Determination of Ammonia and Formaldehyde by Flow Injection Analysis

A flow injection spectrophotometric method for the determination of ammonia and formaldehyde was developed, in which ammonia and formaldehyde were determined with almost the same FIA manifold. The color development reaction of ammonia is based on the formation of an indonaphthol dye in the presence of hypochlorite and 1-naphthol. The FIA system consisted of three flow paths: a carrier (water), a NaClO solution, and a 1-naphthol solution in a mixed solvent (ethanol : acetone : water = 2 : 1 : 2), with flow rates of 0.2, 0.2, and 0.4 ml min−1, respectively. A monochloramine and an indonaphthol dye were formed in a reaction coil (RC1) and a reaction coil (RC2), respectively. The optimum conditions were thoroughly studied by varying the reagent concentrations under a fixed flow rate. The results showed that the optimum conditions were 0.25 M NaOH and 2.0% active chlorine for a NaClO solution, and 1.6% of 1-naphthol. The lengths of the required reaction coils were 3 m and 7 m for RC1 and RC2, respectively. A linear calibration graph was obtained in the range of 0∼2 μg ml−1, and the detection limit, based on three-times the standard deviation of a blank, was 15 ng ml−1. Formaldehyde was determined indirectly using the reaction with ammonia to form hexamethylenetetramine. The residual ammonia was determined with the same FIA system, except that RC1 was replaced by a 20 m reaction coil. The concentration of active chlorine was set to 1.2%. A linear calibration graph was obtained in the range of 0∼1 μg ml−1, and the detection limit was 13 ng ml−1. The time required for the analysis of one sample was 8.1 min for ammonia and 14.8 min for formaldehyde. The time interval required for successional injection of the sample was about 5.5 min in both methods. The proposed method was applied to obtain a decay curve of formaldehyde in a test chamber in the absence or presence of an absorbent for formaldehyde. It was found that an ammonium sulfate solution is effective to absorb formaldehyde in air.