of application of this standard shall satisfy the performance requirements of the procedures for the measurement of chemical agents collected in Standard UNE-EN 482. In any case, the upper limit of the range depends on the reaction capacity of the sampling medium used. The presence of other compounds, such as other aldehydes and ketones, which react with DNPH will affect the maximum retention capacity of formaldehyde in the carrier. The lower limit depends on a number of factors such as targets and reagents, analytical recovery and the noise level of the detector. Any particulate substance that can react in an acidic medium forming formaldehyde is considered interference. Ozone at high concentrations is also a negative interference when reacting with derivatization, which may affect the measurement result. Also considered interference is any other organic compound, which has the same or next retention time as the compound to be analyzed and exhibits absorption at the working wavelength. These interferences can be minimized by selecting the appropriate chromatographic conditions and columns. The procedure of measurement described can be used to carry out measurements to determine the occupational exposure concentration, measurements for comparison with limit values (occupational) to evaluate the exposition via inhalation and periodic measurements. It may also be used to carry out screening measurements of time weighted average concentration (see UNE-EN 482, 4.2) and screening measurements of variation of concentration in time and/or space (see UNE-EN 482, 4.3).