Analysis of formic acid in air samples.

The method reported here is for formic acid in air. Air containing formic acid is drawn through a midget impinger containing 15 ml of 0.1 N NaOH at a rate of one liter per minute for 42 minutes. An aliquot from the impinger is treated with an equal volume of ethanol-sulfuric acid mixture in a gastight reaction vial to produce ethyl formate. Because ethyl formate is volatile, an analysis of its vapor contained in the vial (headspace analysis) can be performed. The ethyl formate is analyzed by gas chromatography and its quantity is proportional to the quantity of formic acid contained in the reaction vial. With a relative standard deviation of 11 percent the method is precise enough for evaluating airborne formic acid at 0.1 of Threshold Limit Value of 9 mg/m3.