Determination of micro amount of ammonia in the atmosphere by using impregnated filter

Abstract

A simple and rapid method was developed for the measurement of atmospheric ammonia using a reaction of indophenol dye formation. A glass fiber filter having the area of 17.3cm² was impregnated with the reagent for the collection of atmospheric ammonia; the reagent used was a 3% boric acid-20% glycerin solution and a 8.6% oxalic acid-50% glycerin solution. This filter was placed in a filter holder and connected to a vacuum pump drawing air at a flow rate of 20l/min. After sampling, the filter was washed with 20ml of water to extract ammonia. To a fixed volume of extract, each 5ml of a phenol-sodium nitroprusside solution and a sodium hypochlorite solution was added, and after developing color the absorbance of the solution was measured at 640nm. Collection efficiency of atmospheric ammonia by the filters was almost 100%. The lower limit of determination of atmospheric ammonia was 0.84 ppb for a filter having 17.3 cm² of effective filtering surface at the flow rate of 20l/min, for 1 h sampling period. The sensitivity of this method is higher than that (16.7 ppb) of the indophenol method using an impinger for collection, that is the new method is almost 20 times as sensitive as the conventional one. The coefficient of variation was 5.3% for a range of ppm level. Besides its greater sensitivity, this technique also had advantages in the field, in the preservation of the sample and in ease of transporting the equipment.