Solvent extraction/spectrophotometric determination of ammonia in the atmosphere with an ion-association reagent

A new solvent extraction/spectrophotometric method for determining trace amounts of ammonia in the atmosphere is described. The procedure is based on the formation of indophenol by the reaction of phenol, hypochlorite and ammonia using a coupling agent. Indophenol solution was concentrated by solvent extraction by forming an ion-associate form indophenol and trioctylmethylammonium chloride (TOMA+ ) using cyclohexane as solvent. The procedure is as follows : Take 20 ml of indophenol solution fromed from an aliquot of ammonia sample solution as mentioned above. Add 2 ml of TOMA+-cyclohexane solution and shake for 1.52 min. After centrifuging, measure the absorbance of the organic phase at 630 nm. Calibration curve is linear over the range 01μl NH3 in 20 ml of indophenol solution (the apparent molar absorptivity is 2.3×104 1 mol-1 cm-1) and the relative standard deviation is 3.8% for the concentration of 0.2μl NH3 in 20 ml of indophenol solution. This represents a 10 fold concentration for indophenol solution. Ammonia above 0.6 ppb for 360l of air sampling volume could be determined by this method.