A procedure for gas chromatographic determination of O-isobutylmethylphosphonate micro-quantities in industrial emissions with a concentration range from 0.5 to 50 mg/m3 has been developed. The target analyte was collected and concentrated using an aspirator of the required volume of the test medium taken from sources of industrial emissions through sampling tubes equipped with ready-made filter materials, two layers of filters of the PFC (Petryanova filter cloth) type, 12 mm in diameter, two layers of filters of the appropriate size, washed in ethyl alcohol and dried in air, made of dense cotton material «moleskin». Recovery of concentrated substances from the sample tubes was performed by extraction with isopropanol. Methylation with diazomethane was carried out to convert the desired substance to a volatile product for subsequent chromatography, by a method improved to obtain micro-quantities of dialkyl esters of MPA and its monoesters. The high efficiency of the proposed methylation method as a factor for obtaining solutions with a low content of impurities of both starting reagents and non-target reaction products has been experimentally proven, which leads to higher accuracy of microconcentration measurements. Trace impurities, including diazomethane residues, were removed by vacuuming the methylated solution for 2 – 5 min. The use of other methods to remove excess diazomethane does not give positive results: blowing diazomethane from the solution with an inert gas does not lead to noticeable changes even for 15 – 20 min, during which time part of the solvent is removed and, therefore, the concentration of the target product changes; the addition of additional chemicals, for example acetic acid, leads to contamination with two products at once-excess acetic acid and methyl acetate, in addition, the addition of excess competing reagent can lead to transalkylation with the participation of the target product and, as a result, to incomplete progress of the target reaction. Quantitative data were obtained by gas chromatography using a Varian CP-3800 gas chromatograph equipped with a pulsed flame photometric detector, the mixture was separated on a CP WAX CB capillary column. The methodology was tested at real control facilities, appropriately certified and implemented in environmental control and monitoring programs.